Yes, the air is just heated as it passes thru the panel. There's about a 1/2" of room between the top of the bumps in the steel and the glass, and that probably causes the air to tumble a bit as it goes thru the panel. But I don't know that that makes much difference. When I first built it I used a bathroom fan on it and that didn't move enough air thru it. The glass was running way too hot. I increased the airflow to about double with the duct fans, and now the glass runs cooler and I get more BTU out of it.
There is no zig-zag airflow pattern or anything. Just air forced in the bottom, it comes out the top, and it works really good. I've heard of some guys using plexi-glass on these things. I know for a fact that plexiglass would melt, or at least warp really bad, if I would've used it on this panel.
Like I said, this is my first attempt at solar heating. I didn't really look at any plans, or copy anybody else's design. I just went "seat of the pants" and built the thing. Not much science or design involved in it. Just a sun heated piece of steel with air blowing over it.
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Chris