[modeleng] Re: Question - maybe off topic- certainly academic
- From: "Clif Walker" <clif.gwr@xxxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Thu, 14 Oct 2004 11:58:57 +0100
Hi All,
This all goes back to the theory of heat transfer which I did at College
back in 1960 so naturally I have completely forgotten it all.
All that I do remember was that it was a swine of a difficult subject which
does bring in a thing called Dimensionless Analysis regarding the thickness
of the boundary layers both on the gas side and the water side.The thickness
of the layers and hence the rate of heat transfer depend on the velocity of
the respective fluids or gas over the surface which change from Laminar at
low speed to Turbulent at high speed and hence affect the flow of heat.A
layer of scale does not help.
These boundary layers if they are not removed act as a layer of insulation
between the metal and the respective fluid or gas.
As I said it was a heck of a difficult subject and when it came to the
exams,out of fifteen subjects as we only needed to only pass in twelve to
qualify , Heat Transfer was the first one dropped unless you were going into
the design of Heat Exchangers as a career.
The whole thing is pretty well common sense but in engineering you have to
be able to prove it.
Regards
Clif
> Thanks Alan,
> >rom what I recall, the theory is / was that the water in contact with the
> >wall would bubble as it boiled, and the circulation of the water would
> >replace it by some more.
>
> This suggests that the important point must be the water circulation, but
> it also suggests that a turbulent, rather than a laminar flow, is
> required.
>
> Peter Chadwick
>
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