[Stoves] Black radiating surfaces

[Kevin Chisholm]

Dear Philip

IPC wrote:
> You cannot get a black body to be black at red heat.  It will be red, no
> matter what you do.  
>
> Sorry to be a damp squib, but the basic physics tells you this, and I
> learned some time ago that when the basic physics tells you something, you
> had better believe it!
>   

Thanks for your comment and insight. While a sheet of iron at a red 
temperature would not be a "black body", the point of interest to John 
is maximizing the emissivity of the iron, so that it radiates the 
maximum amount of heat energy.

A Black Body has an emissivity of 1.0 With a given piece of mild steel 
heated from room temperature to red heat and then brought back down to 
room temperature, would you (or anyone else) know how the emissivity 
would change with temperature?

Thanks!

Kevin
> Philip Lloyd 
>
> -----Original Message-----
> From: stoves-bounces at listserv.repp.org
> [mailto:stoves-bounces at listserv.repp.org] On Behalf Of John Davies
> Sent: 24 May 2008 08:03
> To: Stoves List
> Subject: [Stoves] Black radiating surfaces
>
> Greetings,
>
> We all know that a black body releases radiation heat the best.
>
> My problem is one of creating a black surface, on a surface that becomes red
> hot.
>
> I have rubbed cooking oil on the surfaces of my gasifier coal stove. This
> burns to a nice mat black colour, and the difference in heat radiation can
> be clearly felt.
>
> However the exposed coal tube will not stay black as the carbon layer
> formed, burns off as the metal approaches red hot temperature.
>
> Is there any other way to achieve a black surface that will not burn off?
>
> Now intuition tells me that there must be a solution to this, possibly some
> black salt which will not melt off, or change it's composition at the
> temperatures experienced.
>
> Does anybody have an answer.
>
> Thanking you,
> John Davies.
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