FREE CARO Evaporators and Condensers Questions and Answers

Question 1

An operator observes a steady increase in the condenser approach temperature. Which of the following is the MOST likely cause?

Accepted Answer

Fouling or scale buildup on the condenser's heat transfer surfaces.

Answer

The condenser approach temperature is the difference between the refrigerant's condensing temperature and the temperature of the cooling medium (water or air) leaving the condenser. Fouling, such as mineral scale or algae, acts as an insulator on the heat transfer surfaces, reducing the condenser's efficiency. To reject the same amount of heat, the condensing temperature must rise, which increases the approach temperature. [11, 29]

Question 2

In an industrial ammonia refrigeration system, what is the primary purpose of an automatic purger connected to the high side of the system?

Accepted Answer

To remove non-condensable gases like air and hydrogen.

Answer

Non-condensable gases, such as air that may have entered the system during maintenance or hydrogen from the breakdown of ammonia, accumulate in the condenser. These gases do not condense at the same temperature and pressure as the refrigerant, which increases the overall head pressure, reduces system efficiency, and increases energy consumption. An automatic purger is designed to safely and efficiently remove these non-condensable gases. [3, 15, 18]

Question 3

During a hot gas defrost cycle for a freezer evaporator, which of the following actions occurs?

Accepted Answer

Hot, high-pressure vapor from the compressor discharge is diverted into the evaporator.

Answer

In a hot gas defrost system, hot discharge gas from the compressor is redirected from the condenser to the evaporator inlet. This hot gas flows through the evaporator coil, warming it from the inside out and melting any accumulated frost or ice. The evaporator essentially functions as a condenser temporarily during this cycle. [23, 27]

Question 4

A flooded-type shell-and-tube evaporator is being used to chill brine. Where are the refrigerant and the brine typically located within this component?

Accepted Answer

The brine is in the tubes, and the refrigerant is in the shell.

Answer

In a typical flooded shell-and-tube evaporator used for liquid chilling, the refrigerant fills the shell and boils on the outside surface of the tubes. The liquid being cooled (the brine) flows through the inside of the tubes, transferring its heat to the boiling refrigerant. [37]

Question 5

Which of the following conditions would most likely cause an evaporator to become 'starved' of refrigerant?

Accepted Answer

A dirty or clogged filter-drier upstream of the expansion device.

Answer

A starved evaporator is not receiving enough liquid refrigerant to utilize its entire heat transfer surface effectively, resulting in low suction pressure and high superheat. A restriction, such as a clogged filter-drier, will cause a significant pressure drop before the expansion valve, reducing the flow of liquid refrigerant into the evaporator and causing it to be starved. [19, 26]

CARO - Certified Assistant Refrigeration Operator Practice Test

CARO - Certified Assistant Refrigeration Operator Practice Test

FREE CARO Evaporators and Condensers Questions and Answers