RACT Unit 21 Flashcards
_________ is the process of removing heat from a place it is not wanted and transferring it to a place where it makes little or no difference
refrigeration
Typically, the fresh food compartment temperature is about _____F
35F
Heat in refrigerator is transferred to a cold refrigerant coil and pumped by the system compressor to the condenser where it is released into the room much like using a ______ to move water
sponge
High temp refrigeration applications will normally involve box temperatures of ____F to ____F. High temp is commercial refrigeration
47 to 60F
Medium temp applications range from ___F to ___F. The household refrigerator fresh food compartment is medium temp
28 to 40F
Low temperature applications produces temperature below the freezing point of water, 32F. Low temp food storage applications generally start at ____ and go as low as ____F
0F and as low as -20F
The ________ in a refrigeration system is responsible for absorbing heat into the system from whatever medium is to be cooled.
evaporator
The heat absorbing process is accomplished by maintaining the evaporator coil at a ______ temperature than the medium to be cooled
lower
The evaporator operating at these low temperatures removes ______ and ______ heat
latent and sensible heat
Two important factors in understanding refrigeration are the refrigerating _______ temperature and _______ temperature
boiling temperature and condensing temperature
The _________ temp of the liquid refrigerant determines the coil operating temperature
boiling temperature
When the evaporator removes heat from the air and lowers the temperature of the air, _______ heat is removed
sensible
When moisture is removed from the air, _______ heat is removed
latent
The difference in temperature between the air being cooled and evaporator is directly related to the amount of ________that will be removed
moisture (humidity)
The greater the difference in temperature the more ______ is removed
moisture
The rate of heat exchange is governed by 3 things;
- The evaporator ______ through which heat has to be exchanged
- The _____ to which the heat is transferred.
- The ____ factor. Relationship between the medium giving up heat and the heat exchange surface.
- The _______ _________ between two mediums in which the heat exchange is taking place
- material
- medium
- film factor
- temperature difference
What type of evaporators were the first for cooling air?
natural-convection type
The stamped evaporator was one of the first designs to create a ______ pipe surface that improved efficiency
larger
Finned-tube evaporators are used more today than any other type of heat exchanger. It is efficient because the fins are in good contact with the _____ carrying the refrigerant
pipe
The longer the evaporator the more ______ drop associated with refrigerant flowing through them
pressure drop
The ______ (tonnage) of the heat exchanger can vary with its height and length
capacity
An efficient evap design incorporates an aluminum parallel-flow, flat-plate-and-fin configuration with small parallel channels inside the flat plate. The plates are _______, streamlined _____ , each one of which is split into smaller parallel ports
flattened , tubes
Name two ways to increase internal surface area;
- Increasing the number of ______ channels inside the flat plates
- increasing the number of ____ plates (decreasing space between them)
- parallel
2. flat
The vertical orientation of flat plates allows condensate removal to occur naturally, relieving any water drainage issues from the evaporator. This technology is being used with ______ as well as _________
condensers, as well as evaporators