ABSTRACT

Refrigeration has made the milestone in human life . Since from very long

time the human being has developed so many ways of refrigeration for preserving

food, cooling water, etc. but yet the techniques are developing. The science of

refrigeration has developed so many ways to improve our lifestyle.

Our project considers law of conservation of energy maximum utilization of

the fossil fuel and saving energy. This project has done LPG as refrigerant, instead of

using closed cycle as it is used in normal practice (VCR),the open cycle has been used.

Before burning the LPG in burner, it is passed through the expansion device and

evaporator and produce the refrigeration effect without using electric energy.

LPG is cheap and posses environmental friendly nature with no ozone depletion

potential.

1

CHAPTER – 2

LITERATURE SURVEY

2

2. LITERATURE SURVEY

COOLING METHODS-

From the ancient age man always prefers to have cold water for drinking purpose. Also

in India, our country the weather is too hot. Particularly in summer season, the normal

water temperature in open space is 35 to380 C. The water is not suitable for drinking

purpose. The required temperature is at the most 250 C. Hence lowering down of the

temperature is an essential task.

In old age there was ample space available to keep the earthen container

also the houses were sheltered by the trees and bushes which were enough to lower

down the water container temperature. Because in most of the situations the

temperature was depending on the temperature of the flowing air.

OTHER WATER COOLING PROCESSES:-

The different water cooling processes incorporated are since old age are as

Follows:-

1. Earthen pots

2. Using ice

3. Using vapour compression refrigeration cycles

4. Using vapour absorption cycle

Cooling of water in earthen pot is one of the earliest methods

employed by men for cooling the water in their houses. Only in recent years, it has

been put on sound footing thermodynamically. It is a process of adiabatic saturation of

air when cooling of surface water on container is made to evaporate to cool t with

transfer of heat from water to the surroundings. The initial investment cost of such a

system is low & the operation is simple & cheap. Simple evaporative cooling is

achieved by direct contact of water particles & a moving air stream. The water may be

sufficiently cooled by evaporative process to results a considerable degree of drinking

comfort in climates of high dry-bulb temperatures associated with low relative

humidity. The minimum outdoor temperature required for successful evaporative

cooling is above 350 c & another requirement is a relatively low. Wet bulb temperature.

3

The cooling effect given by the evaporative cooling always depends upon the outdoor

temperature although the evaporative cooling does not perform all the function of true

water-conditioning but it provides coolness by filtering heat & circulating the cooled

air.

LIMITATION OF SIMPLE EVAPORATIVE COOLING SYSTEM:

Its capacity is limited by WBT of the ambient air. Maximum cooling achieved is

the wet bulb temperature. It is not useful for high D.B.T. & high summer weather

conditions. However, even with all this limitations, there are many regions in India as

the part of Rajasthan; part of Bihar Vidharbha in Maharashtra & some hot spot in

North where evaporative cooling will produce a condition well within the summer

comfort zone. There is increasing demand of evaporative earthen pot coolers in these

regions, as they are quite inexpensive compared with refrigerated water-cooling

system. Hence quick operating and reliable Vapour compression system, which is

having the massive capacity of cooling, is used.

Generally refrigeration is defined as any process of heat removal. More

specially, refrigeration is defined as the branch of science that deals with process

of reducing and maintaining the temperature of a space or material bellow the

temperature of the surroundings. Since ancient times, human being searched for

warmth in cold weather and cooling in hot weather. The ordinary people used lakes

and rivers to get relief from hot weather. Others brought the lake water to houses and

circulated it inside the house in the form of channels or fountains. But in modern time

this search led to refrigeration systems. The system maintained at the lower

temperature than surrounding atmosphere temperature is known as refrigeration system

while the equipment used to maintain this lower temperature is known as refrigerating

machines.

4

Fundamentals of refrigeration-

The refrigeration may be defined as the process of removing heat from

substance under controlled conditions. It also includes the process of reducing &

maintaining of temperature of body below the general temperature of its surrounding

in other words, the refrigeration means continue extraction of heat from a body whose

temperature is already below the temperature of surrounding.

