Mitch and Jeff,
I tend to agree with the HVAC companies and Jeff especially for a commercial
application. But with HVAC, the fan units have the fan mounted in the top of
the unit with the heat source on all four sides as in a residential heatpump
or in a cowling built above the heat source with the fan mounted in it.
These are large commercial fan units that do make there own heat and in most
cases are always pulling the air up and out so as again not to fight the
natural flow of heats tendency to rise. They also only run when the unit is
trying to either heat or cool something. They do not care about excess heat
once a given temperature is reached. A heatsink is still trying to dissipate
heat after you have unkeyed.
What you have is a heatsink with no chamber formed from the condenser fins
and no cowling to mount the muffin fan in to hold it up off the heatsink.
This is why I do not care for top mounting the muffin fan. It impedes
natural heat flow and only helps when it is running. If the muffin fan dies,
it will only make your heat problem worse if top mounted. Also with a bottom
mounted fan pushing air through the heatsink, the fan is out of the way for
short QSOs that the fan does not need to be on for and causes little affect
to natural heatsink cooling. Do not get me wrong, even mounting a small
muffin fan on the bottom does effect the heatsinks normal performance, but
not as much as top mounting it.
This is also why most fan kits that one can buy for radio equipment have two
muffin fans built into a cowling that mounts onto the heatsink covering the
minimum heatsink area to get it mounted. Most of these units mount to the
back of the heatsink and blow air sideways into the heatsink with air
spilling out the top and bottom of the heatsink. This is done for two
reasons, one it keeps the amp or radio pack size the same as the original
unit other then depth. If measurements must stay as close to the original as
possible for an application, depth is usually the one that can be cheated
on. Two, it keeps the fan unit out of the way and gives it some protection
by the unit it is mounted to. Its not the most inexpensive way to do it or
the most efficient, but when adding 2 additional fans with a cowling to
force air over the heatsink one has increased the efficiency of the heatsink
so greatly it does not matter about the rest.
I guess all in all its a toss-up. It comes down to what works best for you
and what is easiest for the unit the muffin fan is going on and where one
has the equipment located. As long as the fan is always on when the amp is
on, the heatsink will always be more efficient with a fan mounted somewhere
then with no fan at all.
73, Keith
de KE4TEG
----- Original Message -----
From: "Jeff Modlin" <kd4znc@arrl.net>
To: <tentec@contesting.com>
Sent: Sunday, March 02, 2003 8:29 PM
Subject: RE: [TenTec] Delta II Cooling Fan
> Mitch,
>
> HVAC convention is to have cooling fans suck the air over the heat
> source. The simple reason is that the heat generated by the motor and
> the friction losses in the machine add energy to air and consequently
> raise the temperature. So the air being pushed by a fan has slightly
> more energy in it than air pulled by a fan.
>
> All of this being said and referencing KE4TEG's reply, having the fan
> pulling air over the fins is better as long as the fan is on. If for
> the sake of noise reduction or any other reason, the fan is switched
> off; its presence will impede cooling.
>
>
> 73 de Jeffrey Modlin
> KD4ZNC in Coral Springs, Florida USA
>
>
>
>
>
> -----Original Message-----
> From: tentec-bounces@contesting.com
> [mailto:tentec-bounces@contesting.com] On Behalf Of Mitch Alexander
> Sent: Sunday, March 02, 2003 6:34 PM
> To: tentec@contesting.com
> Subject: Re: [TenTec] Delta II Cooling Fan
>
>
> Hi, Guys --
> Just relaxing after the contest weekend. It's not 0:00 yet, but I'm
> finished. Whew !!
> I've always wondered which is the correct mounting for a cooling fan --
> blowing cool air onto the heat sink, or drawing the heat away? In other
> words, blowing in or blowing out ? I have muffin fans on the top of my
> amp drawing the air out of the tube chimneys -- same principal for heat
> sinks, or not?
> cheers--
> Mitch Alexander -- KJ4DX
>
> Greg Breeden <gbreeden@pivot.net> wrote:List,
>
> I am looking for a cooling fan for my Delta II. It looks as though any
> fan
> would work, provided it would fit the pre drilled screw holes in the
> heat
> sink and was 12 volts.
>
> Can anyone direct me to a good source for this fan, or even the factory
> fan
> which you would part with at a reasonable cost.
>
> Greg, AL0A
>
> in Maine where it is snowing again...
>
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