# Question on Thermal Siphoning velocity?

1. Sep 18, 2007

### derekpearcy

Hello everyone, I'm new here, so this is my first post on here. I've never taken a physics class in my life, but love the stuff. I'm an avid solar researcher. Not photovoltaic panels, but more in the infrared spectrum since that compromises nearly 50% of the light from the sun and could be very useful. Thus far, I've created the Pearcy Solar oven, which can be used for cooking with sunlight only, and reaches temperatures of up to 410 degrees here in Illinois.

I'm also working on building more effecient solar heaters for my home as well. I'm using the thermal siphoning technique to circulate air through them. Hot air comes out of the top of the unit, which pullls more cooler air in thru the bottom. The question I have is the feet per second or feet per minute at which hot air will rise. I'm sure it highly revolves around the temperature difference, but I'm not sure.

I'm getting anywhere from 70-100 degrees warmer than the surrounding air coming out of the top. Any ideas at what speed this will rise? Thanks!

Derek

Last edited by a moderator: Sep 18, 2007
2. Sep 24, 2007

### Maxwell's Beard

Derek, I can't actually answer your question, because I don't possess the necesary knowledge myself, but I will offer a generality and pose a question.

I would suspect it would depend on the change in temperature the air experienced coupled with some coefficient that describes how air expands when heated. And the density of the air into which it was expanding...

Now my question is, can you build an apparatus to actually measure it? I mean, you are clearly proficient in building things, so a guy like you should me able to devise a way to physically take a measurement. Perhaps the number of RPM a pinwheel of know radius can be counted?

3. Sep 24, 2007

### derekpearcy

You can actually see the heat rising on the floor inside. So I covered the opening, then opened it quickly, and then marked the distant the visible heat traveled in 1 second. It was about 2 feet, so I guess its going to rise at about 2 feet per second.... But this isnt anything official, thats what I was after.