Types of refrigeration system-

1. Air refrigeration system –

In air refrigeration cycle, air is used as refrigerant. In olden days, air was

widely used in commercial application because of its availability at free of cost. Since

air does not change its phase ,therefore the heat carrying capacity per kg of air is very

small as compare to vapour absorption system.

2. Vapour compression system-

Vapour compression refrigeration system is an improved type of air

refrigeration system in which a suitable working substance, termed as refrigerant. It

condense and evaporates at temperature & pressure close to atm. Conditions.

Refrigerant used for this purpose is ammonia, carbon dioxide & sulpher dioxide.

3. Vapour absorption system-

The vapour absorption refrigeration system is one of the methods of producing

refrigerating plants. Refrigerant commonly used in vapour absorption system is

ammonia.

4. Steam jet refrigeration system-

In this application, however in the system jet have been supplanted generally

by system using centrifugal compressor. Now the system jet unit is remaining

important especially for industrial uses such as chilling of water to moderate

temperature in process industries.

5

Cold storage –

In country like India the problem of storage of vegetables, fruits, and fishes

is accomplished by the use of cold storage. It is the best known method of

perseveration of food & other things. From very longer time the method of cold

storage is known to human beings.

The temperature designed for the storage is approximately -20±2ºc for most of

the foods. Essential requirement of cold storage is to design a refrigerating system that

would be energy efficient, less costly, and flexible with high reliability & ease of

maintenance. There are various methods of cold storage but as far as medium

temperature is taken while designing a cold storage system 0ºc to 8ºc temperature

range is taken. In case4 of frozen food storage the temperature rang is -18ºc to -22ºc is

taken.

The following table gives different values for different products-

PRODUCT STORAGE TEMP.

(ºC)

PRODUCT LIFE

(WEEKS)

STORAGE SEASON

Tomatoes 7 4-5 April-May, sep-Oct

Lime 8 6 Mar-April, Aug-Sep

Ginger 2-4 14 Feb-April

Orange 7-8 8 Feb-April

Mosambi 6-8 8 Apr-July , Nov-Feb

Apples 0-15 16-20 Oct-Mar

Eggs 1-5 20-40 May-Dec

Mango 8-10 4-6 May-June

Frozen foods -18 to -20 24 & more Year round

Figure 1: Schematic of vapour compression refrigeration cycle.

6

LIQUID VAPOUR

HIGH PRESSURE

VALVE COMPRESSOR

LOW PRESSURE

Win

VAPOUR & Qout VAPOUR

LIQUID

Where,

R.E = Refrigerating Effect

Win= Work Input

The above diagram shows the simple vapour compression system. It includes

following components,

7

CONDENSER

EVAPORATOR

COP = R.E/Win

1. Evaporators –

It is an important device used in low pressure side of refrigerating system. The

liquid refrigerant from the expansion valve enters in to the evaporator where it is boils

& changes in to vapour. The function of evaporator is to absorb heat from surrounding

location or medium. Evaporator becomes cold & remains cold due to following two

reasons –

1. Temperature of evaporator coil is low due to the low temperature of the refrigerant

inside the coil.

2. The low temperature of the refrigerant remains unchanged because any heat absorbs

is converted to latent heat as boiling proceeds.

Compressor-

Compressors are the heart of vapour compression system. It performs two

functions; one is to draw vapour from evaporator & lowers the pressure of refrigerant

in evaporator to desired level. And other is it rises pressure of refrigerating vapour in

condenser enough so that saturation temperature is higher than the temperature of

cooling medium.

In order to secure satisfactory performance, long life, and to protect the

compressor against overload, certain design criteria should be observed. Compressor

application notes and data should always be consulted when designing a system.

Ensure compressors are clearly labelled to indicate that refrigerants are being used in

the system. The use of crankcase heaters should be considered to avoid excessive oil

solubility.

8

Condenser-

This is another important part of refrigeration system, which needs more

considerations its selection. The condenser removes the heat from refrigerant carried

from evaporator & added by compressor & convert the vapour refrigerant into liquid

refrigerant.

It is heat exchanger in which heat transfer takes place from high temperature

vapour to low temperature air or water, which is used as cooling medium.The types of

cooling media available air water. Both can be used separately combines as per the

availability and requirement. The condensers are classified according to cooling

medium used.

