Heat Exchangers

Question 1

Three properties of an air-cooling evaporator.

Answer 1

Transfers heat from the air circulating over it to the refrigerant inside its tubing

Uses air as the primary medium for cooling the conditioned space

Conducts heat through fins, to the tubing, then to the liquid refrigerant in the tubing

Question 2

For what reason does heat transfer somewhat slowly between air and the refrigerant in an air-cooling evaporator?

Answer 2

Air has relatively low density

Question 3

Air defrosting is most commonly used on evaporators in ____ applicaitons

Answer 3

low-temperature

Question 4

A plain coil submerged and mounted inside a container filled with a liquid that provides good heat transfer is a(n) ____ evaporator.

Answer 4

immersed

Question 5

Why might a designer of a liquid-cooling evaporator use a brine bath rather than a sweet water bath?

Answer 5

So the bath could be could below 32 degrees F without freezing

Question 6

Fin-and-tube evaporators circulating the most common types of refrigerants generally have fins made of ____.

Answer 6

aluminum

Question 7

In general, the more fins an air-cooling evaporator has, ____.

Answer 7

the more its cooling ability

Question 8

Dead air and hot spots in a conditioned space can often be eliminated by using ____.

Answer 8

baffles

Question 9

The air-cooling evaporators that are most effective at heat transfer are ____ evaporators.

Answer 9

microchannel

Question 10

Defrost timers commonly control the operation of ____.

Answer 10

Electric heating elements
Fan Motors
Solenoid Valves

Question 11

Defrost timers end a defrost cycle using ____.

Answer 11

Pressure
Temperature
Timers

Question 12

The condition in which a defrost cycle continues too long and conditioned space temperature is raised too high is called ____.

Answer 12

overdefrosting

Question 13

When melted frost cannot be directly drained by gravity alone, it must be removed using a(n) ____.

Answer 13

condensate pump

Question 14

The method of defrost that involves circulating a hot liquid in and around the evaporator is ____ defrosting.

Answer 14

nonfreezing solution

Question 15

The method of defrost that involves circulating air form the conditioned space over an evaporator after the compressor cycles off is ____ defrosting.

Answer 15

off-cycle

Question 16

The method of defrost that involves energizing electric heating elements is ____ defrosting.

Answer 16

electric

Question 17

The method of defrost that involves removing refrigerant from the evaporator is ____ defrosting.

Answer 17

pump-down

Question 18

The method of defrost that involves manually or automatically running tap water over an evaporator is ____ defrosting.

Answer 18

water

Question 19

The method of defrost that involves circulating high-pressure refrigerant through an evaporator is ____ defrosting.

Answer 19

hot-gas

Question 20

Refrigerant entering a condenser is a hot, high-pressure vapor, but refrigeration exiting a condenser should be a ____.

Answer 20

warm, high pressure liquid

Question 21

A condenser that is composed of a long refrigerant cylinder filled with straight copper tubes filled with cooling water is called a(n) ____ condenser.

Answer 21

shell-and-tube

Question 22

A condenser that is composed of a refrigerant cylinder filled with a winding spiral of copper tubing filled with cooling water is called a(n) ____ condenser.

Answer 22

shell-and-coil

Question 23

A condenser that is composed of a coaxial arrangement of tubing with refrigerant and water flowing in opposite directions is called a(n) ____ condenser.

Answer 23

tube-within-a-tube

Question 24

The reason for head pressure control in low ambient temperature can be explained by the concepts expressed in ____ law.

Answer 24

Gay-Lussac’s

Question 25

The position of condenser air louvers for low ambient conditions is directly modulated by ____.

Answer 25

head pressure

Question 26

When head pressure control is done through fan cycling, hotter ambient temperature would result in ____.

Answer 26

more condenser fans in operation

Question 27

In a suction line-liquid line heat exchanger, system capacity is increased as the suction line experiences ____.

Answer 27

more superheating

Question 28

In a suction line-liquid line heat exchanger, system capacity is increased as the liquid line experiences ____.

Answer 28

more subcooling

Question 29

In a suction line-liquid line heat exchanger, refrigerant generally flows ____.

Answer 29

in opposite directions

Question 30

The four major components of a mechanical refrigeration system are ____.

Answer 30

compressor, condenser, evaporator, and metering device

Question 31

Devices used for refrigerant flow control include ____.

Answer 31

check valves, pressure regulating valves, and any electomechanical valve that regulates flow

Question 32

A device used to maintain proper refrigerant quality is the ____.

