Refrigeration Cycle Experiment 1. OBJECTIVE The objective of this laboratory exercise is to construct the Vapour Compression Refrigeration Cycle (Mechanical Refrigeration Cycle) on the ressure!"nthalpy property #iagram for a Refrigeration Cycle $emonstration %nit an# assess its thermal performance& the Coe'cient of erformance ( CR" ). *tu#ents +ill i#entify the components of the mechanical refrigeration apparatus an# the thermo#ynamic processes occurring in these components an# analyse these processes in con#enser, evaporator, compressor an# throttle-expansion valve. *tu#ents +ill measure temperatures an# pressures of the liui# an# gas phases of the refrigerant at various locations (thermo#ynamic states) to construct the refrigeration cycle.
2. THEORY: The Vapor Compre!!ion Cycle The vapour compression cycle is the most commonly use# refrigeration cycle (mechanical refrigeration) an# involves the same four processes as a heat engine cycle but in the reverse or#er (i.e. evaporation compression con#ensation expansion-throttling). / schematic representation of the main four components of the system in this cycle is sho+n in igure 1.
The +or0 input to the vapour compression cycle #rives a compressor +hich maintains a lo+ pressure in an evaporator an# a higher pressure in the con#enser. The temperature at +hich a liui# +ill evaporate (or a vapour +ill con#ense) is #epen#ent on the pressure. Thus if a suitable ui# (refrigerant) is intro#uce#, it +ill evaporate at a lo+ temperature in the lo+ pressure evaporator (ta0ing in heat) an# +ill con#ense at a higher temperature in the high pressure con#enser (rejecting heat).
The high pressure liui# forme# in the con#enser must then be returne# to the evaporator at a controlle# rate through the expansion valve.
"ome note!: !2oth refrigerators an# heat pumps operate in the same +ay using a reverse# heat engine cycle. ! Refrigerators an# heat pumps are #evices that absorb heat at lo+ temperatures an# reject heat at higher temperatures. !$evices that are use# to maintain temperature belo+ ambient are 0no+n as refrigerators (or air con#itioners). !$evices that are use# to supply heat at higher temperatures than ambient are 0no+n as heat pumps. 3. T4"R"T5C/6 C/6C%6/T57* / typical refrigeration system has the follo+ing processes for the i#eal vapour compression cycle8 Table 1
2ase# on your #ata (Table!9), complete the calculations belo+. 1. 4eat Transfer in "vaporator e. 9. 4eat Transfer in Con#enser c. The refrigerant temperature measurements at critical locations of the thermo#ynamic cycle, T3!: ; evaporator temperature, T1!9; con#enser temperature, T1 ; compressor exit temperature)
3. Compressor /bsolute ressure ; ressure
5sentropic e'ciency of compressor&
:. Coe'cient of erformance (C) C for the refrigeration cycle&
(Refer to igure!9) (>) C for a reverse# Carnot refrigeration cycle&
:. T"*T57< R5<
#. $ROCE%&RE 7ormal peration The refrigerant is R99. ressure!"nthalpy #iagram for R99 is given in igure :.
Experiment: In'e!tigation of the Vapor Compre!!ion Refrigeration Cycle i. The euipment is locate# in 6aboratory 3 (Mechanical) on level 9 of *2 /ca#emy (4en#erson Campus). ii. There are a number temperature an# pressure trans#ucers installe# at a various points aroun# the cycle. iii. Their outputs are all connecte# to the instrument panel on the front of the rig, +hich also contains all the necessary controls. iv. ?our @rst tas0 is to i#entify the cycle components, locate the trans#ucers, selector s+itches of throttle type an# sub!cool setting. v. *et pre#etermine# temperature setting, throttle type an# sub!cool setting (on-oA). Consult your experiment supervisor before performing this tas0.
vi. Turn on the main s+itch an# the compressor +ill start an# notice the C unit +ill turn on automatically. vii. Recor# the temperatures an# pressures. /llo+ the unit to run for at least 1> ! 9B minutes to reach approximate thermal euilibrium before any measurements are recor#e#. The time ta0en to stabilise +ill #epen# upon the local ambient con#itions. viii. or the Test 7o 1, recor# all the system parameters in table 9 belo+. ix. 2ase# on your pressure an# temperature measurements of the refrigerant, plot the vapour compression cycle on the large !h #iagram next to the apparatus. ?ou may ta0e a picture of it as a reference.
e set the temperature on () *C an# allo+ the unit to run at least 1> ! 9B minutes.
e set the temperature on (+ *C an# allo+ the unit to run at least 1> ! 9B minutes.
e set the temperature on 22 *C an# allo+ the unit to run at least 1> ! 9B minutes.
6ab. /mbient Temperature 2, *C
The proce!!e! -hich con!titte the cycle are: rocess 1 ! 9& 5sontropic compression, *1 ; *9 rocess 9 D 3& 5sothermal rejection of heat Tc; constant i.e. T9 ; T3 rocess 3 D :& 5sentropic expansion *3 ; *: rocess : D 1& 5sothermal a##ition of heat (heat absorption from the col# reservoir) at Te
D constant i.e. T1 ; T:
Vario! component! !e in /a0 compre!!or !lo+ pressure gas is change# to high pressure gas ! if the +arm air has been absorbe#, the compressor turns +arm air into liui#. %n#er high pressure, it compresses the air into liui#..
!compressor compresses the refrigerant, +hich o+s to the con#enser, +here it gets coole#.
Conen!er 1Con#ensers of air con#itioner are heat exchanger #evice8 it has a similar operation
principle to the evaporator. 1 The con#enser units ta0e in high!pressure, high temperature refrigerant gas from the compressor an# turn it into high!pressure, high temperature liui# refrigerant.
E'aporator 1 evaporator +or0s at the opposite of the con#enser, here refrigerant liui# is converte# to gas, absorbing heat from the air in the compartment. ! The evaporator coil +or0s by #ra+ing hot air over the coil, +hich is @lle# +ith refrigerant, to cool the air.
Compare of 'apor compre!!ion cycle -ith Carnot cycle
The vapour compression cycle is the most +i#ely use# refrigeration cycle in practice. Carnot cycle is one +hose e'ciency cannot be excee#e# +hen operating bet+een t+o given temperature. compressor compresses the refrigerant to a higher pressure an# temperature from an evaporate# vapour at lo+ pressure from an evaporate# vapour at lo+ pressure an# temperature. The Carnot heat engine receives energy at a high of temperature, converts a portion of the energy into +or0, an# #ischarges the remain#er to a heat sin0 a lo+ level of temperature.
