Solar Parabolic Trough Charcoal Oven

[Nitack]

The fatal flaw in our plan was in effect this weekend. Rain and clouds all weekend in my neck of Virginia. Unfortunately since I work during the prime solar hours during the week I have two days for experimentation on weekends and both were a wash this weekend. BAH.

On a more fun note, guess what is coming to my house this week... American Science & Surplus: Lenses and Lens Cleaners

[freeztar]

It rained here all weekend too. That 49" lens looks...hot!

I'm hoping to be able to use multiple small lenses to focus on one point, but it will be difficult and not as effective as that big lens.

[Nitack]

Obviously I don't want 2k+ degrees, so I will not have the lens fully focused on my test vessel. I am hoping to have it just out of focus enough that we will end up getting a larger area in the 700 degree range. So instead of a 1/2" by 1/2" area at 2k+ degrees, we will have a 1'x1' area in the 700 range. My test vessel is going to be a dutch oven, wonderful suggestion by Turtle. first test will be just an empty oven with just an oven thermometer inside it. Leave the light on the oven for about ten or twenty minutes and see what temp we get up to. That should provide all the info needed. From there, assuming we get up to at least 400 degrees, going to be stuffing it full of grass clippings and yard clippings. Turn on the heat and see what happens.

[freeztar]

That sounds like a plan.

Have you obtained the dutch oven yet?
If not, I suggest you try and find one with a loose lid. The water vapor and gases will need an escape route. Ideally I suppose you would need a sealed container with a pressure release valve though I'm betting that such an ideal will not be necessary given the high temps lending to less of a need to maintain pressure.

[Nitack]

Well I was going to find a cheepo cast iron dutch oven. Lid won't be lose, but that I think is a good thing as the presure inside will constantly be such that air (containing oxygen) will never get in. When the presure gets high enough to force open the lid it will only force gas out. And if the lens is covering the whole dutch oven in high temp light we should have a hell of a pyro show when the gases lights on fire.

[Nitack]

I just had a very devious thought...

Everything I have read has said that a lens the size of the one I have coming can create temperatures up to 3000 degrees at the focal point. US nickels are actually worth nearly ten cents in precious metals... I could just melt the suckers down and sell them at a profit. Plus, I have no fuel costs for the melting because I am using my lens

[freeztar]

The nickel black market...

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Regarding the lid of the dutch oven, you bring up a good point. The only problem I can imagine is that the high-pressure flammable gasses might be capable of blowing the lid. Perhaps you can rig a latch to prevent the lid from going past a certain point.

[Turtle]

Originally Posted by freeztar

The nickel black market...

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Regarding the lid of the dutch oven, you bring up a good point. The only problem I can imagine is that the high-pressure flammable gasses might be capable of blowing the lid. Perhaps you can rig a latch to prevent the lid from going past a certain point.

I wouldn't latch it, as that will only make the pressure higher. Based on my own cast-iron Dutch oven, I think the weight of the lid and the inset lip on it will keep it in place, but expect some rattling during outgassing.

[Nitack]

Good point on the lid blowing, my question becomes this...

The gas needs oxygen to combust, and oxygen should only be available outside the oven, so is there a danger of the gases combusting from within the oven and blowing the lid off? Rigging a latch should not be too hard, I can possibly do it with coat hangers and just make loops as a fail safe... that is of course as long as they don't melt...

[Nitack]

Originally Posted by Turtle

I wouldn't latch it, as that will only make the pressure higher. Based on my own cast-iron Dutch oven, I think the weight of the lid and the inset lip on it will keep it in place, but expect some rattling during outgassing.

I figured that gas would slowing squeeze out which is why I was not worried. As long as pressure is going up there will be moments were the upward force it is applying is greater than the weight of the lid and the gas will push out.

As for the nickel black market, I would not be selling what I melted... it is kind of illegal and they will pimp slap you if you are caught doing it. Besides, i would not even know where to sell it. I would end up having lumps of 75% copper and 25% nickel. Any scrap or metal dealer is going to know exactly what I did and probably try to claim a reward turning me into the treasury department... although maybe I can make a nice paperweight for myself.