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stmbtwle

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Reply with quote  #31 
I understand the principal of most solar ovens is to focus the light onto a black pot.

I wonder if a "convection" oven would work, sort of like a black box collector but with a wire shelf in the top for the pot and no fan. We all know how hot they get when they stagnate. I think it could be bigger to capture more heat and might not be as particular about orientation.

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sundug

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Reply with quote  #32 
"There are people who believe that heat is generated inside a box cooker when solar radiation strikes the walls of the cooker. This is very likely the best way to get the best AIR temperatures.

However, its very likely that the best way to heat the FOOD is to make the walls a continuation of the external reflector panels, so that as much radiation as possible gets focused on the container holding the food. To understand this principle, consider the CooKit and other panel cookers, which have NO box and yet manage to cook food.

One of the reasons that the issue will never be resolved is because people use a variety of cooking vessels. If you're using a cooking pan that covers most of the interior of the box, it hardly matters what color the inside of the box is. So the SPORT, which accepts a 3 qt graniteware vessel perfectly, is painted black. But an almost identical unit made in South Africa is left shiny on the inside.

Over the years I've come to realize that the AIR temperature inside a box cooker is mostly irrelevant. The thermometers are always stationed at the top of the box, but it might be 50 degrees cooler at the bottom! Still the food cooks, because light is being reflected down onto it from the external reflectors.

My take is that; the best overall way to make a cooker is with reflective sides and a black bottom. The bottom is black so that light doesn't get bounced straight back out the window ... and into your eyes. The sides are reflective to help focus the light onto the food. It probably helps to put a slight slant on the inner box sides."

http://www.solarcooker-at-cantinawest.com/does-the-type-of-reflective-lining-in-a-box-solar-cooker-matter.html

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stmbtwle

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Reply with quote  #33 
That's my thought as well. 

Still, ordinary electric ovens cook by heating the air, which is then transferred to the food. I was just wondering if something like this would work. oven.png 


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gbwillson

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Reply with quote  #34 
Willie-

You have a passive collector design(Heat Grabber-ish), but with screens, the air won't follow the path of your arrows. SolarDan tried to make a DPZP like that, and even with a fan, the air did not stay within the screen gap. BUT, the much larger collector stagnating intentionally could be ideal as it would get hotter than a small solar oven near the top. Placing a small fan near the pot, but only intending to circulate the hottest air near the top of the collect might have some benefit. But that fan is going to have to withstand 200˚F for several hours. They do make unpowered, passive "fans" that sit on top of a wood stove that spin to circulate a bit of air. Might be the ideal solution for convection assistance.

Greg in MN

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Bert

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Reply with quote  #35 
Quote:
My take is that; the best overall way to make a cooker is with reflective sides and a black bottom. The bottom is black so that light doesn't get bounced straight back out the window ... and into your eyes. The sides are reflective to help focus the light onto the food. It probably helps to put a slight slant on the inner box sides."


Probably what I will do.

The All American Sun Oven has a dark inside. Not sure if they did testing. It may not make a difference with their oven since the pots take up most of the oven.

Even though, if a large regular oven heats up food then  a well insulated solar oven with dark interior is so small that you would think that heat would get to the food fairly fast. It may take a bit longer but should last almost that much longer as the sun goes down.

I will keep my interior shiny with maybe a dark pan or rack at the bottom. If that gets hot enough to cook I will be happy. If not some experimentation.

I need to find some sheet metal for the rack next. Hmmm cut up one of my stainless steel cookie sheets? 




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Bert K.
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gbwillson

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Reply with quote  #36 
I'd look at using a metal grid, shelving, or something similar for the shelf. It lets the sunshine through to the bottom.


Bert

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Reply with quote  #37 
I do have a metal grid that I may be able to use.

My computer went down. I think my hard-drive died. [frown]
I'm using my old media center computer for now util I get it sorted.
Was just getting ready to make a video of my progress.

On top of that I'm on call for jury duty starting tomorrow....

Oh boy.

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stmbtwle

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Reply with quote  #38 
Greg

Yes I got the idea from the "heat grabber", though I didn't remember the name.

I wasn't too concerned with the air staying in the "screen gap", I just figured the screen would help heat the air.  The hot air would find its way to the top one way or another, and the cooler air back to the bottom.

However even if it worked I concluded that as drawn it would be too cumbersome to move around, and hanging off the side of a table would be a hassle to follow the sun either manually or automatically.  So much for that idea [frown]


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gbwillson

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Reply with quote  #39 
Ha, Jury duty...

I served on a criminal jury trial last fall. After a two day trial we get into the jury deliberation room where we picked a foreperson. Right after this person was chosen the new foreperson declares "We might as well send the judge a note that this person is innocent and NOTHING you say can convince me otherwise". Everyone else felt otherwise. And the ONLY person who can send the judge a note is the foreperson. As you can imagine, things went downhill from there... Good experience though. I enjoyed it. 


Greg in MN

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Bert

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Reply with quote  #40 
Here's a very short video of my solar oven's progress so far showing how it tilts and rotates.
Don't laugh, I'm not use to making videos. I will get better. 😉



The noise you hear when I tilt it is Velcro. I had to use it to increase the friction so that it stays in place. I used the course side on both connectors so it doesn't stick.

I may use silicone caulk for the door seal. I don't like that stove rope much. Thought it may work.

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Bert K.
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