Answer 32

filter-drier

Question 33

Install a ____ to protect a compressor after a burnout.

Answer 33

suction line filter-drier

Question 34

The main task of a drier is to ____.

Answer 34

adsorb moisture and other contaminants that could mix to create acids

Question 35

(T/F) Suction line filet-driers can hinder the return of oil to the compressor.

Answer 35

True

Question 36

(T/F) There should not be a measurable pressure difference in pressure measurements taken before and after the filter-drier.

Answer 36

True

Question 37

A liquid receiver is a tank connected between the ____ that is used for refrigerant storage.

Answer 37

condenser and liquid line

Question 38

In a commercial refrigeration system that pumps down during the Off cycle, ____ controls the liquid line solenoid valve.

Answer 38

cooling thermostat

Question 39

Using Off-cycle pump-down on a commercial refrigeration system is a good method of ____.

Answer 39

preventing compressor flooding

Question 40

The sizing of a filter-drier is primarily based on a systems's ____.

Answer 40

capacity rating

Question 41

(T/F) A filter-drier should be replace whenever the system is opened for service.

Answer 41

True

Question 42

(T/F) If a moisture indicator is hot, it may produce an inaccurate reading on the amount of moisture in a system.

Answer 42

True

Question 43

(T/F) Shutoff valves are made so that only refrigeration service valve wrench can be used on them.

Answer 43

True | **Some have handwheels on them

Question 44

Systems that include manifold valves usually have multiple ____.

Answer 44

evaporators

Question 45

Refrigerant line valves are used to accomplish ____.

Answer 45

blocking of refrigerant when flow reverses, isolation of flow, or restriction of flow.

Question 46

A shutoff valve controlling refrigerant flow through a vertical length of refrigerant line is a ____ valve.

Answer 46

riser

Question 47

A valve that allows fluid flow in only on direction is a ____ valve.

Answer 47

check

Question 48

The inefficient operation of a check valve may cause a(n) ____ noise.

Answer 48

hammering

Question 49

To prevent a TXV from opening intermittently during the Off cycly, a(n) ____ can most easily be used to automatically divert high-side pressure to the underside of the TXV's diaphragm during the Off cycle.

Answer 49

three-way solenoid valve

Question 50

A hot-gas defrost valve directs refrigerant into the low-side form the ____.

Answer 50

discharge line

Question 51

A hot-gas bypass valve is primarily used for ____.

Answer 51

controlling low-level conditions

Question 52

The two values on which hot-gas bypass valves operate is ____.

Answer 52

low-side pressure and low-side temperature

Question 53

The value on which liquid injection valves operate is ____.

Answer 53

superheat

Question 54

A liquid injection vave is used in conjunction with a(n) ____.

Answer 54

hot-gas bypass valve

Question 55

A liquid injection valve's primary purpose is to ____.

Answer 55

reduce the temperature of bypass hot-gas

Question 56

As crankcase pressure rises, a crankcase pressure regulator ____.

Answer 56

closes

Question 57

The purpose of a CPR (Crank Case Pressure Regulator) is to prevent ____.

Answer 57

compressor overload

Question 58

The calibration screw on a crankcase pressure regulator (CPR) is adjusted according to which compressor rating?

Answer 58

Rated load amperage (RLA)

Question 59

The primary purpose of evaporator pressure regulators (EPRs) on multiple-evaporator systems is to ____.

Answer 59

maintain different evaporator temperatures

Question 60

EPRs are applied to refrigeration systems primarily based on the principle of ____ law.

Answer 60

Gay-Lussac's

Question 61

An electric evaporator pressure regulator differs from a standard EPR in that it uses a stepper motor to control its valve position and also measures and reacts to ____.

Answer 61

evaporator temerature

Question 62

Relief valves are generally used to protect against high ____.

Answer 62

head pressure

Question 63

A relief valve with a metal core that melts at a low temperature is a ____.

Answer 63

fusible plug

Question 64

A relief valve with an element that burst before system pressure exceeds an unsafe level is a ____.

Answer 64

rupture disk

Question 65

A condenser pressure regulator is a(n) ____ valve.

Answer 65

open on rise of inlet pressure (ORI)

Question 66

A receiver pressure regulator is a(n) ____ valve.

Answer 66

open on rise of differential pressure (ORD)

Question 67

A low-ambient control valve is a combination of which two pressure regulators?

Answer 67

Condenser and receiver