Sample interview questions: Describe the behavior of heat pumps and their relation to thermodynamics.
Sample answer:
Behavior of Heat Pumps
Heat pumps are thermodynamic devices that transfer heat from one reservoir, the cold reservoir, to another reservoir, the hot reservoir, by absorbing heat at a low temperature and releasing it at a higher temperature. They operate on the principle of the reversed Carnot cycle, which involves four processes:
- Isothermal evaporation: Low-pressure refrigerant absorbs heat from the cold reservoir, turning into a gas.
- Adiabatic compression: The gas is compressed by a compressor, increasing its temperature and pressure.
- Isothermal condensation: The high-pressure gas releases heat to the hot reservoir, condensing back into a liquid.
- Adiabatic expansion: The liquid refrigerant expands through an expansion valve, lowering its temperature and pressure.
Relation to Thermodynamics
Heat pumps are governed by the laws of thermodynamics:
- First law of thermodynamics: The total energy of the heat pump and its surroundings remains constant.
- Second law of thermodynamics: Heat flows spontaneously from higher to lower temperatures. Heat pumps manipulate this flow by introducing an external work input.
Thermodynamic Considerations
The coefficient of performance (COP) is a measure of the efficiency of a heat pump. It is defined as the … Read full answer