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In a gas cycle refrigeration, an expander is used instead of a throttle valve for pressure drop of the refrigerant, because

Question

In a gas cycle refrigeration, an expander is used instead of a throttle valve for pressure drop of the refrigerant, because

enough cooling or temperature drop is not obtained by throttling

there can be leakage of gas

there can be even heating of the gas if the temperature before throttling is not below the maximum inversion temperature

there is inadequate content of temperature

Solution

Correct option is A

In a gas refrigeration cycle (e.g., Bell–Coleman / air cycle), the refrigerant is a gas (usually air) that behaves nearly ideally.
For ideal gases, enthalpy is a function of temperature only.
→ In a throttling process (h_1 = h_2), there is no temperature drop for an ideal gas.
→ This means that throttling gives negligible or zero cooling effect.
To obtain the required cooling (temperature drop), an isentropic expansion in a turbine/expander is employed instead. The gas does external work during expansion, which reduces its temperature significantly.