<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>Dean</div><div>Emissivity varies with different metals and their oxides. A refractory metals like Tungsten or Niobium are wicked expensive. So are you asking about a coating on a ceramic substrate or an actual metal ( alloy)?</div><div>G</div><div><br></div><div><br></div><div><br></div><div><br><br>Sent from my iPad</div><div><br>On Apr 25, 2015, at 6:36 PM, Dean Still <<a href="mailto:deankstill@gmail.com">deankstill@gmail.com</a>> wrote:<br><br></div><blockquote type="cite"><div><div dir="ltr">Hi All,<div><br></div><div>We were wondering if an inner refractory metal black wall would absorb the IR (get very hot) and then emit back into</div><div>the fire. The outside of the metal wall would be shiny and then not emit very much into the stove body?</div><div><br></div><div>Best,</div><div><br></div><div>Dean</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Apr 24, 2015 at 3:12 PM, Bamboo Science Group <span dir="ltr"><<a href="mailto:greg@bamboosciencegroup.com" target="_blank">greg@bamboosciencegroup.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Dean<br>
Great topic<br>
When I was designing solar thermal panels for INCO in 1979, we used a coating (selective) process (chrome oxide spinel that had a alpha ( absorptivity) of 0.9 and and epsilon ( emissivity) of 0.04) on stainless steel that allowed it to perform at parity with a black oxide on copper ( fin and tube). The parity was achieved despite the overwhelmingly superior conductance of copper versus s/s.<br>
The high alpha allows absorption of the short wave solar radiation and the low epsilon slows the longer wave radiation emission in this flat plate solar collector application. These "selective" surfaces have cavernous surface area structure, utilizing the peaks and valleys of the coating to slow down the emissivity of the longer wave radiation.<br>
<br>
So you want an low emissivity coating for your refractory material to reduce ( inhibit) the black body radiation. SERI could certainly help out in this area as they are acquainted with high-temperature selective coatings for their work on concentrating collectors.<br>
<br>
Sent from my iPad<br>
<br>
> On Apr 24, 2015, at 5:07 PM, Dean Still <<a href="mailto:deankstill@gmail.com">deankstill@gmail.com</a>> wrote:<br>
><br>
> Hi All,<br>
><br>
> At the Aprovecho weekly meeting we were discussing how to improve performance in a Rocket stove. We were wondering about radiation.<br>
><br>
> Would temperatures rise if the inside of the refractory metal combustion chamber was black and the outside shiny?<br>
><br>
> Best,<br>
><br>
> Dean<br>
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