Navitron Renewable Energy and Sustainability Forum

SOLAR THERMAL => Solar Cooking (using vacuum tubes or more conventional methods) => Topic started by: Eccentric Dyslexic on March 23, 2011, 12:01:29 PM



Title: Spare tubes project... solar grill?
Post by: Eccentric Dyslexic on March 23, 2011, 12:01:29 PM
I have 14 spare tubes, and was wondering what to do with them ...how about a BBQ or grill?  :hysteria Or maybe a hot plate? facepalm

How hot will a 14 (47mm) tube powered hot plate get?  and hows best to configure the tubes for practicality?

I was thinking of putting all 14 in a row at an angle that allows allows a reasonable hight for the cooking plate/grill and putting it near our BBQ area in the south of france.  Workable? wacko

Steve


Title: Re: Spare tubes project... solar grill?
Post by: Eccentric Dyslexic on March 24, 2011, 08:04:27 PM
First prototype-

http://i885.photobucket.com/albums/ac60/BigHairyBloke/DSCF0429.jpg

http://i885.photobucket.com/albums/ac60/BigHairyBloke/DSCF0428.jpg

http://i885.photobucket.com/albums/ac60/BigHairyBloke/DSCF0427.jpg

http://i885.photobucket.com/albums/ac60/BigHairyBloke/DSCF0426.jpg

http://i885.photobucket.com/albums/ac60/BigHairyBloke/DSCF0425.jpg

I have now insulated the botom of the plate from the clear glass of the tubes upwards.  It gets very hot!  Nest step is to buld a parabolic reflector....

Steve


Title: Re: Spare tubes project... solar grill?
Post by: pontiff on March 24, 2011, 08:24:08 PM
Excellent project! Solar burgers mmmmmmmmmmm. How did you attach the metal plate and what is the insulation?
 
I want to build something similar with an old whistle kettle on the top and the three heat pipes somehow sticking up through the bottom of the kettle. Need something visual to educate our yooth in the wonders of sun power.

Do you think it could boil a kettle of water? I'm not sure if the tubes would work if the ends of the heat pipe were submerged in boiling water as the vapour inside might not condense back down the tube.

I'm not sure how I would seal the pipes into the kettle and I also lack some essential equipment, such as a whistle kettle and any tubes!

I love it when the sun comes out and all these ideas begin to surface. Happy cooking! stir:


Title: Re: Spare tubes project... solar grill?
Post by: Eccentric Dyslexic on March 24, 2011, 08:50:13 PM
I have used rock wool for insulation.  Will post more pics tomorrow!  It will defo cook burgers, just not sure how long it will take yet.....

The plate is 3mm steel with 16mm tube welded to the bottom at 40degrees angle.  The heat pipes slide in very tightly into the tubes.  What I want to do is either add two more tubes behind the front three so I have five tubes in total in a circle to provide a burger shaped cooking area.  The extra tubes will catch the sun falling between the front three and with a parabolic mirror made out of some air flex reflective wall/roof insulation a much larger area of sun can be caught and reflected on to the rear tubes and sides of the front tubes.

Will do me best to get some pics of something cooking tomorrow!

Steve


Title: Re: Spare tubes project... solar grill?
Post by: knighty on March 24, 2011, 08:59:25 PM
put some copper ease/copper grease onto the contact area between the tubes and the hot plate pipes.... it'll improve heat transfer ten fold :-)


Title: Re: Spare tubes project... solar grill?
Post by: Ivan on March 24, 2011, 10:09:54 PM
Fantastic. I've been meaning to do this for a long time, but never got round to it.

Somewhere there's a picture of the solar oven that we made - basically a 4" celotex box with a triwall acrylic front door. The door didn't seal particularly well, which limited the temperature it reached. We found that it stalled at 160C, due to the limiting factor of how fast the heat pipe tips heated the air. I planned to make a hotplate for the bottom out of a section of the copper manifold with a plate of copper brazed onto the top....but never got round to it.

So my vote is for a temperature of between 160-200C. Put it inside an insulated box (or any box for that matter) to reduce natural radiative/convective heatlosses from the plate. Don't worry about the insulation melting - the silver foil surface seems to stop that, at least up to 160C!