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Posts: 2,461
Reply with quote  #1 
This studies the performance improvement when adding a swirl tape to the interior of a tube type collector.

Greg in MN[comp]

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Reply with quote  #2 
So where would a person get this swirl ribbon and what does the "3" mean? One twist per 3 feet?

I didn't understand much except that the swirl created more heat transfer. There was something I read once about air flows across surfaces can cause eddies. The info I read was about a carburetor. Perhaps this swirl effect disrupts that.

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Reply with quote  #3 

My understanding is the twist ratio is the ratio between the diameter of the tube, and the distance between the "peaks" of the helix. So if you had a 3" duct, the distance between "peaks" of the helix would be a factor of 3 or 9". I think figure 1 shows this. 

The added swirl breaks up the laminar flow. But the truth is a lot would depend on the speed of the air passing through the tube. As too many twists and the air is slowed too much and heats up, which is good. But it also creates resistance, which means a bigger fan. Probably the best way to test would be to have three long tubes such as a 10' downspout, One tube with nothing inside as a control, and two others to test various twist ratios. A ratio of 3:1 seems like a good place to start. You would not only want to measure the temperature of the air exiting the tubes, but the velocity. Just a note, a rectangular tube such as a downspout will likely behave much differently than a perfectly round tube. A round tapered object could be shoved through the downspout to expand the rectangle into roughly a cylinder shape.

As far as where to buy a swirl ribbon, I've seen machine shops carry rolls of thin metal of various widths. But more twists create a narrower helix swirl. But for testing you could buy some thin flashing rolls and cut "ribbons" by hand or even scissors. Once you have the proper optimal twist ratio, you can seek out a source. 

Greg in MN

Posts: 29
Reply with quote  #4 
 Gas hot water heaters have a swirl in the tube where the hot gases go up the middle.  This is the opposite but the same thing, increases the heat transfer but the other way.   I looked it up and they are calling it a flue baffle.   I read somewhere once that steel wool or metal shavings would make an ideal media for a solar panel collector filler but I've never seen one. 
  I think it's about time to unveil my solar panel for another year,  I covered the front of it for the summer but a cold front is coming tomorrow and I think it's about that time again.   
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