DESIGN AND CONSTRUCTION OF A SOLAR DRYING...

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College of Engineering Mechanical Engineering Department

DESIGN AND CONSTRUCTION OF

A SOLAR DRYING SYSTEM FOR

FOOD PRESERVATION

By:

Team Members: Abdulelah Ali Al-Jumaah Abdullah Mohamed Asiri

Mohamed Fadil Alshehri Ahmed Mohamed Deash Fahd Minajy Al-Hamzi

PROJECT ADVISOR:

Dr. Mahmoud M. El-Haggar Dr. Mahmoud A. Bakry

A Senior Project Report Submitted in Partial Fulfillment of the Requirement for the Degree of Bachelor of Science (B.Sc.) in

Mechanical Engineering

1434 – 1435

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College of Engineering Jazan University



FOOD PRESERVATION

APPROVAL RECOMMENDED:

Examination Committee: Dr. Mohamed Mansour Mostafa

Dr. Elsayed Khalaf

PROJECT ADVISOR:

Dr. / Mahmoud M. El-Haggar Dr. / Mahmoud A. Bakry

DATE

13 / 07 / 1435

Dr. / Ali Saied El-Shahrany DEPARTMENT HEAD

DATE

13 / 07 / 1435

COURSE INSTRUCTOR

DATE

APPROVED:

DEAN, COLLEGE OF ENGINEERING DATE

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ABSTRACT

DESIGN AND CONSTRUCTION OF A SOLAR DRYING SYSTEM FOR

FOOD PRESERVATION

Senior Project Report Submitted to the department of

Mechanical Engineering

The solar drying system utilizes solar energy to heat up air and to dry any food

substance loaded, which is beneficial in reducing wastage of agricultural product and

helps in preservation of agricultural product. Based on the limitations of the natural sun

drying e.g. exposure to direct sunlight, liability to pests and rodents lack of proper

monitoring, and the escalated cost of the mechanical dryer, a solar is therefore

developed to cater for this limitation.

This project presents the design, construction and performance of a mixed-mode

solar dryer for food preservation. In the dryer, the heated air from a separate solar

collector is passed through a grain bed, and at the same time, the drying cabinet absorbs

solar energy directly through the transparent walls and roof. The results obtained during

the test period revealed that the temperatures inside the dryer and solar collector were

much higher than the ambient temperature during most hours of the day-light. The

temperature rise inside the drying cabinet was up to 74% for about three hours

immediately after 12.00h (noon). The dryer exhibited sufficient ability to dry food items

reasonably rapidly to a safe moisture level and simultaneously it ensures a superior

quality of the dried product.

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DEDICATION

To our Parents, who through his financial and moral support were the

source of inspiration and the mainstay in my attaining an education, I dedicate

this project.

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ACKNOWLEDGMENTS

We wish to express our gratitude to all those who provided help and cooperation

in various ways at the different stages of this project. Special thanks are conveyed to

Assistant Prof. Mahmoud El Haggar for supervising and guidance, help and advice in

supervising this project. Also we wish to express our great gratitude and deepest

appreciation to our supervisor, Assistant Prof. Mahmoud Bakry for his efforts in this

project.

Also we would like to express our sincere appreciation to Dean of the College of

Engineering in Jazan University, all staff members in Mechanical Engineering

Department and also for all members in Examination Committee.

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TABLE OF CONTENTS

DESIGN AND CONSTRUCTION OF A SOLAR DRYING SYSTEM

FOR FOOD PRESERVATION

PAGE

ABSTRACT 3

DEDICATION 4

ACKNOWLEDGEMENT 5

TABLE OF CONTENTS 6-8

LIST OF FIGURES 9-10

LIST OF TABLES 11

NOMENCLATURE (Optional) 12-13

1. INTRODUCTION 14

1-1 Literature Review 14-17

1-2 Problem Statement 17-19

1-3 Problem Statement Objectives 20

1-4 Problem justification and Outcomes 20

1-5 Problem Constraints 21

2. DESIGN APPROACH AND METHODOLOGY

2-1 Design approach 22-29

2.1.1 Drying Mechanism 23

2.1.2 Air Properties 27

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2.1.3 Classification of drying systems 29

2-2 Design Methodology 29-51

2.2.1 Types of solar dryers 30

2.2.2 Open sun drying 31

2.2.3 Direct type solar drying 33

2.2.4 Indirect type solar drying 36

2.2.5 Applications of solar dryers 48

2.2.6 Conclusions 52

3. THEORETICAL BACKGROUND

3-1 Design specifications and assumptions 52-54

3.1.1 Solar dryer components 53

3.1.2 Orientation of the dryer 55

3-2 Mathematical models and formulations 55-56

3.2.1 Operation of the dryer 56

3.2.2 Drying mechanism 57

3.2.3 Basic theory of solar dryer (Formulations) 57

3.2.4 Energy balance equation for the drying process 60

4. DESIGN PROCEDURE AND IMPLEMENTATION

4-1 Design Procedures 57-61

4.1.1 The experimental set-up 62

4.1.2 Collector (solar air heater) 63

1.5”

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4.1.3 The drying cabinet and drying racks 64

4.1.4 Drying Mechanism 65

4-2 Design Implementation 66-69

4.2.1 Results and discussions 66-69

5. FEASIBIILITY STUDIES AND MARKET NEEDS 70

6. CONCLUSION AND RECOMMENDATIONS

6-1 Conclusion 71

6-2 Recommendations 72

7. APPENDICES 73-77

REFERENCES 78-81

CAPSTONE DESIGN PROJECT 82-85

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List of Figures

Figure 2.1 Moisture in the drying material.

Figure 2.2 Rate of moisture loss

Figure 2.3 Drying rate with time curve

Figure 2.4 Typical drying rate curve

Figure 2.5 Representation of drying process

Figure 2.6 Working principle of open sun drying

Figure 2.7 Direct solar drying (Natural convection type cabinet drier)

Figure 2.8 A modified natural-circulation solar-energy cabinet dryer

Figure 2.9 Reverse absorber cabinet drier

Figure 2.10 Indirect solar drier (Forced convection solar drier)

Figure 2.11 Green house type solar drier

Figure 2.12 Solar tunnel drier

Figure 2.13 Multiple-shelf portable solar drier

Figure 2.14 Staircase solar drier

Figure 2.15 Rotary column cylindrical drier

Figure 2.16 Solar assisted drying systems

Figure 2.17 Solar grain dryer with rotatable indirect air heater and a PV run fan

Figure 2.18 (a) A simple presentation of first model

Figure 2.18 (b) side view of first model

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Figure 2.19 (a) A simple representation of second model

Figure 2.19 (b) Side view of 2nd model

Figure 3.1 Sectional view of the mixed-mode solar dryer

Figure 3.2 Isometric drawing of the mixed-mode solar dryer

Figure 4.1 Section of the mixed-mode solar dryer

Figure 4.2 Typical solar collectors for air heating

Figure 4.3 Dimension of trays used in the drying chamber

Figure 4.4 Typical day results of the diurnal variation of temperatures in the solar dryer

Figure 4.5 Typical day results of the diurnal variation of relative humidity in the dryer

Figure 4.6 Drying curve for potato chips

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List of Tables

Table 2.1 Typical solar energy dryer designs

Table 2.2 Comparisons of natural-circulation solar-energy dryers

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Nomenclature

SYMBOLS DESCRIPTION UNITS

I Rate of total radiation incident (Wm–2

)

on the absorber‘s surface

Ac Collector area (m

2

)

Qu

Rate of useful energy collected by the air (W)

Qcond Rate of conduction losses from the absorber (W)

Qconv Rate of convective losses from the absorber (W)

QR Rate of long wave re-radiation from the absorber (W)

Qρ Rate of reflection losses from the absorber (W)

UL Overall heat transfer coefficient of the absorber (Wm

–2

K–1

)

Tc Temperature of the collector‘s absorber (K)

Ta Ambient air temperature (K)

Qg Heat gained by the air (kW)

𝒎𝒂.

Mass of air leaving the dryer per unit time (kgs– 1

)

Cpa Specific heat capacity of air (kJkg

– 1

K– 1

)

FR Collector heat removal factor

ηc Thermal efficiency of the collector

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Lv Latent heat (kJ kg-1

)

mw Mass of water evaporated from the food item (kg)

ma Mass of drying air (kg)

T1 Initial temperatures of the drying air (K)

T2 Final temperature of the drying air (K)

Cp Specific heat at constant pressure (kJ kg

–1

K–1

)

mw Mass of water evaporated (kg)

mi Initial mass of the food item (kg)

Me Equilibrium moisture content (% dry basis)

Mi Initial moisture content (% dry basis)

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Chapter 1

Introduction

Drying is one of the methods used to preserve food products for longer periods.

The heat from the sun coupled with the wind has been used to dry food for preservation

for several thousand years.

Solar thermal technology is a technology that is rapidly gaining acceptance as an

energy saving measure in agriculture application. It is preferred to other alternative

sources of energy such as wind and shale, because it is abundant, inexhaustible, and

non-polluting. Solar air heaters are simple devices to heat air by utilizing solar energy

and it is employed in many applications requiring low to moderate temperature below

80°C, such as crop drying and space heating.

Drying is the oldest preservation technique of agricultural products and it is an

energy intensive process. High prices and shortages of fossil fuels have increased the

emphasis on using alternative renewable energy resources. Drying of agricultural

products using renewable energy such as solar energy is environmental friendly and has

less environmental impact.

