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Refrigeration 6B Final
Basic knowledge of refrigeration systems
136
Science
Not Applicable
06/24/2018
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Term
If a liquid-vapor refrigerant mixture has a quality of 75%, it is:
 Definition
mostly vapor
Term
Enthalpy is:
 Definition
the heat content of a substance.
Term
The unit of enthalpy is
 Definition
BTU/LB
Term
The unit of constant volume is
 Definition
Cubic Feet
Term
At sea level pressure, water having a temperature of 180 degrees Fahrenheit is:
 Definition
Subcooled.
Term
The purpose of wearing goggles when handling halocarbon refrigerants is to avoid:
 Definition
the possibility of freezing of the eye.
Term
Copper-plating of compressor parts is:
 Definition
caused by contaminants in the system.
Term
Oil is most readily soluble in:
 Definition
CFC-12
Term
The best way to put oil into a compressor is to:
 Definition
use a pressure pump.
Term
A capillary tube in a liquid refrigerant line is:
 Definition
an essential component of a compression cycle.
Term
The compressor:
 Definition
pressurizes and superheats refrigerant.
Term
In a split system, the condensing unit contains the:
 Definition
condenser.
Term
What comprises the vapor compression cycle?
 Definition
condenser, compressor, evaporator, metering device.
Term
The expansion device in a vapor compression cycle:
 Definition
throttles.
Term
What are four possible methods for reducing capacity of reciprocating compressors?
 Definition
on/off switch, variable drive, multiple compressors, hot-gas bypass.
Term
Cylinder unloading should follow what sequence of capacity percentage?
 Definition
100, 75, 50, 25.
Term
In the hot-gas bypass control method, the system component which is bypassed is:
 Definition
the condenser.
Term
The lowest temperature of water obtainable from a cooling tower is limited by the:
 Definition
wet bulb temperature.
Term
Two types of mechanical draft cooling towers are:
 Definition
induced and forced.
Term
Cooling towers can be constructed in several arrangements as concerns the relative directions of water flow and air flow. Three such arrangements are:
 Definition
Counterflow, parallel flow, and crossflow.
Term
A ton of refrigerant is equal to:
 Definition
12,000 btu/hr
Term
If the pressure exerted on a refrigerant in the vapor state remains constant but its temperature above absolute zero is doubled, the volume of the vapor will be:
 Definition
approximately doubled.
Term
When an object is refrigerated:
 Definition
heat is removed from it.
Term
When a LB of water is heated from 32 degrees to 212 degrees it gains:
 Definition
180 BTU sensible heat.
Term
Absolute zero is calculated to be:
 Definition
-460 degrees Fahrenheit.
Term
The unit used to measure the amount of heat removed from a substance is the:
 Definition
BTU
Term
The boiling point of a liquid:
 Definition
depends on the absolute pressure.
Term
The low side of a vapor compression cycle contains the:
 Definition
evaporator.
Term
The boiling point of refrigeration in a condenser is the same as:
 Definition
condensing temperature.
Term
Which type of heat contains the largest amount of BTU for one LB of water?
 Definition
latent heat of vaporization.
Term
If the evaporator in a vapor compression cycle is not cold enough, it can be made colder by:
 Definition
lowering the evaporator pressure.
Term
The purpose of the condenser in the vapor compression cycle is to:
 Definition
save the refrigerant for re-use.
Term
Water can be made to boil at 50 degrees by:
 Definition
placing it under a high enough vacuum.
Term
What is a halogen?
 Definition
A group of chemicals including chlorine, fluorine, and bromine.
Term
A fluid can be:
 Definition
either a liquid of a gas.
Term
Ammonia is not used as a refrigerant in air conditioning systems because:
 Definition
it is relatively unsafe to use.
Term
Oil is most readily soluble (miscible) in:
 Definition
CFC-12.
Term
In transferring refrigerant from one cylinder to another, it is a good idea to avoid filling the cylinder more than:
 Definition
80% full.
