-80¦C refrigeration, single stage in -20¦C ambient?
-80¦C refrigeration, single stage in -20¦C ambient?
(OP)
Hi,
Thanks for taking the time read this post...
Does anyone know whether there are compressors and refrigerants available that would transfer ~200W at -80°C evaporating, -25°C condensing?
The unit would be located in a -20°C room, hence the low condensing temperature.
I'd like to avoid a cascade system if possible, 55°C delta accross the compressor does not seem too extreme based on my experience of developing R404A based chillers but I'm not aware of any commercailly available units that will provide this performance.





RE: -80¦C refrigeration, single stage in -20¦C ambient?
RE: -80¦C refrigeration, single stage in -20¦C ambient?
What I'm looking for is a compressor / refrigerant combination that would meet the -80 evap, -25 condensing condition. I've spoken with a few of the big manufacturers here in europe and they don't offer anything below -40 evap.
RE: -80¦C refrigeration, single stage in -20¦C ambient?
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Is there any environment with -20 degree centigrade ambient tempreture.
I mean the manufactureres do not have the motive that refrigeration unit.
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Is there any environment with -20 degree centigrade ambient tempreture.
I mean the manufactureres do not have the motive to produce that refrigeration unit.
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Can you guarantee holding the -20C condition with the heat of rejection from the R-508B system.
"You have 200W +/-plus heat of compression."
I would think the system would be far more robust if you built a cascade system.
Most cascade system are built by non-commercial, industrial intities.
I do not understand your last statment re: 55C across the compressor and R-404A. How does that relate to -80 evap.
Regards
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
To clarify a few points:
I can guarantee holding the -20 condition as the unit will be located in a room chilled by with multiple redundant -20 cooling systems.
The condenser could be air cooled by the -20 air resulting in a condensing temperature ~ -25°C.
The 55°C delta and R404A comment was meant as an example. The temperature difference is simular to a -80 evap / -25 condensing system although I appreciate that the pressures may be very different depending upon the refrigerant.
So I'm looking for a single stage system at -80 evap / -25 condensing. (the primary stage of a commercial cascade unit?)
Perhaps the question would be better put as follows,
Which compressors and refrigerants are typically used in small to medium sized cascade systems designed for -80°C cooling? What are the typical evaporating and condensing temperatures accross the cascade?
Thanks again!
RE: -80¦C refrigeration, single stage in -20¦C ambient?
MintJulep, LN2 would be my first choice but it this instance it is impossible to supply it (or any other fluid) to the process to area to be cooled.
A small local mechanical system is the only practical solution I think. Even considered peltiers (for about a nanosecond! - think 200W and ~80 dT across the junctions)
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Be sure of your heat load.
I alluded to using R-508B, which is preferred to R-13 or R-23. (Reference ASHREA Fundamentals Handbook)
You need to use synthetic oil (verify).
Check on you’re location regarding cost of R-508B. It’s not cheap $$$$.
When the system is off the balance pressure can approach 400psi account for that by providing ample expansion space in your system. Then again most expansion tanks are sized for 70-75 F ambient. You still will need an expansion tank and when? –20F or at 70F ?
A Scenario: What if your –20F system fails, your system will go out on high head pressure, and then (temperature/pressure) up to what ever the ambient temperature is at that time. If that’s beyond the relief valve pressure setting you will loose refrigerant.
I still think you should consider a cascade system as these can be more robust.
And not add load to existing systems.
Wishing You Well
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
The quick means would be to modify something made for a materials lab Neslab makes an "Ultralow-Temperature" to -90 C. but I can't tell you how much cooling it will make at min 90.
RE: -80¦C refrigeration, single stage in -20¦C ambient?
http://www.qdrive.com/index.php?page_id=17
check out the 4.2kW input power required. Probably will be A LOT less if you're only going to 193K. You'll probably need to get the temperature setpoint option.
TTFN
RE: -80¦C refrigeration, single stage in -20¦C ambient?
You are right on, with the low temperature capabilities of these exotic types of single stage systems. I am familiar with them and overlooked them for sure. Small capacity at high cost but they could do the job as a single stage. An exotic cocktail of refrigerants are used to achieve these low temps.
With this or any ultra low refrigeration system the cooled space must be kept sealed of moisture intrusion. Using a positive pressure of dry nitrogen gas purging of the cooled space will ensure reduced frosting/icing of the coil or cold finger.