Different types of solar dryers have been designed, developed and tested in the

different regions of the tropics and subtropics. The major two categories of the dryers

are natural convection solar dryers and forced convection solar dryers. In the natural

convection solar dryers the airflow is established by buoyancy induced airflow while in

forced convection solar dryers the airflow is provided by using fan operated either by

electricity/solar module or fossil fuel. Now the solar dryer designed and developed for

and used in tropics and subtropics are discussed under two headings.

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1.1 Literature Review

Crop drying is the most energy consuming process in all processes on the farm.

The purpose of drying is to remove moisture from the agricultural produce so that it can

be processed safely and stored for increased periods of time. Crops are also dried before

storage or, during storage, by forced circulation of air, to prevent spontaneous

combustion by inhibiting fermentation. It is estimated that 20% of the world‘s grain

production is lost after harvest because of inefficient handling and poor implementation

of post-harvest technology, says Hartman‘s (1991). Grains and seeds are normally

harvested at a moisture level between 18% and 40% depending on the nature of crop.

These must be dried to a level of 7% to 11% depending on application and market need.

Once a cereal crop is harvested, it may have to be stored for a period of time before it

can be marketed or used as feed. The length of time a cereal can be safely stored will

depend on the condition it was harvested and the type of storage facility being utilized.

Grains stored at low temperature and moisture contents can be kept in storage for longer

period of time before its quality will deteriorate. Some of the cereals which are normally

stored include maize, rice, beans.

Solar drying may be classified into direct and indirect solar dryer. In direct solar

dryers the air heater contains the grains and solar energy which passes through a

transparent cover and is absorbed by the grains. Essentially, the heat required for drying

is provided by radiation to the upper layers and subsequent conduction into the grain

bed. However, in indirect dryers, solar energy is collected in a separate solar collector

(air heater) and the heated air then passes through the grain bed, while in the mixed-

mode type of dryer, the heated air from a separate solar collector is passed through a

grain bed, and at the same time, the drying cabinet absorbs solar energy directly through

the transparent walls or the roof.

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Energy is important for the existence and development of human kind and is a

key issue in international politics, the economy, military preparedness, and diplomacy.

To reduce the impact of conventional energy sources on the environment, much

attention should be paid to the development of new energy and renewable energy

resources. Solar energy, which is environment friendly, is renewable and can serve as a

sustainable energy source.

Hence, it will certainly become an important part of the future energy structure

with the increasingly drying up of the terrestrial fossil fuel. However, the lower energy

density and seasonal doing with geographical dependence are the major challenges in

identifying suitable applications using solar energy as the heat source. Consequently,

exploring high efficiency solar energy concentration technology is necessary and

realistic [24].

Solar energy is free, environmentally clean, and therefore is recognized as one of

the most promising alternative energy recourses options. In near future, the large-scale

introduction of solar energy systems, directly converting solar radiation into heat, can be

looked forward. However, solar energy is intermittent by its nature; there is no sun at

night. Its total available value is seasonal and is dependent on the meteorological

conditions of the location. Unreliability is the biggest retarding factor for extensive solar

energy utilization. Of course, reliability of solar energy can be increased by storing its

portion when it is in excess of the load and using the stored energy whenever needed.

Solar drying is a potential decentralized thermal application of solar energy

particularly in developing countries [21]. However, so far, there has been very little

field penetration of solar drying technology. In the initial phase of dissemination,

identification of suitable areas for using solar dryers would be extremely helpful

towards their market penetration.

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Solar drying is often differentiated from ―sun drying‖ by the use of equipment to

collect the sun‘s radiation in order to harness the radiative energy for drying

applications. Sun drying is a common farming and agricultural process in many

countries, particularly where the outdoor temperature reaches 30 oC or higher. In many

parts of South East Asia, spice s and herbs are routinely dried. However, weather

conditions often preclude the use of sun drying because of spoilage due to rehydration

during unexpected rainy days. Furthermore, any direct exposure to the sun during high

temperature days might cause case hardening, where a hard shell develops on the

outside of the agricultural products, trapping moisture inside. Therefore, the

employment of solar dryer taps on the freely available sun energy while ensuring good

product quality via judicious control of the radiative heat. Solar energy has been used

throughout the world to dry products. Such is the diversity of solar dryers that

commonly solar-dried products include grains, fruits, meat, vegetables and fish. A

typical solar dryer improves upon the traditional open-air sun system in five important

ways [21]:

It is faster. Materials can be dried in a shorter period of time. Solar dryers

enhance drying times in two ways. Firstly, the translucent, or transparent, glazing

over the collection area traps heat inside the dryer, raising the temperature of the

air. Secondly, the flexibility of enlarging the solar collection area allows for

greater collection of the sun‘s energy.

It is more efficient. Since materials can be dried more quickly, less will be lost to

spoilage immediately after harvest. This is especially true of products that require

immediate drying such as freshly harvested grain with high moisture content. In

this way, a larger percentage of products will be available for human

consumption. Also, less of the harvest will be lost to marauding animals and

insects since the products are in safely enclosed compartments. It is hygienic.

Since materials are dried in a controlled environment, they are less likely to be

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contaminated by pests, and can be stored with less likelihood of the growth of

toxic fungi. It is healthier. Drying materials at optimum temperatures and in a

shorter amount of time enables them to retain more of their nutritional value such

as vitamin C. An added bonus is that products will look better, which enhances

their marketability and hence provides better financial returns for the farmers. It is

cheap. Using freely available solar energy instead of conventional fuels to dry

products, or using a cheap supplementary supply of solar heat, so reducing

conventional fuel demand can result in significant cost savings.

1.2 Problem Statement

Food scientists have found that by reducing the moisture content of food to

between 10 and 20%, bacteria, yeast, mold and enzymes are prevented from spoiling it.

The flavor and most of the nutritional value is preserved and concentrated

[16].Wherever possible, it is traditional to harvest most grain crops during a dry period

or season and simple drying methods such as sun drying are adequate. However,

maturity of the crop does not always coincide with a suitably dry period. Furthermore,

the introduction of high-yielding varieties, irrigation, and improved farming practices

have led to the need for alternative drying practices to cope with the increased

production and grain harvested during the wet season as a result of multi-cropping.

Drying and preservation of agricultural products have been one of the oldest uses

of solar energy. The traditional method, still widely used throughout the world, is open

sun drying where diverse crops, such as fruits, vegetables, cereals, grains, tobacco, etc.

are spread on the ground and turned regularly until sufficiently dried so that they can be

stored safely. However, there exist many problems associated with open sun drying. It

has been seen that open sun drying has the following disadvantages. It requires both

large amount of space and long drying time. The crop is damaged because of the hostile

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weather conditions; contamination of crops from the foreign materials, degradation by

overheating, and the crop is subject to insect infestation, the crop is susceptible to re-

absorption of moisture if it is left on the ground during periods of no sun, and there is no

control on the drying process. This could lead to slow drying rate, contamination and

poor quality of dried products, and loss in production.

Although the spreading of the crop on the ground or on a platform and drying it

directly by the sun is cheap and successfully employed for many products throughout

the world, where solar radiation and climatic conditions are favorable, because of the

above mentioned factors of open sun drying process and a better understanding of the

method of utilizing solar energy to advantage, have given rise to a scientific method

called solar drying. Solar drying of farm crops offers the following advantages by

permitting: early harvest which reduces the field loss of products from storm and natural

shattering.

The field conditions (dry and fewer weeds) are often better for harvesting earlier

in the season, planning the harvesting season to make better use of labor. Farm crops

can be harvested when natural drying conditions are unfavorable, long-time storage with

little deterioration. Extended storage periods are becoming increasingly important with

large amount of grain being stored and carried over through another storage year by the

farmer, government, and industry, and the farmer‘s taking advantage of higher price a

few months after harvest although in some years there may be no price advantage. By

removing moisture the possibility of the grain heating with subsequent reduction or

destruction of germination is decreased.

The farmer‘s selling a better quality product which is worth more to him and to

those who must use those products [2].Therefore, by providing a sheltered drying area

or chamber in which the crops to be dried and stored, a stream of air is heated by solar

energy to reduce its relative humidity which is then passed over the crops. This form of

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solar drying could improve the quality of the crop to be dried, reduce spoilage by

contamination and local overheating, reduce spillage losses, speed up the drying

process, achieve better quality control, and reduction in drying time.

The disadvantages of open sun drying need an appropriate technology that can

help in improving the quality of the dried products and in reducing the wastage. This led

to the application of various types of drying devices like solar dryer, electric dryers,

wood fuel driers and oil-burned driers. However, the high cost of oil and electricity and

their scarcity in the rural areas of most third world countries have made some of these

driers very unattractive. Therefore interest has been focused mainly on the development

of solar driers [23].Solar dryers are usually classified according to the mode of air flow

into natural convection and forced convection dryers. Natural convection dryers do not

require a fan to pump the air through the dryer. The low air flow rate and the long

drying time, however, result in low drying capacity. Thus, this system is restricted to the

processing of small quantities of agricultural surplus for family consumption. Where

large quantities of fresh produce are to be processed for the commercial market, forced

convection dryers should be used [1].

One basic disadvantage of forced convection dryers lies in their requirement of

electrical power to run the fan. Since the rural or remote areas of many developing

countries are not connected to the national electric grids, the use of these dryers is

limited to electrified urban areas. Even in the urban areas with grid-connected

electricity, the service is unreliable. In view of the prevailing economic difficulties in

most of these countries, this situation is not expected to change in the foreseen able

future. The use of natural convection solar dryer could boost the dissemination of solar

dryers in the developing countries [1]. Therefore, experimental performance of solar

dryer has been evaluated in this project.

