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doolittledon

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Posts: 4
Reply with quote  #1 
Many years ago - mid to late '60s - I took an adult education class at Harper College in Palatine, IL.  As part of that class, we built a solar collector at an arboretum in Evanston.  I remember a couple of government publications associated with that class, but they have long since disappeared along with most of my memory and I can't find them any more.

Here is my question - well, two actually.  The first is, I am writing this in a "reply" section.  I could not find a label for submitting a new post.

But the main question is this:  From that class, one thing I remember is a word called "turbulence".  I don't remember the reason for this turbulence; only that it's imortant.  I am going to be building a (probably) downspout collector and I don't have the resources for trial and error.  I would therefore appreciate any thoughts on the idea of inserting a thin strip of corrugated aluminum (ribs perpendicular to the tube length) the length of the tubes to set up a turbulence.  Practical or not?

Thank you,
Don

SolarInterested

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Reply with quote  #2 
Welcome Don. I've moved your post into it's own topic.

Turbulence is important to transfer heat from the downspout to the airflow. Adding 'turbulators' can aid this but at the cost of increased resistance to airflow. Like most things in life, it's a tradeoff and finding a balance is important.

Mike
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Both temperature rise and airflow are integral to comparing hot air collectors
gbwillson

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Reply with quote  #3 
Don-

Inside a tube or downspout the air has a laminar flow in which the air in the center of the tube moves at a different speed than the air close to the surface. Turbulence will break up this laminar flow. So in the case of a downspout being heated by the sun, the air is heated more effectively.

Do a search above using helix, turbulator, or insert as keywords. You will find several discussions regarding added turbulence inside a collector. As Mike alluded to, there is a fine line regarding the optimal twist/performance ratio. This will vary greatly depending on several factors including size of the passage and flow speed. I posted a scientific study of inserts a couple of years ago. 

Greg in MN[wave]


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