Why is the throttling valve not replaced by an isentropic turbine in the ideal vapor-compression refrigeration cycle?

Answer 1

In an ideal vapor-compression refrigeration cycle, the throttling valve is used to reduce the pressure of the refrigerant, allowing it to expand and cool without doing work. Replacing it with an isentropic turbine would introduce additional complexity and cost, as the turbine would need to extract work from the refrigerant during expansion. This would alter the cycle's efficiency and require a more complex control system, deviating from the simplicity and effectiveness of the refrigeration cycle that relies on the throttling process to achieve the desired cooling effect. Thus, the throttling valve effectively maintains the cycle's simplicity while achieving the necessary pressure drop.