A regenerative air refrigeration system for an aeroplane is designed to take a load of 30 TR. The temperature and pressure conditions of the atmosphere are 5°C and 0.85 bar. The pressure of the air is increased from 0.85 bar to 1.2 bar due to ramming action. The pressure of air leaving the main compressor is 4.8 bar. 60% of the total heat of the air leaving the main compressor is removed in the heat exchanger and then it is passed through the cooling turbine. The temperature of the rammed air which is used for cooling purposes in the heat exchanger is reduced to 50°C by mixing the air coming out from the cooling turbine, and in the process, the cooling air from the turbine gets heated to 100°C before it is discharged. The isentropic efficiencies of the compressor and turbine are 90% and 80% respectively. The pressure and temperature required in the cabin are 1 bar and 25°C respectively. Assuming isentropic ramming and mass of cooled air passing through the heat exchanger equal to the mass of cooling air, find: 1. the ratio of by-passed air to ram air used for cooling purposes; and 2. the power required for maintaining the cabin at required condition. [Ans. 41.2%; 445 kW]

A regenerative air refrigeration system for an aeroplane is designed to take a load of 30 TR. The temperature and pressure conditions of the atmosphere are 5°C and 0.85 bar. The pressure of the air is increased from 0.85 bar to 1.2 bar due to ramming action. The pressure of air leaving the main compressor is 4.8 bar. 60% of the total heat of the air leaving the main compressor is removed in the heat exchanger and then it is passed through the cooling turbine. The temperature of the rammed air which is used for cooling purposes in the heat exchanger is reduced to 50°C by mixing the air coming out from the cooling turbine, and in the process, the cooling air from the turbine gets heated to 100°C before it is discharged. The isentropic efficiencies of the compressor and turbine are 90% and 80% respectively. The pressure and temperature required in the cabin are 1 bar and 25°C respectively. Assuming isentropic ramming and mass of cooled air passing through the heat exchanger equal to the mass of cooling air, find: 1. the ratio of by-passed air to ram air used for cooling purposes; and 2. the power required for maintaining the cabin at required condition. [Ans. 41.2%; 445 kW]

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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