Term
Air in a refrigeration system results in:
 Definition
an increase in compressor discharge pressure.
Term
The lowest temperature to which a direct-expansion (DX) air conditioning coil can cool the air is limited by:
 Definition
the refrigerant temperature.
Term
The refrigerant distributor pressure drop:
 Definition
need not necessarily affect system capacity.
Term
If dirty filters in an air conditioning system reduce the quantity of air flowing over the DX coil:
 Definition
system capacity will decrease.
Term
Refrigerant leaves the expansion valve as:
 Definition
a mixture of liquid and saturated vapor.
Term
If all other conditions in a given system remain unchanged, a decrease in condensing pressure results in:
 Definition
a drop in evaporator temperature.
Term
A shaft seal is required in:
 Definition
an open compressor.
Term
As compared to the speed of the prime mover, the speed of a direct-drive compressor:
 Definition
is always the same as that of the prime mover.
Term
The compressor ___ condenser pressure and temperature.
 Definition
increases.
Term
The compressor ___ evaporator pressure and temperature.
 Definition
decreases.
Term
One type of compressor is the helical-rotary (scroll) type, other types are:
 Definition
rotary, centrifugal, and reciprocating.
Term
The condensing unit contains:
 Definition
the compressor and motor, and the condenser.
Term
What type of acid should be used for chemically cleaning a condenser?
 Definition
inhibited.
Term
What can cause an increase in the amount of heat to be rejected by the condenser?
 Definition
Increase in condensing pressure. Decreasing water supplied to a water-cooled condenser.
Term
A water-cooled condenser does NOT:
 Definition
superheat.
Term
What two sources of heat is removed by the condenser?
 Definition
the evaporator and the compressor.
Term
Dry coil operation of an evaporative condenser depends on:
 Definition
transfer of sensible heat.
Term
A refrigeration system has an air cooled condenser which is located outside, the remainder of the system being located inside. If the system cycles off during cold weather, the compressor may not start on the next on cycle because:
 Definition
the evaporator pressure may be too low.
Term
Three characteristics of air-cooled condensers which are considered to be advantages over water-cooled condensers are:
 Definition
air is readily available; maintenance is simple; no freezing problems.
Term
Three methods of controlling the capacity of air-cooled condensers are:
 Definition
cycle one or more fans; dampers; liquid throttling valve.
Term
A refrigeration system has a hand-operated needle valve for the refrigerant expansion device. If refrigeration load and suction pressure remain constant, a decrease in condensing temperature will:
 Definition
result in reduced refrigerant flow unless the valve is opened.
Term
The proper location of a high-side float is:
 Definition
between the evaporator and condenser.
Term
The low-side float should be located:
 Definition
between the evaporator and compressor.
Term
An advantage of a capillary tube is that:
 Definition
it allows the use of a less expensive compressor motor.
Term
The constant pressure expansion valve:
 Definition
maintains constant evaporator pressure.
Term
The thermostatic expansion valve measures:
 Definition
evaporator pressure and superheat.
Term
What are the three principle parts of a thermostatic power element?
 Definition
power head; capillary tube; bulb.
Term
What are the three forces involved in operation of a thermostatic expansion valve?
 Definition
pressure; thermostatic element; spring.
Term
If a thermostatic expansion valve hunts severely, hunting might be reduced by:
 Definition
setting the valve for a higher superheat.
Term
When an increase in the temperature of refrigerant vapor causes the vapor to become superheated, the volume occupied by the vapor:
 Definition
increases only slightly.
Term
The purpose of the external equalizer line used with a thermostatic expansion valve is to compensate for:
 Definition
refrigerant friction through the evaporator.
Term
It is especially important that the power head does not become colder than the bulb when a thermostatic expansion valve has a:
 Definition
gas charge.