JMOwen, let us know which way you go wuth this, ok?
Best Regards
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
I liked the cryocooler - looks like an interesting technology, but It would be impossible to integrate and certainly more expensive that a single stage or even cascade conventional mechanical system.
The area I am trying to cool is located on a robot arm in a resricted area into which human access is undesireable.
This is the main reason why I do not consider LN2 to be an appropriate solution as I cannot see a way of delivering the liquid from a remote vessel. Locating a vessel on the robot is not an option due to space and payload contraints and filling issues.
An ideal solution would be a small single stage / cascade unit mounted on the robot adjacent to the area to be chilled. I have had good experience of small ~200 to 300W danfoss condensing units for which I've designed the evaporators and fitted expansion valves to cool a variety of applications, however being R404a the evaporatng temp is limited to ~ -40°C.
Given the -20 ambient I'm wondering whether the second stage of a cascade system similar to that found in a -80 lab freezer would do the job. The interstage could be replaced by a air cooled condenser.
The simplest solution, it appears to me, would be to take one of the danfoss condensing units and replace the oil and refrigerant to achieve a lower evaporating temperature. I have spoken to danfoss about this - it is done but not by themselves and they will not endorse any modifications as the units are only approved for R404a.
I have no practical experience of cascade systems (yet)and would be looking for a partner to develop the unit
RE: -80¦C refrigeration, single stage in -20¦C ambient?
I am wondering if you could use vacuum jacketed hose to and from your point of use. Use LN2 and exhaust it out of the building. Or use flexible refrigeration hoses to and from your evaporator back to the compressor/s. Let the flex hose move with the robot.
View this site for vacuum jacketed hose
http://www.vbsflex.com/index.html
How do you achieve the -20 room temperature at this point?
Cascade refrigeration systems of your needs are fairly easy.
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
I'm familiar with vacuum insulated hose and but it is not appropriate for this application because of the design of the robot and concerns over its longevity (it could be flexed up to 3 million times over its life). -20 will be acheived using multiple dx refrigeration systems. I'm unable to describe the application in much more detail because of confidentiality issues but would appreciate more information on the development / specification / supply of cascade systems.
The unit should be as small as possible (less than 0.3m high x 0.5m wide x 0.5m deep and idealy weigh less than 15kg.
Thanks again for your continued help
JMOwen
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Where are you located?
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
RE: -80¦C refrigeration, single stage in -20¦C ambient?
Ok! that explains your reference to Danfoss.
I'd like to give it a go and help you but it's a little difficult through this forum.
Tell me what you'd like to do?
pennpoint
RE: -80¦C refrigeration, single stage in -20¦C ambient?
-Jeff
RE: -80¦C refrigeration, single stage in -20¦C ambient?
If you don't need much lift, look into the technology used by Labconco, Titan, and other companies in their single-stage freeze driers. I _think_ the new ones are rated as low as -80 single stage, at 32C ambient. I'm looking into this myself, so let me know if you find anything. My older units use a Danfoss FR7.5B, which is nominally a general purpose R12 compressor, though I'm not certian R12 is used. Oddly enough, it's marked HBP: perhaps this designation deosn't so much define operating range, but compression ratio. I _think_ the capillary is intentionally restricted a bit more than usual so the evaporator "starves", perhaps falling to below atmospheric pressure, even: however, it may be that the low load leads to such low evaporator temperatures that the system "starves" even with a standard size capillary. I think this also makes the compressor run a bit hot. I think as you look for components, you must keep in mind that you'll probably be "off all the maps" in terms of manufacturers' specs. With luck you'll be able to find compression ratio specs, and by looking at the vapor pressure vs. temperature curves for various refrigerants, find a suitable operating point. I have yet to see a low temp spec that was not also accompanied by a power spec @ that temp: these designs flirt with the absolute limits of the media and components near 0 power lift.
Of course, if your lift is _really_ low you might consider thermoelectrics. They are notoriously inefficient, especially at low temperatures. Whereas a temperature differential of 55C is fairly practical for a single stage to maintain with a hot side temp of 25C, with a hot-side temp of -20 I don't think a single stage design will cut it. This might be a $100-$200 solution vs. $500-$1000.
Eh, I shouldn't have started a new thread (which see), my problem is too closely related to yours.
-Jeff