Ultra-Low, Cascade and Autocascade systems Flashcards
What temperature do cryogenic systems operate
-150°C (302°F) or less
General rule of thumb for Condensor size vs Evaporator
1.25% larger
Define a secondary refrigerant
a refrigerant that does not change state within the system (ie. chilled water)
Define Saturation Temperature
when the product is the same temperature as the refrigerant
What is the purpose of the oil separator
to separate 90% of the oil from the refrigerant
According to “some guy”, where is the filter drier located on a cascade system
on the discharge line of the compressor (removed TQ question)
Autocascade has 3 _______ _______ refrigerants that ________ with one compressor
Autocascade has 3 blended zeotropic refrigerants that fractionate with one compressor
On startup, low temp refrigerants act as _____ and drive discharge pressure ___
On startup, low temp refrigerants act as Non-condensables and drive discharge pressure up
Autocascade is ___ to pull down, Cascade is ___ to pull down
slow, fast. 3 hours vs 30 min
When checking pressures on an autocascade system, it is important to use a ___ (long/short) hose
short
when a leak on an auto cascade system is detected, you can top up refrigerant (true/false)?
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
on ultra low systems, it is important to achieve ___ microns blank off
200
Define Rebound
the Re-expansion of remaining refrigerant in a Recip compressor before a pressure differential is achieved to allow suction gas to enter
formula to convert Inch-Mercury to PSIA
14.7 - (InMerc/2.04)
formula for compression ratio
discharge pressure/ suction pressure IN ABSOLUTE
what is the purpose of subcooling refrigerant
to minimize the amount of flash gas
For the following answer increase or decrease
A bigger load will ____ suction pressure, ____ specific volume, ____mass flow, _____ capacity (btu/H), and ____ compression ratio
A bigger load will INCREASE suction pressure, DECREASE specific volume, INCREASE mass flow, INCREASE capacity (btu/H), and DECREASE compression ratio
For the following answer increase or decrease
A smaller load will ____ suction pressure, ____ specific volume, ____mass flow, _____ capacity (btu/H), and ____ compression ratio
A bigger load will DECREASE suction pressure, INCREASE specific volume, DECREASE mass flow, DECREASE capacity (btu/H), and INCREASE compression ratio
What is Glide
the difference between saturated vapor and saturated liquid temp
What is the temperature range for an ultra low system
140 - -150°C (-40°F - -240°F)
Name the 3 types of Ultra Low Systems
Multistage
Cascade
Auto-Cascade
What is the purpose of the intercooler
to remove sensible heat from the frist stage discharge vapour before it enters the second stage compressor
4 Factors to consider when choosing Oil
refrigerant and oil miscibility
chemical stability
compatibility of the refrigerant or oil with the materials in the system
system design
2 types of Liquefied Natural Gas production facilities
Peak Shavingand Base Load
What is another name for the expansion tank on a cascade system and what is it’s purpose
Fade Out Vessel, it limits discharge on start up to allow refrigerant to expand at a safe rate
