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Fab October 10, 2007 13:42

'Heat Transfer'

I would like to calculate a channel for windshield defrosting without the energy equation by just looking at the flow field. What do you think would be the best variable to look at to judge the performance of the defrosting, i.e. heat transfer? Right now, I would think that a pretty good indicator would be the wall shear stress and the turbulent intensity at the windshield... What do you think?


otd October 10, 2007 15:36

Re: 'Heat Transfer'
The convective heat transfer coefficient at the window is related to the wall shear stress by Reynolds Analogy for a turbulent boundary layer. High heat transfer is better (assuming that the heater air is warmer than the glass!). My guess is that:

shear stress sorts 'great HT'

from 'good HT'

from 'so-so HT'

from 'it just freezes over! HT'.

The amount of moisture in the heated air will have an influence as well.

Hope this helps.

momentum_waves October 11, 2007 00:37

Re: 'Heat Transfer'
You may want to be careful assuming that knowledge of a velocity flow field will provide adequate information on the energy field.

The two fields actually may not completely coincide in some applications, although the energy solution uses the existing velocity flowfield values.

This is why, in practice, in a tube for example, there is a velocity profile & a temperature profile - which are generally different.



Fab October 14, 2007 13:39

Re: 'Heat Transfer'
Hi to both,

thanks for your help! It seems that I can use the shear stress as a first hint and should check it with the energy field distribution... Fab

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