One primary engineering purpose of sub-cooling liquid refrigerant before expansion is to________________?
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Answer: D. ensure that only liquid and not the vapour enters the expansion (throttling) valve
Explanation
Sub-cooling the liquid refrigerant before the expansion valve ensures that only pure liquid enters, preventing flash gas formation. Sub-cooling lowers the liquid temperature below its saturation point, increasing the net refrigeration effect per unit mass. Eliminating vapor bubbles prior to throttling guarantees accurate metering performance across the expansion device orifice. Sub-cooling is represented on pressure-enthalpy diagrams as a horizontal shift of the liquid state to the left. Additional heat rejection in a liquid sub-cooler improves overall thermodynamic cycle efficiency significantly. Thermodynamic calculations prove that every degree of sub-cooling directly enhances the specific refrigeration capacity.
Sub-cooling liquid refrigerant does not directly reduce compressor overheating, which is managed via suction gas superheat. Compressor discharge temperature depends primarily on suction superheat and pressure ratios rather than liquid sub-cooling. Stating that none of the options are correct ignores the primary purpose of ensuring pure liquid phase entry.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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