dear sir i am engineering student. would you like to tell me that how a cascading refrigeration system works?
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dear sir i am engineering student. would you like to tell me that how a cascading refrigeration system works?
A cascade system is two complete refrigeration systems, joined together by an interstage heat exchanger. The interstage heat exchanger is the evaporator for the high stage system and the condenser for the low stage system.
The reason one would use a cascade system is to achieve low temperatures (typically around -100°F) with some reasonable operating efficiency. The drawback, of course, is you have two operating systems and its associated costs.
It is possible to achieve -100°F evaporating temperatures with a single refrigeration cicuit, but you would likely have to fool around concocting a suitable refrigerant blend to do it, perhaps use a two-stage compressor, and still end up exceeding the compressor manufacturer's allowable operating pressure ratios.
Would that be an auto-cascade system your are referring to, professor? Do such things exist? I am not even sure I am using the right words, but I am recalling a single system with dramatically diverse refrigerants in it... something I read about but never have seen.Quote:
It is possible to achieve -100°F evaporating temperatures with a single refrigeration cicuit, but you would likely have to fool around concocting a suitable refrigerant blend to do it, perhaps use a two-stage compressor, and still end up exceeding the compressor manufacturer's allowable operating pressure ratios.
Perhaps, R134 and R404a. The first refrigerant to boil off removes heat from the other refrigerant... a heat exchanger in the middle, but both refrigerants mixed up and running together through the compression and evaporation process.?
the refrigerants in an auto cascade work as glides, meaning yes 1 boils off wich condenses the next and so on. they use multiple heat exchangers and the charge is critical, the last thing you want is to hook up gauges cause then your in trouble.
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Please don't leave me hanging here. May I ask "why?"Quote:
the last thing you want is to hook up gauges cause then your in trouble. these systems are capable of obtaining -150c and colder
Also, when is an auto-cascade a good idea as opposed to separate cascades?
I have seen the latter, but have only heard about the former.
Beacause the charge is so precise with such an odd blend (including argon) that any amount taken from system can cause seriouse problems in system. The exact measurments are patented and kept secret. This single bottle containing the charge, you would need for 1 auto cascade unit , can cost over 1000$ ouch
yes they mail you a 30lb bottle with the charge in it.
A story was told to me by a major manufacturer. Aparently the man who invented the auto cascade, did so by sitting down with a peice of paper and drawing it! (garsh he got smerts)
The patent was first held by the company QUEUE. Queue built excellent products, and atempted to utilize the auto cascade in other aplications. The main problem with the -80c auto cascade was the oil logging. This required a flush and 1 fresh 1000$ bottle charge(ouch).
once you go below -80c you need another cascade, or heatexhanger system,(dont hold me to that ill have to ask my dad but im pretty sure) Before the auto cascade there would be 4, 5, and even 6 stage cascade systems. I'm sure you can imagine the pain of getting 6 compressors to learn to live in harmony:)
Have some experience with auto cascadesystems of Polycold.
The mixtures are not that magic at all. They can be found on http://patft.uspto.gov/netahtml/search-bool.html and do boolean search on cryogenic AND gas AND mixture AND refrigeration AND low AND temperature. (Patent 6,631,625 is such a mixture)
The question is more, what charge was exactly used in your machine?
There exists also manufacturer maded top-off charges if you losed a little bit of gas.
The clogging of the capilalry tubes is mostly prevented by adding some 'high boiling refrigerant' , p.a. R134a wich stays liquid in the complete cycle and flushes the capillary tubes.
Peter