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1.3 Problem Statement Objectives

The objective of this study is to develop a mixed-mode solar dryer in which the

grains are dried simultaneously by both direct radiation through the transparent walls

and roof of the cabinet and by the heated air from the solar collector. The problems of

low and medium scale processor could be alleviated, if the solar dryer is designed and

constructed with the consideration of overcoming the limitations of direct and indirect

type of solar dryer. So therefore, this work will be based on the importance of a mixed

mode solar dryer which is reliable and economically, design and construct a mixed

mode solar dryer using locally available materials and to evaluate the performance of

this solar dryer.

1.4 Problem Justification and Outcomes

Food crops are usually for immediate consumption needs, resulting in wastage of

food surpluses during the short harvest periods and scarcity during post harvest periods.

Drying is one of the methods used to preserve food products for longer periods. It has

been established as the most efficient preservation technique for most tropical crops.











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1.5 Problem Constraints

Drying processes play an important role in the preservation of agricultural

products. They are defined as a process of moisture removal due to simultaneous heat

and mass transfer. The purpose of this project is to present the developments and

potentials of solar drying technologies for drying grains, fruits, vegetables, spices,

medicinal plants.

The traditional method of drying, known as ‗sun drying‘, involves simply laying

the product in the sun on mats, roofs or drying floors. Major disadvantage of this

method is contamination of the products by dust, birds and insects – Some percentage

will usually be lost or damaged, it is labour intensive, nutrients loss, such as vitamin A

and the method totally depends on good weather conditions.

Because the energy requirements - sun and wind - are readily available in the

ambient environment, little capital is required. This type of drying is frequently the only

commercially used and viable methods in which to dry agricultural products in

developing countries. The safer alternative to open sun drying is solar dryer.

This is a more efficient method of drying that produces better quality products, but

it also requires initial investments. If drying conditions such as weather and food supply

are good, natural circulation solar energy, solar dryers appear to be increasingly

attractive as commercial proposition.

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Chapter 2

DESIGN APPROACH AND METHODOLOGY

Solar drying refers to a technique that utilizes incident solar radiation to convert it

into thermal energy required for drying purposes. Most solar dryers use solar air heaters

and the heated air is then passed through the drying chamber (containing material) to be

dried. The air transfers its energy to the material causing evaporation of moisture of the

material.

2.1 Design approach

2.1.1 Drying Mechanism

In the process of drying, heat is necessary to evaporate moisture from the material

and a flow of air helps in carrying away the evaporated moisture. There are two basic

mechanisms involved in the drying process: the migration of moisture from the interior

of an individual material to the surface, and the evaporation of moisture from the

surface to the surrounding air.

The drying of a product is a complex heat and mass transfer process which

depends on external variables such as temperature, humidity and velocity of the air

stream and internal variables which depend on parameters like surface characteristics

(rough or smooth surface), chemical composition (sugars, starches, etc.), physical

structure(porosity, density, etc.), and size and shape of products. The rate of moisture

movement from the product inside to the air outside differs from one product to another

and depends very much on whether the material is hygroscopic or non-hygroscopic.

Non-hygroscopic materials can be dried to zero moisture level while the hygroscopic

materials like most of the food products will always have residual moisture content.

This moisture, in hygroscopic material, may be bound moisture which remained in the

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material due to closed capillaries or due to surface forces and unbound moisture which

remained in the material due to the surface tension of water as shown in Figure 2.1 [14].

Figure 2.1 Moisture in the drying material.

When the hygroscopic material is exposed to air, it will absorb either moisture or

desorbs moisture depending on the relative humidity of the air. The equilibrium

moisture content (EMC = Me) will soon reach when the vapour pressure of water in the

material becomes equal to the partial pressure of water in the surrounding air [14]. The

equilibrium moisture content in drying is therefore important since this is the minimum

moisture to which the material can be dried under a given set of drying conditions. A

series of drying characteristic curves can be plotted. The best is if the average moisture

content M of the material is plotted versus time as shown in Figure 2. 2.

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Figure 2.2 Rate of moisture loss

Another curve can be plotted between drying rate i.e. dM/dt versus time t as

shown in Figure 2.3. But more information can be obtained if a curve is plotted between

drying rate dM/dt versus moisture content M as shown in Figure 2.4.

Figure 2.3 Drying rate with time curve

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Figure 2.4 Typical drying rate curve

As is seen from Figure 2.4 for both non-hygroscopic and hygroscopic materials,

there is a constant drying rate terminating at the critical moisture content followed by

falling drying rate. The constant drying rate for both non-hygroscopic and hygroscopic

materials is the same while the period of falling rate is little different. For non-

hygroscopic materials, in the period of falling rate, the drying rate goes on decreasing

till the moisture content become zero. While in the hygroscopic materials, the period of

falling rate is similar until the unbound moisture content is completely removed, then

the drying rate further decreases and some bound moisture is removed and continues till

the vapour pressure of the material becomes equal to the vapour pressure of the drying

air. When this equilibrium reaches then the drying rate becomes zero [14].

The period of constant drying for most of the organic materials like fruits,

vegetables, timber, etc. is short and it is the falling rate period in which is of more

interest and which depends on the rate at which the moisture is removed. In the falling

rate regime moisture is migrated by diffusion and in the products with high moisture

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content, the diffusion of moisture is comparatively slower due to turgid cells and filled

interstices. In most agricultural products, there is sugar and minerals of water in the

liquid phase which also migrates to the surfaces, increase the viscosity hence reduce the

surface vapour pressure and hence reduce the moisture evaporation rate [14].

Drying is done either in thin layer drying or deep layer drying. In thin layer

drying; which is done in case of most of fruits and vegetables, the product is spread in

thin layers with entire surface exposed to the air moving through the product and the

Newton‘s law of cooling is applicable in the falling rate region. Most of the grains are

dried in deep layer which can be considered as a series of thin layers and the

temperature and the humidity varies from layer to layer [14].

2.1.2 Air Properties

The properties of the air flowing around the product are major factors in

determining the rate of removal of moisture. The capacity of air to remove moisture is

principally dependent upon its initial temperature and humidity; the greater the

temperature and lower the humidity the greater the moisture removal capacity of the air.

The relationship between temperature, humidity and other thermodynamic properties is

represented by the psychometric chart. It is important to appreciate the difference

between the absolute humidity and relative humidity of air. The absolute humidity is the

moisture content of the air (mass of water per unit mass of air) whereas the relative

humidity is the ratio, expressed as a percentage, of the moisture content of the air at a

specified temperature to the moisture content of air if it were saturated at that

temperature.

The changes in condition of air when it is heated using the solar energy and then

passed through a bed of moist product are shown in Figure 2.5. The heating of air from

temperature TA to TB is represented by the line AB. During heating the absolute

humidity remains constant at A whereas the relative humidity falls from to . As

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air moves through the material to be dried, it absorbs moisture. Under (hypothetical)

adiabatic drying; sensible heat in the air is converted to latent heat and the change in the

condition of air is represented along a line of constant enthalpy, BC. Both absolute

humidity and relative humidity increase from B and C and from to C, respectively,

but air temperature decreases to, TC. The absorption of moisture by the air would be the

difference between the absolute humidities at C and B. (C - A). If unheated air is

passed through the bed, the drying process would be represented by the line AD.

Assuming that the air at D to be at the same relative humidity,C , as the heated air at C,

then the absorbed moisture would be((D - A), considerably less than that absorbed by

the heated air ((C - A).

Figure 2.5 Representation of drying process

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2.1.3 Classification of drying systems

All drying systems can be classified primarily according to their operating

temperature ranges into two main groups of high temperature dryers and low

temperature dryers. However; dryers are more commonly classified broadly according

to their heating sources into fossil fuel dryers (more commonly known as conventional

dryers) and solar-energy dryers. Strictly, all practically-realized designs of high

temperature dryers are fossil fuel powered, while the low temperature dryers are either

fossil fuel or solar-energy based systems [5].

1. High temperature dryers

High temperature dryers are necessary when very fast drying is desired. They are

usually employed when the products require a short exposure to the drying air. Their

operating temperatures are such that, if the drying air remains in contact with the

product until equilibrium moisture content is reached, serious over drying will occur.

Thus, the products are only dried to the required moisture contents and later cooled.

High temperature dryers are usually classified into batch dryers and continuous-flow

dryers. In batch dryers, the products are dried in a bin and subsequently moved to

storage. Thus, they are usually known as batch-in-bin dryers. Continuous-flow dryers

are heated columns through which the product flows under gravity and is exposed to

heated air while descending. Because of the temperature ranges prevalent in high

temperature dryers, most known designs are electricity or fossil-fuel powered. Only a

very few practically-realized designs of high temperature drying systems are solar-

energy heated [5].

2. Low temperature dryers

In low temperature drying systems, the moisture content of the product is usually

brought in equilibrium with the drying air by constant ventilation. Thus, they do tolerate

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intermittent or variable heat input. Low temperature drying enables products to be dried

in bulk and is most suited also for long term storage systems. Thus, they are usually

known as bulk or storage dryers. Their ability to accommodate intermittent heat input

makes low temperature drying most appropriate for solar-energy applications. Thus,

some conventional dryers and most practically-realized designs of solar-energy dryers

are of the low temperature type [5].

2.2 Design Methodology

2.2.1 Types of solar driers

Solar-energy drying systems are classified primarily according to their heating

modes and the manner in which the solar heat is utilized. In broad terms; they can be

classified into two major groups, namely [5]:

Active solar-energy drying systems (most types of which are often termed hybrid

solar dryers); and

Passive solar-energy drying systems (conventionally termed natural-circulation

solar drying systems).

Three distinct sub-classes of either the active or passive solar drying systems can

be identified which vary mainly in the design arrangement of system components and

the mode of utilization of the solar heat, namely [5]:

Direct (integral) type solar dryers;

Indirect (distributed) type solar dryers.

