Cooling an Environmental Chamber with Dry Ice. What's the coldest you can get the air temp down to? 3

[Shockdesigner331]

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.

 

[dvd]

Don't forget to breathe oxygen with all of that CO2 floating around on the floor. People get in serious trouble (dead) in enclosed spaces where the oxygen has been depleted.

 

[tbuelna]

One last suggestion. If you need to get some thermal exposure testing done fairly quickly you might consider renting a test chamber. This would allow you to perform testing and collect reliable data while you continue to work out design, control, instrumentation and calibration issues with your own thermal chamber.

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.

 

[Shockdesigner331]

DVD, good call on the oxygen. No worries there, we've got the chamber in a giant warehouse with climate control. Moving air and the percentage of CO2 would be extremely low.

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.

 

[georgeverghese]

Points to take away from all this feedback:
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.

 

[gruntguru]

CO2 is slightly different to other asphyxiants because the body does have a response to increased concentrations. High CO2 levels in the blood are the body's cue to increase respiration rate (not reduced O2 levels as you would think).

"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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