Refrigeration Power Engineering Technology Exam with Questions and Answers

Refrigeration Power Engineering Technology Exam with Questions and Answers A working substance in a refrigeration system absorbs heat from a low-temperature region and rejects it to a high-temperature region. Which statement best describes this process in terms of the second law of thermodynamics? a. Heat naturally flows from cold to hot without external work b. Heat transfer from cold to hot requires external work input c. Heat transfer is independent of temperature difference d. Energy is destroyed during refrigeration Correct Answer: b Rationale: The second law of thermodynamics states that heat does not flow spontaneously from a colder body to a hotter body. In a refrigeration cycle, external work (usually compressor work) is required to drive heat from the low-temperature reservoir to the high-temperature environment. This is the fundamental principle behind all refrigeration systems. A vapor compression refrigeration system operates between an evaporator temperature of −10°C and a condenser temperature of 35°C. Which of the following best describes the effect of lowering the evaporator temperature while keeping condenser temperature constant? a) COP increases because refrigeration effect increases b) COP decreases because refrigeration effect decreases and compressor work increases c) COP remains constant because temperature difference does not affect performance d) Compressor work decreases due to reduced pressure ratio Correct Answer b) Rationale Lowering the evaporator temperature increases the pressure ratio across the compressor. This leads to higher compressor work input and typically reduces the refrigeration effect per unit mass because the refrigerant enters the evaporator at a lower