Passive cooler using layers of blackened foil and evaporative cooling.?

Question

I'm trying to develop an inexpensive solar cooler for camping.

I've made a solar box COOKER before, using nested cardboard boxes painted black, with aluminum foil glued on the inside. The black surface absorbs heat from the sun's rays, while when the heat is re-emitted inside, the reflective foil tends to keep it in. It is a slow cooker which can develop about 325 degrees F.

Now I am thinking about trying the same idea inverted. I know I won't be able to freeze things. but if I start with something frozen, could I keep it frozen this way without having to use those pre-frozen plastic containers of blue chemical?

Anybody ever make a cooler like this? anybody know how? Any sites for plans? (not the cooker sites, I already have those.)

Please include ideas for evaporative cooling using wet towels, if that has worked for you in the past. I'm trying to do this no-electricity, no chemicals, no bottle of gas. I want to travel light.

Thanks!

Answer 1

Although I'm familiar with what you are trying to do (and it does work) I don't know any way to do it light weight.

The clear sky is really cold and heat will radiate off. But if the air is warm you need a window to prevent convection (air circulation) from defeating your purpose.

If it gets cloudy and warm (as it will in some areas) you have a problem.

There are naturally occurring "ice caves" where there is sufficient thermal mass that radiative cooling can keep water frozen year round.

I think just super good insulation is the biggest key. If you can open a box to the night sky when the air is cool and close it up during the day...

Evaporative cooling is my favorite. It does require that the air be reasonably dry - not good in humid climates. It can be effective with something a simple as a wet towel, but a filter pad that air can flow through while wet is the best.

Answer 2

What you propose violates all 3 laws of thermodynamics, and is akin to building a perpetual motion machine. The heater works because the sun is a powerful radiator, and you can concentrate that energy to raise temperature. Without a heat engine (referigerator), you can't move heat from "cold ambient" to "hot ambient" Now... you could make a self-contained solar powered solid-state referigerator, using solar cells, and Peltier heat exchangers, but this is an "active" device -- portable, but active. I've seen plans for these on the internet. Google: Peltier solar power. There's alot of hits and some DIY on page 1