4. A refrigerating plant having R-12 as the working fluid, comprises three evaporators of 10 TR at-10°C, 20 TR at 5°C and 30 TR at 10°C. Each of the evaporators is having the individual expansionvalve arrangement. The refrigerant from the higher stage expansion valve is bled and mixed withdelivery from the lower stage compressor and sent to the higher stage compressor suction thus effectingintercooling of the delivery gas from the lower stage and bringing the suction of the higher stagecompressor to dry and saturated conditions. There is only one condenser operating at 40°C and sub-cooling the liquid refrigerant to 30°C. The compression during each stage of compression may beassumed isentropic. The evaporator discharge is dry saturated in cach of the evaporators. Determinethe power required by the entire system.5. A refrigeration system using R-12 as refrigerant consists of three evaporators of capacities 20 TR at -5°C, 30 TR at 0°C and 10 TR at 5°C. The vapours leaving the three evaporators are dry and saturated.The system is provided with individual compressors and multiple expansion valves. The condensertemperature is 40°C and the liquid refrigerant leaving the condenser is saturated. Assuming isentropiccompression in each compressor, find (a) the mass of refrigerant flowing through each evaporator, (b)the power required to drive the system, and (c) the C.O.P. of the system.[Ans. 27.4 kg/min, 42.25 kg/min; 34.12 kg/min 38.4 kW; 5.56]6. A refrigeration system using R-12 as refrigerant has three evaporators of capacities 30 TR at-10°C, 20 TR at 5°C and 10 TR at 10°C. The refrigerant leaving the evaporators is dry and saturated.The system is provided with compound compression, individual expansion valves and flashintercoolers. The condenser temperature is 40°C. Assuming isentropic compression in each compressor,find the power required to run the system and C.O.P. of the system when the liquid refrigerant leavingthe condenser is (a) saturated, and (b) sub-cooled to 30°C.[Ams. 45.46 kW, 4.62; 44 kW, 4.76)

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4. A refrigerating plant having R-12 as the working fluid, comprises three evaporators of 10 TR at -10°C, 20 TR at 5°C and 30 TR at 10°C. Each of the evaporators is having the individual expansion valve arrangement. The refrigerant from the higher stage expansion valve is bled and mixed with delivery from the lower stage compressor and sent to the higher stage compressor suction thus effecting intercooling of the delivery gas from the lower stage and bringing the suction of the higher stage compressor to dry and saturated conditions. There is only one condenser operating at 40°C and sub- cooling the liquid refrigerant to 30°C. The compression during each stage of compression may be assumed isentropic. The evaporator discharge is dry saturated in cach of the evaporators. Determine the power required by the entire system.

4. A refrigerating plant having R-12 as the working fluid, comprises three evaporators of 10 TR at -10°C, 20 TR at 5°C and 30 TR at 10°C. Each of the evaporators is having the individual expansion valve arrangement. The refrigerant from the higher stage expansion valve is bled and mixed with delivery from the lower stage compressor and sent to the higher stage compressor suction thus effecting intercooling of the delivery gas from the lower stage and bringing the suction of the higher stage compressor to dry and saturated conditions. There is only one condenser operating at 40°C and sub- cooling the liquid refrigerant to 30°C. The compression during each stage of compression may be assumed isentropic. The evaporator discharge is dry saturated in cach of the evaporators. Determine the power required by the entire system.

Refrigeration and Air Conditioning Technology (MindTap Course List)

8th Edition

ISBN:9781305578296

Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Chapter28: Special Refrigeration Applications

Section: Chapter Questions

Problem 15RQ: Why is two-stage compression popular for extra-low-temperature refrigeration systems?

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