What term describes the decrease in pressure due to friction of a fluid or vapor as it passes through a tube or duct?

The term that describes the decrease in pressure due to the friction of a fluid or vapor as it passes through a tube or duct is known as "Pressure Drop." This phenomenon occurs because the energy in the fluid is dissipated as it encounters resistance from the surfaces of the tube or duct, leading to a reduction in pressure along the flow path.

Pressure drop is critical in the design and operation of air conditioning and refrigeration systems because it can significantly affect the system's efficiency and performance. Engineers must account for pressure drop when specifying the dimensions of ducts and piping, ensuring that the system maintains adequate pressure levels for optimal operation. Recognizing and calculating pressure drop helps in designing effective air distribution systems and minimizes energy losses.

The other options describe different concepts: pressure gain refers to an increase in pressure, pressure loss is often used interchangeably with pressure drop but can also refer to other pressure reduction factors, and pressure balance typically refers to a situation where pressures on either side of a system are equal. Understanding these distinctions is essential in troubleshooting and optimizing HVAC systems.