Lab 1 Refrigeration Cycle

EXPERIMENT NO: 1 (REFRIGERATION CYCLE)

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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OBJECTIVE: •

To determine the coefficient of performance of a refrigeration unit.

•

To study the effect of evaporating and condensing temperature on the refrigeration rate and condenser heat output.

•

To investigate the effect of compressor pressure ratio on system performance.

•

To determine the overall heat transfer coefficient between R141b and water in the evaporator and condenser.

KEYWORDS Refrigeration, air conditioning

OVERVIEW: Refrigeration is used in many applications such as preservation of food and material. In air conditioning, refrigeration is the heart of the system. It is important to understand the principle of operation of a refrigeration unit in particular the efficiency of the system commonly known as Coefficient of Performance.

1.

INTRODUCTION

A refrigerator is defined as a machine whose prime function is to remove heat from a low temperature region. Since energy cannot be destroyed, heat taken in at a low temperature plus any other energy input must be dissipated to the surroundings. If the temperature at which the heat is dissipated is high enough to be useful for example space heating, the machine is then called a heat pump.

Clausius statement of the Second Law states that heat will not pass from a cold to a hotter region without the aid of an external agency. Thus a refrigerator requires a compressor to operate. The most common type of refrigerator operates on a vapor compression cycle. The components of a vapor refrigeration system are: i.

Compressor- which uses work input to reduce the pressure in the evaporator and increase the pressure of the vapor being transferred to the condenser

ii.

Condenser- where the high pressure vapor condenses, rejecting heat to its surroundings

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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iii.

expansion device- controls the flow of liquid refrigerant and reduces the pressure

iv.

evaporator- heat is taken from low temperature region as the liquid evaporates at low pressure

Condenser

Expansion device

Compressor

Evaporator

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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Figure 1 Refrigeration Demonstration Unit CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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THEORY The refrigeration cycle can be plotted on a Pressure enthalpy diagram

P

3

2

4

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h The Coefficient of Performance (COP) is an indicator of performance of a refrigeration cycle.

COP

= Refrigeration effect Compressor work

= h1-h4 h2-h1

2.

EXPERIMENTS

2.1

Procedure

•

Start the unit and ensure that the unit is air free by venting air from the condenser.

•

Set the evaporator water flow to a mid range value and allow the unit to run approximately 15-20 minutes.

•

Record all system parameters

•

Repeat the experiment for 5 different condenser pressures

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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DATA SHEET Test no

1

2

3

4

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Gauge Evaporator pressure Pe ( KN/m2) Absolute Evaporator Pressure Pe ( KN/m2) Evaporator temperature T5 (oC) Evaporator Water Flow Rate ms ( gm /s) Evaporator Water Inlet Temp T1 ( oC) Evaporator Water outlet Temp T2 ( oC) Condensed Liquid Temp T8 (oC) Gauge Condenser Pressure Pc ( kN/m2) Absolute Condenser Pressure Pc ( kN/m2) Compressor Discharge Temp T7 ( oC) Condenser Temp T6 (oC) Condenser Water Flow Rate mc (gm/s) Condenser Water Inlet Temp T4 ( oC) Condenser Water Outlet Temp T3 ( oC) Compressor Power input W ( watts)

3.

TUTORIALS

a)

i. Plot the cycle on the P-h diagram for different condenser pressure to determine the enthalpy values ii. Determine the COP for different condenser pressure Use the chart provided

b)

i. Calculate the heat transfer to water in evaporator for different condenser pressure. ii. Calculate the heat transfer to water in condenser for different condenser pressure.

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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iii. Calculate the compressor pressure ratio ( Pc/Pe ) iv. Plot graph heat transfer (W) in evaporator and condenser vs the pressure ratio. v. Calculate the overall heat transfer coefficient in evaporator and condenser at different condenser pressure.

CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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CLB 2O403 : Thermodynamics Exp. 1 : Refrigeration cycle

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