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Step 5Using the test chamber
Make sure you are well stocked on liquid nitrogen and dry ice. SAFETY is very important here. You can really hurt yourself with these items; they WILL freeze you if you come in contact with them. Use strong insulative gloves, safety glasses, closed sealed boots, pants & long sleeved shirts. Also, getting moisture inside of the coil could cause it to clog and burst with very hazardous results. Don't do that. Ensure your coil is dry and empty of all moisture and fluids (best method is to make sure water doesn't get in there in the first place..) In addition, ventilation is very important. nitrogen can displace o2 in the air, which means you've got yourself a vapor version of iocaine powder. Odorless, tasteless, deadly. Make sure you've got lots of room and a source of fresh air.
Liquid nitrogen can splash, which sends -321F liquid all over the place. This is bad, don't let it happen. It will boil at room temperature. Seek the guidance of a professional on the safe handling of dry ice and liquid nitrogen.
Start off by staging your work area. Have cleanup devices handy, and plenty of room to work. Get out your supplies and objects you wish to freeze.
Load the cooler with the dry ice and reusable ice packs. Don't use normal ice; this will create moisture in your test chamber, which is a pain. It will freeze and condense on your coil, which reduces the effectiveness.
The reusable ice packs increase the thermal capacitance of the system. Pre-freezing them in your freezer is a good idea.
Place your thermal probes inside of the cooler, at positions you wish to measure the temperature. On your first run, you will likely discover that your thermal probe won't measure as low as required. Some testing will be needed.
The dry ice should be placed between the coil and fan, staged such that the fan blows air over them. Once the lid is sealed and the fan is turned on, you should start to see a rapid drop in temperature. This will not cool past -30c to -42c due to heat loss. Once the chamber has hit a stable temperature, it's time for the liquid nitrogen.
This is the hazardous part. Use due care.
The liquid nitrogen when it enters the reservoir will phase change almost instantly. This creates nitrogen vapor, which is of a much larger volume. So it will tend to spray and burp until it cools the reservoir down to a point where it is not boiling so rapidly. If you just 'dump' much liquid nitrogen into this reservoir, it will likely splash back into your face blinding you. Don't do that.
One trick to help with the out gassing is to vent the funnel. This can be done with a simple tube run down inside of the funnel. This allows the gaseous nitrogen to escape without it blasting up liquid nitrogen into your face. In addition, ensure that the other end of the coil is not blocked or clogged, or it could burst/explode.
Slowly pour the liquid nitrogen into the funnel. At first, the temp of the system will not change, as the liquid nitrogen needs a chance to pre-chill the external reservoir and coil. Closely monitor the temp to ensure that you don't get below your target temp. Do not overfill the reservoir.
As shown on the multimeters below, you can reach very cold temperatures very easily.
That is it! you've now built yourself a el-cheapo thermal test chamber!
Liquid nitrogen can splash, which sends -321F liquid all over the place. This is bad, don't let it happen. It will boil at room temperature. Seek the guidance of a professional on the safe handling of dry ice and liquid nitrogen.
Start off by staging your work area. Have cleanup devices handy, and plenty of room to work. Get out your supplies and objects you wish to freeze.
Load the cooler with the dry ice and reusable ice packs. Don't use normal ice; this will create moisture in your test chamber, which is a pain. It will freeze and condense on your coil, which reduces the effectiveness.
The reusable ice packs increase the thermal capacitance of the system. Pre-freezing them in your freezer is a good idea.
Place your thermal probes inside of the cooler, at positions you wish to measure the temperature. On your first run, you will likely discover that your thermal probe won't measure as low as required. Some testing will be needed.
The dry ice should be placed between the coil and fan, staged such that the fan blows air over them. Once the lid is sealed and the fan is turned on, you should start to see a rapid drop in temperature. This will not cool past -30c to -42c due to heat loss. Once the chamber has hit a stable temperature, it's time for the liquid nitrogen.
This is the hazardous part. Use due care.
The liquid nitrogen when it enters the reservoir will phase change almost instantly. This creates nitrogen vapor, which is of a much larger volume. So it will tend to spray and burp until it cools the reservoir down to a point where it is not boiling so rapidly. If you just 'dump' much liquid nitrogen into this reservoir, it will likely splash back into your face blinding you. Don't do that.
One trick to help with the out gassing is to vent the funnel. This can be done with a simple tube run down inside of the funnel. This allows the gaseous nitrogen to escape without it blasting up liquid nitrogen into your face. In addition, ensure that the other end of the coil is not blocked or clogged, or it could burst/explode.
Slowly pour the liquid nitrogen into the funnel. At first, the temp of the system will not change, as the liquid nitrogen needs a chance to pre-chill the external reservoir and coil. Closely monitor the temp to ensure that you don't get below your target temp. Do not overfill the reservoir.
As shown on the multimeters below, you can reach very cold temperatures very easily.
That is it! you've now built yourself a el-cheapo thermal test chamber!
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