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Bob,
This statement of yours got posted to the type 3 list. I like your
choice of blue for a Propane engine, but I think I would like to take
issue with you on your analysis of the effect of color on the
cooling. I am posting my response to the T3 list as well as directly
to you. I will be happy to post any reply you wish to make there as
well.
> To reiterate a point that some still find confusing, those portions
> of the engine that come in contact with the lubricating oil and can
> therefore radiate heat, will be painted flat black. The tin-ware
> serves to seal the engine compartment and to form the shroud that
> contains the cooling air. It may be painted any color or even
> plated with chrome without having any effect on the engine's ability
> to cool itself.
>
> -Bob Hoover
The engine cools by both radiation and conduction. Radiated heat
will be absorbed by the tin itself, but only if the tin is a
good absorber. Most of this heat will be transferred to the
layer of air that flows next to the tin. Some of the heat from the
tin will be radiated to the outside of the tin, and some of it
will be re-radiated back inwards. Still, this is a better situation
that having it all reflected back into the engine. After all, if
this were not important, then it would not matter what color the
direct radiators of the engine were, because air does not absorb
infra-red and the direct radiators of the engine are almost
completely surrounded by tin, so most of what got radiated would get
reflected right back to the engine.
It is hard to predict what colors or coatings will be good absorbers
in the infra-red, but I don't think chrome plating is one of them.
Choosing a coating that is a poor absorber in the infra-red means
that your engine will only cool by conduction (directly to the
airflow that passes next to it) and this can only result in a net
loss of cooling.
Jim
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Melissa Kepner Jim Adney
Laura Kepner-Adney
jadney@vwtype3.org
Madison, Wisconsin
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