Refrigeration systems Flashcards
1
Q
2 types of refrigeration systems
A
- compression refrigeration systems
- - absorption refrigeration systems
2
Q
Components of a refrigeration system
A
- compressor
- evaporator
- condenser
- txv
- thermal bulb/temp. sensor
- oil feed pump
- oil separator
- drier
- sight glass
- receiver
- strainer/filter
3
Q
2 types of compressors
A
- positive displacement
- dynamic
4
Q
describe positive displacement compressors
A
- refrigerant pressure is increased by reducing the volume in the compressing chambres
5
Q
what are positive displacement compressors composed of?
A
- reciprocating (piston/cylinder)
- rolling piston
- rotary vane
- rotary screw compressors
6
Q
describe dynamic compressor
A
- refrigerant pressure increased by continuous transfer of angular momentum (centrifugal compressors)
7
Q
characteristics of reciprocating compressors
A
- single or multiple cylinders
- fully or semi hermetic
- direct drive system
- small : on-off
- large : cylinders un-loaders
- 1 to 1.5 hp/ton of cooling
- noisy due to vibrations
8
Q
what are rolling piston compressors
A
- uses a roller mounted on accentric shaft
- single blade slides up and down as roller turns
- used in household refrigeratos and air conditionin systems up to 3hp cap
9
Q
what are rotary vane compressors
A
- consists of a rotor with vanes
- eccentrically mounted with the housing
- low weight-to-displacement ratio and suite in transporation application
- b/n 3 to 50 hp
10
Q
what are rotary screw compressors
A
- cap. ranges b/n 20 to 1300 tons
- acts like a gear pump and the refrigeration moves parallel to the shaft
- compression is obtained by volume reduction w/ rotary motion
- capacity control is achieved through an external sliding pin mechanism
- other types consists of main rotor and gate-rotors
11
Q
what are centrifugal chillers
A
- large flow rates (60 to 30 000 cfm)
- single or multiple impellers
- centrifugal offer greater volume cap. for same size
- little/no vibration b/c of steady motion
- suction temp. b/n 50 to -150 F
- suction pressure : 2-100 psia
discharge pressure : up to 300
12
Q
5 elements for compressor capacity control
A
- on-off control
- multiple compressor control
- cylinder unloading
- hot-gas bypass
- compressor speed control
13
Q
cooling tower operation : 6 good habits
A
- check blow down devices, nozzles, float valve functions
- inspect for bacterial growth, dirt, deterioration of tower
- check suction screen
- check fan alignment, belt drives
- provide unobstructed air flow
- proper water flow rates
14
Q
multiple chillers : 3 types
A
- series arrangement
- parallel arrangement
- combination
15
Q
describe series arrangement
A
- reduces water temperature successively
- all water pumped through all chillers regardless of their status
- only second chiller suffer performance penalty
