Does anyone have much experience in cold-testing payloads with dry ice? A few students on our team tried to use dry ice for a test, and didn't have much luck. The objective is to try and test the payload box in very cold exterior temperatures to see if the interior can be kept warm. They have an experiment that won't tolerate cold very well. The initial attempt was to use a small battery powered hand warmer (which has a thermostat to keep from getting too warm) inside the payload box to keep the temperature around 70f. The "hoped for" outcome was that they would measure some very cold (-40ish) temps outside the payload box, but that the interior would remain toasty warm. In practice, the test didn't work out so well.
I didn't see the test, but they apparently got 8 pounds of dry ice and put it in a large cooler. They put the payload box in the cooler, and ran some thermocouples into the payload box and surrounding container. The larger cooler was a snug fit around the payload box.
They left it closed for an hour, and the "outer cooler" temp only went down to about 7c. Unfortunately, the payload box interior temp went down to just about the same during the test. Apparently, the hand warmer failed at some point during the test.
They'd like to be able to create very cold conditions outside the payload box (colder than 7c) while they sort out the interior heating issue.
If anyone has some experience, war stories, or scars they can share, the team would appreciate it.