Thermodynamics Flashcards
The state of matter is determined by what two things
Pressure and temperature
What best describes heat
Molecular motion
When matter is in a gaseous state. It has
No size or definite shape
What are the units to measure heat
British thermal units (btu’s)
What is the process where a substance changos directly from a solid to gaseous state without becoming a liquid?
Sublimation
The zero state of enthalpy is: (water)
32 F
Name the three physical states of matter.
Solid
Liquid
Gas
Name the four stages of refrigeration cycle
Expansion
Evaporation
Condensation
Compression
Name the three methods of heat transfer.
Conduction
convection
Radiation
Name the two substances used to cool condensers.
Air
Water
Name four common heat exchangers used in your plant: (excluding - condenser and evaporator),
a. TRANSFORMERS COOLING RADIATOR
b. COMPRESSOR Aftercooler/intercooler
C. SURFACE AIR COOLERS
d. OIL TUB COOLING COILS
When heat is applied to any substance, the density of the substance will:
(Exception-water)
Decrease
Water is an its densest point at approximalety:
39F
The beat that causes a change of state without a temperature change is called
Latent heat
The amount of heat in BTU’s required to increase the temperature of one pound of a particular substance one degree at ges level pressure is called:
Specific heat
A Fluid that picks up heat by evaporating at a low temperature and pressure and gives up heat by condensing at a higher temperature and pressure is called a refrigerant compound.T/F
True
Temperature is the measure of the intensity of heat T/F
True
When a unit of heat is added to a substance and the temperature increases,
this ter is called specific heat T/F
False
The theoretical temperature at which molecular motion stops is caved absolute motion T/F
False
A refrigerant gives up heat when it evaporates T/F
False
What takes place inside the evaporator of a refrigeration system?
B. Latent heat of vaporization
The heat required to change the state of water to vapor is called:
D. Latent heat of vaporization
There are two kinds of dry steam. What are they?
D. Saturated and superheated
What takes place inside the condenser of a refrigeration system?
A. Latent heat of condensation
Steam in its purest form is?
C. Invisible to the eye
The temperature at which a refrigerant will change state from a liguid to a vapor or vice versa?
A. Saturation temperature
The main purpose of a condenser is to
B. Remove heat from the refrigerant
The ability of a substance to conduct heat, or the rate of conduction is called
D. Thermal conductivity
Water vapor that is heated above its saturation point and is no longer in the presence of water is
D. Superheated steam
When heat is added to water at atmospheric pressure what would happen to the molecules
C increase in speed
if the temperature of air that flows through a heat exchanger decreases from high temperature to a lower temperature this is a(n);
A. Evaporator
The transfer of heat from a place where it is not wanted to a place where it is unobjectionable:
C. Refrigeration
When a substance is at its critical point. the properties of:
B. Liquid and vapor are indistinguishable
What component is not part of the high side in an AC system?
B. Evaporator
How many BTU’s will it take to heat 10 pounds of lead at atmospheric pressure, from 22F to 350F? Specific heat of lead is .03)
Weight•specific heat•(t1-t2) = BTU
10•.03•(350-22)= 98.4
When one pound of waler at 32F evaporates it will’ remove about:
Sensible heat• latent heat of vaporization=
180+970= 1150BTU’s
What is the specific heat of gold if a 5 pound bar requires 21 BTU’s to rise is temperature from 95° F to 235• F at atmospheric pressure
Specific heat= weight•( T1-T2)
5•(235-95)=700
21/700=
.03 is the answer
Change 90° Fahrerhat to kelvin
F to C
= 5/9(F-32) = 5/9(90-32)= 32C
C to K
=C+273 = 32+273= 305K
Answer = 305K
How many BTU’s are required to change 15 pounds of -10F ice to 300F steam at atmospheric pressure?
BTU=weight•specific heat•(t1-t2)
15•.5•(32+10)= 315
315+(15•144)+(15•180)+(15•970)+(15•.5•(300-212))=
Answer= 20,385BTU’s
Change 315° Kelvin to Fahrenheit.
K to C
K-273 = 315-273 = 42
C to F
9/5C+32 = 9/5(42)+32 = 107.6F
Answer= 107.6F
How many BTU’s will it take to heat 20 pounds of water at atmospheric pressure, from 60F to 212F
BTU=weight•specific heat•(t1-t2)=
20•1•(212-60)= 3040
3040+(20•970)=
22440BTU’s= answer
How many BTU’s must be added to one pound of ice at 30° F. To change It to
32F water?
BTU=weight•specific heat•(t1-t2)
1•.5•(32-30)= 1
1+144=
145BTU’s= answer
Explain what happens in the refrigeration cycle. Include components, their purpose within the system and the prosesses that take place within each
Explain