Expansion valve-

It is an important device used in refrigeration. It performs two functions, one

is it reduces high pressure liquid refrigerant to low pressure liquid refrigerant before

being fed to evaporator. And second it maintains desired pressure difference between

high & low pressure side & it also controls the flow of refrigerant.

Design and selection criteria are the same as those for conventional

fluorinated refrigerants. Capillary tube length is specific to each refrigerant. Computer

programmers and tables are available for determining capillary tube size and length,

although trial and error is generally the preferred route. Thermostatic Expansion

Valves (TEVs) for hydrocarbons are available. Alternatively TEVs for other

refrigerants that operate with similar pressure-temperature relationships can be used.

Electronic Expansion Valves (EEV) may also be used. EEV’s used in hydrocarbon

systems must conform to the requirements of electrical components.

9

Refrigerants-

Definition-

Any substance capable of absorbing heat from another required substance can be used as

refrigerant.

Desirable properties of refrigerants-

Low boiling point.

High critical temperature.

High latent heat of vaporization.

Low specific heat of liquid.

Low specific volume of vapour.

Easy to liquify at moderate pressure & temperature.

Easy of locating leaks by odour or suitable indicator.

It should be nonpoisonous.

It should be non explosive

It should be non corrosive

It must be nonflammable

Leaks should be easy to detect.

Leaks should be easy to locate.

It should operate under low pressure.

Part moving in the fluid should be easy to lubricate.

It should be nontoxic (not harmful if inhaled or if spilled on skin).

It should be a stable gas.

Classification of refrigerants-

10

Halo carbon refrigerants –

1. R11(CCL3F) -

Synthetic, non flammable, non toxic, low pressure refrigerant

0.2 bar at -15ºc

1.2606 bar at 30ºc

B.P=23.77ºc at atm. Temp.

Used in centrifugal compressor system of 200 TR,

Leak detected by soap solution halide torch,

Cylinder colour code is orange

R12 (CCL2 F2) -

Popular, colourless, almost odourless, non toxic, non corrosive, non flammable

B.P= -29ºc at atm. Pressure

Low latent heat value,

Require less sensitive & more positive,

Low but positive head & good volumetric efficiency.

Refrigerator, freezer, water coolers, room & window Arcs , etc.

0.82 bar at -15 ºc & 6.4 bar at 30ºc

Latent heat of 159KJ/Kg at -15ºc

Leak can be detected by soap solution, halide torch & electronic detector

R22 (CHClF2)-

Man made, to maintain temp. of -29ºc to-40ºc

11

A/C units & household refrigerators

Reciprocating &centrifugal compressors

B.P= -41ºc at atm. Pressure

Latent heat is 216.5KJ/Kg at -15ºc

Non toxic, non corrosive, no irritating, non flammable

Water mixes well with R22 than R12 by ratio as 3:1 hence drier has to be used

Colour code is green

Azeotrope refrigerants –

R500 -

Non flammable, non corrosive, less toxic

Reciprocating compressor

20% greater refrigerating capacity than R12

Condensing pressure 7.78 bar at -30ºc & evaporating pressure 1.37 bar at -15ºc

Latent heat 198KJ/Kg at -15ºc

Highly soluble in oil

Cylinder colour code is yellow

Inorganic refrigerants –

R717 ( NH 3) -

12

Oldest, used in large & commercial plants, where toxicity is secondary

Absorption system

Under normal condition it is colourless gas

B.P= -33.33ºc at atm. Pressure

M.P= -78ºc from solid

Latent heat of vaporisation is 1315KJ/Kg at -15ºc

Large refrigerating effects with small sized machinery

Condensers pressure at 30ºc is 10.78 bar & water cooled type

Poisonous & toxic, irritating to eyes, nose & throat

Flammable, with 16% to 25% air by volume

Lighter than oil hence oil can be easily separated

Large reciprocating compressors

Ice manufacturing; bear mfg. Food freezing, cold storage, etc.

