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

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BPSC AE Paper V Mechanical 2024 Official Paper

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there is inadequate content of temperature
there can be even heating of the gas if the temperature before throttling is not below the maximum inversion temperature
there can be leakage of gas
enough cooling or temperature drop is not obtained by throttling

Answer 1

Explanation:

Expander in Gas Cycle Refrigeration

In gas cycle refrigeration systems, an expander is used instead of a throttle valve for the pressure drop of the refrigerant. The expander works by allowing the refrigerant to expand, reducing its pressure and temperature while recovering work from the expansion process. This contrasts with the use of a throttle valve, where the pressure drop occurs without work recovery, leading to inefficiencies.
In gas cycle refrigeration, the cooling effect is achieved by reducing the temperature of the refrigerant as it expands. When a throttle valve is used for this pressure drop, the process is essentially isenthalpic (constant enthalpy).
In an isenthalpic process, the temperature drop obtained is often inadequate for efficient cooling because the refrigerant does not perform work during the pressure drop. On the other hand, an expander allows the refrigerant to expand in a manner that performs work, reducing its temperature more significantly. This enhanced temperature drop makes the expander a more effective component for achieving the desired cooling effect in gas cycle refrigeration systems.
The expander also contributes to higher overall efficiency in the refrigeration system because the work recovered during expansion can be utilized elsewhere in the system, reducing the energy input required for operation. Thus, the inadequate cooling effect of throttling is the primary reason for using an expander instead of a throttle valve in gas cycle refrigeration.