02_basic concepts of refrigeration

7/30/2019 02_Basic Concepts of Refrigeration

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BASIC CONCEPTS OF

REFRIGERATION


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REFRIGERATION

Is the science of producing and

maintaining temperatures below that of the

surrounding atmosphere.

This means the removal of the heat from a

substance to be cooled.


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Before refrigeration

To cool a warm object before refrigeration

was invented, humans placed material to

be cooled near a cold object like a block of

natural ice, or in a cool well, pond, or lake.


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iceman


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Major uses

The largest application of refrigeration, which is

the process of cooling, is for air conditioning.

Refrigeration embraces industrial refrigeration,

including the processing and preservation offood;

Removing heat from substances in chemical,

petroleum, and petrochemical plants; and

Numerous special applications such as those in

the manufacturing and construction industries.


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Specific applications

Air conditioning of medium-sized and largebuildings.

Industrial air conditioning Spot heating and cooling

Environmental laboratories Printing

Textiles

Precision parts and clean rooms

Photographic products Computer rooms

Power plants


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Specific applications

Residential air conditioning

Air conditioning of vehicles

Food storage and distribution Food processing

Dairy products

BeveragesChemical and process industries


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Special applications of refrigeration

Drinking fountains

Dehumidifiers

Ice makers Ice-skating rinks

Construction

Desalting of seawater


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Construction refrigeration

Refrigeration is sometimes used to freeze soil to

facilitate excavations. A further use of

refrigeration is in cooling huge masses of

concrete (the chemical reaction which occursduring the hardening gives off heat, which must

be removed so that it cannot cause expansion

and stress the concrete).

Concrete may be cooled by chilling the sand,gravel, water, and cement before mixing, and by

embedding chilled-water pipes in the concrete.


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Concrete cooling system


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Vapor compression refrigeration

system (Reversed Carnot Cycle)

Recall: A cycle needs four factors:

Working substance

Hot reservoir / heat source

Cold reservoir / heat sink

Engine / heat pump


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Schematic of heat engine


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Schematic of heat pump


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Parts of Basic Vapor Compression

Cycle

Compressor

Condenser

Evaporator Expansion valve


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Parts of refrigeration

Compressor- A machine used for

increasing the pressure of a gas or vapor.

The compressor does work on the system

increasing the pressure from the existingevaporator and to that existing in the

condenser.


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parts

Condenser- A heat transfer device that

reduces a thermodynamic fluid from its

vapor phase to its liquid phases.

the high pressure, high temperature vapor

that enters the condenser has heat removed

from it and as a results it is condensed back

in a liquid phase. It is where the refrigerant is liquefied and

discharges its heat to the environment.


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Parts (cont)

Evaporator any of many devices inwhich liquid is changed to the vapor stateby the addition of heat, for example,

distiller, still, dryer, water purifier, orrefrigeration system element whereevaporation proceeds at low pressure andconsequent low temperature.

heat is absorbed to boil the liquid at a lowtemperature, therefore a low pressure mustbe maintained in this section.


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parts

Throttle valve a choking device to

regulate flow of a liquid, for example, in a

pipeline, to an engine or turbine, from a

pump or compressor. the high pressure liquid from the condenser is

expanded through this valve, allowing its

pressure to drop to that existing in theevaporator.


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Schematic diagram


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Actual set-up


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Household

refrigerator


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refrigerants

Is the substance used for heat transfer in a

refrigerating system. It pucks up heat by

evaporating at a low temperature and

pressure and gives up this heat bycondensing at a higher temperature and

pressure.


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What is freon?

Is a group of organic compounds used as

refrigerants. Freon is DuPonts trade name

for its chlorofluorocarbon and

hydrochlorofluorocarbon refrigerants, usedin air conditioning and refrigeration

systems.

It is a brand name!!! duPont refrigerants!


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DuPont

DuPont pioneered much of thescience that makes airconditioning and refrigerationpossible. With over 75 years ofproven leadership inrefrigerants science and

technology we offer thebroadest range of refrigerantsolutions for new and existingequipment, and we arecommitted to leveraging TheScience of Cool to lead thesearch for new cooling

solutions that improve comfortand enhance the quality of lifearound the world.
http://refrigerants.dupont.com/Suva/en_US/science/index.htmlhttp://refrigerants.dupont.com/Suva/en_US/science/index.htmlhttp://refrigerants.dupont.com/Suva/en_US/science/index.htmlhttp://refrigerants.dupont.com/Suva/en_US/science/index.html


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History of freon

Refrigerators from the late 1800s until 1929used the toxic gases, ammonia (NH3), methylchloride (CH3Cl), and sulfur dioxide (SO2), asrefrigerants. Several fatal accidents occurred in

the 1920s because of methyl chloride leakagefrom refrigerator. People started leaving theirrefrigerators in their backyards. A collaborativeeffort began between three American

corporations, Frigidaire, General Motors andDuPont to search for a less dangerous methodof refrigeration.


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In 1928, Thomas Midgley, Jr. aided by CharlesFranklin Kettering invented a "miraclecompound" called Freon. Freon representsseveral different chlorofluorocarbons, or CFCs,

which are used in commerce and industry. TheCFCs are a group of aliphatic organiccompounds containing the elements carbon andfluorine, and, in many cases, other halogens

(especially chlorine) and hydrogen. Freons arecolorless, odorless, nonflammable, noncorrosivegases or liquids.


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One ton of refrigeration(standard commercial ton of refrigeration)

The American Society of Heating,

Refrigerating and Air-Conditioning

Engineers (ASHRAE): is the transfer of

200 Btu/min, or 12,000 Btu/hr. It is thebasis of all refrigeration calculations,

whether for cold storage, air conditioning,

ice making, or ice-cream manufacture.


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Another definition

Is the equivalent to the amount of heat it

takes to melt one ton of ice in 24 hrs. thus,

which the latent heat of ice equal to 144

Btu/lb, this requires 288,000 Btu in 24 hr.or 12,000 Btu/hr or 200 Btu/min.


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Horsepower per ton

Horsepower per ton is the mechanical

input in horsepower divided by the number

of tons of refrigerating effect produced by

the unit.

02_basic concepts of refrigeration

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