Hydrocarbons-

13

Code Chemical name Triple (°c) Boil (°c) Critical(°c)

R290 Propane -189 -42.08 96.70

R600a Isobutene -145 -11.76 134.70

R600 normal butane -138 -0.54 52.01

commercial

propane

values vary

commercial

butane

mixtures of the

above

COMPARISON OF REFRIGERANT PRRFORMANCE -

14

Refrigerant R12 R134a R600a RC270

Chemical classification CFC HFC LPG HC

Molar mass (g/mol) 120.9 102.0 58.1 42.1

Refrigerating effect (J/g) 116.9 150.7 262.3 359.1

30°C sat. Liquid volume (L/kg) 0.773 0.844 1.835 1.636

30°C sat. Vapour volume (L/kg) 23.59 27.11 95.26 62.41

30°C sat. Vapour viscosity (µPas) 12.95 12.48 7.81 9.07

Condenser pressure (k Pa) 743.2 770.7 403.6 827.0

Evaporator pressure (k Pa) 181.9 163.6 89.2 206.0

Condenser gauge (k Pa) 641.9 669.4 302.3 725.7

COP 0 K suction superheat 4.69 4.62 4.69 4.88

COP 20 K suction superheat 4.71 4.71 4.82 4.79

Compressor discharge temp. (°C) 39.3 36.6 30.0 52.7

Effective displacement (L/kJ) 0.79 0.81 1.52 0.65

Cond. loss par. (µPas) 1.45 1.31 0.64 1.00

15C sat. Liquid kµ (kJ/kgK) 0.278 0.293 0.496 0.792

Liquid molar volume (mL/mol) 93.5 86.1 106.7 68.8

Leakage speed (1/ns) 1.62 1.67 0.75 2.10

Table : Comparison of refrigerant properties and parameters affecting the measured

Energy consumption of domestic refrigerators for an idealized reversed Rankin

Cycle operating between -15°C and 30°C saturation temperatures.

Table compares refrigerant properties (Gallagher et al. 1993) and parameters

Affecting COP for domestic refrigerators. Saturated vapour at -15°C is assumed to

Enter an ideal compressor and saturated liquid at 30°C to enter the expansion valve

15

Except for calculating COP with 20 K suction superheat. ASHRAE (1993), Table 7

On page 16.7 also uses these assumptions. Table 5 includes the three refrigerants

Currently in mass-produced domestic refrigerators and RC270 which was not in

ASHRAE (1993)'s

Table shows R600a has one irrelevant disadvantage and many significant

Advantages for domestic refrigerators discussed in the following:.

1. When R12 was introduced, open-drive compressors were common and R600a's

Below atmospheric evaporator would cause ingress of air through the shaft Seals

reducing reliability. Domestic refrigerators no longer use open-drive Compressors.

2. When the refrigerator is in storage, the evaporator must withstand pressures

which normally occur only in the condenser. The condenser gauge pressures For

R600a are less than half those for the other refrigerants so many metal thicknesses can

be half. This reduces capital cost and environmental impacts and increases COP

through reduced heat transfer resistance.

3. The COP calculated for a simple reversed Rankine cycle (Figure 1) with zero

sub cooling of liquid and superheat of suction vapour and ideal heat transfer and

compression is 1% higher for R600a than R134a. All the refrigerants are close to the

reversible COP of 5.74 which is the maximum thermodynamically possible.

4. Domestic refrigerators use a capillary tube in close thermal contact with the

compressor suction line instead of an expansion valve. The liquid-suction heat

exchange increases COP for some refrigerants and reduces it for others. With 20 K

16

superheat R600a has an idealized COP only 2% higher than R134a. The measured

difference of 10% to 20% must contain other effects.

5. The low compressor discharge temperature for R600a allows a cheaper and

more efficient design of electric motor.

6. The large effective displacement of R600a implies a larger compressor but

because condenser gauge pressures are half compressor wall thickness can behalf. An

overall reduction in compressor mass and hence capital cost is possible. The

compressor will still be much smaller than the driving electric motor. The surface

finish of the piston and valves will be the same for R600a and R134a. Because the

R600a compressor is bigger the relative roughness will be smaller allowing an R600a

compressor to be more efficient.

7. Small refrigerators usually have a serpentine condenser with laminar flow at

the beginning of condensation. For condensers of the same length and tube mass but

differing diameter and wall thickness, the condenser loss parameter includes all

refrigerant properties which contribute to COP loss caused by pressure drop. R600a

has about half the COP loss due to pressure drop of

the other refrigerants.

8. Heat transfer by forced convection in the condenser and evaporator tubes of

small units occurs mainly by conduction through the thin liquid _lm on the wall. The

usual correlations for this heat transfer (ASHRAE 1993) depend mainly on the ratio of

the thermal conductivity of the liquid to its dynamic viscosity, kµ. Hence heat transfer

conductance is greater for R600a than for R12 and R134a. A high heat transfer

conductance means a smaller COP loss

due to heat transfer resistance.

9. For hermetic compressors diffusion through the ceiling compounds is a major

source of refrigerant loss. Liquid molar volume is related to the size of the molecule. A

large molecule means a lower loss rate and a longer period of operation with high

17

COP. In the absence of measurements, R600a's larger molecule suggests it will have

lower diffusion loss.

10. Significant refrigerant leaks occur typically by laminar isothermal flow through

pinholes or cracks. The leakage speed is approximately inversely proportional to the

time a complete charge of a given refrigerant takes to leak out. R600a systems with

large leaks will function with high COP much longer. These advantages make R600a

desirable in other applications where equipment mass and leakage is important and

evaporator or condenser temperatures are high e.g., transport air conditioning and

domestic water heat pumps. RC270 is a better replacement for R12 and R134a but if

the equipment must be redesigned to minimize GWP; R600a will give a better result.

Ammonia R717 has higher heat transfer than all these but its vapour pressure,

corrosion and toxicity are higher. The toxicity is especially a disadvantage in domestic

applications. LPG refrigerants are completely soluble in and compatible with

hydrocarbon lubricants. LPG liquid absorbs only trace amounts of water, like R12, so

LPG refrigerants are completely compatible with R12 driers. LPG refrigerants with

appropriate vapour pressures are `drop-in' replacements for CFCs on equipment using

thermostatic expansion valves. Other expansion devices may require adjustment or

replacement.

LPG as a refrigerant-

18

LPG is liquid petroleum product. It is a mixture of crude oil at the head

quantity.LPG is also obtained by product during cracking of heavy oil or from natural

gas leak, if it occurs.

LPG is nothing but mixture of propane & butane viz. in gaseous state at

normal temp. & pressure however for convenience in handling, transporting & storage.

the cylinder contains a liquid, which vaporize at normal atm. pressure & temperature.

What comes out at burner is then gas which you ignite with lighter. LPG is a mixture

of hydrocarbon gases used as a fuel in heating appliances & vehicles, & increasing

replacing fluro carbons as a refrigerant to reduce damage to the Ozone layer. They are

mixture of propane & butane usually with propylene & butylenes present in small

concentration. A powerful odorant, ethyl mercaptan, is added so that leaks can be

detected easily. LPG is manufactured during refining crude oil or extracted from oil &

gas stream as they emerge from the ground.

It becomes liquid at room temp. & pressure, so is supplied in pressurized

steel bottles. These are usually filled to 85% their capacity with the liquefied gas to

provide room for liquid to expand if the bottle gets hot. It has density almost twice as

that of air. LPG will ignite only when air is mixed with it in certain proportion called

explosive range very narrow.

Composition of LPG-

19

LPG is mixture of C3 & C4 type of hydrocarbons. The chief constituents of LPG are

propane (C3H8) & butane (C4H10). Owing to the demand for industry LPG sold as

fuel mode largely as propane.

Table no. 4- BIS specifications for LPG (IS 14861-2000)-

Properties of LPG-

Density of LPG = 496.47Kg/m3

20

Boiling range at 1 atm.= -42ºc to 0ºc

Gross calorific value of LPG =11400Kcal/Kg

Limit of flammability (lower)=1.8%(gas in air /gas mixture ),upper=9%

Flash point = -37.73ºc

Auto ignition temp.=493.33ºc to 548.89ºc

Advantages of LPG as refrigerant -

The cooling capacity of LPG is 10% higher than R-12 & vapour pressure is

appropriate.

LPG is naturally occurring & non toxic .

Use of LPG as refrigerant also improves the overall efficiency by 10% to 20%.

The ozone depletion potential of LPG is zero.

It is user friendly & also gives cost advantages.

