two stage refrigeration system for *****

[Incoruptibilul]

Dear all,
I'm not quite sure about posting my problem in the proper place, but I can asure you that if so, next time it won't happen again.
I will jump directly to my problem now, in order to be as short as possible; my hvac proffessor mention in the last course something regarding a 2stage ref. system using *****, and also sketch a scheme of it's components;I did my best in order to understand how it works, but I'm quite failing...
It has two compressors with one intermediary cooler between them,an usual condesor, two subcoolers, tow throtlling valves, and it ends with an evaporator.
Could someone indicate me some documentaion/handbooks which could make me understand this situation?
thank you!

[Magoo]

Was the professor talking about compounded systems or cascade systems, one is totaly different from the other. Quite often confused by people.
As well ***** is a brand name of Du- Pont chemicals.
Generally compounded system are an energy saving/ efficiency design for low temp systems, in region of - 30 > -40 'C.
Your sketch is confusingly difficult to understand.

[lana]

Hi there,

you have to correct your diagram as I posted.

Subcooler B is for cooling the liquid line with suction gas. Then suction gas goes into the suction of first stage compressor.

Subcooler C is for sub cooling the liquid line which goes into the main TEV at the evaporator.
Small TEV must be before subcooler C as shown. Line D which is a cold liquid is used to cool the intermediate stage.

This is a simple double stage system with additional sub cooler. In real life you only have one sub cooler (C).

Hope this helps.
Cheers

[norseman]

Hi there.

I have some old stuff made from Revco for may be 30 Years ago, but the schematic is in colour and show an early model using capillary tubes. May be this one can show some details better? They used two oil separators at the time due to oil and separator quality. Seldom used on smaller units today expect for -135/152c auto cascade units.

[doorgesh]

Hi,

I want to know if a 2 stage refrigeration compressor is reliable. Many people tell that such compressor is very delicate to operate and due to the injection of gas directly on the valve plate make such system unreliable.

[norseman]

Hi
I am not sure about what you ask for, but here is some information who may be clear out some issues.
In many cases, the compressor for the both stages is the same, but sometimers in different sizes. The first/high is bigger (higher capacity)
The main lifetime problem is that the second/low stage has a much harder working condition due to a very low suction pressure and by that less cooling back to the compressor. The discharge pressure is higher than most other systems. The combination of up to 140c discharge temperature (R23) and the low suction makes the low stage compressor to survive shorter than in "normal" use. Systems who make the heat exchanger working temperature as low as possible gives a better lifetime for the low stage compressor. My experience is also that systems with big fans blowing over the low stage makes them survive much better due to that the compressors stay colder. Most compressors get only gas back and what is the story about the gas back on the valve plate? Some bigger systems use an extra injection to the compressors suction side to feed some liquid to cool the compressor. Test chambers I have worked on can start the cooling at +200c and have to get some extra liquid on the suction to survive the hot gas return. Either by a bulb controlled mechanical device or an electronic controlled by a sensor on the suction line. Again mostly the compressors is the same, but the working condition makes the system unreliable

[doorgesh]

HI,
Thanks for info. I have been discussing with one french refrigeration technician who has worked and installed many application and according to him 2 stage ref system are not popular as this system has a shorter lifetime due to the suction being done directly on the valve plate and it may happen in uncontrolled situation when the evaporator is clogged with ice , there may be liquid suction and thus damages the compressor. I have a new project of a blast freezer cap 24kW, where I need a chamber temp of -35 to -40 C and from all selection software I have found a 2 stage compressor to be more energy efficient and cost effective, but I do not know how long it will last.

[Brian_UK]

Doorgesh, I think that you have misunderstood the original post.

This thread is discussing 2 stage refrigeration systems not 2 stage compressors.

[sterl]

AS to the man's original question:

Stoecker; "Industrial Refrigeration Handbook"

FES Systems: Fuller Rotary, selection Manual (could not find it on the Web)


http://books.google.com/books?id=Pr0...page&q&f=false


http://www.scribd.com/doc/29348262/M...ration-Systems