Fundamentals of Refrigeration
Ice melts in iceboxes because ____.
a. heat flows through the insulated walls b. heat enters when the door is opened c. heat enters when warm food is placed in the icebox Selected: d. All of the above.
The evaporator in a refrigeration system
absorbs heat from the product to be cooled
The law requires technicians to recover refrigerant from all refrigeration systems so that they ____.
all of the above.
At a constant pressure, the volume of a gas varies as to the absolute temperature and at a constant volume the pressure of the gas varies directly with the absolute temperature. This is known as
charles law
If the temperature remains constant and the volume that a gas occupies increases, the pressure will
decrease
Fire extinguishers that can be used on any type of fire, A, B, or C generally contain a _____ to extinguish the fire.
dry chemical powder
The only location where the refrigerant vapor is superheated is in the evaporator.
false
Vapor is more dense than liquid and, as the liquid refrigerant boils, it has a tendency to sink.
false
Specific volume is the term used to indicate the space a weight of gas will occupy.
true
The temperature on the Celsius scale where all molecular activity stops is
-273 Deg C
The temperature on the Fahrenheit scale where all molecular biology activity stops is
-460 F
How many Btus are required to change five pounds of ice at 20°F to steam at 220°F?
6,520 Btu
How many watts of electrical power are equal to 1 horsepower
746
Fires that involve ordinary materials such as paper, cardboard, and wood are classified as Type __________ fires.
A
Aluminum ladders are safe to use around electrical equipment as long as they have insulation pads on the bottom of the rungs.
false
An example of a fossil fuel is hydrogen
false
As long as the torch is kept moving below the level of the liquid refrigerant in the cylinder so as not to create a hotspot, it is OK to heat the cylinder in this manner.
false
If a cylinder of R-22 is moved from a 100°F truck body into an 80°F shop, the quantity of liquid refrigerant in the cylinder will remain the same.
false
A double insulated drill ____.
generally has a plastic case with the electrical connections and motor insulated within the tool
Power tools that are not double insulated must have three-prong plugs to ensure that the tool is properly _.
grounded
In electrical circuits, the _____ wire protects the operator.
grounding
A vapor material exerts a pressure or force
in all directions
The law that states that "energy is neither created or destroyed, but can be converted from one form to another" is called the
law of conservation of energy
A fusible plug is a metal fitting that has a hole drilled through it and the hole is filled with ____.
material with a low melting point
A material that occupies space and has mass is called
matter
A liquid material exerts a pressure or force
outward & downward
A way to move equipment across a roof is to use rollers and _ for a base.
plywood
PSIG indicates
pounds per square inch gauge pressure
A Bourdon tube is often found in a(n)
pressure gauge
The compressor in a refrigeration system
pumps refrigerant through the system
The _ is another positive displacement compressor and is used for larger air conditioning and refrigeration applications.
screw compressor
Matter exists in three states: _, _, and _.
solid, liquid, & gas
The refrigerant vapor picks up additional heat as it flows from the evaporator to the compressor. The heat is picked up from the _.
suction line
Most of the energy we use comes from something we already have on Earth. The only "new" energy we get comes from the
sun
Only liquid refrigerant should enter the metering device.
true
The boiling point of a refrigerant should be low enough at atmospheric pressure to keep the system pressure above 0 psig when operating at low temperatures.
true
The discharge gas from the compressor is a high pressure, high temperature, superheated vapor.
true
The evaporator can be thought of as a "heat sponge."
true
The evaporator in a refrigeration system must be colder than the refrigerated space in order to absorb heat.
true
The halide leak detector should be used in well ventilated areas as the resulting blue or green flame indicates that phosgene gas is being produced.
true
The laws of thermodynamics can help us to understand what heat is all about.
true
To insure proper operation of an oxygen cylinder regulator, make sure no oil residue is present.
true
The unit of measurement of electrical power is the
watt
The unit used to measure electrical power is the
watt
How many Btus are required to change one pound of ice at 20°F to steam at 220°F?
