RE: [T3] Polishing?

["Squareback" <tjfink@home.com>]

Ok, quick lesson in Heat Transfer.  There are 3 forms of heat transfer.
Conduction, Convection, and Radiation.

Conduction and Convection are the main forms of heat transfer in the VW
motor.  Conduction is straight forward.  It is dependent on surface area,
thickness, and the conduction coefficient, which is different for all
materials.  Convection has more factors.  Convection is dependent on the
fluid temperature, fluid velocity, surface area, surface temperature, and
the convection coefficient for the fluid.  Fins and rough surfaces are one
way to increase surface area, which will increase the heat transfer due to
convection.

Color does play a large role in radiation heat transfer.  A black
case/engine operates as a black body radiator.  A black body radiator is a
perfect emitter.  This means that it does not store any of the energy that
it receives in the form of radiation from the surrounding, i.e., hot engine
sheet metal, exhaust, etc., and it also radiates the maximum amount of
energy that is generated from inside the engine.  A white case/engine will
radiate all the energy that it receives from the surroundings, but will not
radiate any from within the engine.  This explains why a black asphalt road
is very hot and the white stripe dividing the road is much cooler.

You will have to accept that color actually acts this way.  I will be glad
to direct you to my Heat Transfer text from college.  I hope this helps
some.
-----Original Message-----
From: Steven Ayres [mailto:comwest@well.com]
Sent: Tuesday, June 08, 1999 2:23 AM
To: type3@vwtype3.org
Subject: Re: [T3] Polishing?



Me=> a polished surface does not transmit heat quite as well as an
  => unpolished one.

JMac=> Really?  Why?

Less polish = more surface area = more air contact.
That's why finned cylinders work better than smooth B¼ãteven Ayres, Prescott AZ
'66 Big Ghia

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