Assignment on Refrigeration

8/12/2019 Assignment on Refrigeration

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ASSIGNMENT ON

R FRIG R TION

Course name: Pharmaceutical Engineering

Course code: PHRM 414

SUBMITTED TO:

Meena Afroze Shanta

Lecturer

Department of Pharmacy

East West University

SUBMITTED BY: Fariza Huq Oishi (ID: 2010-1-70-008)

Joynab Akhter Jolly (ID: 2010-1-70-016)

Jannat Mahal Rume (ID: 2010-1-70-048)

Zenifar Karim (ID: 2010-1-70-042)

Debasree Paul (ID: 2010-3-70-036)

Priyata Dey (ID: 2010-3-70-042)

Samiya Khondaker Rinta (ID: 2010-3-70-048)

Submission date: 6th

April, 2014



CONTENT

Refrigeration 1

Occurrence of Mechanical Refrigeration 1

Instrumentation: Internal Parts of the Domestic Refrigerator 1

Instrumentation: External Visible Parts of the Refrigerator 4

Mechanism of Action 5

Refrigerant 6

Current Application of Refrigeration 7

Reference 9



1

REFRIGERATION

Refrigeration is a process in which work is done to move heat from one location to another. It is

the process of removing heat from an enclosed space or from a substance for the purpose of

lowering the temperature (Trane, 1999).

This process keeps an item below room temperature by storing the item in a system or substance

designed to cool or freeze. The most common form of refrigeration is provided by systems (i.e.

refrigerators) that use a refrigerant chemical to remove heat from items stored inside the system.

The process of refrigeration is used for many day-to-day applications. It is used to chill water,

make ice and ice cream, keep the food fresh and a host of other purposes. It helps to preserve

fruits, vegetables and other food items. The food items get damaged at atmospheric temperature

because bacteria can easily survive in these conditions. At temperatures below 40C, the bacteria

cease to exist and hence the food items remain safe and fresh (Khemani, 2010).

The simplest form of refrigeration observed in daily life is the use of ice. Ice absorbs heat from

the surroundings and melts. During this process the surrounding air becomes cool due to the loss

of heat the capacity of refrigeration is expressed in tonne (Trane, 1999).

OCCURRENCE OF MECHANICAL REFRIGERATION

Mechanical refrigeration is the removal of heat from a material or space, so that its temperature

is lower than that of its surroundings. Refrigerant absorbs the unwanted heat from a material or

space and this raises the refrigerant‘s temperature so that it changes from a liquid to a gas — it

evaporates. Thus it decreases the temperature of the material or space than that of thesurroundings.

The system then uses condensation to release the heat and change the refrigerant back into a

liquid. This is called ―Latent Heat‖. This cycle is based on the physical principle, that a liquid

extracts heat from the surrounding area as it expands (boils) into a gas. To accomplish this, the

refrigerant is pumped through a closed looped pipe system. The closed looped pipe system stops

the refrigerant from becoming contaminated and controls its stream. The refrigerant will be both

a vapor and a liquid in the loop (Rouse, 2012).

INTERNAL PARTS OF DOMESTIC REFRIGERATOR

The internal parts of the refrigerator are ones that carry out actual working of the refrigerator.

The domestic refrigerator is one found in almost all the homes for storing food, vegetables,

fruits, beverages, and much more. Some of the internal parts are located at the back of the

refrigerator, and some inside the main compartment of the refrigerator.



2

Figure 1: Front view of the internal parts of a refrigerator (Khemani, 2010)

Figure 2: Internal parts of a domestic fridge



3

Some internal parts of the refrigerator are listed as follows:

1) Refrigerant: The refrigerant flows through all the internal parts of the refrigerator. It is the

refrigerant that carries out the cooling effect in the evaporator. It absorbs the heat from the

substance to be cooled in the evaporator (chiller or freezer) and throws it to the atmosphere via

condenser. The refrigerant keeps on recirculating through all the internal parts of the refrigeratorin cycle.

2) Compressor: The compressor is located at the back of the refrigerator and in the bottom area.

The compressor sucks the refrigerant from the evaporator and discharges it at high pressure and

temperature. The compressor is driven by the electric motor and it is the major power consuming

devise of the refrigerator.

3) Condenser: The condenser is the thin coil of copper tubing located at the back of the

refrigerator. The refrigerant from the compressor enters the condenser where it is cooled by the

atmospheric air thus losing heat absorbed by it in the evaporator and the compressor. To increasethe heat transfer rate of the condenser, it is finned externally.

4) Expansive valve or the capillary: The refrigerant leaving the condenser enters the expansion

devise, which is the capillary tube in case of the refrigerators. The capillary is the thin copper

tubing made up of number of turns of the copper coil. When the refrigerant is passed through the

capillary its pressure and temperature drops down suddenly.

5) Evaporator or chiller or freezer: The refrigerant at very low pressure and temperature enters

the evaporator or the freezer. The evaporator is the heat exchanger made up of several turns of

copper or aluminum tubing. The refrigerant absorbs the heat from the substance to be cooled in

the evaporator, gets evaporated and it then sucked by the compressor. This cycle keeps on

repeating.

6) Temperature control devise or thermostat: To control the temperature inside the

refrigerator there is thermostat, whose sensor is connected to the evaporator. The thermostat

setting can be done by the round knob inside the refrigerator compartment. When the set

temperature is reached inside the refrigerator the thermostat stops the electric supply to the

compressor and compressor stops and when the temperature falls below certain level it restarts

the supply to the compressor.

7) Defrost system: The defrost system of the refrigerator helps removing the excess ice from thesurface of the evaporator. The defrost system can be operated manually by the thermostat button

or there is automatic system comprising of the electric heater and the timer.

8) Ventilation Fins: These are located on the back of the fridge and is responsible for releasing

the heat produced by the condenser (Honeywell Control Systems Ltd., 2004).



4

EXTERNAL VISIBLE PARTS OF REFRIGERATOR

The external parts of the compressor are the parts that are visible externally and used for the

various purposes. The figure below shows the common parts of the domestic refrigerator.

Figure 3: External parts of refrigerator (Khemani, 2010).

Some the common parts are described as follows:

1) Freezer compartment: The food items that are to be kept at the freezing temperature are

stored in the freezer compartment. The temperature here is below 00C so the water and many

other fluids freeze in this compartment.

2) Thermostat control: The thermostat control comprises of the round knob with the

temperature scale that help setting the required temperature inside the refrigerator. Proper setting

of the thermostat as per the requirements can help saving lots of refrigerator electricity bills.

3) Refrigerator compartment: The refrigerator compartment is the biggest part of the

refrigerator. Here all the food items that are to be maintained at temperature 00C but in cooled

condition are kept. The refrigerator compartment can be divided into number of smaller shelves

like meat keeper, and others as per the requirement.

4) Crisper: The highest temperature in the refrigerator compartment is maintained in the crisper.Here one can keep the food items that can remain fresh even at the medium temperature like

fruits, vegetables, etc.

5) Refrigerator door compartment: There are number of smaller subsections in the refrigerator

main door compartment. Some of these are egg compartment, butter, dairy, etc.



5

6) Switch: This is the small button that operates the small light inside the refrigerator. As soon

the door of the refrigerator opens, this switch supplies electricity to the bulb and it starts, while

when the door is closed the light from the bulb stops. This helps in starting the internal bulb only

when required (Khemani, 2010).

MECHANISM OF ACTION

Figure 4: Domestic refrigerator details (Khemani, 2010).

The refrigerator is made up of the freezer compressor; the pipes as heat exchanging unit both

from inside and outside; the refrigerant; and the expansion valve. The entire process of

refrigeration has a whole lot to do with the freezer compressor. If the compressor goes wrong the

refrigerator will lose its freezing capacity. The basic mechanism behind the cooling process

evaporation of a liquid substance that in turn helps in absorbing the heated air. The entire process

begins in the freezer compressor.



6

Figure 5: Mechanism of Action of Refrigerator (MacIntosh, 2014).

Initially, the refrigerant at very low pressure and temperature enters the evaporator as a liquid.

The evaporator is the heat exchanger made up of several turns of copper or aluminum tubing.

The refrigerant absorbs the heat from the substance to be cooled in the evaporator, gets

evaporated and turned into a gas and it then sucked by the compressor.

The refrigerant is in the gaseous state and the compressor exerts pressure on it. Simultaneously

the pressure of the refrigerant gas increases along with its temperature. Now it is the turn of the

heat exchanging pipe attached in the outside position that helps in the transmission of heat under

the pressurized condition of the refrigerant.

Once the first level of the transfer of heat is complete the refrigerant gas condenses to liquid in a

condenser. The refrigerant liquid makes its path through the expansion valve inside the

refrigerator. The refrigerant leaving the condenser enters the expansion device. When the

refrigerant is passed through the capillary its pressure and temperature drops down suddenly.

Now the cycle is again ready to be repeated by entering into the evaporator coil and so on.

The refrigerator thus gets cool from inside. As this mechanism repeats over time starting from

the action of the evaporator coil, the refrigerator remains cold till it is on (MacIntosh, 2014).

REFRIGERANTS

Refrigerant is a liquid which readily absorbs heat when evaporated at a low temperature and

pressure and gives out heat on condensing at a higher temperature and pressure.

