JHON ARNOLD P. MALABAG 21.
06314 MECHANICAL ENGINEERING DEPARTMENT
PROBLEM SET NUMBER 1
ME 3209 Standard and Actual Vapor Compression Refrigeration System
Problem Solving – given the following problems, determine the required values. Graph the P-h diagram
and T-s diagram for each problem. Show your hand-written solution.
1. A refrigeration cycle is used to keep a refrigerated space at −25 ◦C in an environment at 27 ◦C. The
refrigeration load of the space is 11.5 kW and the COP of the refrigerator is estimated to be 0.90. Determine
(a) the power input, (b) the rate of heat rejected in the condenser
2. A commercial refrigerator is to cool eggplants from 28 to 12 ◦C at a rate of 660 kg/h. The power input to
the refrigerator is 10 kW. Determine the rate of cooling in kJ/s and the COP of the refrigerator. The specific
heat of eggplant above freezing is 3.92 kJ/kg· ◦C.
3. An ideal refrigeration cycle is used to keep a food department at −15◦C in an environment at 22◦C.
The total heat gain to the food department is estimated to be 1750 kJ/h and the heat rejection in
the condenser is 3250 kJ/h. Determine (a) the power input to the compressor, (b) the COP of the
refrigerator
4. A 45,000 Btu/h refrigeration system operates on the ideal vapor-compression refrigeration cy- cle
with R-22 as the refrigerant. The evaporator pressure is 150 kPa and the condenser pressure is
1500 kPa. The refrigerant exchanges heat with air at −5 C in the evaporator and with air at 19 ◦C
in the condenser. If the air conditioner operates at full c◦ooling load, determine(a) the mass flow
rate of R-22, (b) the power input in horsepower, hp (c) the COP, and (d) the heat rejected at
condenser per kg.The enthalpies of R-22 at various states are given as:
h1 = 391.58 kJ/kg, s1 = 1.8051 kJ/kg·K
h2 = 450.98 kJ/kg,
h3 = 248.58 kJ/kg, s3 = 1.1632 kJ/kg·K,
h4 = 248.58 kJ/kg, s4 = 1.2119 kJ/kg·K.
5. A 4-cylinder, single acting ammonia compressor 25 cm x 30 cm operates at 300 rpm. Condenser and
evaporator pressure are 1204 kPa and 227 kPa,respectively. The vapor from the evaporator to the suction of
the compressor is dry saturated and there is no subcooling in the condenser. Clearance factor of the
compressor is 2 percent. Compression process is polytropic with n = 1.20. Determine(a) the refrigerating
effect per kg (b) the horsepower required (c) the heat rejected to the compressor jacket water and (d) the
heat rejected at the condenser.
h3 = hf at 1204 kPa = 346.6 kJ/kg
h1 = hg at 227 kPa = 1442.6 kJ/kg
v1 = vg at 227 kPa = 528.26 L/kg
h2 = 1610 kJ/kg
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