Al Gietzen wrote:

I was considering getting my manifold coated on the inside in an effort to

reduce wall temps and

heating in the cowl.  Before committing to the cost I want to know how

much it will really help;

seemed suspicious to me that the very thin coatings (.005-.010") would

provide anywhere near the

temp reductions claimed by Jet-Hot.

I estimated the heat flux from a 1600F wall by conduction, natural

convection, and radiation to

total about about 5 watts/sq-cm.  Most of this is by radiation.  If you

have air blowing over the

surface it might go up by a few W/sq cm.

I called Jet-Hot to get the thermal conductivity of the coating.  They

refuse to provide any

engineering data of any kind.  They did tell me that the coating on the

inside would only be about

0.001"; and about .005" on the outside.

It is hard to imagine that the thermal conductivity could be less than a

ceramic, so using that, a

.001" coating gives a temp drop of a whopping 6 C, or about 10 F drop in

wall temp.  Adding

another .005-.010" on the outside may drop the temp a total of about 100F.

So unless you're doing it to make your manifold and pipes look nice (or

I've made an error in my

calcs - entirely possible) these coatings are a waste of money; especially

a .001" coat on the

inside.  No wonder they don't give out any engineering info.

Al Gietzen

Except for one thing Al and I am not saying this because I necessarily think
its true.
I am just saying it is a possibility.  Steel and SS tends to oxidize at high
temp.
If you can keep the oxygen away from the surface they might not corrode so
badly
and perhaps last longer. Mild steel flakes off in large chunks when used for
rotary engine exhaust.

Paul Lamar

Valid point.  I was focusing on the temperature issue; and I'm not much
concerned about oxidation on inconel.  I wonder if it could inhibit
intergranular stress corrosion on SS, like 321, at our exhaust temps.
There's a research project for someone.

Al

 
The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2002 All world wide rights reserved.