Multi-stage Compression systems Flashcards
Red Seal question Cryogenic temperatures?
-150C
-238F
123 kelvin
Multi-stage or booster compression systems as used for low temp or extra low temp applications for the following reasons;
- decrease compression _____
- To obtain extra low temp for _______ applications
- ratios
2. cryogenics
*Two stage compression systems are required if compression ratios exceed ___ on reciprocating compressors
10:1
Two stage compression systems are also required on systems that operate at approximately ___F evaporator temperatures
-40F
Two stage compression systems help avoid excessive ratios and high ______ temperatures
discharge
Multi-stage compression can be accomplished in two ways: name them
- direct staging
2. cascade staging
Direct staging systems use one refrigerant and one circuit with more than one ________
compressor
Direct staging is used on systems that have high compression ______
ratios
Direct staging requirements:
- Requires refrigerants that have boiling points low enough for the application, and yet it will condense at normal air or water _______
temperatures
Direct staging requirements:
- Practical limit -___F for R12, R134A, R502, and R507 or R404a
-125F
Direct staging requirements:
- Intercoolers are required to cool discharge gas from first stage compression before entering ______ stage
second
CASCADE STAGING:
Cascade systems uses two or more refrigerant circuits each using refrigerants with progressively lower _____ points
boiling
CASCADE STAGING:
Application - normally used in ____ ___ temperature applications
ultra low
Requirements of Cascade Staging:
- receivers are not normally used so the systems are _______ charged
- ___ _____ is not normally a problem as in direct staging
- critically
2. oil return
Direct Stage system intercoolers:
Types and operation; cooling of the refrigerant vapour between the several stages of compression (__________) is necessary. This is to avoid overheating the higher stage ________
desuperheating, compressor
Intercoolers:
Due to the large temperature difference between the condenser and the evaporator, cooling of the liquid is desirable to avoid heavy ______ in refrigeration effect
losses
Intercoolers:
There are 3 common methods of doing this for direct staging;
- The open ____ type intercooler
- the closed shell and ____ type intercooler
- the dry _______ type intercooler
- flash
- coil
- expansion
Open Type Intercoolers:
Liquid from condensers is expanded in the intercooler and its temp is ______ by flashing down to intermediate temperature
reduced
Open Type Intercoolers:
The discharge gas is de-superheated by causing it to bubble up through the _____ in the sub cooler
Advantages are; simple operation, low cost, and good liquid temperature reduction
liquid
Shell and Coil type intercoolers:
- Sometimes called the _____ type
- Only a portion of the liquid is expanded into the intercooler while the rest passes through a coil submerged in the _____
- Advantages: higher liquid line ______
- Advantages: 10-20 degrees _______ obtained
- closed
- liquid
- pressures
- sub cooling
Direct expansion:
- This type is not suitable for _______ systems but is widely used for R-12 and R-22 systems
- The liquid is sub cooled as it passes thru the _______
- De-superheating occurs by ________ the intercooler
- ammonia
- intercooler
- overfeeding
Direct expansion con’t
- There is a small amount of liquid carried over into the de-superheating area where it is vaporized by the hot gas from low stage, in turn cooling the hot _____
- Advantages: simple operation, low cost, good sup cooling, good de-superheating
- vapour
Direct Stage systems: Oil return
- There is no assurance that oil return to the individual compressors will be ____
- Some form of equal ____ return must be provided
- Connection in parallel compressors (requires equal ______ in all crankcases)
- equal
- oil
- pressure