LPG does not form acid & thereby eliminates the problem with blocked

capillaries.

There is 60% reduction in weight of system due to higher density of LPG

Considering the above data it is clear that liquid LPG can be certainly used as

refrigerant, but some precautions are to be taken due to the following properties of

LPG:

Hazards and precautions for refrigerants:

The principal hazards are:

21

Explosion in space -

Any refrigerant with vapour pressure above ambient can _ash

to a larger volume. The potential increase in volume is greater if combustion

of lubricant or refrigerant occurs. Explosion venting may be necessary to

limit pressure rise to what the space can safely withstand. 2 kPa can blow

window glass off a building.

Fire -

Combustible lubricant and refrigerant must be discharged safely outside

a building when a _re occurs especially if the heat of combustion exceeds

200 MJ.

Asphyxiation or poisoning -

All refrigerants except air and oxygen are asphyxiants.

Ventilation must prevent serious injury or death on a sudden total

release of refrigerant. The quantity of ventilation necessary varies greatly

between refrigerants.

Flying metal-

System must comply with piping and pressure vessel codes.

Corrosion or chemical reaction -

LPG refrigerants are non-reactive and chemically

stable at refrigeration temperatures.

Chemical or cold burns-

Accidental contact between skin and cold metal must be

prevented by insulation. Accidental releases of liquid refrigerant must drain

22

safely.

THEORY OF DESIGN

Considering LPG as refrigerant, the system for cooling water is as designed below .

23

In this section the layout & various components like cylinder , regulating valve, pipe ,

heat exchanger ,etc used in the system are explained. Also considering various

properties of material properties ,standard specimens, & various theories of design

&heat transfer the system is designed.

(A) Layout-

The main principle behind this project is of making use of liquid LPG as coolant for

this latent heat required for phase transformation of liquid LPG in to gaseous state is

taken from water which is to cooled thus the layout of system is as shown in following

fig.

Block Diagram &Technical Specification

24

The layout consist of cylinder ,regulator , suraksha pipes, heat exchanger, burner ,etc.

cylinder is as shown in inverted form & regulating valve connected to it so as to get

liquid LPG at the outlet of the valve . the heat exchanger is placed in between burner &

cylinder with the help of pipe (wire reinforced ). The length of pipe between cylinder

& heat exchanger is less as compare with length between het exchanger & burner . so

as to allow liquid LPG to enter in heat exchanger & pipe connected between heat

exchanger is long enough so as to convert remaining liquid LPG into gaseous state.

(B) System components-

1. Cylinder-

25

2. Regulating valve-

26

3. Pipes-

27

4. Clamping clips-

5. Heat exchanger:

28

5. Coil.

6. Burner:

29

7. Insulation-

30

Energy conservation has gained great importance in the recent years,

due to rapidly escalating cost of fuel .Energy conservation calls for better thermal

insulating .insulting materials have extremely low thermal conductivity. Properly

applied insulation helps in economic running of refrigerating plants. The selection of

proper insulating material for a particular purpose depends upon desired properties of

insulating material , economics & structural conditions.

Desired properties of an ideal insulating material-

1. Low thermal conductivity

2. Strength

3. Light in weight

4. High resistance disintegration as result of internal chemical activity

5. Water proof

6. Odorless

7. Sanitary

8. fire proof

9. low cost

10.easily available

31

Types of insulating material-

1. Flake insulation - it composed of small particles that finely divide the air space

E.g-expanded mica

2. Fibrous insulation – It is composed of small diameter fibers that finely devide

the air space e.g- inorganic fibers of rock wool ,glass wool

3. Granular insulation-It is composed of small nodules containing voids e.g-

magnesia cork , calcium silicate

4. cellular insulation-it is composed of small individuals cells that finely divide

the air space e.g –glass, rubber, or plastic.

32

MATERIAL SELECTION

RAW MATERIAL & STANDARD MATERIAL

S.N

.

