[Gasification] Radiant vs Convecative heat transfer

[Kevin Chisholm]

Dear Tom

This is fascinating!!

How far apart should the shields be, to get this effect?

How would the effect be changed if there was air between the radiation 
shields? Would it tend to "help the heat across the gap" and reduce the 
effect?

Thanks!!

Kevin
----- Original Message ----- 
From: "Tom Reed" <tombreed at comcast.net>
To: "Jeff Davis" <jeff0124 at velocity.net>
Cc: <gasification at listserv.repp.org>
Sent: Thursday, August 17, 2006 1:15 PM
Subject: [Gasification] Radiant vs Convecative heat transfer


> Dear Jeff and AllJeff Davis wrote:
>
> Before my "midlife career change" in 1976 (at 50 ...hmmm, maybe atime
> for another) I designed furnaces to reach 2600 C in argon or vacuum in
> my role as resident crystal grower at MIT.
>
> Among other things I designed a transparent (200 angstrom thick) gold
> furnace relying on the reflection of this thin layer of gold which had
> the insulating value of 1 inch of fibrous (asbestosXXX, KaowoolL***)
> insulation.
>
> For the 2600 C furnaces we used tantalum heat shields.  Each layer of
> metal reduces the radiant heat loss by a factor of 2/e, where e is the
> emissivity of the surface.  The emissivity of aluminum is ~0.05, so each
> layer reduces radiant heat loss by 40.  At room temperature the
> convecative and radiant heat transfer coefficients are about equal, but
> radiation increases as T^4 power, while convective is ~ constant.
>
> So a lining of a few layers on the inside of each of our WoodGas stoves
> keeps the outer surface below 100C and keeps the paint from frying.
>
> Forward,
>
> TOM REED        BEF
>