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!
Best answer:
Answer by tlbs101
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
Give your answer to this question below!
Every Gram of Water that evaporates will absorb approx 560 calories of heat, depending on environmental factors.
ReplyDeleteBy carefull design there is no violation of any thermodynamics. These principles are what coolss the refigerator, in your house..
In fact there are kerosine burning refigerators.
The change of state of matter .
Water is going from a liquid , to a vapor and it is taking in energy.
Water vapor is therefore less stable than liquid water, .
Water vapor is produced by liquid and heat .
Conversly
As the Vapor cools to a liquid the reverse occurs and heat is released .
The change of state pf matter is the principle involved
The trick of course is to vaporize water efficiently.
A large surface area where the water, can come in contact with the air, is what is needed.
Passive cooling is the problem, since you can not use an electric fan, but you can use solar power.
You might use a wind driven water pump, to bring the water to the top of tower , where a container is located to distribute the water through numerous holes and run down a series of strips,
The more strips the more surface area, available to expose the water to air, for evaporatve cooling.
The strips can be aluminum foil, cloth, or almost anything, as long as it permits air flow, and enhances evaporation.
It may also be possible to use direct solar energy in your solar cooker, to heat the water, to a steam.
The steam pressure can then be used to force water and steam out of a mist nozzel .
The finer the mist the more surface area of water droplets are exposed to exaporation .
Making evapoation more efficient .
If the humidity is low enough and
if the temperature warm enough and
if there is a breeze
then the fine mist will change from water droplets to water vapor . and cool the air.
Strategically placed mist nozels, You can achieve a 20 degrees drop in air temperature
For a warming effect approx 50 calories of heat are released for every gram of water that changes from a liquid to a solid .
So by spraying water into the air when the temperature is below freezing , you will produce a solid (snow), releasing heat and warming the air nearby.
This is why it seems to warm up as a result of a snow storm, major amounts of heat are released.,
Theoretically 560 calories of heat are absorbed per gram of water, turned to vapor.
What about a gram of water vapor becoming liquid.
560 calories of energy will be released instead of being absorbed.
However ,not all the energy is heat energy.
If you watch a rain storm as it moves you notice the lightning in front of the rain.
There must be something generating the electricity, and what better source than the change of state of matter,
The vapor is becoming a liquid, releasing 560 colories of energy.
Some of it as heat, some of it as electricity.
In addition, as the liquid rain evavorates , it is reversing the energy flow again, with all this energy exchange, it is easy to see that a storm has a lot of energy, and can do considerable damage.
You may want to research "heat pumps" They actually follow thermodynamic laws and are able to make cold from heat sources such as the sun.
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