Channel Jumper wrote:

Irv Finkleman VE6BP;840688 Wrote:
I have been wondering which way the fans on my TS-930 should be
blowing. Should they take the ambient air from outside and blow
it on the heat sink, or should they be evacuating the inside air
in the vicinity of the heat sink and blowing it out? I have been
restoring the unit and both fans required replacement.

I've surfed a number of sites on the subject but can never get
a definitive answer.

Thanks in advance for any assistance...

de Irv, VE6BP

If the fans are forcing the air in, it is forcing the hot air deeper
inside of the heat sink, making it hotter, not colder - unless the air
outside of the radio is colder than the air inside of the heat sink.

Which it obviously will be and your wording implies that the heat
sinks are closed to air flow.

In a good design, heat sinks are put on the hottest part of the equipment
and the thing that needs cooling the most. The best way to do that is
to blow outside air into the heat sink. If the design was done properly,
there will be an air path out of the heat sink back to the outside.

We tried push pull on a set of car stereo amplifiers in a box and found
that if the fans drew the air away from the box, the amplifiers ran
cooler than if we tried to push air into the box and then draw air back
out of the box.

That result will depend on where you put the fans and the air flow
in the box. If the box was not originally designed for forced air
cooling, your results with add on fans will be entireyly random.

You need almost twice as much fan drawing the hot air out as what you
use to push it in.

Again, that would entirely depend on the equipment design.

I would make sure that I used your radio in an open air space and not
inside of a box or cabinet.

Lots of equipment routinely operates inside of a box or cabinet. If the
enclosed equipment generates much heat, then the cabinet needs its own
set of fans to ensure enough cool outside air for the enclosed equipment.

Obligatory war story: Years ago we were building racked equipment and
the controversy arose as to whether it was better to blow air into
the rack from the top or the bottom.

The bottom blower group maintained that since heat rises, you would
get better airflow from blowing in from the bottom.

A quick calculation showed that the fans overpowered the convection
flow by many orders of magnitude, so it should be irrelevant.

So an empirical test was done with two cabinets side by side.

The long term result was ths bottom blower cabinet got hotter because
the fans at the bottom picked up more dust and crap from the environment
clogging things up while the top blowers remained much cleaner.

--
Jim Pennino