Powerpoint notes pg. 3+4 Flashcards
Screw compressors are ________ displacement compressors
positive
The rotation of the two screws in a screw compressor causes the chambers to move vapour from ______ to _______ side
suction to discharge
Screw compressor capacity controls; (2)
speed control and slide vane
Centrifugal compressor is a ____________ displacement compressor
non-positive
The increase in static pressure is known as _____ or ______ pressure
lift or head pressure
Lift/head pressure is the difference between the pressure of the refrigerant in the _________ and pressure of the refrigerant in the _________
condenser
evaporator
Single stage centrifugal compressor has ___ impeller
one
Multistage centrifugal compressor has _______ impellers
2 or more
Purpose of the economize is to reduce _________ by having a two stage pressure drop through the float section
flash gas
Purpose of purge unit :
remove non-condensable gases from the system
Reciprocating Compressors- factors that control efficiency; (4)
piston/compressor displacement
suction/discharge valve designs
clearance picket sizes
number of cylinders
Positive displacement compressors _______ a contained gas
squeeze
Non-positive/dynamic compressor works to build up molecular velocities and converts this energy into ____________
static pressure
Most compressors are limited to the types of _________ selected by the manufacturers
refrigerants
Ref properties are different from ref to ref and will impact the operation of the ________
compressor
Max discharge temperature is measured from the _____
head
Max discharge temperature: _____F to ____F
225F to 275F
Max suction temperature high temp application: ____F to ____F
65F to 95F
Minimum suction superheat: ___F
20F
Net positive oil pressure: ____psig to ____psig (minimum ____psig)
30 to 40psig and minimum 10psig
SST?
saturation suction temp (PT CHART)
SDT
saturated discharge temp (PT CHART)
CFM?
Cubic feet per minute
SEER?
Seasonal energy efficiency rating (btu output/watt input)
EER?
Energy efficiency rating
COP?
coefficient of performance (output/kw and input in btu)
SPF?
Seasonal performance factor
Maximum compression ratios:
Reciprocating:
- single comp = ___ to ___
- multiple comp = ___ to ___
10 to 1
20 to 1
Maximum compression ratios:
Rotary compressor = ___ to ____
Centrifugal comp = ____ to ____
5 to 1
3 to 1
Maximum compression ratios:
- Screw compressor = ____ to ____
- Scroll compressor = ____ to ____
20 to 1
20 to 1
Flooding: liquid refrigerant returning to the compressor during the __________
running cycle
Slugging: Extreme flood back of liquid refrigerant or oil, _________ migration results in liquid refrigerant in the crankcase
off cycle
Migration: Off cycle refrigerant gas returning to a ____________ crankcase. gas condenses in the oil
cold compressor
Liquid dilution: Crankcase has a mixture of _______ refrigerant and __________ refrigerant sinks to the bottom, and the oil floats on top
liquid refrigerant and oil liquid refrigerant
Liquid washout: Compressor starting when crankcase has a mixture of _________ refrigerant and _____
liquid refrigerant and oil
