regrigeration 2 Flashcards
Heat will flow from a ____ surface to a _____ surface.
a. hot, cold
b. cold, hot
c. dark, light
d. large small
e. high, low
a. hot, cold
What connects the evaporator with the condenser in a “split” air-conditioning system?
refrigeration pipping
Which device in the basic compressive refrigeration cycle is used to cause a pressure drop?
Metering device
Heat flows from _____ to ____ in the condensing section of an operating refrigeration system.
c. Refrigerant; air
Heat flows from ______ to ________ in the evaporator section of operating refrigeration system.
d. Air; refrigerant
Describe refrigeration
Is the process of moving heat from an area where it is undesirable to an area where the heat is not objectionable. According to the second law of thermodynamics, heat always flows from a material at a high temperature to a material at a low
What occurs in the two sides of a refrigeration system?
One side of a refrigeration system decreases the temperature and pressure on the refrigerant, which causes the refrigerant to absorb heat from the medium (air to water) in the system. The air or water is cooled when heat is absorbed from the air to water. The air or water is then used for cooling building spaces. The other side of a refrigeration system increases the temperature and pressure on the refrigerant, which causes the refrigeration to reject heat to the air or water in the system. The air or water is heated and used for heating or the heat is exhausted.
List the main parts of a mechanical compression refrigeration system and describe their functions.
A mechanical compression refrigeration system consists of a compressor, refrigerant, condenser, expansion device, evaporator, refrigeration lines, and accessories.
Is a mechanical device that ________ refrigerant or other fluid. Increases the temperature of and pressure on refrigerant vapor and produces the high pressure side of the system.
Compressor
Is a fluid that is used for transferring heat in a refrigeration system. Have a low boiling point, which allows ________ to boil and vaporize at room temperature.
Refrigerant
Is a heat exchanger that removes heat from high-pressure refrigerant vapor. High-pressure refrigerant vapor flows through the ______ and the condensing medium passes across the outside of the ______. Heat flows from the refrigerant vapor to the cold condensing medium.
Condenser
Is the fluid in the condenser of a refrigeration system that carries heat away from the refrigerant. Air and water are ____________ used in refrigeration systems. As refrigerant vapor gives up heat to the ____________, the vapor condensing to a liquid.
Condensing Medium
Is a valve or mechanical device that reduces the pressure on a liquid refrigerant by allowing the refrigerant by allowing the refrigerant by allowing the refrigerant to expand.
Expansion device
Is a heat exchanger that adds heat to low-pressure refrigerant liquid. Low-pressure refrigerant liquid. Low-pressure refrigerant liquid flows through the _______ and an evaporating mediums passes across the outside of the ________. Heat flows from the hot evaporating medium to the cold refrigerant.
Evaporator
Is a fluid that is cooled when heat is transferred in the evaporator from the evaporating medium to cold refrigerant. An evaporating medium adds heat to a refrigerant because is has a higher temperature than the refrigerant. As the liquid refrigerant absorbs heat from the evaporating medium, the refrigerant boils and vaporizes.
Evaporating medium
What are the two condensing mediums used in refrigeration systems?
Air and water
What causes the temperature of refrigerant to decrease as it leaves the expansion device and enters the evaporator?
As the pressure in the liquid refrigerant decreases, some of the liquid refrigerant vaporizes because it has a lower boiling point. The refrigerant absorbs heat as it vaporizes, which cools the remainder of the refrigerant. The refrigeration then flows as a liquid-vapor mixture to the evaporator.
What instrument is used to measure atmospheric pressure?
A mercury Barometer is an instrument used to measured atmospheric pressure and is calibrated in inches of mercury absolute.
Define gauge pressure.
is pressure above atmospheric pressure that is used to express pressures inside a closed system. Is expressed in pounds per square inch. guage (psig or psi)
Explain the relationship between the boiling point of a liquid and the pressure on the liquid.
If the pressure on a liquid decreases, the boiling point of the liquid decreases. If the pressure on a liquid increases, the boiling point of the liquid
Where does heat transfer occur in a mechanical compression refrigeration system?
In a mechanical compression refrigeration system, heat transfer occurs in the condenser and the evaporator.
What connects the condenser and the expansion device?
liquid line
What maintains the high pressure in the high-pressure side of a refrigeration system?
Compressor discharge flow maintains the high pressure in the high-pressure side of a refrigeration system.
Describe how water provides a refrigeration effect when it vaporizes.
In dry climates, water soaked canvas bags are used to cool water. As the water evaporates, it absorbs heat from water inside the bag. The evaporation provides a cooling effect on the water inside the bag.
Describe how the number assigned to a refrigerant identifies the chemical composition of the refrigerant.
Refrigerants are identified by numbers. The numbers are assigned according to the physical and chemical composition of a refrigerant. Numbers less that 170 are assigned to refrigerants based on the chemical composition of the refrigerant. Numbers above 170 are assigned arbitrarily.
How has the clean air act of 1992 impacted the duties of contractors and HVAC technicians when working with refrigerants?
Refrigerants that used chlorofluorocarbons (CFCs) and fully halogenated chlorofluorocarbons (HCFCS) such as R-11, R-12, and R-22 are believed to have deteriorated the earth’s ozone layer. The ACT banned them in 1995.
What is retro-fitting?
Refrigerants that used chlorofluorocarbons (CFCs) and fully halogenated chlorofluorocarbons (HCFCS) such as R-11, R-12, and R-22 are believed to have deteriorated the earth’s ozone layer. The ACT banned them in 1995.
Define saturation conditions.
the temperature and pressure at which a refrigerant changes state. The properties listed on a refrigerant property table are volume, density, enthalpy, and entropy.
List the desirable refrigeration properties.
Low boiling point, low freezing point, nontoxic, high critical point, low specified volume, high density, high latent heat, low compression ratio, nonflammable, noncorrosive, stable, and miscible with oil.
If the entering water temperature of a coil is 175 degrees F and the leaving water temperature is 145 D F, then the coil is heating.
True
Heat will flow from a hot surface to a cold surface.
true
Heat flows from refrigerant to air in the condensing section of an operating refrigeration.
True
heat flows from refrigerant to air in the evaporator section of an operating refrigeration system.
false
How many btuh’s are in 100 MBH?
100 x 1000 = 100,000 bths/hr
