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To Study the Effects of Changing

Different Components in a

Compression Refrigeration System

Title of the Mini Project

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Group Description

Hashim Hasnain

Hadi

Roll No: 13ME36

Ashtar Abbas

Roll No:13ME38

Ghulam Sarwar

Roll No: 13ME19

Group Advisor

Engr. Faisal Maqbool

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Introduction of a Vapor compression

Refrigeration System:

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The vapor-compression refrigeration cycle is the idealmodel for refrigeration systems, air conditions and heatpumps.

It is comprised of four components:1) Evaporator2) Compressor3) Condenser4) Expansion valve

• It consist of four processes:

1-2 Isentropic compression in compressor.

2-3 Constant-pressure heat rejection in a condenser.

3-4 Throttling in an expansion device.

4-1 Constant-pressure heat absorption in an evaporator.

Two-phase

liquid-vapor mixture

Introduction of a Vapor

compression Refrigeration

System:

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Compressor:

Reciprocating ,

Discharge: 8m3/hr

Cooling Unit in

Thermodynamic

s Lab of MED

BUETK.

Throttling

Valve

Condens

er

Capacity 3000 kCal/Hr

For 60 Hz Power Supply,

2500 kCal/Hr For 50 Hz Chille

r

Types of Compressors :

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Reciprocating compressors

Rotary compressors

Centrifugal compressors

Using Reciprocating

compressors:

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Most commonly used compressor for small scale

applications (refrigerators, freezers, ice machines,

etc.…)

Very economical to operate

Piston and cylinder design, Works on the principal

of trapping and compressing refrigerant vapor

(positive displacement compressor

High output pressure

Low flow rate

Using Rotary compressors:

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Typically small in size (used for lower capacity

applications – ie. window air conditioners,

PTAC’s, etc.…)

Very reliable

Quiet

Less efficient

Works on the principal of trapping and

compressing refrigerant vapor

(positive-displacement compressor)

Using Centrifugal compressors:

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Typically large in size (used for high refrigeration

capacity applications – i.e.. Water chillers,

commercial air-conditioning & refrigeration

systems, etc.…)

Very reliable

High flow rate

Highly efficient

Low output pressure

Uses centrifugal force via a rotating impeller to

compress refrigerant vapor(Dynamic

Compressor)

Usage of different type of

Compressors according to the

Required cooling Capacities:

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Type of condensers:

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Air-Cooled condensers

Water-Cooled Condensers

Evaporative Condensers

Using Air-Cooled condensers:

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Advantages:

Simple in construction__ no pipes are required for air.

Disposal of warm air not a problem

Less fouling(scaling inside tubes)

Low maintenance cost.

• Disadvantages:

Less specific heat Capacity of air

Large flow rate of air is required

Low thermal conductivity

Small heat transfer co-efficient of air

Less cop.

Using Water-Cooled condensers:

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Advantages:

High thermal conductivity of water

High specific heat of water

Less flow rate is required to compensate the same heat as that in case of air-cooled compressor

High heat transfer co-efficient

High cop

• Disadvantages:

Large installation and maintenance cost

Pump is required for water circulation

Large energy consumption

Using Evaporative condensers:

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30% to 40% less compressor KW consumed

than air cooled condensing

Less Air over coil, therefore quieter than

air cooled condensing

Less coil required so less space on roof for

equipment than air cooled.

an evaporative condenser requires less coil.

In comparison with an air-cooled condenser,

surface and airflow to reject the same heat,

or alternatively, greater operating efficiencies

can be achieved by operating at a lower

condensing temperature

• Greater Compressor Life since Evap Condensing

Compressors work at lower pressures

Reduced Connected kW:

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Wire Size

# 350 MCM

Wire Size

# 2/0

Typical 100 Ton

Air Cooled Condenser

205 Operating Amps 135 kW

Typical 100 Ton

Evap Cooled Condenser

157 Operating Amps 103 kW

Expansion valve:

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If the refrigerant at the condenser exit is not

completely condensed. Because vapor occupies

much more space than liquid, the throttling valve

will not function properly if vapor can enter from

the condenser. One approach to dealing with this

is to locate a liquid receiver downstream of the

condenser to assure the availability of liquid to

the expansion device

Evaporators:

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Evaporator for

Domestic

Refrigerators

Evaporator for

Domestic

Refrigerators

Using Multi Evaporators:

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Expansion process is one of the main factors responsible for energy loss

Not only the cooling capacity but also increase the size of evaporator.

This problem can be eliminated by adopting multi-stage expansion with flash chamber where the flash vapors is removed after each stage of expansion as a consequence there will be increase in cooling capacity and reduce the size of the evaporator.

Work input can also be reduced by replacing multi-stage compression or compound compression with single stage compression.

Refrigeration effect can also be increased by passing the refrigerant through sub cooler after condenser to evaporator.

Schematic diagram of a Vapor Compression

Refrigeration System with Actual Multiple

Evaporators

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