Handputs
LINK: Refrigeration System
Topics:
Reversed Carnot Cycle
Performance of a Heat Pump
Refrigeration Cycle
Types of Multi-Pressure Vapor Compression Cycle
Multi-Pressure Vapor Compression Cycles
Product Load Calculations
Refrigerants
Exercises
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1. 80 tons refrigeration system has a COP of 5. Find the gallons per minute of cooling water required in the condenser for a temperature of 10oC. a. 127.9 gpm b. 137.9 gpm c. 147.9 gpm d. 157.9 gpm 2. A vapor compression cycle is designed to have a capacity of 85 tons of refrigeration. It produces chilled water from 30oC to 3oC. Its COP is 4.5 and 25% of the power supplied is lost. Determine the size of electric motor required to drive the compressor in kW. a. 85.6 kW b. 88.6 kW c. 80.6 kW d. 91.6 kW 3. A reversed Carnot cycle that operates between -3oC and 45oC needs 50 kW of compressor power. Determine the tons of refrigeration the system needed. a. 72 tons b. 80 tons c. 83 tons d. 85 tons 4. An ammonia compressor operates at an evaporator pressure of 320 kPa and a condenser pressure of 1515.2 kPa. The refrigerant is subcooled by 8oC and is superheated by 5oC. For an evaporator load of 80 kW, determine the quantity of cooling water in the condenser if the increase in temperature of water is 7oC. Condenser entrance = 1720 kJ/kg, exit = 360.1 kJ/kg. Evaporator entrance = 360.1 kJ/kg, exit = 1475 kJ/kg. a. 1200.1 kg/hr b. 12114.2 kg/hr c. 11985.7 kg/hr d. 15986.3 kg/hr 5. A refrigeration compressor has a volume flow rate of 0.20 m3/s. The percent clearance is 9% and has a compression ratio of 6.5. The bore and stroke are equal running at 350 rpm. Find the bore of the compressor. a. 552 mm b. 624 mm c. 532 mm d. 442 mm 6. Find the performance factor of a heat pump operating between -5oC and 25oC. a. 5 b. 15 c. 18 d. 10 7. A heat pump has a compressor power of 15 kW and heat rejected of 65 kW to the low temperature region. Find the temperature of the low temperature region if the high temperature region is 50oC. a. 258oC b. 248.4oC c. 258.8oC d. -24.6 oC 8. A heat pump operates between 37oF and 128oF. If heat added from the low temperature region is 489 Btu/min, find the horsepower needed by the compressor. a. 1.80 hp b. 2.20 hp c. 1.55 hp d. 1.75 hp 9. A heat pump operates between -5oC and 33oC. If the compressor power needed is 8 kW, find the kJ/min added from the low temperature source. a. 3390 kJ/min b. 3385 kJ/min c. 2385 kJ/min d. 1326 kJ/min 10. A refrigeration system has an evaporator temperature of -6oC and compressor suction temperature of 10oC, find the degree of superheat. a. 16 oF b. 55.6 oF c. 60.8 oF d. 65.8 oF 11. A cascade refrigeration system operates between 110 kPa and 810 kPa. Find the cascade condenser pressure. a. 285 kPa b. 265 kPa c. 305 kPa d. 298 kPa 12. Find the mass of water that can be cooled from 30oC to -8oC from a 20 tons refrigeration system for 12 hrs. a. 20093 kg b. 19652 kg c. 19873 kg d. 19093 kg 13. A 12,000 kg of fish is to be cooled from 30oC to 5oC in 12 hrs. The freezing temperature of fish is -1oC and latent heat of fusion is 281 kJ/kg. The specific heat above freezing is 3.82 kJ/kg-K and below freezing is 1.9 kJ/kg-K. Determine the tons of refrigeration required. a. 31 tons b. 35 tons c. 37 tons d. 28 tons 14. A 15 tons of beef is to be cooled from 28oC to -15oC with freezing temperature of -5oC in 18 hrs. The Cp above freezing is 3.0 kJ/kg-K and below freezing is 1.8 kJ/kg-K. The latent heat of fusion is 225 kJ/kg. If the miscellaneous losses is found to be 14%, find the tons of refrigeration needed for the system. a. 15.7 tons b. 17.6 tons c. 14.8 tons 15. A refrigeration system is used to cool 9 kg per second of water in the evaporator from 31 to 3oC. Find the tons of refrigeration required. a. 300 tons b. 354.3 tons c. 234.7 tons d. 263.8 tons 16. A reversed Carnot cycle has an evaporator temperature of -6oC and condenser temperature of 48oC. Find the performance factor if it will operate as a heat pump.
a. 5 b. 6 c. 7 d. 8 17. A simple saturated refrigeration cycle uses R12, operates at an evaporating temperature of -6oC and a condensing temperature of 42oC. For refrigerating capacity of 12 kW, determine the work of the compressor. At 42oC, hf=241.6 kJ/kg, at -6oC, hg = 350.1 kJ/kg. Enthalpy at the entrance of the condenser is h = 378 kJ/kg. a. 1.0 b. 2.0 c. 3.0 d. 4.0 18. A refrigeration system using refrigerant 22 is to have a refrigerating capacity of 55 TOR. The evaporating temperature is -12oC and the condensing temperature is 43oC. Determine the heat rejected by the condenser. Enthalpy of condenser entrance = 448 kJ/kg, exit=255 kJ/kg. Evaporator exit = 407 kJ/kg, evaporator entrance = 255 kJ/kg. a. 285 b. 286 c. 299 d. 245 |
