Evaporator Systems Flashcards
7 cards from real RSES practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Evaporator Systems flashcards as text
What condition causes frost to form unevenly on an evaporator coil, with heavy frost near the inlet and little near the outlet?
Answer: Low refrigerant charge
Low refrigerant charge causes the available refrigerant to evaporate early in the coil, leaving the outlet section with only superheated vapor and no frost formation.
A direct-expansion evaporator serving a walk-in cooler shows adequate airflow but poor temperature pull-down. The suction pressure is normal. What is the most likely cause?
Answer: Dirty evaporator coil fins
Dirty or frosted fins restrict heat transfer between the air and refrigerant even when airflow volume appears adequate, reducing the effective cooling capacity.
Which evaporator design is best suited for applications requiring precise humidity control, such as produce storage?
Answer: Large surface area, low TD evaporator
A large surface area evaporator operating at a low temperature difference (TD) between air and refrigerant minimizes moisture removal from the stored product.
In a multi-circuit evaporator, what is the purpose of a distributor assembly?
Answer: To divide liquid refrigerant equally among all circuits
A distributor ensures each parallel circuit receives an equal mass flow of refrigerant, preventing some circuits from flooding while others starve.
What happens to evaporator capacity when the suction pressure is lowered below design conditions?
Answer: Capacity decreases because the refrigerant density and mass flow rate drop
Lower suction pressure reduces refrigerant vapor density, which decreases mass flow through the compressor and lowers the actual refrigerating effect.
A technician measures 20°F superheat at the evaporator outlet on a system designed for 10°F. What adjustment should be made to the TXV?
Answer: Open the valve (decrease spring tension) to allow more refrigerant flow
High superheat indicates the TXV is underfeeding the evaporator; reducing spring tension allows the valve to open more and feed more refrigerant.
Which refrigerant property most directly determines the evaporating temperature in an evaporator operating at a fixed suction pressure?
Answer: Saturation temperature corresponding to that pressure
The evaporating temperature is the saturation temperature of the refrigerant at the prevailing suction pressure, as defined by the pressure-temperature relationship.