Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
(OP)
I've got an insulated 2 Part ev chamber. One part of the chamber holds many blocks of dry ice, the other part holds the test specimen to be cooled. 2 insulated ducts with fans push and pull air through the chambers circulating the cold air.
After a day of circulating the cold air the AIR temperature flat lines at -45°F. I know dry ice is -100°F. What is the coldest temp that I can get the air to?
The EV chamber is quite well insulated. Outside of the chamber is not cold to the touch, no condensation visible, fans running with no problems. I need to get the air to a lower temp.
Any thoughts? thanks.
After a day of circulating the cold air the AIR temperature flat lines at -45°F. I know dry ice is -100°F. What is the coldest temp that I can get the air to?
The EV chamber is quite well insulated. Outside of the chamber is not cold to the touch, no condensation visible, fans running with no problems. I need to get the air to a lower temp.
Any thoughts? thanks.





RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
Dry ice sublimes at about -75F at std. atmospheric pressure. You have enough heat leakage to drive a 30F delta-T.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
btrueblood - The first chamber is loaded with dry ice, we tried maximizing the surface area, leaving airflow space around each stack of blocks. We've got 10 of the 10" x 10" blocks in there. We'll try adding some blocks to the other chamber.
So -75° would be the coldest that we'd ever even hope to get to with all things being perfect.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
Look again at your "well-insulated" outer walls. What actual temperature is each part of each wall? Use a IR/non-touch thermometer - or better a heat camera - then correct the corners, joints, and hinge areas that are coolest. Try again, then insulate the next cool area.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
-270°C, -452°F
Chris, CSWA
SolidWorks '15
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RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
Your setup doesn't do that.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
The system in question is basically the mass of air in the chambers. If it wasn't working at all, the chamber would be at room temperature not 45 below.
The flatline air temperature is just the equilibrium point between heat transfer in from outside the chamber and heat transfer into the dry ice. Plus added heat from the fans, which may or may not be significant compared to the other two values. You can lower the temperature by reducing heat transfer into the air or increasing heat transfer out of the air. More insulation is probably the hard way unless you have a big heat leak (at the very least we know it's not a sealed environment, might be worth a look). Increasing surface area of the dry ice or placing it so that either the fan or natural convection get it more airflow is one way to increase heat transfer out of the air. So is using something colder, like liquid nitrogen.
If your dry ice chamber is deep and the vents are at the top, you might not be getting circulation of the cold air at the bottom which would make a big difference.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
2. Seal the chambers tightly, except for one vent at the top. Cold CO2 is much denser than ambient air and will leak out of any low openings will drawing-in warm humid air. Your chamber should be able to hold water like a bathtub.
3. Your fan is adding heat to the system and mixing cold CO2 with warmed CO2 from the walls. Place the blocks at the top of the chamber. The dry ice that sublimates will fall rapidly over your sample. CO2 that warms at the walls will rise to the top of the chamber where it can vent out. Your insulated ducts are basically just heaters.
4. Use an aluminum foil liner inside to reduce radiated heat from the walls.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
If the goal of your environmental testing is to establish the effect of extremely cold air on your test article, then you need to isolate/control the atmosphere within the test cell from any uncontrolled outside influences. This would mean using some type of heat exchanger to chill the circulated air flow within the test cell. As MintJulep noted, your existing arrangement is not a good approach for this application.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
What is the ratio of solid co2 volume to overall volume?. I suspect until this is 1 to 3 or 4 you won't get much below your current temp.
You have a lot of options expressed here, let us know how it goes and there's no such thing a too much insulation
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RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
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RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
Don't know what financial resources you have available for this test effort, or how important the accuracy of the test results are to you. But I have been involved in a few test programs during my career, and one thing I have learned is that the worst mistake you can make is attempting to conduct a test using unproven/unvalidated test equipment. Your test results are only as reliable as the procedures and equipment used to produce them.
If you need to perform environmental testing at temps down to -100degF, you might consider using a commercially available conditioning unit that uses liquid nitrogen. It should not be difficult to integrate one of these conditioning units with your existing test chamber.
http://www.russells-tech.com/images/pcu-cutsheet.p...
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
I guess the system is not "air tight", I mean every opening is sealed but I'm sure that it isn't hermetic. We are not building up any pressure...
The chambers start off with ambient air. The ratio of dry ice to volume is 1:3. I think I may have found a culprit. After running it for 48 hours we took the setup apart. Noticed that one of the fans had a pretty good buildup of ice, it was still working, but the ice meant that there was an air leak nearby. There was a gash in the insulation at that point.
If this allowed humid air into the CO2 chamber then the blocks could have had a layer of insulating ice on them too. perhaps.
We've got 5 thermocouples arranged throughout the chamber to map the temperatures. All read within a degree of each other, none had ice build up.
I like the idea of a top mount vent to vent off air, going to have to incorporate something like that on the next project.
We are just going to switch over to the liquid nitrogen setup. From all your input I know that I should be able to get colder with dry ice, but the amount of redesign and effort makes it a no brainer to just use the liquid nitrogen.
Thanks for all your input and advice, I truly appreciate it. I think my rule of thumb from now on will be -45°F min for dry ice chambers. Any colder and just go with the liquid nitrogen.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
You did not mention what device you are testing or what application the test data is intended for. But if the thermal test is part of a qualification/certification effort, it is extremely important that your test equipment calibration is documented. Otherwise, the validity of data collected from any testing performed using the equipment may be questioned.
Best of luck to you.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
As far as calibration of the chamber. This chamber is just for low temperature soaks. Our PID controllers and fan setup keeps the temperature constant, it actually works quite well. If we had to thermal cycle we would rent out testing at another facility that had a large ev chamber.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
a) Replace wet air recirculation with either dry CO2 gas or dry N2 gas.
b) Seal off any leaks into / out of the test chamber.
c) Dry ice blocks (once the risk of water ice covering it is removed) are poor heat transfer agents.
c) Nothing mentioned on how enclosure pressure control is enabled between these push and pull fans - if there is an overlap on inbreathing / outbreathing pressure control setpoints, you could be pulling in warm gas beyond the vaporisation capability of the dry ice - once you've sealed off this gash near one of the fans, you should get some idea of how to minimise / stop inflow of fresh N2 or CO2 as makeup. There should be a reasonable gap between the settings for these 2 controllers.
There may be more you could get out of this EV once these heat in leaks are fixed, so it is yet to be seen how close you can get to approx -77degC.
RE: Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to?
"Carbon dioxide poisoning.
Langford NJ1.
Abstract
Carbon dioxide is a physiologically important gas, produced by the body as a result of cellular metabolism. It is widely used in the food industry in the carbonation of beverages, in fire extinguishers as an 'inerting' agent and in the chemical industry. Its main mode of action is as an asphyxiant, although it also exerts toxic effects at cellular level. At low concentrations, gaseous carbon dioxide appears to have little toxicological effect. At higher concentrations it leads to an increased respiratory rate, tachycardia, cardiac arrhythmias and impaired consciousness. Concentrations >10% may cause convulsions, coma and death. Solid carbon dioxide may cause burns following direct contact. If it is warmed rapidly, large amounts of carbon dioxide are generated, which can be dangerous, particularly within confined areas. The management of carbon dioxide poisoning requires the immediate removal of the casualty from the toxic environment, the administration of oxygen and appropriate supportive care. In severe cases, assisted ventilation may be required. Dry ice burns are treated similarly to other cryogenic burns, requiring thawing of the tissue and suitable analgesia. Healing may be delayed and surgical intervention may be required in severe cases."
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