Principles of Food and Bioprocess Engineering (FS 231)

Refrigeration (Laboratory #8)Objectives1. To get acquainted with a vapor-compression refrigeration system2. To be able to use pressure-enthalpy diagrams and tables3. To determine the C.O.P. of a vapor-compression refrigeration system

ApparatusRefrigeration trainer (with R-414B refrigerant) with thermocouples & data logger to recordtemperatures and pressure gauges to monitor pressures

Procedure1. Ensure that valves ACI, ACO, LRI, FMB, HP4, and HP1 are open.2. Ensure that valves ACB, LRB, HP3, and HP2 are closed.3. Close valves TXV & AXV. Open valve CTV to include expansion valve #1 in the system loop.4. Set the evaporator and condenser fans to HIGH.

15. Turn ON the compressor and allow the system to operate for ~15-20 mins so that T ~95 /C.6. Record the temperatures and pressures of the refrigerant at various locations in the system.7. Turn OFF the compressor and fans. Turn OFF the power to the system.Note: Reverse the positions of HP1, HP2, HP3, and HP4 for reversing the refrigeration cycle

Data

Channel Description Temperature (/C)

1 Refrigerant at exit of compressor 1T =

22 Refrigerant at inlet of condenser T =

3 Refrigerant at exit of condenser 3T =

44 Refrigerant at inlet of evaporator T =

55 Refrigerant at exit of evaporator T =

6 Refrigerant at inlet of compressor 6T =

77 Ambient air at inlet of fan of evaporator T =

88 Cooled ambient air near evaporator coils T =

1Pressure at exit of compressor (P ) = psig = psia = bar

2Pressure at exit of condenser (P ) = psig = psia = bar

3Pressure at inlet of evaporator (P ) = psig = psia = bar

4Pressure at inlet of compressor (P ) = psig = psia = bar

Note: In reading pressures, use the outermost ring on the gauge and the longer end of the needle

Conversions1 atm = 14.696 psia 1 psia = 0.06895 bar

Laboratory Report1. Draw the vapor-compression refrigeration cycle for the system (use R-12 chart and submit it)

1 4 1 3 6(Use the pressures P & P and temperatures T , T , and T in drawing the refrigeration cycle)

1 2 32. Determine the enthalpy of the refrigerant at various points in the cycle (H , H , and H )3. Determine the degree of superheat in the evaporator4. Determine the degree of sub-cooling in the condenser5. Determine the C.O.P. of the system6. If the mass flow rate of the refrigerant is 1.1 lbs/min, determine the cooling load rate in kW

Name:

Vapor-Compression Refrigeration System

The above pressure-enthalpy diagram depicts the system operating under “ideal” (a-b-d-e-a loop) and“non-ideal” or “real” (a’-b’-d’-e’-a’ loop) conditions.

Constant temperature lines are horizontal within the dome, vertical in the sub-cooled region, andcurved downwards in the superheated region. For both ideal and non-ideal conditions, the followingequations are valid:

w 3 2Compressor: Work done on refrigerant by compressor = Q = (H - H )

c 3 1Condenser: Energy released by refrigerant in condenser = Q = (H - H )

e 2 1Evaporator: Energy absorbed by refrigerant in evaporator = Q = (H - H ) = Cooling Load Rate

e w cNote: Q + Q = Q

For non-ideal conditions:Degree of superheating in evaporator = Difference in temperatures at points a’ and aDegree of sub-cooling in condenser = Difference in temperatures at points d and d’

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