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post #2 of Old 04-24-2012
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Re: Solar chimney

No first hand experience with this, but I'm a mechanical engineer and took heat transfer 101 almost 2 decades ago. You can't heat the air directly with sunlight as it is transparent. You can largely only heat it by getting it in contact with a hot surface. Also, you don't need hot and cold parts, just make sure your hot parts are all at greater elevation than the cabin you want to cool. With that, just a black tube, as long as you can practically make it should work well. You might do a little research and find the "solar emmisivity" value for various materials (colors) (may be difficult to find.) Just because it is black doesn't necessarily mean its solar emmisivity value is low. An easy comparison can be had by laying candidate materials on a horizontal surface in the sun and measuring their temperature with an IR (laser) thermometer after the temperatures have reached steady state. An absorbing tube in a clear tube would be more efficient because you wouldn't have as much convection on the outside of the tube, but I'd be surprised if it was worth the trouble. Just make your tube taller to compensate.

My $.02

Islander 30 MKII "Sojourn"

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