Term
Liquid floodback from the evaporator to the compressor is most likely to occur when a thermostatic expansion valve has a:
 Definition
liquid charge.
Term
For low temperature work, a thermostatic expansion valve power element having a ___ charge should not be used.
 Definition
liquid.
Term
Receivers are usually required in systems having:
 Definition
evaporative condensers.
Term
An important feature of a refrigerant receiver, in the case where the liquid line to the evaporator comes out of the top of the receiver, is a:
 Definition
dip tube.
Term
A liquid refrigerant receiver has two liquid level test cocks, one near the top of the receiver and one near the bottom. If the system contains enough refrigerant, where the lower cock is opened:
 Definition
the test cock should discharge liquid refrigerant.
Term
Desiccants are used in:
 Definition
driers.
Term
A refrigerant heat exchanger might cause:
 Definition
the compressor to overheat.
Term
The purpose of a suction line accumulator is to:
 Definition
trap liquid refrigerant.
Term
The proper location of an oil separator is near the:
 Definition
compressor.
Term
If not properly installed, a hot-gas muffler might trap:
 Definition
oil.
Term
The oil separator is intended to remove oil from the ___ pipe.
 Definition
discharge.
Term
Dry coil operation of an evaporative condenser depends on:
 Definition
transfer of sensible heat.
Term
A refrigeration system has an air cooled condenser which is located outside, the remainder of the system being located inside. If the system cycles off during cold weather, the compressor may not start on the next on cycle because:
 Definition
the evaporator pressure may be too low.
Term
Three characteristics of air-cooled condensers which are considered to be advantages over water-cooled condensers are:
 Definition
air is readily available; maintenance is simple; no freezing problems.
Term
Three methods of controlling the capacity of air-cooled condensers are:
 Definition
cycle one or more fans; dampers; liquid throttling valve.
Term
A refrigeration system has a hand-operated needle valve for the refrigerant expansion device. If refrigeration load and suction pressure remain constant, a decrease in condensing temperature will:
 Definition
result in reduced refrigerant flow unless the valve is opened.
Term
The proper location of a high-side float is:
 Definition
between the evaporator and condenser.
Term
The low-side float should be located:
 Definition
between the evaporator and compressor.
Term
An advantage of a capillary tube is that:
 Definition
it allows the use of a less expensive compressor motor.
Term
The constant pressure expansion valve:
 Definition
maintains constant evaporator pressure.
Term
The thermostatic expansion valve measures:
 Definition
evaporator pressure and superheat.
Term
What are the three principle parts of a thermostatic power element?
 Definition
power head; capillary tube; bulb.
Term
What are the three forces involved in operation of a thermostatic expansion valve?
 Definition
pressure; thermostatic element; spring.
Term
If a thermostatic expansion valve hunts severely, hunting might be reduced by:
 Definition
setting the valve for a higher superheat.
Term
When an increase in the temperature of refrigerant vapor causes the vapor to become superheated, the volume occupied by the vapor:
 Definition
increases only slightly.
Term
The purpose of the external equalizer line used with a thermostatic expansion valve is to compensate for:
 Definition
refrigerant friction through the evaporator.
Term
It is especially important that the power head does not become colder than the bulb when a thermostatic expansion valve has a:
 Definition
gas charge.
Term
Liquid floodback from the evaporator to the compressor is most likely to occur when a thermostatic expansion valve has a:
 Definition
liquid charge.
Term
For low temperature work, a thermostatic expansion valve power element having a ___ charge should not be used.
 Definition
liquid.
Term
Receivers are usually required in systems having:
 Definition
evaporative condensers.
Term
An important feature of a refrigerant receiver, in the case where the liquid line to the evaporator comes out of the top of the receiver, is a:
 Definition
dip tube.
Term
Desiccants are used in:
 Definition
driers.
Term
A refrigerant heat exchanger might cause:
 Definition
the compressor to overheat.
Term
The purpose of a suction line accumulator is to:
 Definition
trap liquid refrigerant.
