Opsin/ST6 - Thermal Target Test 2 Dry Ice

This test is to see if dry ice can be used to cool a steel target enough to make it thermally distinct, and last long enough for competition. Ambient in the evening was about 65F, and in the morning was about 55F. Intermittent There was an intermittent light rain all night, and the morning was a little foggy.

The dry ice was a 15lb 10x10x3-ish block purchased earlier in the day ($35 retail). I wrapped the dry ice in two plastic bags and a double-layer paper bag (the paper bag was what it was purchased in). I also added some thin insulation along the rear and bottom of the dry ice block. To secure it I looped some velcro straps through the handles and over the top of the target to suspend the dry ice in contact with the target. This was an ad-hoc solution for the first test.

I consider this test successful - the test target was about 15F cooler than the control target and could be easily distinguished against either a warm or cool background. However, the bag sagged beneath the target, reducing surface area contact. The bag also accumulated some water ice on the bottom, indicating a need for better insulation.

My conclusion for this test is that dry ice is a viable solution, though more expensive. I believe that we can use less dry ice with a better container - perhaps some kind of insulated bag with a shim to keep the ice against the target and possibly an elastic hanging mechanism to pull it up as the ice sublimates. Also, cooling the head portion of the target was a problem - unlike the chemical heaters, it's not immediately obvious how to place dry ice against the upper portion of the target. The container must also be relatively tough, as it is going to be knocked around by impacts.

Onward!