paper...not dirt...

Hey everyone,

I was doing some basic 1-D steady state conduction with a fridge design and came up with some pretty nice numbers...

Using polyurethane as the outside and inside "skeletons" my original idea called for adobe due to its high thermal mass (i.e. it takes a relatively long time for adobe, of the correct thickness, to change its temperature). After running into some difficulty finding any information (and at Dr. Wilson's website it appears that the thermal conductivity has never been found???), I decided to go with another cheap and readily available material...paper. Paper has a thermal conductivity of 0.05 (W/mK), which when compared to other materials and factoring in price...its pretty good. For a frame of reference, fiberglass has a thermal conductivity of 0.04 (W/mK) but is not as cheap as paper.
Another option to reduce cost is to build the outside "skeleton" with wood and then fill the inside gap with paper. If we kept the polyurethane (which by the way has a low thermal conductivity of 0.02 (W/mK)) for the inside box to retain easy cleaning and an inert surface for the milk, we could reduce the cost even more.
Anyway, here are the numbers (all polyurethane w/ paper fill): q= 4.62 Watts

This is the heat that escapes through the fridge walls and doesn't include heat losses due to gaps in the fridge.