IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
HEAT TRANSFER LAB
TRIAL ON A VAPOUR COMPRESSION REFRIGERATOR
OBJECTIVE: To conduct performance test on Vapor Compression type Refrigerator
and to find out co-efficient of performance (COP), Tonnage of the Refrigerator.
SYSTEM COMPONENTS:
01. Hermetically sealed compressor – 1/3 HP cap.
02. Air Cooled condenser –1/3HP, size: 12” x 13” x 2 rows
03. Fan motor with blade, 1/83 HP
04. Expansion Device –Capillary & Thermostatic Expansion valve
05. Rotameter-0.4 to 4 lph (Eureka)
06. Hand shut off valves-1/4”
07. Filter Drier
08. Energy meter: 2.5 – 5 amps
09. Solenoid Valve
10. Thermostat
11. Pressure/compound gauges
12. Digital Temperature Indicator - 50 to + 150°C
13. Thermocouple selector switch
14. Thermocouples – k type (Cr/Al)
15. DP switch for mains
16. Refrigerant R-134a
17. Evaporator coil placed in a chiller
18. Density of refrigerant (134a) =1374 kg/m3
DESCRIPTION:
The apparatus is a laboratory scale working model of a Refrigeration cycle unit,
portable–trolley mounted, housed on a MS square tube frame with powder–coated
metallic platform to give elegant finish.
The compressor is fitted on the platform with fan-cooled condenser. The
evaporator (chiller) - made of copper coil, placed in a insulated Stainless Steel vessel
with fiber glass coated interior, housed in a wooden chamber.
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
The Rotameter, thermostat expansion valve, solenoid valve, pressure/compound
gauge, LP/HP cutout, and voltmeter, ammeter & temperature indicator with selector
switch (to measure temperature at different points of the refrigeration system) are
mounted on the panel. Hand shut off valves are provided at different points to control
the flow of refrigerant.
THEORY:
The major difference in theory and treatment of vapor refrigeration system as
compared to the air refrigeration system is that, the vapor alternatively undergoes a
change of phase from vapor to liquid and liquid to vapor during the completion of a
cycle. The latent heat of vaporization is utilized for carrying heat from the refrigerator,
which is quite high compared with the air-cycle, which depends only upon the sensible
heat of the air.
The substances used do not leave the plant but are circulated through the system
alternately after condensing and re-evaporating. During evaporating, it absorbs its latent
heat from the brine, which is used for circulating around the cold chamber. In
condensing, it gives out its latent heat to the circulating water or air of the cooler, the
machine is, therefore, known as Latent Heat Pump. It absorbs its latent heat from the
brine and gives out in the condenser.
All the principal parts are shown on the diagram, and path of the refrigerant flow is
also shown on the diagram. The pressure is maintained at different levels in two parts
of the system by the expansion valve (high side float valve). The function of the
expansion valve is to allow the liquid-refrigerant under high pressure to pass at a
controlled rate into the low-pressure part of the system. Some of the liquid evaporates
passing through the expansion valve, but greater portion is vaporized in the evaporator
at low pressure (low temperature). The liquid refrigerant absorbs its latent heat of
vaporization from the air, water or other material, which is being cooled. The function
of the compressor is to increase the pressure and temperature of the refrigerant above
atmospheric, which will be ready to dissipate its latent heat in the condenser. In passing
through the condenser, the refrigerant gives up the heat, which is absorbed in the
evaporator plus the heat equivalent of the work done upon it by the compressor. This
heat is transferred to the air or water, which is used as cooling medium in the condenser.
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
2 3
CONDENSOR
COMPRESSOR EXPANSION DEVICE
EVAPORATOR
1 4
BLOCK DIAGRAM OF VAPOUR COMPRESSION CYCLE
T
E 2
P
M 3 2
R 3
P
E
E
S
R
S
A
U
T 4 1 1
R 4
U
E
R
E
ENTROPY ENTHALPY
T-S AND P-H CHART
THE STANDARD VAPOUR COMPRESSION CYCLE CONSISTS OF
FOLLOWING PROCESS:
1. Process-2 represents reversible adiabatic compression from saturated vapor
to the condenser pressure or superheated vapor.
2. Process 2-3 represents reversible heat rejection at constant pressure, de
preheating and condensation.
3. Process 3-4 represents irreversible constant enthalpy expansion from
saturated liquid to the evaporator pressure.
4. Process 4-1 represents reversible heat addition at constant pressure
(Evaporation to saturated vapor)
The refrigerants such a R-12, R-22, R-134a (commercially known as freons) are used
as working medium because of their properties, which are required at refrigeration
cycles.
PERFORMANCE OF STANDARD VAPOUR COMPRESSION CYCLE:
Process 1-2 is the compression process where Mechanical work is to be supplied
(usually in the form of electrical energy) to a compressor. This is the quantity to be
spent. Process 4 –1 represents the useful refrigeration effect. The index of performance
is defined as coefficient of performance (not as efficiency, as for heat engines)
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
C.O.P. is defined as follows: (Theoretical)
C.O.P. = Useful refrigeration (output) = h1 – h4
Network (compressor work, input) h2 - h1
CARNOT COP:
A Carnot refrigeration cycle consists of all reversible process. It will have the
highest coefficient of performance when operating between any temperature limits.
C.O.P (Carnot) = ___T1 = __ Tlow______
T2-T1 Thigh – Tlow
T = Temperature in Kelvin
Note: Carnot cycle C.O.P. depends only on condenser and evaporator temperatures
Carnot is an ideal cycle. It cannot be constructed in practice. However, it is used as a
guideline for comparison.