Term
If not properly installed, a hot-gas muffler might trap:
 Definition
oil.
Term
The oil separator is intended to remove oil from the ___ pipe.
 Definition
discharge.
Term
The term which involves the instantaneous evaporation of refrigerant is called:
 Definition
flash gas.
Term
A system using an ___ is sometimes called a dry system.
 Definition
automatic expansion valve.
Term
A flooded evaporator system could use a ___ for its metering device.
 Definition
low-side float.
Term
Connecting the capillary tube to the suction line will produce a ___
 Definition
heat exchanger.
Term
When an evaporator is only receiving a very small amount of refrigerant, it is said to be:
 Definition
starving.
Term
The term used that refers to the difference in temperature between the vapor in the low side and the sensing bulb is called the:
 Definition
superheat.
Term
The capacity of a thermostatic expansion valve could vary according to:
 Definition
orifice size.
Term
The solenoid valve is simply an ___ with a movable core.
 Definition
electromagnet.
Term
The ___ compensates for any pressure drop through the evaporator while the compressor is running.
 Definition
equalizer.
Term
Allowing liquid refrigerant to enter the compressor is referred to as:
 Definition
liquid refrigerant slugging.
Term
Refrigerant control that is operated by both low-side temperature and pressure.
 Definition
Thermostatic expansion valve.
Term
Refers to a mechanism/control that, when in action, goes too far in one direction and then returns too far in the other direction.
 Definition
Hunting.
Term
Refrigerant control located on the high-pressure side.
 Definition
High-side float.
Term
Valve which allows fluid to flow in one-direction only.
 Definition
Check valve.
Term
Tubing with a small inside diameter that is used as a refrigerant control.
 Definition
Capillary tube.
Term
As a rule of thumb, heat rejection from an air conditioning system is about ___ BTU/hr for every ___ BTU/hr of cooling capacity.
 Definition
15,000; 12,000.
Term
Condensing temperatures are usually ___ with air-cooled condensers than with water-cooled condensers.
 Definition
Higher.
Term
The performance of a condenser means its capacity to remove heat from hot refrigerant vapor. What are the three given factors that affect capacity?
 Definition
Temperature difference; velocity of water; cleanliness of tubes.
Term
Capacity can be ___ by increasing the water quantity.
 Definition
Increased.
Term
As a rule of thumb, the superheat setting for relatively high temperature application, such as air conditioning, might be ____.
 Definition
10 to 15 degrees.
Term
___ filter both solid particles and moisture.
 Definition
Filter-driers.
Term
If a sight glass on a receiver is showing bubbles...
 Definition
there might be gas in the liquid refrigerant.
Term
Reducing pipe size ___ velocity.
 Definition
Increases.
Term
Increasing pipe size ___ velocity.
 Definition
Decreases.
Term
A ___ at the bottom of a riser can assist in getting oil to begin upward flow.
 Definition
Trap.
Term
A term that refers to the total actual length of straight pipe plus equivalent lengths of fittings in a piping system.
 Definition
Equivalent length.
Term
What are three good practices for sizing hot-gas discharge lines?
 Definition
Maximum pressure drop of 2 degrees; maximum velocity of 4,000 fpm; minimum velocities of 500 fpm for horizontal lines and 1,000 to 1,500 fpm for vertical upflow risers.
Term
What are two good practices for sizing liquid lines?
 Definition
Maximum pressure drop of 2 degrees; velocity of liquid in the piping should not exceed 300 fpm.
Term
What are three good practices in sizing suction lines?
 Definition
Maximum pressure drop of 2 degrees; maximum velocity of 4,000 fpm; minimum velocities of 500 fpm for horizontal lines and 1,000 to 1,500 fpm for vertical upflow risers. (SAME AS HOT-GAS LINES)
Term
If the riser is very long, additional traps approximately ___ apart are recommended.
 Definition
20 feet.
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