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Heat Shield material

Heat Shield material

(OP)
A friend of mine has decided carbon fibre would be a good material to craft a heat shield from. His theory being that if he can shield some of the heat coming from the block (it's a rotary engined vehicle), and avoid it getting to the intake manifold, it will improve intake temps.

I was under the impression carbon fibre did not make a very good heat shield. His thoughts were that he had a bike with a carbon muffler on it, and it could be touched and you would not burn yourself, while a stainless steel muffler would quite clearly burn you.

I know in top level motorsport gold leaf is the go, or even some sort of reflective cover on stainless steel. But for a street car? Would carbon work? Or even better, work well?

RE: Heat Shield material

I guess it might. I did build a glass/polyester/mica composite heat shield in college. The thermal  conductivity of carbon fibre is relatively high, I dont know where in relation to steel. Often heat shielding is more about the finish of the shield and the size of the air-gaps.

RE: Heat Shield material

A look at anything required to reflect heat will give you the answer.  First thing to mind is a radiant heater. Shiny surfaces to reflect the heat out.

I would use a thin 0.6 Stainless steel sheet that is highly polished.

Ken

RE: Heat Shield material

There are 3 methods of heat transfer.

Radiation
Conduction
Convection

Shiny stops radiation only.
Low conductivity stops conduction.
Baffles and or containment of surrounding air stops convection.

Carbon is an excellent conductor of electricity, but a moderate to poor conductor of heat, and does not approach metal as a conductor of heat, but is still higher than glass. High is poor for this.

A major influence on the conductivity will also be the resin matrix. The resins used tend to have very low conductivity for heat.

Glass fibre will do a better job and is a lot cheaper.

Special heat insulation materials can be purchased from such places as welders supplies and industrial supplies.

It might be easier to insulate the intake air duct than the engine block.




Regards

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RE: Heat Shield material

i know that ceramic fibre blanket & e-glass mat is used for the automotive industry. u might consider finding out more information if it helps in your application.

also, aluminized fabric can reflect 95% at a temperature of 3000deg.F if i dun remember wrongly.

in your problem, you might consider aluminzed fibreglass fabric.

RE: Heat Shield material

Carbon fiber would probably have high oxidation rates under such high heat. I don't think it's a well suited application, especially in a heat pump like a rotary.

I've used titanium in the past to some success in brake backing plates.

RE: Heat Shield material

I believe Pat's advice is good, it is better to insulate the intake manifold/ducting.
There are a number of insulation materials that use Al sheet with ceramic paper between the sheets. ACL manufacture some, but there may be something more local for you?

RE: Heat Shield material

I am a sucker for innovative ideas. At the same time, I am not an automotive engineer and not familiar with the details but I know that the thermal conductivity is much larger in the plane of the crystal as opposed to orthogonal to it. This concept has been expolited in the carbon nano tube technology and now there are carbon pads used in the electronics packaging industry which is used to spread heat - and thus lower surface temperatures.

I wonder if a combination of steel and carbon pads may be developed that would act as a thermal shield?

RE: Heat Shield material

There is no need to get that technical nor expensive.

Fibreglass based insulation works just fine. Even better if one side is metallised with a very thin coating of shiny metal to improve reflection, improve structural integrity, and provide protection against saturation with liquids.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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