Refrigeration and Air Conditioning
A refrigerating system operating on reversed Brayton refrigeration cycle is used for maintaining 250 K. If the temperature at the end of constant pressure cooling is 300 K and rise in the temperature of air in the refrigerator is 50 K, then the net work of compression will be (assume air as working substance with Cp = 1 kJ/kg)

100 kJ/kg
125 kJ/kg
25 kJ/kg
50 kJ/kg

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Refrigeration and Air Conditioning
In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

The positive work in isentropic expansion of liquid is very small
It leads to significant cost reduction
It considerably reduces mass of the system
It improves the C.O.P., as the condenser is small

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