1,304 Btu
At standard conditions on the Celsius scale, water will boil at
100 C
Pure water boils at a temperature of 212°F at which of the following standard conditions
14.696
PSIA at sea level under standard conditions is
14.696psi
The Celsius equivalent of 80°F is
26.7 C
A ton of refrigeration is equal to
288,000 Btu/24 h
The standard atmospheric pressure at sea level is
29.92 In hg
One watt of electrical energy is equal to
3,413 Btu/h
Of the following choices, the warmest temperature is
303 deg K
How many Btus must be removed from one pound of water at 200°F for it to end up as ice at 30°F
313 Btu
______ ft-lb of work is accomplished when an 800-lb condensing unit is lifted to the top of a 40-ft building
32,000
One horsepower of work energy equals the amount of work done when lifting _ pounds to the height of _ foot in _ minute.
33,000, 1, 1
The temperature inside the refrigerator fresh food section should be about ____.
35 f
When it is necessary to perform electrical work in an area that has a damp or wet floor, which of the following can be done to minimize the chance of electrical shock?
All of the above
The volume of gas varies inversely with the absolute pressure, provided the temperature remains constant. This is called
Boyles law
Fires that involve electrical equipment are classified as Type _____ fires.
C
The total pressure of a confined mixture of gases is the sum of the pressures of each of the gases in the mixture. This is known as _
Daltons law
The two common temperature scales used by air conditioning and refrigeration technicians are called _ and
F & C
As heat is applied to a closed container containing a gas, the pressure inside the container will decrease
False
Both sensible heat and latent heat transfers can be read with a thermometer.
False
Temperature difference does not affect heat transfer rate.
False
The difference in the volume of two substances will determine the heat transfer rate between the substances.
False
Water at 0°F has no heat energy or molecular activity.
False
Water boils at 212°C.
False
The Celsius absolute scale is called the _ scale.
Kelvin
Which of the following refrigerants has the lowest boiling temperatures at atmospheric pressure?
R-502
The Fahrenheit absolute scale is called the _ scale
Rankine
The amount of heat needed to change the temperature of a substance will vary with the type of substance. This heat quality is called the ____ of the substance.
Specific Heat
What happens when room temperature soda is poured into a glass of ice?
The ice melts because it is absorbing heat from the soda.
In order for water at 60°F to boil, it must absorb both sensible and latent heat
True
The Fahrenheit scale is used in the English measurement system by the United States.
True
The difference in the level of heat between two substances will determine the heat transfer rate between the substances.
True
When water at 212°F boils, it is only absorbing latent heat
True
An example of a pressure vessel is ____.
a cylinder containing refrigerant
Temperature can be thought of as
a description of the level of heat
High temperature refrigeration is that produced by
an air-conditioning system
Good ventilation is important when working around refrigeration equipment because modern refrigerants
are heavier than air and may displace the oxygen around you
The ____ are used to change the vapor to a liquid and the liquid form back into a vapor, the refrigeration cycle.
condenser and evaporator
A solid material exerts a pressure or force
downward only
The amount of heat a refrigerant contains with -40 degree F as the 0 heat content reference point is called _.
enthalpy
When a refrigerant enters the compressor, it is a ____ and when it leaves the compressor, it is a ____.
low pressure low temperature superheated vapor, high pressure high temperature superheated vapor
Reciprocating compressors have ____.
piston and cylinder
The condenser
rejects heat from the refrigerant
The ____ relationship correlates the vapor pressure and the boiling point of water and is the basis for controlling the cooling system's temperatures.
temperature/pressure
Refrigeration can be described as
the process of removing heat from a place where it is not wanted to a place where it makes little or no difference
As the temperature of a material increases, the molecules in the material
travel faster
A law of conservation of energy states that energy is neither created nor destroyed.
true
An expansion valve is the pressure reducing device that controls the flow of liquid refrigerant into the evaporator.
true
Heat is a form of energy because of the motion of molecules
true
If you are a refrigeration technician, a warm coat and gloves should be in your truck, even in the middle of the summer.
true
Modern refrigerators have become state-of-the-art appliances and some models even include automatic beverage and ice dispensers, built in television screens and connections to the World Wide Web.
true
Which of the following represents a different temperature than the other three
475 deg K
A helicopter is lifting an 800-pound unit at a rate of 200 feet per minute. How many horsepower of work energy is the helicopter using in the process?
4,848 hp
