Ultra-Low, Cascade and Autocascade systems

Question 1

What temperature do cryogenic systems operate

Answer 1

-150°C (302°F) or less

Question 2

General rule of thumb for Condensor size vs Evaporator

Answer 2

1.25% larger

Question 3

Define a secondary refrigerant

Answer 3

a refrigerant that does not change state within the system (ie. chilled water)

Question 4

Define Saturation Temperature

Answer 4

when the product is the same temperature as the refrigerant

Question 5

What is the purpose of the oil separator

Answer 5

to separate 90% of the oil from the refrigerant

Question 6

According to “some guy”, where is the filter drier located on a cascade system

Answer 6

on the discharge line of the compressor (removed TQ question)

Question 7

Autocascade has 3 _______ _______ refrigerants that ________ with one compressor

Answer 7

Autocascade has 3 blended zeotropic refrigerants that fractionate with one compressor

Question 8

On startup, low temp refrigerants act as _____ and drive discharge pressure ___

Answer 8

On startup, low temp refrigerants act as Non-condensables and drive discharge pressure up

Question 9

Autocascade is ___ to pull down, Cascade is ___ to pull down

Answer 9

slow, fast. 3 hours vs 30 min

Question 10

When checking pressures on an autocascade system, it is important to use a ___ (long/short) hose

Answer 10

short

Question 11

when a leak on an auto cascade system is detected, you can top up refrigerant (true/false)?

Answer 11

false, refrigerant is a blended mixture that’s a bigger secret than Colonel Sanders’ 11 herbs an spices. Aside from knowing the proper mixture it is next to impossible to know how much and what refrigerant leaked out

Question 12

on ultra low systems, it is important to achieve ___ microns blank off

Answer 12

200

Question 13

Define Rebound

Answer 13

the Re-expansion of remaining refrigerant in a Recip compressor before a pressure differential is achieved to allow suction gas to enter

Question 14

formula to convert Inch-Mercury to PSIA

Answer 14

14.7 - (InMerc/2.04)

Question 15

formula for compression ratio

Answer 15

discharge pressure/ suction pressure IN ABSOLUTE

Question 16

what is the purpose of subcooling refrigerant

Answer 16

to minimize the amount of flash gas

Question 17

For the following answer increase or decrease
A bigger load will ____ suction pressure, ____ specific volume, ____mass flow, _____ capacity (btu/H), and ____ compression ratio

Answer 17

A bigger load will INCREASE suction pressure, DECREASE specific volume, INCREASE mass flow, INCREASE capacity (btu/H), and DECREASE compression ratio

Question 18

For the following answer increase or decrease
A smaller load will ____ suction pressure, ____ specific volume, ____mass flow, _____ capacity (btu/H), and ____ compression ratio

Answer 18

A bigger load will DECREASE suction pressure, INCREASE specific volume, DECREASE mass flow, DECREASE capacity (btu/H), and INCREASE compression ratio

Question 19

What is Glide

Answer 19

the difference between saturated vapor and saturated liquid temp

Question 20

What is the temperature range for an ultra low system

Answer 20

140 - -150°C (-40°F - -240°F)

Question 21

Name the 3 types of Ultra Low Systems

Answer 21

Multistage
Cascade
Auto-Cascade

Question 22

What is the purpose of the intercooler

Answer 22

to remove sensible heat from the frist stage discharge vapour before it enters the second stage compressor

Question 23

4 Factors to consider when choosing Oil

Answer 23

refrigerant and oil miscibility
chemical stability
compatibility of the refrigerant or oil with the materials in the system
system design

Question 24

2 types of Liquefied Natural Gas production facilities

Answer 24

Peak Shavingand Base Load

Question 25

What is another name for the expansion tank on a cascade system and what is it’s purpose

Answer 25

Fade Out Vessel, it limits discharge on start up to allow refrigerant to expand at a safe rate