Direct solar dryers have the material to be dried placed in an enclosure, with a

transparent cover on it. Heat is generated by absorption of solar radiation on the product

itself as well as on the internal surfaces of the drying chamber. In indirect solar dryers,

solar radiation is not directly incident on the material to be dried. Air is heated in a solar

31

collector and then ducted to the drying chamber to dry the product. Specialized dryers

are normally designed with a specific product in mind and may include hybrid systems

where other forms of energy are also used [21]. Although indirect dryers are less

compact when compared to direct solar dryers, they are generally more efficient. Hybrid

solar systems allow for faster rate of drying by using other sources of heat energy to

supplement solar heat.

The three modes of drying are: (i) open sun, (ii) direct and (iii) indirect in the

presence of solar energy. The working principle of these modes mainly depends upon

the method of solar-energy collection and its conversion to useful thermal energy.

2.2.2 Open sun drying (OSD)

Fig. 2.6 shows the working principle of open sun drying by using solar energy.

The short wave length solar energy falls on the uneven product surface. A part of this

energy is reflected back and the remaining part is absorbed by the surface. The absorbed

radiation is converted into thermal energy and the temperature of product stars

increasing. This results in long wavelength radiation loss from the surface of product to

ambient air through moist air. In addition to long wave length radiation loss there is

convective heat loss too due to the blowing wind through moist air over the material

surface. Evaporation of moisture takes place in the form of evaporative losses and so the

material is dried. Further apart of absorbed thermal energy is conducted into the interior

of the product. This causes a rise in temperature and formation of water vapor inside the

material and then diffuses towards the surface of the and finally losses thermal energy in

the end then diffuses towards the surface of the and finally losses the thermal energy in

the form of evaporation. In the initial stages, the moisture removal is rapid since the

excess moisture on the surface of the product presents a wet surface to the drying air.

Subsequently, drying depends upon the rate at which the moisture within the product

moves to the surface by a diffusion process depending upon the type of the product [22].

32

Fig. 2.6 Working principle of open sun drying

In open sun drying, there is a considerable loss due to various reasons such as

rodents, birds, insects and micro-organisms. The unexpected rain or storm further

worsens the situation. Further, over drying, insufficient drying, contamination by

foreign material like dust dirt, insects, and micro-organism as well discoloring by UV

radiation are characteristic for open sun drying. In general, open sun drying does not

fulfill the international quality standards and therefore it cannot be sold in the

international market [21].

With the awareness of inadequacies involved in open sun drying, a more

scientific method of solar-energy utilization for drying has emerged termed as

controlled drying or solar drying. The main features of typical designs of the direct and

of indirect types solar -energy dryers are illustrated in Table 2.1.

33

Table 2.1 Typical solar energy dryer designs

2.2.3 Direct type solar drying (DSD)

Direct solar drying is also called natural convection cabinet dryer. Direct solar

dryers use only the natural movement of heated air. A part of incidence solar radiation

on the glass cover is reflected back to atmosphere and remaining is transmitted inside

cabin dryer. Further, a part of transmitted radiation is reflected back from the surface of

the product. The remaining part is absorbed by the surface of the material. Due to the

absorption of solar radiation, product temperature increase and the material starts

emitting long wave length radiation which is not allowed to escape to atmosphere due to

presence of glass cover unlike open sun drying. Thus the temperature above the product

34

inside chamber becomes higher. The glass cover server one more purpose of reducing

direct convective losses to the ambient which further become beneficial for rise in

product and chamber temperature respectively [21].

However, convective and evaporative losses occur inside the chamber from the

heated material. The moisture is taken away by the air entering into the chamber from

below and escaping through another opening provide at the top as shown in Fig. 2. A

direct solar dryer is one in which the material is directly exposed to the sun‘s rays. This

dryer comprises of a drying chamber that is covered by a transparent cover made of

glass or plastic. The drying chamber is usually a shallow, insulated box with air-holes in

it to allow air to enter and exit the box. The product samples are placed on a perforated

tray that allows the air to flow through it and the material. Fig. 2.7 shows a schematic of

a simple direct dryer [15]. Solar radiation passes through the transparent cover and is

converted to low-grade heat when it strikes an opaque wall. This low-grade heat is then

trapped inside the box by what is known as the ‗greenhouse effect.‘‘ Simply stated, the

short wavelength solar radiation can penetrate the transparent cover. Once converted to

low-grade heat, the energy radiates.

Reference [5] reported a modification of the typical design. This cabinet dryer

(Fig. 2.8) was equipped with a wooden plenum to guide the air inlet and a long plywood

chimney to enhance natural-circulation. This dryer was reported to have accelerated the

drying rate about five times over open sun drying.

35

Fig. 2.7 Direct solar drying (Natural convection type cabinet drier)

Fig. 2.8 A modified natural-circulation solar-energy cabinet dryer

36

2.2.4 Indirect type solar drying (ISD)

This type is not directly exposed to solar radiation to minimize discolorations and

cracking. Reference [7] has proposed and analyzed reverse absorber cabinet dryer

(RACD), the schematic view of RACD is shown in Fig. 2.9. The drying chamber is used

for keeping the in wire mesh tray. A downward facing absorber is fixed below the

drying chamber at a sufficient distance from the bottom of the drying chamber. A

cylindrical reflector is placed under the absorber fitted with the glass cover on its

aperture to minimize convective heat losses from the absorber. The absorber can be

selectively coated. The inclination of the glass cover is taken as 45o from horizontal to

receive maximum radiation. The area of absorber and glass cover are taken equal to the

area of bottom of drying chamber. Solar radiation after passing through the glass cover

is reflected by cylindrical reflector toward an absorber. After absorber, a part of this is

lost to ambient through a glass cover and remaining is transferred to the flowing air

above it by convection. The flowing air is thus heated and passes through the placed in

the drying chamber. The exhaust air and moisture is removed through a vent provided at

the top of drying chamber [21].

Fig. 2.9 Reverse absorber cabinet drier

37

Fig. 2.10 describes another principle of indirect solar drying which is generally

known as conventional dryer. In this case, a separate unit termed as solar air heater is

used for solar energy collection for heating of entering air into this unit. The air heater is

connected to a separate drying chamber where the product is kept. The heated air is

allowed to flow through wet material. Here, the heat from moisture evaporation is

provided by convective heat transfer between the hot air and the wet material. The

drying is basically by the difference in moisture concentration between the drying air

and the air in the vicinity of product surface. A better control over drying is achieved in

indirect type of solar drying systems and the product obtained is good quality.

Fig. 2.10 Indirect solar drier (Forced convection solar drier)

There are several types of driers developed to serve the various purposes of

drying products as per local need and available technology. The best potential and

popular ones are natural convection cabinet type, forced convection indirect type and

green house type. Apart from the above three, as seen from the literature, ‗‗Solar tunnel

drier‘‘ is also found to be popular. These conventional types are shown in Figs 2.11, 12.

38

Fig. 2.11 Green house type solar drier

Fig. 2.12 Solar tunnel drier

39

Apart from the obvious advantages of passive solar-energy dryers over the active

types (for applications in rural farm locations in developing countries), the advantages

of the natural circulation solar-energy ''ventilated green house dryer'' over other passive

solar-energy dryer designs include its low cost and its simplicity in both on-the-site

construction and operation. Its major drawback is its susceptibility to damage under

very high wind speeds.

Table 2 gives a concise comparison of the integral and distributed natural-

circulation solar energy dryers [5]. A multi-shelf portable solar dryer [19] is developed.

It has four main parts, i.e., multi-tray rack, trays, movable glazing and shading plate (see

Fig. 2.13). The ambient air enters from the bottom and moves up through the material

loaded in different trays.

After passing through the trays, the air leaves from the top. The multirack is

inclined depending upon the latitude of the location. Four layers of black HDP sheet are

wrapped around the multi-rack such that heat losses are reduced to ambient air from

back and sides. There are seven perforated trays, which are arranged at seven different

levels one above the other. The product to be dried is loaded in these trays. To facilitate

loading and unloading, a new concept of movable glazing has been developed. It

consists of a movable frame (on castor wheels) and UV stabilized plastic sheet. After

loading the product, the movable glazing is fixed with the ulti-tray rack so as to avoid

any air leakage.

40

Table 2.2 Comparisons of natural-circulation solar-energy dryers

Fig. 2.13 Multiple-shelf portable solar drier

41

A staircase type dryer [9] is developed which is in the shape of a metal staircase

with its base and sides covered with double walled galvanized metal sheets with a cavity

filled with no degradable thermal insulation (see Fig.2.14). The upper surface is covered

with transparent polycarbon sheet to allow the sun‘s rays to pass through and be

trapped. The upper polycarbon glazed surface is divided into three equal parts which

can swing open, to provide access to the three compartment inside the dryer. The base

of the dryer has four entry points. The partition walls between the compartments also

have four port holes for easy airflow. Air moves by natural convection as it enters

through the bottom and leaves from the top.

Fig. 2.14 Staircase solar drier

Another system called rotary column cylindrical dryer (Sarsilmaz et al., 2000) is

developed which contains essentially three parts—air blow region (fan), air heater

region (solar collector) and drying region (rotary chamber) (see Fig. 2.15). A fan with

variable speed of air flow rate is connected to the solar collector using a tent fabric. The

connection to the dryer or rotary chamber was again through another tent fabric. The

42

dryer is manufactured from wooden plates at the top and bottom and thin ply wood

plates at the sides to make cylindrical shape. A rectangular slot is opened on side wall

where it faces the solar air heater for the passage of hot air via tent fabric. On the

opposite side of this wall a door is provided for loading and unloading of the products.

