Cooling Cycle & Heat Transfer Principles Flashcards
7 cards from real ATP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cooling Cycle & Heat Transfer Principles flashcards as text
The overall heat transfer coefficient (U-value) of a heat exchanger accounts for:
Answer: Combined resistances of convection on both sides and conduction through the wall
U-value combines all thermal resistances in series: inside convection, wall conduction, and outside convection.
A heat pump operating in heating mode rejects heat at the:
Answer: Condenser, which faces the indoors
In heating mode, the indoor coil acts as the condenser, rejecting heat absorbed from outside to warm the indoor space.
Which factor most significantly reduces the evaporator's heat transfer effectiveness over time in a humid climate?
Answer: Ice or frost buildup on the coil surface
Frost acts as an insulating layer with low thermal conductivity, dramatically reducing heat transfer between air and refrigerant.
Stefan-Boltzmann Law describes the rate of heat transfer by radiation as proportional to:
Answer: The fourth power of absolute temperature
Stefan-Boltzmann Law states Q = εσAT⁴, making radiation extremely sensitive to absolute temperature.
In a two-stage refrigeration system, an intercooler between stages is used to:
Answer: Desuperheat first-stage discharge gas and subcool liquid refrigerant
The intercooler cools hot first-stage discharge vapor and subcools the liquid refrigerant, improving second-stage efficiency and reducing discharge temperature.
What is the significance of the critical point on a refrigerant's phase diagram?
Answer: The point above which liquid and vapor phases cannot be distinguished
Above the critical point, the substance exists as a supercritical fluid and no distinct liquid-vapor interface can form.
A technician measures a lower-than-normal temperature difference between evaporator inlet and outlet air. This most likely indicates:
Answer: Excessive airflow or reduced refrigerant load through the evaporator
A small air-side temperature split across the evaporator suggests either too much airflow or insufficient load, reducing the heat exchange per unit air volume.