Refrigeration Flashcards
The amount of heat removed to lower the temperature of 15 pounds of water from 48°F to 39°F is:
135 BTU
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:
Approx. doubled
When an object is refrigerated:
Heat is removed from it
The boiling point of a liquid:
Depends on the absolute pressure
A ton of refrigeration is equal to ______________ Btu per hour.
12,000
Absolute zero is calculated to be ______________ degrees Fahrenheit.
–460
The unit used to measure the amount of heat removed from a substance is the ________.
BTU
The low side of a vapor compression cycle contains the:
Evaporator
The boiling point of refrigerant in a condenser is the same as:
Condensing temperature
Of the following items the largest amount in Btu for one pound of water is:
It’s latent of vaporization
If the evaporator in a vapor compression cycle is not cold enough, it can be made colder by:
Lowering the evaporator pressure
The purpose of the condenser in the vapor compression cycle is to:
Save the refrigerant for re-use
In the vapor compression cycle, the compressor:
Heats and compresses refrigerant vapor and reduces evaporator pressure
Water can be made to boil at 50F by:
Placing it under a high enough vacuum
A fluid:
Can be either a liquid or a gas
Refrigerant HCFC-22 is a:
Halogeneated hydrocarbon
Halocarbon
Chlorinated hydrocarbon
Ammonia is not used as a refrigerant in air conditioning systems because:
it is relatively unsafe to use.
List 4 desirable traits of a refrigerant
Non-corrosive Low leak tendency Does not conduct electricity Chemically stable ... Chemically inert Solvable in oil Harmless to oil
In an air conditioning system using CFC-12 evaporator pressure should not be less than ______ psig if icing of the coil is to be avoided.
30
If a liquid-vapor refrigerant mixture has a quality of 75 percent, it is:
Mostly vapor
Enthalte is:
The heat content of substance
At sea level pressure, water having a temperature of 180F is:
Subcooled
In a system containing CFC-12, the temperature of the refrigerant is 120°F. The refrigerant is:
Saturated, superheated or subcooled depending on pressure,
The unit of enthaltsamem is
BTU per pound
The unit of constant volume is
BTU per pound
The purpose of wearing goggles when handling halocarbon refrigerants is to:
The possibility of freezing the eye
Copper-plating of compressor parts is:
Caused by contaminants in the system
Oil is most readily soluble in:
CFC-12
The best way to put oil into a compressor is to:
use a pressure pump.
A noncondensable in a refrigeration system can be:
Carbon dioxide, methane or air
Air in a refrigeration system results in:
an increase in compressor discharge pressure.
List four materials which are considered to be contaminants in a refrigeration system.
- air
- water
- moisture
- antifreeze or antifreeze agenets
- alcohol
- soldering fluz
- chlorinated solvents
- iron oxide
- rust
- copper oxide
- corrosion
- metal chips or particles
- dirt
In transferring refrigerant from one cylinder to another, it is a good idea to avoid filling the cylinder more than _________ percent full.
80
A capillary tube in a liquid refrigerant line is:
An essential component of a compression cycle
The compressor
Heats the refrigerant,
increases refrigerant pressure and superheat the refrigerant
The expansion device in a vapor compression cycle:
Throttles
In a split system, the condensing unit contains the:
Condenser
List the four essential components of the vapor compression cycle:
- compressor
- condenser
- evaporator
- expansion device (or expansion valve)
The lowest temperature to which a direct-expansion air conditioning coil can cool the air is limited by:
refrigerant temperature.
The refrigerant distributor pressure drop:
need not necessarily affect system capacity.
If dirty filters in an air conditioning system reduce the quantity of air flowing over the DX coil:
system capacity will decrease.
Refrigerant leaves the expansion valve as:
a mixture of liquid and saturated vapor
If all other conditions in a given system remain unchanged, a decrease in condensing pressure results in:
a drop in evaporator temperature.
A shaft seal is required in:
an open compressor.
As compared to the speed of the prime mover, the speed of a direct-drive compressor:
is always the same as that of the prime mover.
One type of compressor is the helical-rotary type; other types are the ___________________, the ________________________, and the _____________________.
rotary, reciprocating, centrifugal
Of the four essential components of the vapor compression cycle, the condensing unit contains ________________________________.
the compressor and the condenser
In a single-phase motor, the starting winding is
Out of phase with the running winding
A split-phase motor:
May have a starting capacitor
A potential relay operates from:
Counter-emf
A current relay:
Has normally-open contacts
An electric motor can overheat because of
High voltage
Low voltage
Excess current draw
An air cooled condenser has a propeller fan driven by an air-oven motor, and the condenser has dampers for capacity control. If the dampers inadvertently remain tightly closed while the fan runs, the motor:
May overheat
What doe the following abbreviation stand for: PSC
Permanent split capacitor
What doe the following abbreviation stand for: CSR
Capacitor start
What doe the following abbreviation stand for: CSIR
Capacitor start - induction run
The part of an electric motor that rotates is called the ___ and the stationary part containing the field winding is called the ____
Rotor, stator
An electric motor turns because of its rotating ____
Magnetic field
A north magnetic pole attracts a ___ magnetic pole, but it repels a ____ magnetic pole.
South, north
