Air enters the compressor of an ideal Brayton refrigeration cycle at 100 kPa, 30

Question

Air enters the compressor of an ideal Brayton refrigeration cycle at 100 kPa, 300 K. The compressor pressure ratio is 3.75, and the temperature at the turbine inlet is 350 K.

The Brayton refrigeration cycle of Problem 5 is modified by the introduction of a regenerative heat exchanger. In the modified cycle, compressed air enters the regenerative heat exchanger at 350 K and is cooled to 320 K before entering the turbine. For the modified cycle, determine

(a) the lowest temperature, in K. [9 points]

(b) the net work input, per unit mass of air flow, in kJ/kg. [9 points]

(c) the refrigeration capacity, per unit mass of air flow, in kJ/kg. [6 points]

(d) the coefficient of performance. [6 points]

7. Reconsider Problem 6, but include in the analysis that the compressor and turbine have isentropic efficiencies of 85% and 88%, respectively. Determine

(a) the lowest temperature, in K. [9 points]

(b) the net work input, per unit mass of air flow, in kJ/kg. [9 points]

(c) the refrigeration capacity, per unit mass of air flow, in kJ/kg. [6 points] (d) the coefficient of performance. [6 points]

Explanation / Answer

From the above given

data

lowest temprature=45c

net work = 867 kj/kg

Refrigeration capacity = 89

cop = 4

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