The choice of a suitable refrigerant depends upon many factors, although a few are mentioned

below:



7

1. The latent heat of vaporization should be large so that the desired cooling effect is

produced.

2. At normal temperature and pressure, refrigeration must be in vapour phase and on

compression and cooling it should be liquefied easily.

3. The pressure required to liquefy the vapour of the refrigerant in the condenser section must

be so as to maintain it usually at room temperature.

4. The vapour pressure of the refrigerant liquid in the evaporator section must be maintained

at about -15ºC greater than the atmospheric pressure.

5. The specific volume of refrigerant vapour should not be large (Andrew et al., 2003).

CURRENT APPLICATION OF REFRIGERATION

Most widely used current applications of refrigeration are for air conditioning of private homes

and public buildings, and refrigerating foodstuffs in homes, restaurants and large storage

warehouses.

Refrigerators are used in kitchens for storing fruits and vegetables has allowed adding fresh

salads to the modern diet year round, and storing fish and meats safely for long periods.

Refrigeration also helps keep fruits and vegetables edible longer.

Refrigeration is used to liquefy gases - oxygen, nitrogen, propane and methane, for example.

Synthetic ammonia plants condense ammonia gas with temperatures between – 200C to +10

0C

before storage or before shipment.

In compressed air purification, it is used to condense water vapor from compressed air to reduce

its moisture content.

In oil refineries, chemical plants, and petrochemical plants, refrigeration is used to maintain

certain processes at their needed low temperatures (for example, in alkylation of butenes and

butane to produce a high octane gasoline component).

Metal workers use refrigeration to temper steel and cutlery. The cutting tool can be increased

many folds by refrigerating the tool for 15 minutes at -1000C. Magnetic strength and stability of

magnets can be improved by low temperature treatment at -800C for 8 hours.

In transporting temperature-sensitive foodstuffs and other materials by trucks, trains, airplanes

and seagoing vessels, refrigeration is a necessity. Dairy products are constantly in need of

refrigeration, and it was only discovered in the past few decades that eggs needed to be

refrigerated during shipment rather than waiting to be refrigerated after arrival at the grocery

store. Refrigeration can maintain quality and taste by preserving dairy products as follows:

i. Milk 2 to 50C

ii. Ice cream -250C

iii. Butter 00C



8

iv. Cheese 00C

Meats, poultry and fish all must be kept in climate-controlled environments before being sold.

Meat and poultry products are refrigerated as follows:

i. -250C in the frozen state

ii. 10

C for long storageiii. Fish at -15

0C

Medical applications of refrigeration include:

i. Blood plasma and antibiotics are manufactured using a method called freeze drying

ii. Dead bodies are preserved at -700C for few days.

Preservation of thermolabile substances requires refrigeration. For example, insulin, ACTH,

pituitary hormones and vaccines are stored in refrigeration.

Refrigeration is used to control fermentation. Heat is generated during fermentation and must be

removed otherwise temperature will rise beyond control i.e. refrigeration maintains 5 to 10 0C

during the following processes:

i. In the manufacture of alcohol in a brewery

ii. In the manufacture of penicillin

Many chemical reactions are exothermic (as mentioned below) but these must take place at

temperatures below atmospheric temperature. Therefore refrigeration is required to remove the

heat of reaction.

i. In the manufacture of viscous rayon

ii. In the manufacture of cellulose acetate

iii. In the manufacture of synthetic rubber (Andrew et al., 2003)



9

REFERENCE

Andrew D. Althouse, Carl H. Turnquist, Alfred F. Bracciano (2003) ‗Modern Refrigeration and

Air Conditioning‘ 18th

Edition. Goodheart-Wilcox Publishing.

Honeywell Control Systems Ltd. (2004) ‗THE REFRIGERATION SYSTEM: ANINTRODUCTION TO REFRIGERATION‘ Available from: http://c.ymcdn.com/sites/

www.rfmaonline.com/resource/resmgr/crfp/honeywell_the_refrigeration_.pdf

Khemani, H. (2010) ‗Domestic Refrigerator Parts and their Working‘ Bright Hub Inc. Available

from: http://www.brighthubengineering.com/hvac/66729-domestic-refrigerator-parts-and-their-

working/

MacIntosh, T. (2014) ‗Basic Mechanism of Freezer Compressor‘ Street directory. Available

from: http://www.streetdirectory.com/travel_guide/134797/technology/basic_mechanism_of_

freezer_compressor.html

Rouse, M. (2012) ‗mechanical refrigeration‘ TechTarget

Trane (1999) ‗Refrigeration Cycle: Heat and Refrigeration‘ American Standard Inc.

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