Its a common mis-conception that I run into professionally all the time.
The fact is that unless the height of the vertical fins would be quite
large, coupled with a large delta T, there is not enough convection air
induced to make any real difference in the cooling. The combination of
radiation, and cooling by convection aided by stray air currents is ample in
most cases. The low transmit duty cycle combined with the large mass of the
sink is also a help.
Heat sink extrusions are cheapest when you buy the long, slender ones, and
the fins always run lengthwise on those.
Of course you could buy wide extrusions, and then cut them off into short
pieces. But the limited benefit would never repay the cost.
In a perfect world, where everything was free, I'd take the 5% gain from
orienting the fins the other way. In fact I have done so, on professional
projects where getting the last 5% was vital.
73 de Gary, AA2IZ
----- Original Message -----
From: "Duane Calvin" <ac5aa1@gmail.com>
To: "'Discussion of Ten-Tec Equipment'" <tentec@contesting.com>
Sent: Wednesday, August 27, 2008 6:55 PM
Subject: Re: [TenTec] Hercules II fan noise
> Re: thermal engineering at TT - - Clearly not their forte, Steve, nor is
> acoustics (your fan is an example, as was the Centaur amp). Back to the
> thermal side, check the heat sinks on the power module on the Orion (and
the
> Omni VI+ and probably others) - - the fins are mounted horizontally.
Seems
> to me you would want to aid convection and orient them vertically. But,
> hey, I'm just a EE with a semester of thermodynamics and fluid mechanics,
> not an ME! (hi!)
>
> 73, Duane
>
> Duane Calvin, AC5AA
> Austin, Texas
> www.ac5aa.com
>
> -----Original Message-----
> From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
> On Behalf Of Steve Hunt
> Sent: Wednesday, August 27, 2008 10:56 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Hercules II fan noise
>
> Today I did a few checks on the present fan.
>
> 1) I unbolted it from the under-tray and held it in place by hand. There
> was no reduction in noise, so I don't think resilient mountings will help.
>
> 2) I removed the fan completely and ran it on the bench from an external
> PSU. It was a little quieter, but not by much.
>
> 3) I tried a small amount of lubrication but that made no difference.
>
> 4) One thing that made a surprising difference was the presence or
> absence of the "finger guard". In fact anything close to the fan and in
> the intake airflow made quite a difference to the noise level. Just
> holding a pencil across the intake brought the level up noticeably.
>
> 5) Surprisingly there was very little dust around the fan or the
heatsinks.
>
> I've managed to locate a new fan that seems to have an equivalent spec -
> it should be here in a few days, and hopefully will solve the problem.
>
> I wasn't too impressed by Ten Tec's thermal engineering. The fan is on
> the underside of a central chassis plate, and the PA transistor heat
> sinks are the other side. There are just a couple of very small holes in
> the plate where the air can flow from the fan side through to the
> heatsink side!
>
> 73,
> Steve G3TXQ
>
>
>
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