Evaporative Fridge

I ran out of gas for the fridge today. There is another bottle but it seems a little bit wasteful to run a fridge and freezer just to keep some milk fresh. Today I tried out an old method that I think my Grandpa told me about.

I got a tray (an Esky lid), and a wire dish rack. I filled the tray up with water and covered the lot in a wet towel. I tried a pillow case first but the water was evaporating faster than it was getting wicked up from the tray.

The idea is quite simple. It’s based on the principle that when an element changes phase between gas, liquid or solid the transformation comes at the cost of heat energy. The breeze blows over the wet towel causing the water to evaporate which makes the towel cold. While the humidity is low, which is usually the case when the temperature is hot where I live, the air will readily absorb the moisture causing evaporation and cause a refrigeration effect. The difference in the inner temperature and the ambient temperature will converge as the humidity increases but hopefully by that time the ambient temperature will have dropped.

The quick experiment worked really well. The ambient temperature is 34 degrees. The temperature under the towel is 21 degrees. The hygrometer that I have says that the ambient humidity is at 41% but I’m not sure if it’s accurately calibrated.

I expect that what I will end up having is an environment that has a very stable temperature and humidity. Hopefully a temperature between ambient at the lower end of the scale, to low twenties at the higher end. I expect the humidity will remain at close to 100%.

The results so far aren’t as good as a fridge, but it runs on a bit of water instead of gas or electricity. I think it will work well enough to prolong the life of my milk for enough time to give me a chance to use it.

I may also work on trying to insulate it better too. There is a fare more sophisticated system which uses two terracotta pots, one inside the other. Between the two pots you fill it with sand, then poor water into the sand to keep it damp. It works exactly the same way but there is better heat insulation between the inside and the outside.

I’m going to try and bring the contraption inside. There is obviously a lot less breeze, but the ambient temperature is lower as well. It may end up working just as well and be more convenient to use.

Edit: It’s not working as well inside. The air is still and though it does have a lower temperature than ambient, it’s much warmer inside. 24 degrees with an ambient temperature of 32 degrees. That’s 5 degrees worse than when it was outside.

Edit2: I usually keep my eggs in the fridge. Until now I’ve really never given it much thought. After a bit of a Google, I’m happily convinced that it’s quite safe to keep eggs refrigerated, however they may not keep as long. I’m fine with that compromise as six eggs lasts me about a week. Source. Source of Source