RSES Evaporator Systems 2

Question 1

What condition causes frost to form unevenly on an evaporator coil, with heavy frost near the inlet and little near the outlet?

Accepted Answer

Low refrigerant charge

Answer

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.

Question 2

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?

Accepted Answer

Dirty evaporator coil fins

Answer

Dirty or frosted fins restrict heat transfer between the air and refrigerant even when airflow volume appears adequate, reducing the effective cooling capacity.

Question 3

Which evaporator design is best suited for applications requiring precise humidity control, such as produce storage?

Accepted Answer

Large surface area, low TD evaporator

Answer

A large surface area evaporator operating at a low temperature difference (TD) between air and refrigerant minimizes moisture removal from the stored product.

Question 4

In a multi-circuit evaporator, what is the purpose of a distributor assembly?

Accepted Answer

To divide liquid refrigerant equally among all circuits

Answer

A distributor ensures each parallel circuit receives an equal mass flow of refrigerant, preventing some circuits from flooding while others starve.

Question 5

What happens to evaporator capacity when the suction pressure is lowered below design conditions?

Accepted Answer

Capacity decreases because the refrigerant density and mass flow rate drop

Answer

Lower suction pressure reduces refrigerant vapor density, which decreases mass flow through the compressor and lowers the actual refrigerating effect.

(RSES) Refrigeration Service Engineers Society Certification Practice Test

(RSES) Refrigeration Service Engineers Society Certification Practice Test

RSES Evaporator Systems 2