Multi-stage Compression systems

Question 1

Red Seal question Cryogenic temperatures?

Answer 1

-150C
-238F
123 kelvin

Question 2

Multi-stage or booster compression systems as used for low temp or extra low temp applications for the following reasons;

1. decrease compression _____
2. To obtain extra low temp for _______ applications

Answer 2

1. ratios

2. cryogenics

Question 3

*Two stage compression systems are required if compression ratios exceed ___ on reciprocating compressors

Answer 3

10:1

Question 4

Two stage compression systems are also required on systems that operate at approximately ___F evaporator temperatures

Answer 4

-40F

Question 5

Two stage compression systems help avoid excessive ratios and high ______ temperatures

Answer 5

discharge

Question 6

Multi-stage compression can be accomplished in two ways: name them

Answer 6

1. direct staging

2. cascade staging

Question 7

Direct staging systems use one refrigerant and one circuit with more than one ________

Answer 7

compressor

Question 8

Direct staging is used on systems that have high compression ______

Answer 8

ratios

Question 9

Direct staging requirements:

1. Requires refrigerants that have boiling points low enough for the application, and yet it will condense at normal air or water _______

Answer 9

temperatures

Question 10

Direct staging requirements:

2. Practical limit -___F for R12, R134A, R502, and R507 or R404a

Answer 10

-125F

Question 11

Direct staging requirements:

3. Intercoolers are required to cool discharge gas from first stage compression before entering ______ stage

Answer 11

second

Question 12

CASCADE STAGING:

Cascade systems uses two or more refrigerant circuits each using refrigerants with progressively lower _____ points

Answer 12

boiling

Question 13

CASCADE STAGING:

Application - normally used in ____ ___ temperature applications

Answer 13

ultra low

Question 14

Requirements of Cascade Staging:

1. receivers are not normally used so the systems are _______ charged
2. ___ _____ is not normally a problem as in direct staging

Answer 14

1. critically

2. oil return

Question 15

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 ________

Answer 15

desuperheating, compressor

Question 16

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

Answer 16

losses

Question 17

Intercoolers:

There are 3 common methods of doing this for direct staging;

1. The open ____ type intercooler
2. the closed shell and ____ type intercooler
3. the dry _______ type intercooler

Answer 17

1. flash
2. coil
3. expansion

Question 18

Open Type Intercoolers:

Liquid from condensers is expanded in the intercooler and its temp is ______ by flashing down to intermediate temperature

Answer 18

reduced

Question 19

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

Answer 19

liquid

Question 20

Shell and Coil type intercoolers:

1. Sometimes called the _____ type
2. Only a portion of the liquid is expanded into the intercooler while the rest passes through a coil submerged in the _____
3. Advantages: higher liquid line ______
4. Advantages: 10-20 degrees _______ obtained

Answer 20

1. closed
2. liquid
3. pressures
4. sub cooling

Question 21

Direct expansion:

1. This type is not suitable for _______ systems but is widely used for R-12 and R-22 systems
2. The liquid is sub cooled as it passes thru the _______
3. De-superheating occurs by ________ the intercooler

Answer 21

1. ammonia
2. intercooler
3. overfeeding

Question 22

Direct expansion con’t

1. 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 _____
2. Advantages: simple operation, low cost, good sup cooling, good de-superheating

Answer 22

1. vapour

Question 23

Direct Stage systems: Oil return

1. There is no assurance that oil return to the individual compressors will be ____
2. Some form of equal ____ return must be provided
3. Connection in parallel compressors (requires equal ______ in all crankcases)

Answer 23

1. equal
2. oil
3. pressure