Difference between Carnot cycle and standard Vapor Compression cycle
1. Process 1-2 is a wet compression process on Carnot cycle whereas it is a dry
compression process in SVCC
2. Process 3-4 is a reversible process in Carnot cycle whereas it is an irreversible
process in SVC
➢ THERMOCOUPLE DETAILS:
1. T1 = Temp.of refrigerant @ inlet of compressor
2. T2 = Temp.of refrigerant @ outlet of compressor
3. T3 = Temp.of refrigerant @ outlet of condenser
4. T4 = Temp.of refrigerant @ outlet of expansion
5. T5 = Temp.of water @ chiller
C= Condenser, E= Evaporator
Let P1, P2 be pressure,
h1, h2, h3 and h4 be the specific enthalpies of the refrigerant (R-12, R-22, R-134a
etc.) respectively.
These are to be found out from relevant p-h chart
1. (h2-h1) denotes the compressor work input
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
2. h3 = h4 (throttling process is also a constant Enthalpy process)
3. (h1-h4) is the enthalpy rise on the evaporator i.e. the refrigeration effect
C.O.P theoretical = h1 –h4
h2 – h1
Units of h- KJ/KG
OPERATING PROCEDURE / INSTRUCTIONS:
Check the pressure gauges and note down the readings before starting the
unit.
1. Switch on the mains through the D.P switch.
2. Fill the chiller with known quantity of water.
3. Select the operating system i.e. capillary or thermostatic expansion through solenoid
valve and open the corresponding valve.
4. Note the initial temp. of water and time.
5. Switch on the condenser fan and compressor by rotating the thermostat in clock
wise direction.
6. Allow the operating system to run for a known time (30 minutes)
7. Note down the corresponding readings.
8. Change the operating system and repeat the above steps from 4 to 7.
PRECAUTIONS:
1) Check the pressure gauge readings weather they are showing above 65 psi
before starting the unit.
2) Do not open the bypass valve between the main line & filter.
3) Do not close the bypass valve between the filter & Rota meter.
It is recommended to keep it always open.
4) Before starting the compressor, put ON the condenser fan &
Then switch ON the compressor.
5) Study the working procedure before starting the process
6) Do not try to attempt any repair work without informing us.
7) Do not open the charging valve.
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
8) Run the unit for at least thrice a week for 15 min.
9) Mishandling may lead to accidents.
10) Please contact us for any query.
OBSERVATION TABLE:
Sl.No Particulars Symbol Units
01 Duration of Test t seconds
02 Pressure at inlet to compressor P1 kgf/cm2
03 Pressure at outlet to compressor P2 kgf/cm2
04 Temperature at inlet to T1 o
C
compressor
05 Temperature at outlet to T2 C
o
compressor
06 Temperature of refrigerant at T3 C
o
outlet of condenser
07 Temperature of refrigerant at T4 C
o
outlet of expansion
08 Initial temperature of water at T5initial C
o
chiller
09 final temperature of water at T5final C
o
chiller
10 Energy meter impulsions ne
12 Flow rate of refrigerant Vref LPH
11 Time taken for n impulsions te seconds
SPECIMEN CALCULATIONS:
➢ Theoretical COP
COPth = h1 –h4
h2 – h1
from P-H chart for134a,
h1 = Enthalpy in kJ/kg corresponding to pressure P1 & temperature T1
(Vapor phase)
h3 = Enthalpy in kJ/kg corresponding to pressure P2 & temperature T3
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
But, h3 = h4
h2 = Enthalpy in kJ/kg corresponding to pressure P2 & temperature T2
➢ Actual COP
COP (actual) = __Q__ = ___Refrigerating Effect_
W Compressor input
Q = ___mw x Cpw (Tf –Ti)__ kJ/sec(kW)
Duration of test
where,
mw = Mass of water = 14 kg
Cpw = 4.18 kJ/kg oK
Tf = Final chiller water temperature in oC
Ti = Initial chiller water temperature in oC
𝑛𝑒 𝑋 36000
Power input to compressor W =
3200 𝑋 𝑡𝑒
where,
ne = no. of revolution of energy meter disc (or) no. of imp. Of energy meter
te = time taken
Emc = energy meter constant = 3200 rev/kWh or imp./ kWh
➢ Relative COP
COP (relative) = COP (actual)
COP (theoretical)
➢ Mass of Refrigerant
V(ref) = _Rotameter reading__=…………m³/sec
1000 x 3600
ρ (ref) @ T3 (condenser outlet temperature) from R 134a table (almost ambient)
ie,1374 kg/m3 @ liquid state.
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
IMPACT COLLEGE OF ENGINEERING AND APPLIED SCIENCES
SAHAKARA NAGAR SOUTH, BENGALURU - 560092
DEPARTMENT OF MECHANICAL ENGINEERING
ρ (ref) = ----- -------------- kg/m³
𝑚̇r = ρ x V(ref) ----------- kg /sec
𝑚̇𝑟 (ℎ1 −ℎ4 )
➢ Tonnage of Refrigerator = =…………tons
3.5
➢ Theoretical work input to compressor = 𝑚̇r (h2 – h1) = ………kW
➢ Energy rejected in condenser = (h2 – h3) = ………. kJ /kg
RESULTS:
Tabulate COP and TOR of the refrigerator as obtained practically and theoretically.
Saleha Nadeem B.E., M. Tech (Thermal) Asst. prof., Dept. of ME, ICEAS.
