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62 Cards in this Set
- Front
- Back
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Describe the operating principles of a evaporator in a refrigeration system |
Finned tubes or more cuircuits take liquid vapor mix and turns it into a lt lp superheated vapor |
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What is the refrigeration effect |
Heat gained per pound of refrigerant in vapor |
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Latent heat is |
Heat from changing state |
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Sensible heat |
Felt heat or heat measurable on a thermometer |
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Total heat |
Sensible + latent heat |
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Describe the construction and operating principles of a condenser |
Tubes in one cuircuit changes HT HP SHG into NSH HP SC LIQUID |
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Methods to increase refrigeration effect |
No greater than 20% flash gas, minimal line from meter to evaporator, finned tubes on evaporator, more cuircuits in evaporator and condensator, sub cooling in condenser |
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Subcooling defined |
Temperature below saturation temperature as liquid, prevents flashing |
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Flash gasses importance |
Occurs because of design, increases efficiency, increases refrigeration effect |
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The life cycle of superheated steam begins and ends at |
Begins in evaporator ends in condesor |
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Purpose of compressor in modern refrigeration system |
Positive displacement pump used to raise pressure and allows for a higher condensation temps than evaporator temperature |
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Define refrigeration ton |
12000 btuh |
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Liquid line receiver location |
Liquid line |
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Receiver function |
Store refrigerant not required for current set point |
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Dangers of handling refrigerants |
Frostbite, toxic, suffocation |
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Ammonia is used because |
Highest refrigeration effect |
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Ammonia is dangerous because |
Highly toxic |
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Purpose of oil in the system and where can it be found |
Lubricates compressor and can be found throughout the system |
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Most common molocule in refrigerants |
Ethane C1 methane C2 Carbon |
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How is a gas displaced through a container |
Evenly throughout the container |
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Evaporation can be defined as |
Is where a liquid is heated to the point where molocules won't touch |
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Boiling can be achieved by |
Using heat or pressure |
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How can you tell if a refrigeration box is working |
It's blowing hot air |
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Atmospheric pressure is |
14.7 psi |
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Block of ice on the txv means |
It's sucking liquid refrigerant through the txv |
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How do you measure superheat |
Add 5 to pressure at Blue gauge (suction side)measure temperature at end of evaporator |
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Primary controls in basic cycle are |
Start and stop |
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Secondary controls in basic cycle are |
Regulate and protect |
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A control system that uses a small diameter piping system to communicate |
Pneumatic |
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A pneumatic thermostat used as a primary control would |
Sense temperature and send a pressure signal starts or stops the cycle |
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When a humidity is used as a primary control the main concern of the designer is air |
Moisture content |
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Partially halogenated |
Some hydrogen |
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Fully halogenated |
All hydrogen has been removed |
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Purpose and operating characteristics for sensing bulb On a txv |
Sends pressure signal to txv providing 7-10 degrees of superheat |
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The three major low pressure refrigerants |
R11 cfc, R123 hcfc, R113 cfc, R114 CFC |
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Recovery |
To remove refrigerant from site |
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Recycle |
Remove on site refrigerant and filter it |
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Reclaim |
Refrigerant recovered off site and brought up to epa standards |
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Problems with using refrigerant from burned out compressors on a small appliance |
Refrigerant could stil contain contaminants that form acid and sludge. |
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Problems with having oil in high pressure refrigerants |
Excessive oil could build up in evaporator and lower refrigeration effect |
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Procedure to remove non condensable gasses from low pressure refrigerant system |
Line up installed purge unit on top of condenser. |
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A cooling coil is kept at 40f inside tubes while 80f air passes outside because heat flows downhill it will move from |
The air into the coil surface |
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Radiation heat |
Heat through waves |
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Heat through touch |
Conduction |
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Heat through air circulation |
Convection |
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Btu means |
British thermal unit |
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The total heat (in btu) a substance can contain is called |
Enthalpy |
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In order to be used as a refrigerant a fluid must be |
Able to absorb heat by evaporating at a low temperature |
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The difference between a dx coil and a cooler is |
One cools air while the other cools liquid |
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Saturation temperature is |
The temperature of a substance where any extra heat which is added causes a change of state |
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4 types of air conditioning systems are |
All air, air water, all water, direct refrigerant |
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Minimum components which make up an air handling unit are |
Filter coil fan |
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Out of the capacity controls the one most often changed to adjust compressor capacity to match load is |
Compressor displacement |
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What function gives reciprocating compressors their inefficiency |
Their clearance volume |
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Cylinder unloading has the same effect as |
Reducing the number of cylinders it has |
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In which way is a rotary compressor similar to the welded hermetic compressor |
Theu both orient the motor and drive shaft vertically in the compressor casing with the motor above the compressor |
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What do the scroll and sliding vane rotary compressors have in common |
They gradually move the compression chamber into a smaller shape |
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How can you tell how many stages a centrifugal compressor has |
Look at number of impellers |
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What is the purpose of the compressor condenser |
To remove or reject heat from the system |
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The symptom which most readily indicates a blocked or dirty condenser coil is |
High head pressure |
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When a system fails to deliver adequate chilling capacity at peak load conditions how could you find out if it's a design error |
Find out if the system ever performed adequately at peak load conditions |
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Tje goal of head pressure Control system is to keep the high side pressure from getting too |
Low as outdoor temperature decreases |