A column is constructed at the center of the rotary chamber to mount the products and

the column rotates due to a 12 V dc motor and a pulley and belt system.

Fig. 2.15 Rotary column cylindrical drier

Other solar assisted drying systems are also developed. The use of V-grooved

absorbers improves the heat transfer coefficient between the absorber plate and the air.

The present dryer uses collector of the V-groove absorber type (see Fig. 2.16(a)). A

double pass collector is also developed which consists of a porous medium [16] in the

second pass to store the energy and supply during cloudy weather or in the evenings

(see Fig. 2.16(b)).

Some have been improved further by using other methods such as increased

convection, etc., which are briefly discussed below.

43

Fig. 2.16 Solar assisted drying systems

Since the products need to be spread in a single layer for efficient drying, total

trays are available in the dryer for spreading the product is important. In an attempt to

acquire the area, the roof top of a farm house has been used as a collector. In extension

to this type of drier [10], a dual purpose of illuminating the room by providing a low

temperature roof integrated solar flat plate air heater is introduced. The heated air is

used to dry the product grains spread on perforated plates of aluminum and acrylic,

inside the room. The perforation size for ground nut and paddy is calculated. In yet

another method, a sun tracking system is used along with a dc driven solar fan [14] for a

controlled heating of the product, as shown in Fig. 2.17. For example, maize requires

being heated below 60 oC to avoid overheating and microbial attack. A biomass backup

heater is used to supplement the heat required for faster drying process [2].

Six different types of cabinet driers (all natural circulation type) are constructed

with same fabrication materials and absorber areas, but different height of air gaps, air

pass methods and configurations of absorber plates [11]. The air flow rate is maintained

constant in all the cases. Out of all, the single covered/glazed and the front pass type

44

with black painted aluminum sheet as absorber plate is found to be most efficient. Also

it is found that, the effect of the shape of the absorbing surface on the performance is

considerably less.

In order to make the driers cost effective and comparable to open sun drying,

natural convection type green house driers [11] are developed and tested. There are two

types of driers (see Figs. 2.18 and 2.19). The driers are tested without load–without

chimney, with load–without chimney and with load–with chimney. When the driers are

loaded (pepper in the present case), the efficiency reduces. It is found that the green

house driers are increase the air temperature by 5–9 oC and the chimney provides better

natural circulation of air.

Fig. 2.17 Solar grain dryer with rotatable indirect air heater and a PV run fan

45

Fig. 2.18 (a) A simple presentation of first model

Fig. 2.18 (b) Side view of first model

46

Fig. 2.19 (a) A simple representation of second model

Fig. 2.19 (b) Side view of internal representation of second model

47

Totally different methods of drying have been developed which continue to dry

the products even in the night times thereby reducing the drying time drastically. The

desiccant materials [20] are used which absorb the moisture from the products to be

dried. The cost of desiccant materials is high causing the final product cost to be high.

Hence, low cost desiccants [23] particularly suitable for tropical countries are identified

as bentonite-calcium chloride and kaolonite-calcium chloride. Yet another type is the

one with thermal storage (sensible) to take care of intermittent incoming solar radiation.

The length and width of the air heater, the gap between the absorber plate and glass

cover and thickness of the storage material are optimized in this type of drier [15]. The

thermal efficiency of the air heater is found to be sufficient for drying of various

materials.

In all the types of driers stated above, the hot air enters the drying chamber and

leaves to the atmosphere. But the hot air can be recirculated to save the energy [13].The

drying of coconut and cocoa in a scaled down drier of a large scale drier is considered in

which the recirculation of hot air yields 31 and 29% of energy saving, respectively. The

recirculation of exhaust hot air is also applied to hay driers. Lack of uniform drying and

inability to accurately predict drying times are some of the existing problems. A new

drier is developed which uses forced heated-air circulation through hay stacks. A drying

rate difference of 7% is observed due to recirculation of hot air. By recirculating all of

the exhaust air, the previous driers either increased drying time or proved to be

uneconomical, so only30% of the hot air is recirculated in the present case. The

favorable conditions to recirculate the exhaust air are presented [15].

A drier called FASD (Foldable Agro Solar Dryer) is developed which is a

foldable type that can be stored and transported as desired. The performance of the drier

is tested to find that the inner temperature is about 8 oC higher than ambient and

humidity is lesser by 6% inside. Out of all types, the well known heat pump [15]

48

principle has been used to dry the products and this has been found to be excellent

alternative to the solar drying.

2.2.5 Applications of solar driers

The drying process has been experimentally studied and analyzed to simulate and

design a drier. As drying is a process of removing moisture to a safe level, the

equilibrium moisture content is defined as the moisture content in equilibrium with the

relative humidity of the environment. The equilibrium moisture content is divided into,

static and dynamic. While the static is used for food storage process, dynamic is used

for drying process. The drying process is experimentally obtained and presented as

moisture content on x-axis and rate of drying on y-axis. A deep bed of food grains is

assumed to be composed of thin layers normal to the hot air flow direction. The

equations for thin layer were written initially, using empirical, theoretical and semi

theoretical equations. The conditions of the grain and air change with position and time

during drying of a deep bed of grains. Logarithmic and partial differential equation

models to simulate the deep bed dry modeling are dealt in detail [15].

A computer program in C++ language is developed for modeling of deep bed

drying systems and considers eight different configurations of flow of hot air over

absorber plates of solar collectors. The usual parameters such as heat removal factor,

overall loss coefficient, top loss coefficient, etc., can be determined. The model prompts

for basic data [15] such as amount of grain to be dried, initial moisture content, number

of thin layers and weather data.

In a different direction, the first and second laws of thermodynamics [25] have

been used to develop the design methods for a particular application. Semi-empirical

formulae are developed to calculate the rise in air temperature as it passes through the

heater.NTU (number of transfer units) has been defined analogous to the heat

49

exchangers, as a part of design. Using entropy balance the maximum temperature

reached by solar collector is written and then Entropy Generation Number is developed

to find the entropy generated during thermal conversion of solar energy. Finally, the

drying temperature is established as a function of the maximum limit of temperature the

material might support.

The drying chamber of a drier consists of meshes on which product is spread for

drying. Also, the drying chamber [40] is a wooden cabinet. Hence, the heat loss to the

side walls of the drying chamber is considered. As the hot air passes through the mesh,

in forced convection driers, turbulence is created. A solar drier without either heat

storage or air recycling is considered with a solar collector containing offset plate fins.

Experiments are conducted to calculate heat losses (through Nusselt number).In

the above models, the variation of incoming solar radiation is not taken into account.

For modeling purpose, a constant artificial flux is adopted to study the drying

phenomenon [8]. A drier with three beds of wool is considered with a solar collector.

The drying process in the three zones of the bed is theoretically analyzed. The

solar collector is equipped with a flat plate absorber and offset plate fins absorber plate.

Under constant incident fluxes, at the same mass flow rate of air, the drying rate and

time has been studied to find that offset plate fins collector is better. The known facts

that, the inlet temperature of the air is variable (because of variable incoming solar

radiation) and the products shrink as drying process continues are taken into

consideration for modeling [17]. A most common cabinet type drier is considered for

the study. A moving co-ordinate is defined to take into account of the shrinkage effects.

The experimental data from previous workers is considered for validation of the

mathematical model. The carrot cubes are used as product to test the model. It is

proposed that the estimation of solar irradiance on the drier is essential to predict the

response of the drier [6].Considering a semi-cylindrical solar tunnel drier, the irradiance

50

is calculated by taking the geometric quantities, relative motion of sun and optical

properties into account.

The change of main variables such as moisture content along the drying tunnel is

considered unlike in previous works where uniform distribution is assumed [4].This is a

study of tunnel green house drier which is continuous type. The conditions for

improvement of efficiency are evaluated. A linear relationship between the tunnel

output temperature and incident solar radiation is obtained. The drier production is

presented by a performance parameter which is defined as the ratio between the energy

actually used in the evaporation and the total available energy for the drying process. A

non-dimensional variable is also defined which has all the meteorological information.

It is found that, the average moisture content value of the tunnel can be considered to be

constant [15].

The construction and working of solar tunnel drier is explained in detail. Three

fans run by a solar module are used to create forced convection. The drying procedure

and the instrumentation are also described. The major advantage of solar tunnel drier is

that the regulation of the drying temperature is possible. During high insulation periods,

more energy is received by the collector, which tends to increase the drying temperature

and is compensated by the increase of the air flow rate. The variation of voltage with

respect to radiation in a given day and variation of radiation with respect to time of the

day are presented. The comparative curves using the tunnel dryer and natural sun drying

are presented to show that, the tunnel drying time is less [15]. A substantial increase in

the average sugar content is observed. The economics of the drier is worked out to show

that, the payback period is 3 years.

The solar tunnel drier is modified to develop a green house tunnel drier whose

working principle and construction is explained in detail. Some additional features of

the tunnel drier are highlighted such as improvement in the drier efficiency, lowering of

51

the labor cost and ease in installing a conventional heater as an auxiliary heating system

for continuous production [4]. The drier is considered as a solar collector, and its

instantaneous efficiency is measured. Products were dried in various configurations.

The plots of time in a given day vs. moisture content are plotted. The working principle

of auxiliary heating system is also presented.

Throughout the literature, decrease in drying time has been the main concern.

Further, the natural convection type drier is not preferred as low buoyancy forces may

cause reverse effect leading to the spoilage of the product. In order to resolve these two

issues, an integral type natural convection drier coupled with a biomass stove is

developed [15].

The constructional details and operation of the drier are presented in detail.

