Step 2: Theory of Operation
But what does that mean!? Hot air rises. As the hotter air rises, it can draw cooler air up with it. Convection cycles can occur when hot air rises, and draws cooler air from lower elevation. When the hot air rises and loses energy it begins to fall. This is the bare bones explanation. There's a ton more information out there from people who know more than I do. I did a lot of reading before starting this project, and I'd encourage you to do likewise. I've listed some sources for more information at the end of this step for your convenience : )
We are using water in this project as our cooling agent. Evaporation is when a substance changes from liquid to gas at it's surface. Links to fun evaporation information down below.
3. Cohesion and Adhesion:
Cohesion and Adhesion are two properties of water, and closely related. Cohesion means that water tends to stick to itself, or try to stick together. You can see this by placing small drops of water onto wax paper. You'll notice that the drops tend to ball up. This is because of the strong polar bonds in the water that attract individual molecules to one another. Adhesion means that water sticks to other stuff. This effect is best seen by dipping part of a paper towel into a small amount of water, and watching as the water makes its way up the paper towel.
(*7/23/2012: shannonlove was nice enough to point out that a more accurate term for this water property is "capillary action". I was going from what I remembered in my chemistry classes, however doing a search for "capillary action" may lead to more helpful information.)
These three principles make the Unit what it is. The sun will shine on the unit and heat the air at the bottom of the shaft. The air will rise, and also draw in more air from the bottom. As the air rises, it will cause water in a small chamber to evaporate. When the water evaporates, it will take energy away from the heated air in order to change from a liquid to a gas. This will cause the surrounding air to get cooler. The water is brought into contact with the moving air by a piece of fabric. The fabric will pull up water from the chamber to increase the surface area of the water with respect to the moving air. As the water evaporates and the fabric gets dry, more water will be drawn up the fabric due to the awesomeness of cohesion and adhesion.
Got it? Awesome. Let's get building!
Jump over here (step 11) to see my video on how it works: http://www.instructables.com/id/DIY-Solar-Air-Conditioning-Unit/step11/Videos/
More on Convection:
More on Evaporation:
More on Cohesion/Adhesion: