Re: [Amps] tube cooling

[Gary Schafer <garyschafer@comcast.net>]

Ian White, G3SEK wrote:
> Turbulence is vital for effective cooling. If the air flow over a hot 
> surface is gentle (laminar) there is always a stagnant boundary layer of 
> hot air which effectively insulates the surface from the bulk of cool 
> air flowing past it. Turbulence scrubs away the boundary layer, so it 
> greatly increases the heat transfer.
>
> The key point about the "Blow or suck?" discussion is that turbulence 
> only exists *downstream* from the blower or fan blades - so there is a 
> real difference.


I don't entirely agree here. You can have as much turbulence sucking air 
as you can by blowing it. It depends on the speed of the air and the 
surface that the air is passing over as to how turbulent it is.

Ask an air conditioning company how they deal with turbulence in air 
inlet ducts that are noisy.

When you are sucking air you are really lowering the pressure on one 
side and allowing the atmospheric pressure to push. You can not really 
suck air via a vacuum. It always gets "pushed".
The only difference when "sucking air" is that it is a little less 
dense. Lower pressure on it.


> In desktop amps with the Alpha-type through flow cooling system, the
> blower is buried deep inside (which helps reduce noise) and it delivers
> highly turbulent air direct to the tubes. However, the inward air flow
> from the rear of the amp is much more gentle, almost laminar,
>

Not familiar with the alpha but I would suspect that the air inlet is a 
lot larger than the outlet thus lower velocity which would make it gentler.

73
Gary  K4FMX


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