Drying time was lowest for solar-biomass method. The uniformity of drying was

questionable as there was significant variation in moisture content when samples were

tested from trays at top, middle and bottom. Even within a tray, when temperature,

relative humidity and velocity of air were measured, variations were observed the

drying efficiency of the drier was evaluated and it is noted that, type of product and its

final moisture content level influences the drying efficiency.

The final moisture in a product generally requires more energy to extract than the

initial moisture and the preparation of the products prior to drying such as slicing,

boiling affects the drying efficiency. These factors make it difficult to make

comparisons with the drying efficiencies of other solar driers reported in the literature.

52

2.2.6 Conclusions

This chapter is focused on the available solar dryer‘s systems and new

technologies. The dependence of the drying on the characteristics of product remains

still as a problem, for comparison of drying efficiencies of various driers. Author

presented a comprehensive review of the various designs, details of construction and

operational principles of the wide variety of practically realized designs of solar-energy

drying systems. Two broad groups of solar energy dryers can be identified, viz., passive

or natural-circulation solar-energy dryers and active or forced-convection solar-energy

dryers (often called hybrid solar dryers). Three sub-groups of these, which differ mainly

on their structural arrangement, can also be identified, via integral or direct mode solar

dryers, distributed or indirect-modes. This classification illustrates clearly how these

solar dryer designs can be grouped systematically according to their operating

temperature ranges, heating sources and heating modes, operational modes or structural

modes. Though properly, designed forced-convection (active) solar dryers are agreed

generally to be more effective and more controllable than the natural-circulation

(passive) types. This chapter also presents some easy-to-fabricate and easy-to-operate

dryers that can be suitably employed at small-scale factories. Such low-cost drying

technologies can be readily introduced in rural areas to reduce spoilage, improve

product quality and overall processing hygiene.

53

Chapter 3

THEORETICAL BACKGROUND

3.1 Design specifications and assumptions

3.1.1 Introduction

Solar drying may be classified into direct and indirect solar dryer. In direct solar

dryers the air heater contains the grains and solar energy which passes through a

transparent cover and is absorbed by the grains. Essentially, the heat required for drying

is provided by radiation to the upper layers and subsequent conduction into the grain

bed. However, in indirect dryers, solar energy is collected in a separate solar collector

(air heater) and the heated air then passes through the grain bed, while in the mixed-

mode type of dryer, the heated air from a separate solar collector is passed through a

grain bed, and at the same time, the drying cabinet absorbs solar energy directly through

the transparent walls or the roof. The objective of this study is to design a mixed-mode

solar dryer in which the grains are dried simultaneously by both direct radiation through

the transparent walls and roof of the cabinet and by the heated air from the solar

collector.

The materials used for the construction of the mixed-mode solar dryer are cheap

and easily obtainable in the local market. Figure3.1 shows the main components of the

dryer, consisting of the solar collector (air heater), the drying cabinet and drying trays.

3.1.2 Solar Dryer Components

The solar dryer consists of the solar collector (air heater), the drying cabinet and

drying trays:

54

1. Collector (Air Heater):

The heat absorber (inner box) of the solar air heater was constructed using 2 mm

thick aluminum plate, painted black, is mounted in an outer box built from well-

seasoned woods. The space between the inner box and outer box is filled with foam

material of about 40 mm thickness and thermal conductivity of 0.043 Wm–1

K–1

. The

solar collector assembly consists of air flow channel enclosed by transparent cover

(glazing). An absorber mesh screen midway between the glass cover and the absorber

back plate provides effective air heating because solar radiation that passes through the

transparent cover is then absorbed by both the mesh and back-plate. The glazing is a

single layer of 4 mm thick transparent glass sheet; it has a surface area of 820 mm by

1020 mm and of transmittance above 0.7 for wave lengths in the rage 0.2 – 2.0 μm and

opaque to wave lengths greater than 4.5 μm. The effective area of the collector glazing

is 0.8 m2

. One end of the solar collector has an air inlet vent of area 0.0888 m2

, which is

covered by a galvanized wire mesh to prevent entrance of rodents, the other end opens

to the plenum chamber.

2. The Drying Cabinet:

The drying cabinet together with the structural frame of the dryer was built from

well-seasoned woods which could withstand termite and atmospheric attacks. An outlet

vent was provided toward the upper end at the back of the cabinet to facilitate and

control the convection flow of air through the dryer. Access door to the drying chamber

was also provided at the back of the cabinet. This consists of three removable wooden

panels made of 13 mm plywood, which overlapped each other to prevent air leakages

when closed. The roof and the two opposite side walls of the cabinet are covered with

transparent glass sheets of 4 mm thick, which provided additional heating.

55

3. Drying Trays:

The drying trays are contained inside the drying chamber and were constructed

from a double layer of fine chicken wire mesh with a fairly open structure to allow

drying air to pass through the food items.

3.1.3 The orientation of the Solar Collector:

The flat-plate solar collector is always tilted and oriented in such a way that it

receives maximum solar radiation during the desired season of used. The best stationary

orientation is due south in the northern hemisphere and due north in southern

hemisphere. Therefore, solar collector in this work is oriented facing south and tilted at

45o

to the horizontal. This inclination is also to allow easy run off of water and enhance

air circulation.

Fig. 3.1 Sectional view of the mixed-mode solar dryer

56

3.2 Mathematical models and formulations

3.2.1 Operation of the Dryer

Fig. 3.2 shows the isometric drawing of the mixed-mode solar dryer. The dryer is

a passive system in the sense that it has no moving parts. It is energized by the sun‘s

rays entering through the collector glazing. The trapping of the rays is enhanced by the

inside surfaces of the collector that were painted black and the trapped energy heats the

air inside the collector. The green house effect achieved within the collector drives the

air current through the drying chamber. If the vents are open, the hot air rises and

escapes through the upper vent in the drying chamber while cooler air at ambient

temperature enters through the lower vent in the collector. Therefore, an air current is

maintained, as cooler air at a temperature Ta enters through the lower vents and hot air at

a temperature Teleaves through the upper vent.

Fig.3.2 Isometric drawing of the mixed-mode solar dryer

57

When the dryer contains no items to be dried, the incoming air at a temperature

‗Ta‘ has relative humidity ‗H

a‘ and the out-going air at a temperature ‗T

e‘, has a relative

humidity ‗He‘. Because T

e >T

a and the dryer contains no item, H

a >H

e. Thus there is

tendency for the out-going hot air to pick more moisture within the dryer as a result of

the difference between Ha

and He. Therefore, insulation received is principally used in

increasing the affinity of the air in the dryer to pick moisture.

3.2.2 Drying mechanism



mechanisms involved in the drying process:

1) The migration of moisture from the interior of an individual material to the

surface, and

2) The evaporation of moisture from the surface to the surrounding air [40]. The

drying of a product is a complex heat and mass transfer process which depends on

external variables such as temperature, humidity and velocity of the air stream and

internal variables which depend on parameters like surface characteristics (rough or

smooth surface), chemical composition (sugars, starches, etc.), physical structure

(porosity, density, etc.), and size and shape of product.

3.2.3 Basic Theory (Formulations)

The energy balance on the absorber is obtained by equating the total heat gained

to the total heat loosed by the heat absorber of the solar collector. Therefore,

IAc = Q

u + Q

cond + Q

conv + Q

R + Q

ρ, (1)

Where:

I = rate of total radiation incident on the absorber‘s surface (Wm–2

);

58

Ac = collector area (m

2

);

Qu = rate of useful energy collected by the air (W);

Qcond

= rate of conduction losses from the absorber (W);

Qconv

= rate of convective losses from the absorber (W);

QR

= rate of long wave re-radiation from the absorber (W);

Qρ = rate of reflection losses from the absorber (W).

The three heat loss terms Qcond

, Qconv

and QR

are usually combined into one-term (QL),

i.e.,

QL

= Qcond

+ Qconv

+ QR. (2)

If τ is the transmittance of the top glazing and IT

is the total solar radiation incident on

the top surface, therefore,

IAc = τ I

TA

c . (3)

The reflected energy from the absorber is given by the expression:

Qρ

= ρτ ITA

c, (4)

Where ρ is the reflection coefficient of the absorber. Substitution of Eqs. (2), (3) and (4)

in Eq. (1) yields:

τITA

c= Q

u + Q

L + ρτ I

TA

c, or

Qu

= τ ITA

c (1 – ρ) – Q

L.

For an absorber (1 – ρ) = α and hence,

Qu

= (ατ) ITAc– QL, (5)

Where α is solar absorbance.

QL

composed of different convection and radiation parts. It is presented in the following

form (Bansal et al. 1990):

QL

= ULA

c (T

c – T

a), (6)

59

Where:

UL

= overall heat transfer coefficient of the absorber (Wm–2

K–1

);

Tc = temperature of the collector‘s absorber (K);

Ta = ambient air temperature (K).

From Equations (5) and (6) the useful energy gained by the collector is expressed as:

Qu

= (ατ) ITAc– ULA

c (T

c – T

a). (7)

Therefore, the energy per unit area (qu) of the collector is

qu= (ατ)I

T – U

L(T

c – T

a). (8)

If the heated air leaving the collector is at collector temperature, the heat gained by the

air Qg is:

Qg = 𝒎𝒂

. Cpa

(Tc – T

a), (9)

Where:

𝑚𝑎. = mass of air leaving the dryer per unit time (kgs

– 1

);

Cpa

= specific heat capacity of air (kJkg– 1

K– 1

).

