Question

To produce the desired evaporator temperature, the power input is reduced by keeping head pressure ________?

1) constant
2) increased
3) decreased
4) varied

Answer 1

The correct answer is decreased. Lower head pressure in refrigeration systems reduces power input by enhancing heat transfer and allowing the refrigerant to condense at a lower temperature, in accordance with Boyle's law and the direct relationship shown in pressure vs. temperature graphs.

Step-by-step explanation:

The correct answer is option 3) decreased. To produce the desired evaporator temperature in refrigeration and air conditioning systems, the power input can be reduced by keeping the head pressure low.

This is because lower pressure in the condenser leads to a higher temperature difference between the refrigerant and the cooling medium, which enhances heat transfer and allows the refrigerant to condense at a lower temperature, thus reducing compressor work. According to Boyle's law, at constant temperature, the volume of a fixed amount of a gas is inversely proportional to its pressure.

So if head pressure is decreased, the volume can increase, which could potentially lead to a lower temperature. Additionally, a graph of pressure vs. temperature illustrates a direct relationship, indicating that as gas is cooled at constant volume, its pressure decreases.