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stmbtwle

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Reply with quote  #61 
For an experiment on the double glaze idea would be to either apply heat-shrink right on top of the screen, or or simply lay a piece of glass on top of it. If it works then refine the idea.

A potential problem would be reflection. Any glazing reflects some the light that strikes it, and the extra surface might do more harm than good. On the other hand the customary twinwall could be replaced with something with better transmissivity, a possible improvement.

I think one of the reasons the ZP works as well as it does is because the screen is non-reflective, unlike glass or plastic.

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Rick H Parker

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Reply with quote  #62 

Double glazing with twin wall poly might be a wash, as the a 6mm only allows roughly 82% of the light through. Who much would get through with two layers? “

 

100% *0.82^2= 67.24%

 

However it would be a little higher then 67.24% because some of the light would bounce back and forth between the two glazeings .. maybe 70%?

 

 

Maybe the air is moving too fast for a small gap, but slows when the gap is larger. “

 

As the cross section increases the velocity does decrease and vice versa. It seems a reasonable assumption that as the velocity increases the leakage through the top screen increases also.

 

The more the air moves around between the top screen and the glazing the higher the heat loss through the glazing. A slower velocity does not remove heat as fast. When your doing gap testing, your seeking the sweet spot between the two.

 

Air is a very good insulator until it starts moving around … heat transfer by means of convection. Heat transfer by means of convection is what you want between the screens by not between the top screen and glazing.

 

Insulation gets it insulating proprieties, not from the material it is made of but, from the material’s ability to slow down the movement of air. The less the air movement the less the heat transfer by means of convection.

 

The idea of the second glazing is to bring air movement between the top screen and top glazing to a minimum. Would it be a good trade off ... good question.

 

 


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Rick H Parker
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Rick H Parker

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Reply with quote  #63 
"A potential problem would be reflection. Any glazing reflects some the light that strikes it, and the extra surface might do more harm than good. On the other hand the customary twinwall could be replaced with something with better transmissivity, a possible improvement."

Standard soda lime glass, 8% is reflected and 1-2% is absorbed. That is 90% transparent.

100% * 0.90^2 = 81.00%

The transparency of soda lime glass double glazing is the same as single glazing 6mm thin wall poly.

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Rick H Parker
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stmbtwle

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Reply with quote  #64 
Yes but every piece of glass adds to the reflection. Two sheets of plain glass would probably be best but the cost may well be more than twinwall. Then there's breakage risk.

There is a point of no return. 

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Rick H Parker

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Reply with quote  #65 
"Two sheets of plain glass would probably be best but the cost may well be more than twinwall. Then there's breakage risk."


Every engineered design in the world is a compromise of cost, performance and risk. The trick is to find the best compromise.

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Rick H Parker
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stmbtwle

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Reply with quote  #66 
That's why so many of us use twinwall. It's "relatively" cheap, easy and safe to work with, and tough. 


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gbwillson

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Reply with quote  #67 
Twinwall is also very light compared to glass. Any glass used for a collector should be tempered, and you can't cut tempered glass. 

Back to the question of why does a larger gap perform better than a smaller gap??? If the screen gap opening is 1.375" as it leaves the intake manifold, what happens to the air as it suddenly has 2-3 times the space to move around before it enters the once again 1.375" exhaust manifold opening??? I know from testing there is very little air movement above and below the screen gap.

Air entering the screen gap:
-Has more vertical space to move in
-The air slows
-The air is heated by the screens
-???

Greg in MN
stmbtwle

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Reply with quote  #68 
So if I understand correctly the opening in the manifold is smaller than the screen gap itself? Now it makes sense.

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KevinH

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Reply with quote  #69 
The openings from the plenum into the collector are the same size as the screen gap.  The "2-3 times the space" is the total height of the collector which includes the space above and below the screen.

In hindsight, another test that could have been done is to set the velocity inside the screen channel the same (different CFMs at round duct output).  There may be an optimal velocity for each screen gap.

Kevin H
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Rick H Parker

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Reply with quote  #70 
"In hindsight, another test that could have been done is to set the velocity inside the screen channel the same (different CFMs at round duct output).  There may be an optimal velocity for each screen gap."

Shoot! .... thinking boost fans on the return instead of the input are the way to go .. think about what happens when one draws hard on a cheap straw.

Create a partial vacuum in the collector instead of pressurizing the collector. That is draw air through through the collector instead of pushing air through the collector. Air in the collector will tend to move toward the lowest pressure area, when one is pushing air through the collector, the lowest pressure area in near the top glazing. When one is drawing air through a collector the lowest pressure area would be the channel below the screen.

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Rick H Parker
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