The collector heat removal factor, FR, is the quantity that relates the actual useful energy

gained of a collector, Eq. (7), to the useful gained by the air, Eq. (9). Therefore,

or

Qg = A

cF

R[(ατ)I

T – U

LA

c(T

c – T

a)]. (11)

The thermal efficiency of the collector is defined as (Itodo et al. 2002) is given in Eq.

(12):

60

3.2.4 Energy Balance Equation for the Drying Process

The total energy required for drying a given quantity of food items can be

estimated using the basic energy balance equation for the evaporation of water (Youcef-

Ali, et al. 2001; Bolaji 2005):

mwL

v= m

aC

p(T

1 – T

2), (13)

where:

Lv = latent heat (kJ kg-1

)

mw= mass of water evaporated from the food item (kg);

ma= mass of drying air (kg);

T1 and T

2 = initial and final temperatures of the drying air respectively (K);

Cp = Specific heat at constant pressure (kJ kg

–1

K–1

).

The mass of water evaporated is calculated from Eq. 14:

Where:

mi= initial mass of the food item (kg);

Me = equilibrium moisture content (% dry basis);

Mi = initial moisture content (% dry basis).

During drying, water at the surface of the substance evaporates and water in the

inner part migrates to the surface to get evaporated. The ease of this migration depends

on the porosity of the substance and the surface area available. Other factors that may

enhance quick drying of food items are: high temperature, high wind speed and low

relative humidity. In drying grains for future planting, care must be taken not to kill the

embryo. In drying items like fish, meat, potato chips, plantain chips etc., excessive

heating must also be avoided, as it spoils the texture and quality of the item.

61

Chapter 4

DESIGN PROCEDURE AND IMPLEMENTATION

4.1 Design Procedures

In many parts of the world there is a growing awareness that renewable energy

have an important role to play in extending technology to the farmer in developing

countries to increase their productivity [39]. Solar thermal technology is a technology

that is rapidly gaining acceptance as an energy saving measure in agriculture

application. It is preferred to other alternative sources of energy such as wind and shale,

because it is abundant, inexhaustible, and non-polluting [28].

Solar air heaters are simple devices to heat air by utilizing solar energy and

employed in many applications requiring low to moderate temperature below 80o

C, such

as crop drying and space heating [36]. Drying processes play an important role in the

preservation of agricultural products.

They are defined as a process of moisture removal due to simultaneous heat and

mass transfer [33]. According to [34] two types of water are present in food items; the

chemically bound water and the physically held water. In drying, it is only the

physically held water that is removed. The most important reasons for the popularity of

dried products are longer shelf-life, product diversity as well as substantial volume

reduction. This could be expanded further with improvements in product quality and

process applications.

The application of dryers in developing countries can reduce post harvest losses

and significantly contribute to the availability of food in these countries. Estimations of

these losses are generally cited to be of the order of 40% but they can, under very

adverse conditions, be nearly as high as 80%. A significant percentage of these losses

62

are related to improper and/or untimely drying of foodstuffs such as cereal grains,

pulses, tubers, meat, fish, etc. [31].

Traditional drying, which is frequently done on the ground in the open air, is the

most widespread method used in developing countries because it is the simplest and

cheapest method of conserving foodstuffs. Some disadvantages of open air drying are:

exposure of the foodstuff to rain and dust; uncontrolled drying; exposure to direct

sunlight which is undesirable for some foodstuffs; infestation by insects; attack by

animals; etc [37].

In order to improve traditional drying, solar dryers which have the potential of

substantially reducing the above-mentioned disadvantages of open air drying; have

received considerable attention over the past 20 years [31]. Solar dryers of the forced

convection type can be effectively used. They however need electricity, which

unfortunately is non-existent in many rural areas, to operate the fans. Even when

electricity exists, the potential users of the dryers are unable to pay for it due to their

very low income. Forced convection dryers are for this reason not going to be readily

applicable on a wide scale in many developing countries. Natural convection dryers

circulate the drying air without the aid of a fan. They are therefore, the most applicable

to the rural areas in developing countries.

4.1.1 THE EXPERIMENTAL SET-UP

The mixed-mode solar dryer with box-type absorber collector was constructed

using the materials that are easily obtainable from the local market. Figure 4.1 shows a

section of the solar dryer. The dryer has four main features namely: the box-type

absorber solar air collector, the drying chamber, the drying rack and two fines electric.

63

Fig. 4.1 Section of the mixed-mode solar dryer

4.1.2 Collector (solar air heater)

The heat absorber (inner box) of the solar air heater was constructed using 1 mm

thick galvanized plate, painted black, the surface facing sunlight was painted with black

paint containing (5%)black chromium powder to increase its absorbing capability. The

solar collector was insulated with rock wool of about 5 cm thickness and thermal

conductivity of 0.04 Wm-1

K-1

on all sides. The solar collector assembly consists of air

flow channel enclosed by transparent cover (glazing). The glazing is a single layer of 4

mm thick transparent glass sheet. It has a surface area of 0.82 by 1.20 cm and of

transmittance above 0.86 (Figure 4.2).

64

Fig. 4.2 Typical solar collector for air heating

4.1.3 The drying cabinet and drying racks

The designing of the drying chamber depends on many factors such as the

product to be dried, the required temperature and velocity of the air to dry food material,

the quantity of the dried product and the relative humidity of the air passing over the

food material. The drying chamber houses four drying racks, between a tray and another

tray is 10 cm as shown in Figure 1. Four trays of dimension (0.75 x 0.30 x 0.08 m) were

fabricated and stacked uniformly/evenly at distances (0.02 m) apart, for placing of

material to be dried. The tray was made from an aluminum wire mesh (0.003 x 0.003 m

in size) attached to it. Metal handles (0.076 m) were attached on each tray for ease of

handling and sliding the trays inside the chamber through the produce to be dried. The

drying chamber was also lined with foam insulation material 5 cm thick to prevent loss

of heat (Figure 4.3).

65

Fig. 4.3 Dimension of trays used in the drying chamber

4.1.4 Drying mechanism



mechanisms involved in the drying process:

1) The migration of moisture from the interior of an individual material to the

surface.

2) The evaporation of moisture from the surface to the surrounding air [40]. The

drying of a product is a complex heat and mass transfer process which depends on

external variables such as temperature, humidity and velocity of the air stream and

internal variables which depend on parameters like surface characteristics (rough or

smooth surface), chemical composition (sugars, starches, etc.), physical structure

(porosity, density, etc.), and size and shape of product.

66

4.2 Design Implementation

Two digital sensors have been positioned to measure the air temperature and

humidity at the inlet and outlet portion of the air heater. Other sensors have been placed

at trays 1, 2, 3 and 4 in order to measure the temperature and humidity of trays. Ambient

temperature was also recorded during the course of experiments with the help of digital

sensor. The experiment was conducted at the location of the faculty of engineering,

Jazan University and the orientation of the solar collector has been fixed towards the

south direction, inclined at an angle of 45°.

Successful tests were conducted between May 1 and May 3, 2014 and in this

project work, one of the test data was used to evaluate the drying curves, humidity and

temperature measurements in the dryer. During the tests period, the heated air was used

to dry potato.

4.2.1 Results and Discussion











67

1. Variation of the temperatures in the solar collector and the drying cabinet

compared to the ambient temperature

Fig. 5.1 shows a typical day results of the hourly variation of the temperatures in

the solar collector and the drying cabinet compared to the ambient temperature. The

dryer is hottest about mid-day when the sun is usually overhead. The temperatures

inside the dryer and the solar collector were much higher than the ambient temperature

during most hours of the daylight. The temperature rise inside drying cabinet was up to

24oC (74%) for about three hours immediately after 12.00h (noon). This indicates

prospect for better performance than open-air sun drying.

Fig. 4.4 A typical day results of the diurnal variation of

temperatures in the solar dryer

68

2. Variation of the relative humidity of the ambient air and drying chamber

Fig. 5.2 shows the diurnal variation of the relative humidity of the ambient air and

drying chamber. Comparison of this figure with Fig. 3 shows that the drying processes

were enhanced by the heated air at very low humidity.

Fig. 4.5 A typical day results of the diurnal variation of

relative humidity in the dryer

69

3. The drying curve for Potato chips in the mixed-mode solar dryer

Fig. 5.3 shows the drying curve for potato chips in the mixed-mode solar dryer. It

was observed that the drying rate increased due to increase in temperature between

10.00h and 14.00h but decreased thereafter, which shows the earlier and faster removal

of moisture from the dried item.

Fig. 4.6 Drying curve for potato chip

70

Chapter 5

FEASIBIILITY STUDIES AND MARKET NEEDS

Feasibility Study for Food Solar dryer System

Cost Economics, of Food Solar dryer System enterprises are worked out for fruits

and vegetables. 1 Million For one unit of 10 dryers. It can transact 10 tons of fruits or

fruit bars in dehydrated form. This is an excellent income and profitable venture in rural

Saudi Arabia. The cost benefit analysis of our dryers indicates that a commercial

venture of a project with 10 solar dryers will give the payback period of 2 - 2½ years.

The profitability of the technology in terms of employment potential and income

generation is established and acceptability of the product in the market is evaluated from

the proven market demand. Our expectation about the feasibility of the technology for

rural employment has been realized .

The reasons for the success are :

1. The grass root level Non Government and voluntary organizations have devotion

for service to rural people and have the ability to capacity building and skill

development among rural women .

2. Food Solar drying process is the integration of food science and technology and

solar drying technology disciplines. So the practice followed in solar food

processing is based on these two techniques. To make the solar food processing

products, one needs rigorous training in this technology by well qualified persons,

close monitoring and supervision of the operations and following the food safety,

clean & hygienic practices, quality consciousness and assurance in day to day

production. The social entrepreneurs have proved very successful in this respect .

