[Stoves] the 150 gasifier in operation in Vietnam (Matt Redmond)

[rongretlarson at comcast.net]

Paul, Matt, List: 

This is to follow along the line of Matt's message. 

I have concluded from the prior discussion that we need to help Paul O. more on the side of getting energy into the radiant element. 

I went to the local hardware store and bought and tested 5+ different products -all were failures. This is to help others not go down same path. 

a. 3M "stripping pad" Model 10111NA 3.5 x 5 x 7/8 in. Flexible - Thought it might be fire resistant. Was not. 
b. Norton "steel wool replacement" Model01729 4 3/4 x 5 1/2 x 1/2. Ditto 
c. 3M Drywall screen Model 9090NA 4 3/4 x 11 1/4 x "thin" mesh (think it is labeled silicon carbide - which means only the "coated grit") Ditto (the mesh [about 10 to the inch] was combustible. In phone call, 3M no help in identifying a more durable mesh. 
d. Norton almost identical to (c) Model 04169 Ditto 
e. Three "grades" of steel wool. Rhodes American 12-pack Item 10121114. The two finest were hard to put out (peculiar kind of sparking) when lit with a match (a big surprise!). The most coarse wool "burned" only slightly. I can conceive that this one or a still more coarse steel wool might last if we could "coat" it with a suitable ceramic "glaze". More on this next message along with what I didn't find in fairly long google search. 

The other key thing we need to talk about is how to maximize the (mostly convective) heat transfer to the object we wish to achieve red hot condition. Paul's present (too-short lifetime) strainer probably had about a 50% open ratio. His desire for a size 60 (openings per inch) would have an open-ness ratio of about 30%. We can probably eventually find an optimum - but perhaps we should instead have multiple layers (as with steel wool). So far I have not found any literature on this aspect of the optimization search. 

This is also to ask for anyone's expertise on stainless steel types that are available for low cost strainers - as Paul's desire for type 446 isn't obviously available (from the searches I have made). Is there any metal plating (chrome, etc) that might give much longer life to typical low cost kitchen strainers of the type Paul has been using? 

Ron 
----- Original Message -----
From: "Matthew Redmond" <mredmond3 at gatech.edu> 
To: stoves at lists.bioenergylists.org 
Sent: Tuesday, March 6, 2012 6:54:51 AM 
Subject: Re: [Stoves] the 150 gasifier in operation in Vietnam (Matt Redmond) 

Kevin, 


You make a good point about both temperature and atmosphere being important as to whether a material will oxidize. If there was 0% oxygen available, oxidation would not occur even at high temperatures. However, when the stove is turned off, the wire mesh would still be very hot, and probably able to oxidize in atmospheric air. 


Silicon Carbide seems like a reasonable mesh choice - chemically stable and able to withstand high temperatures. It even has a higher emissivity than stainless steels in the 0.7-10 micron wavelength range (red visible light - mid-IR range), meaning that it will emit more EM radiation than a stainless steel at the same temperature. http://www.pyrometry.com/emissivity_materials.php 


I was able to find some Silicon Carbide meshes using a google search for "silicon carbide mesh". Note they are not called wire meshes, but are just called meshes. They are a bit expensive, though. 


Perhaps some inspiration can be taken from lanterns used for camping? http://en.wikipedia.org/wiki/Gas_mantle 


-Matt Redmond 

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