Heat Exchangers Flashcards
Three properties of an air-cooling evaporator.
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
For what reason does heat transfer somewhat slowly between air and the refrigerant in an air-cooling evaporator?
Air has relatively low density
Air defrosting is most commonly used on evaporators in ____ applicaitons
low-temperature
A plain coil submerged and mounted inside a container filled with a liquid that provides good heat transfer is a(n) ____ evaporator.
immersed
Why might a designer of a liquid-cooling evaporator use a brine bath rather than a sweet water bath?
So the bath could be could below 32 degrees F without freezing
Fin-and-tube evaporators circulating the most common types of refrigerants generally have fins made of ____.
aluminum
In general, the more fins an air-cooling evaporator has, ____.
the more its cooling ability
Dead air and hot spots in a conditioned space can often be eliminated by using ____.
baffles
The air-cooling evaporators that are most effective at heat transfer are ____ evaporators.
microchannel
Defrost timers commonly control the operation of ____.
Electric heating elements
Fan Motors
Solenoid Valves
Defrost timers end a defrost cycle using ____.
Pressure
Temperature
Timers
The condition in which a defrost cycle continues too long and conditioned space temperature is raised too high is called ____.
overdefrosting
When melted frost cannot be directly drained by gravity alone, it must be removed using a(n) ____.
condensate pump
The method of defrost that involves circulating a hot liquid in and around the evaporator is ____ defrosting.
nonfreezing solution
The method of defrost that involves circulating air form the conditioned space over an evaporator after the compressor cycles off is ____ defrosting.
off-cycle
The method of defrost that involves energizing electric heating elements is ____ defrosting.
electric
The method of defrost that involves removing refrigerant from the evaporator is ____ defrosting.
pump-down
The method of defrost that involves manually or automatically running tap water over an evaporator is ____ defrosting.
water
The method of defrost that involves circulating high-pressure refrigerant through an evaporator is ____ defrosting.
hot-gas
Refrigerant entering a condenser is a hot, high-pressure vapor, but refrigeration exiting a condenser should be a ____.
warm, high pressure liquid
A condenser that is composed of a long refrigerant cylinder filled with straight copper tubes filled with cooling water is called a(n) ____ condenser.
shell-and-tube
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.
shell-and-coil
A condenser that is composed of a coaxial arrangement of tubing with refrigerant and water flowing in opposite directions is called a(n) ____ condenser.
tube-within-a-tube
The reason for head pressure control in low ambient temperature can be explained by the concepts expressed in ____ law.
Gay-Lussac’s
The position of condenser air louvers for low ambient conditions is directly modulated by ____.
head pressure
When head pressure control is done through fan cycling, hotter ambient temperature would result in ____.
more condenser fans in operation
In a suction line-liquid line heat exchanger, system capacity is increased as the suction line experiences ____.
more superheating
In a suction line-liquid line heat exchanger, system capacity is increased as the liquid line experiences ____.
more subcooling
In a suction line-liquid line heat exchanger, refrigerant generally flows ____.
in opposite directions
The four major components of a mechanical refrigeration system are ____.
compressor, condenser, evaporator, and metering device
Devices used for refrigerant flow control include ____.
check valves, pressure regulating valves, and any electomechanical valve that regulates flow
A device used to maintain proper refrigerant quality is the ____.
filter-drier
Install a ____ to protect a compressor after a burnout.
suction line filter-drier
The main task of a drier is to ____.
adsorb moisture and other contaminants that could mix to create acids
(T/F) Suction line filet-driers can hinder the return of oil to the compressor.
True
(T/F) There should not be a measurable pressure difference in pressure measurements taken before and after the filter-drier.
True
A liquid receiver is a tank connected between the ____ that is used for refrigerant storage.
condenser and liquid line
In a commercial refrigeration system that pumps down during the Off cycle, ____ controls the liquid line solenoid valve.
cooling thermostat
Using Off-cycle pump-down on a commercial refrigeration system is a good method of ____.
preventing compressor flooding
The sizing of a filter-drier is primarily based on a systems’s ____.
capacity rating
(T/F) A filter-drier should be replace whenever the system is opened for service.
True
(T/F) If a moisture indicator is hot, it may produce an inaccurate reading on the amount of moisture in a system.
True
(T/F) Shutoff valves are made so that only refrigeration service valve wrench can be used on them.
True
**Some have handwheels on them
Systems that include manifold valves usually have multiple ____.
evaporators
Refrigerant line valves are used to accomplish ____.
blocking of refrigerant when flow reverses, isolation of flow, or restriction of flow.
A shutoff valve controlling refrigerant flow through a vertical length of refrigerant line is a ____ valve.
riser
A valve that allows fluid flow in only on direction is a ____ valve.
check
The inefficient operation of a check valve may cause a(n) ____ noise.
hammering
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.
three-way solenoid valve
A hot-gas defrost valve directs refrigerant into the low-side form the ____.
discharge line
A hot-gas bypass valve is primarily used for ____.
controlling low-level conditions
The two values on which hot-gas bypass valves operate is ____.
low-side pressure and low-side temperature
The value on which liquid injection valves operate is ____.
superheat
A liquid injection vave is used in conjunction with a(n) ____.
hot-gas bypass valve
A liquid injection valve’s primary purpose is to ____.
reduce the temperature of bypass hot-gas
As crankcase pressure rises, a crankcase pressure regulator ____.
closes
The purpose of a CPR (Crank Case Pressure Regulator) is to prevent ____.
compressor overload
The calibration screw on a crankcase pressure regulator (CPR) is adjusted according to which compressor rating?
Rated load amperage (RLA)
The primary purpose of evaporator pressure regulators (EPRs) on multiple-evaporator systems is to ____.
maintain different evaporator temperatures
EPRs are applied to refrigeration systems primarily based on the principle of ____ law.
Gay-Lussac’s
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 ____.
evaporator temerature
Relief valves are generally used to protect against high ____.
head pressure
A relief valve with a metal core that melts at a low temperature is a ____.
fusible plug
A relief valve with an element that burst before system pressure exceeds an unsafe level is a ____.
rupture disk
A condenser pressure regulator is a(n) ____ valve.
open on rise of inlet pressure (ORI)
A receiver pressure regulator is a(n) ____ valve.
open on rise of differential pressure (ORD)
A low-ambient control valve is a combination of which two pressure regulators?
Condenser and receiver