71

Chapter 6

CONCLUSION AND RECOMMENDATIONS

6.1 Conclusion

From the test carried out, the following conclusions were made. The solar dryer

can raise the ambient air temperature to a considerable high value for increasing the

drying rate of agricultural crops. The product inside the dryer requires less attentions,

like attack of the product by rain or pest (both human and animals), compared with

those in the open sun drying. Although the dryer was used to dry Potato, it can be used

to dry other crops like yams, cassava, maize and plantain etc. There is ease in

monitoring when compared to the natural sun drying technique. The capital cost

involved in the construction of a solar dryer is much lower to that of a mechanical dryer.

Also from the test carried out, the simple and inexpensive mixed-mode solar

dryer was designed and constructed using locally sourced materials. The hourly

variation of the temperatures inside the cabinet and air-heater are much higher than the

ambient temperature during the most hours of the day-light. The temperature rise inside

the drying cabinet was up to 24o

C (74%) for about three hours immediately after 12.00h

(noon). The dryer exhibited sufficient ability to dry food items reasonably rapidly to a

safe moisture level and simultaneously it ensures a superior quality of the dried product.

72

6.2 Recommendations

The performance of existing solar food dryers can still be improved upon

especially in the aspect of reducing the drying time, and probably storage of heat energy

within the system by increasing the size of the solar collector. Also, meteorological data

should be readily available to users of solar products to ensure maximum efficiency and

effectiveness of the system. Such information will probably guide a local farmer on

when to dry his agricultural produce and when not to dry them.

73

APPENDICES

Table 1: A typical day results of the diurnal variation of temperatures in the solar dryer

Time Ambient Temperature Drying Chamber Temperature Collector Temperature

09:00 32 34 37

10:00 33 37 42

11:00 35 40 50

12:00 38 46 58

13:00 35 50 62

14:00 34 45 58

15:00 32 42 50

16:00 31 39 47

17:00 30 36 44

18:00 30 34 39

Table 2: A typical day results of the diurnal variation of relative humidity in the dryer

Time Ambient Air Humidity Drying Chamber Humidity

09:00 40 81

10:00 33 79

11:00 29 77

12:00 32 73

13:00 36 70

14:00 38 74

15:00 39 78

16:00 46 79

17:00 48 81

18:00 50 83

Table 3: Hourly Moisture Loss and Mass of the Potato

Time Mass of

Potato (g)

Moisture

Loss (g)

% Moisture

Loss

Total Moisture

Loss (%)

9:00 560 - -- 58

10.00 547 13 2.3 55.7

11.00 528 19 3.4 52.3

12:00 503 25 4.5 47.8

13:00 474 29 5.2 42.6

14:00 436 28 6.8 35.8

15:00 399 37 6.6 29.2

16:00 365 34 6.0 23.2

17:00 338 27 4.8 18.4

18:00 318 20 3.6 14.8

74

Table 4: Hourly Moisture Content

Time Moisture Content

9:00 2.4

10.00 2

11.00 1.4

12:00 0.8

13:00 0.62

14:00 0.56

15:00 0.53

16:00 0.49

17:00 0.46

18:00 0.44

The Thermocouple

The Thermocouple is by far the most commonly used type of all the temperature

sensor types. Thermocouples are popular due to its simplicity, ease of use and their

speed of response to changes in temperature, due mainly to their small size.

Thermocouples also have the widest temperature range of all the temperature sensors

from below -200oC to well over 2000

oC.

Thermocouples are thermoelectric sensors that basically consist of two junctions

of dissimilar metals, such as copper and constantan that are welded or crimped together.

One junction is kept at a constant temperature called the reference (Cold) junction,

while the other the measuring (Hot) junction. When the two junctions are at different

temperatures, a voltage is developed across the junction which is used to measure the

temperature sensor as shown below.

75

Thermocouple Construction

The operating principal of a thermocouple is very simple and basic. When fused

together the junction of the two dissimilar metals such as copper and constantan

produces a ―thermo-electric‖ effect which gives a constant potential difference of only a

few millivolts (mV) between them. The voltage difference between the two junctions is

called the ―Seebeck effect‖ as a temperature gradient is generated along the conducting

wires producing an emf. Then the output voltage from a thermocouple is a function of

the temperature changes.

If both the junctions are at the same temperature the potential difference across

the two junctions is zero in other words, no voltage output as V1 = V2. However, when

the junctions are connected within a circuit and are both at different temperatures a

voltage output will be detected relative to the difference in temperature between the two

junctions, V1 - V2. This difference in voltage will increase with temperature until the

junction‘s peak voltage level is reached and this is determined by the characteristics of

the two dissimilar metals used.

Thermocouples can be made from a variety of different materials enabling

extreme temperatures of between -200 oC to over +2000

oC to be measured. With such a

large choice of materials and temperature range, internationally recognised standards

have been developed complete with thermocouple colour codes to allow the user to

76

choose the correct thermocouple sensor for a particular application. The British colour

code for standard thermocouples is given below.

Thermocouple Colour Codes

Thermocouple Sensor Colour Codes

Extension and Compensating Leads

Code

Type Conductors (+/-) Sensitivity

British

BS 1843:1952

E Nickel Chromium /

Constantan -200 to 900

oC

J Iron / Constantan 0 to 750oC

K Nickel Chromium /

Nickel Aluminum -200 to 1250

oC

N Nicrosil / Nisil 0 to 1250oC

T Copper / Constantan -200 to 350oC

U

Copper / Copper Nickel

Compensating for

"S" and "R"

0 to 1450oC

The three most common thermocouple materials used above for general

temperature measurement are Iron-Constantan (Type J), Copper-Constantan (Type T),

and Nickel-Chromium (Type K). The output voltage from a thermocouple is very small,

only a few millivolts (mV) for a 10oC change in temperature difference and because of

this small voltage output some form of amplification is generally required.

77

Calibration Curve of Sensor

78

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82

CAPSTONE DESIGN PROJECT

Project Submission And

ABET Criterion 3 a-k Assessment Report

Project Title:



FOOD PRESERVATION

DATE: 13 / 07 / 1435

PROJECT ADVISOR: Assistant Prof. / Mahmoud El-Haggar

Assistant Prof. / Mahmoud Bakry

Team Leader: Abdulelah Ali Al-Jumaah

Team Members: Abdullah Mohamed Asiri

Mohamed Fadil Mohamed Alshehri

Ahmed Mohamed Deash

Fahd Minajy Al-Hamzi

Design Project Information

Percentage of project Content- Engineering Science 40%

Percentage of project Content- Engineering Design 60%

Please indicate if this is your initial project declaration □ Project Initial Start Version

or final project form ■ Final Project Submission Version

Do you plan to use this project as your capstone design project? Yes

83

Mechanism for Design Credit ■ Projects in Engineering Design

□ Independent studies in Engineering

□ Engineering Special Topics

Fill in how you fulfill the ABET Engineering Criteria Program Educational Outcomes

listed below:

Outcome (a). An ability to apply knowledge of mathematics, science, and

engineering fundamentals.

Please list here all subjects (math,

science, and engineering) that have

been applied in your project. (Yes)

Thermodynamics

Fluid mechanics

Heat Transfer

Computer programs and simulation.

Outcome (c).

An ability to design a system, component or process to meet desired

needs within realistic constraints such as economic, Environmental,

Social, political, ethical, health and safety, manufacturability, and

sustainability

All projects should include a design

component. By design we mean both

physical and non physical systems.

(Yes)

In our Project, we were able to

present the design, construction and

performance of a mixed-mode solar

dryer for food preservation.

Outcome (d).

An ability to function in multi-disciplinary teams.

(Yes)

This outcome is achieved

automatically by the fact that our

project composed of 5 students in the

same field, and they are formed a

team work in the project.

84

Outcome (e).

An ability to identify, formulate and solve engineering problems.

(Yes)

This outcome is achieved

automatically by the fact that our

project has a Problem Statement

section (such as the mathematical

model used for designing and

constructing the solar dryer).

Outcome (g).

An ability for effective oral and written communication.

Good report and good presentation

will fulfill this outcome. (Yes),

because we are already learned how

can write the project thesis and make

oral presentations several times

along this period.

Outcome (h).

The broad education necessary to understand the impact of

engineering solutions in a global economics, environmental and

societal context

This outcome is usually fulfilled by

highlighting the economic feasibility

of the project, and emphasizing that

the project would not harm the

environment and does not negatively

affect human subjects. (Yes),

because the main aim from our

project was to design a mixed-mode

solar dryer for food preservation

Outcome (i).

A recognition of the need for, and an ability to engage in life-long

learning.

This outcome is fulfilled by suggesting

a plan for future studies and what

else could be done based on the

outcome of the current project. (Yes),

because we made a theoretical study

to design and construct our device

and making an experimental study to

obtain the optimum performance of a

mixed-mode solar dryer.

85

Outcome (k).

An ability to use the techniques, skills, and modern engineering tools

necessary for engineering practice.

List all technologies included in the

project (hardware and software).

(Yes)

In our project we used:

Mathematical Simulation

Computer Simulation

Computer Programs

Software Package

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above.

Student Team Signatures:

Abdulelah Ali Al-Jumaah

Abdullah Mohamed Asiri

Mohamed Fadil Mohamed Alshehri

Ahmed Mohamed Deash

Fahd Minajy Al-Hamzi

Project Advisor Signature: Dr. / Mahmoud Mohamed El-Haggar

Dr. / Mahmoud Ahmed Bakry

Date: 13/07/1435

College Coordinator of Capstone Projects:

Approved By:

DESIGN AND CONSTRUCTION OF A SOLAR DRYING...

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