NAME OF THE COMPONENT MATERIAL QTY

1 GAS STOVE MA 1

2 GAS PIPE STEEL - RUBBER m

3 EVAPORATOR PIPE CU 0.m

4 REGULATOR STD 1

5 PIPE CLIP MS 4

6 TANK STEEL 1

7 TEMP INDICATOR STD 1

33

CALCULATIONS-

Evaporator design-

The heat absorbed or heat transfer capacity of an evaporator is given by

Q = UA(T2-T1) W or J/S

U = Overall heat transfer coefficient W/ m2k

A = Area of evaporator surface in m2

T 2= Temperature of medium to be cooled

T 1= Saturation temperature of refrigerant at evaporator pressure

CP = Specific heat at constant pressure of LPG = 1.64244 KJ/Kgk

CV= Specific heat at constant volume of LPG = 1.4534KJ/Kgk

ρ = Density of LPG = 496.47Kg/m3

Di = Inside diameter of evaporator coil

DO = Outside diameter of evaporator coil

µ = Viscosity = 7.7 N-Sec /m2

hi = Internal corrective heat transfer coefficient

ho= Water side coefficient

34

Refrigeration effect is given by ,

RE = mCp∆T

3.5 = m×1.64244 × (-)

m =

but m = ρ × π /4 × Di2 × V

V=

U = 1

1h i ri

+1k∈(

RoRi

)+1

h o Ro

hi = CkD (VDp

μ )0.8

( CPμK

)0.4

Q = UA(T2-T1)

A =

2πL =

Length of evaporating coil = L =

For L =

Q =

35

TESTING OF SYSTEM

Working-

The working of LPG cooling prototype may be described as follows-

Before starting the experiment some arrangements are necessary which

may have given high priority. Firstly LPG cylinder is placed in inverted position on

stand properly. Then proper connections are made to evaporator & expansion device.

After this regulator is operated & equipment is checked for leakage keeping the

regulator in open position. If any leakage is found, it is rectified.

For safety, the everything is kept away from burner. The first step is

lightening the burner. The flow of LPG is controlled by regulator fitted on cylinder.

Thus the controlled flow is maintained to avoid the frosting & liquid accumulation at

the burner inlet. After performing many trials we got proper position of valve, at which

burner works properly. In our refrigeration there is no need of compressor &

condenser, because in LPG cylinder it is stored under high pressure & very low

temperature. So the compression process is adopted directly by LPG cylinder.

In case of condensation process high pressure vapour is converted into

liquid form. The LPG heavier than air. It is stored in liquid form in cylinder. By

keeping cylinder vertically downward position, we get high pressure liquid LPG. The

liquid form LPG coming out from cylinder is passed through expansion device. Where

they converted in low pressure & low temperature & then passed through evaporator.

The vapour state LPG coming out from evaporator chamber is then passed through gas

chamber to gas burner. Where it burns & gives energy for cooking purpose. The liquid

coming out from cylinder takes heat from surrounding to change the phase from liquid

to gaseous. For that purpose the length of rubber pipe have kept longer, so it will give

enough time for change in phase.

The digital thermocouple is used to measure the temperature readings in

the experiment. The readings are taken out for varying temperature & time. Thus from

that readings we will come to know the change in temperature for specific time.

36

Actual construction of project-

37

Demo test in college campus-

Actual readings taken during demo test-

38

OBSERVATION & RESULTS-

DEMO TEST NO -1 (with domestic regulator)

Demo test readings -Duration of test is 34 hour.

NO. TIME(MIN.) READINGS IN (ºC)

1 INITIAL 34.7

2 3 34.7

3 6 34.6

4 12 34.5

5 15 34.3

6 18 34.1

7 21 33.8

8 24 33.4

9 27 33.1

10 30 32.8

11 33 32.5

12 36 32.2

13 39 31.8

14 42 31.8

15 45 31.9

Table - Observation table

The above readings are taken in demo test . That time we used the

household/domestic regulator. The flow of liquid LPG through this regulator is very

small as compare to industrial regulator. Thus because of this reason the readings we

got are not accurate. The above chart shows those readings ,they shows very minor

cooling effect thus for solving that problem in next demo test we used industrial

regulator.

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0 3 6 12 15 18 21 24 27 30 33 36 39 42 4530

30.531

31.532

32.533

33.534

34.535

Time -Temperature Graph

Time(min)

Tem

pera

ture

(ºc)

Diagram - Time –temperature graph

The above graph shows the readings taken during first demo test. The test readings

taken may show very minor temperature change . The test readings shows the

temperature difference of approximately 2.8ºc .Thus in refrigeration this temperature

difference is very low as compare to other refrigerating techniques. There is loss of

energy which causes decrease in efficiency of refrigerating effect.

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OBSERVATION & RESULTS-

DEMO TEST NO -2 (with industrial regulator)

Demo test readings - Duration of test is ½ hour.

NO. TIME(MIN.) READINGS IN (ºC)

1 INITIAL 29.1

2 2 27.3

3 4 26.1

4 6 24.8

5 8 23.8

6 10 22.7

7 12 21.5

8 14 20.1

9 16 19.1

10 18 18.3

11 20 17.8

12 22 16.3

13 24 15.4

14 26 14.5

15 28 13.7

16 30 12.9

Table - Observation table

The above readings are taken in demo test .In previous test we have used the

domestic regulator because of its low flow rate ,we used industrial regulator in place of

it. They shows gradual decrease in temperature as time get lapsed. The initial reading

is 29.1ºc &final reading is 12.9ºc. Thus the difference between them shows decrease in

temperature. In this case the temperature difference we get is very high as compare to

previous test. It shows approximately 16.2ºc decrease in the initial temperature within

½ hour.

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TIME-TEMPERATURE GRAPH

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280

5

10

15

20

25

30

35

Time -Temperature Graph

Time(min)

Tem

pera

ture

(ºc)

Diagram - Time–Temperature

The above diagram shows the readings taken during demo test with

industrial regulator. The time temperature diagram shows the change in temperature &

time. As in first case flow rate is less due to domestic regulator but in this case the

industrial regulator is used which increases flow of liquid LPG through regulator . This

causes the increase in efficiency of refrigeration . The temperature difference given is

approximately 16.2ºc for 30 min. But as time increases the refrigerating effect also

increases.

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CONCLUSION

Studying all aspects of LPG it can be stated that, LPG is versatile fluid can be utilized

as better cooking gas . A better fuel for IC engine as well as better & eco friendly

refrigerant .The zero phenomenon of system is most existing one of this project, which

the potential of LPG is directly harnessed from commercial LPG cylinders.

Actually the system employed is designed for chilling effect equal to 5ºc

& practically the result obtained are in the range of 6ºc to 6.6ºc indicating the efficacy

& accuracy of the system. Hence it can be concluded that , whatever the consumption

of commercial LPG is considerably high , the system will definitely work positively.

This system in beginning fruitful in case of restaurant ,hotels, where

consumption of LPG is high enough. The only limitation of the system can be

inflammable property of LPG . But the proper arrangement & operation an easily

evade this limitations , as the construction & operation made during the process are

very handy.

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SCOPE OF IMPROVEMENT

LPG refrigerant system is sufficient only for hotels & restaurant the many of this

system having scope of improvement.

By proper maintaining pressure we can re-circulate when burning is not

required.

It can be converted into close type system.

LPG refrigerants can be used for air-conditioning , ice-plant purpose.

It can be used in household refrigerator.

In areas with electricity problems or rural or remote areas LPG can be used for

cooling purposes.

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REFERENCE

1. FROM BOOKS

1. “THERMAL ENGINEERING” R.S.KHURMI ; S.CHAND 2008

2. “HEAT & MASS TRANSFER” PAVASKAR ; NISHANT 2007

3. “REFRIGERATION & AIR CONDITIONING” V.K.JAIN 2008

4. “REFRIGERATION & AIR CONDITIONING” C.P.ARORA 2009

2. FROM PAPERS

1. http://en.wikipedia.org/wiki/Shell_and_tube_heat_exchanger

2. Heat Exchangers: Selection, Rating and Thermal Design (2nd Edition ed.)

http://www.southwestthermal.com/shell-tube-exchanger.html. Retrieved

2009-05-08.Sadik Kakaç and Hongtan Liu (2002).

3. A screening method for the optimal selection of plate heat exchanger

configurations by J.M.Pinto and J.A.W.Gut, University of São Paulo,

Brazil(2000).

4. Guidelines for the use of Hydrocarbon Refrigerants in Static Refrigeration

and Air Conditioning SystemsFirst Published February 2001

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