"Ron(UK)" wrote:

Eeyore wrote:
N_Cook wrote:

For fan blown o/p devices the heatsink surely does not have to be much more
that a metal matrix for holding the devices to.

The larger area the better.

Does not have to be multifluted

That certainly helps.


or with those chisseled multi-vanes etc (sorry don't know the
generic term , end up curved )

Those increase surface area which is a GOOD THING.


or a great mass of metal for convection cooling

It most certainly DOES NOT need to have great weight. But almost none of the
cooling in SR amps is classic convection anyway. What typically helps is maximum
surface area of the fins/vanes to create the best opportunity to let the heat
transfer to the air flow, but you can improve even that by 'slotting' the
'vanes' to create a slightly turbulent air flow.

You can btw see this in many 'CPU cooler' designs. However it can cause dust and
fluff to collect.


Trust me I could write a lecture on the subject.

I recall many years ago that there was a 'manufacturers mod' for some
power amp or other ( dont recall which) where you had to bend all the
vanes of the heatsinks - which were like combs - away from the vertical
in various different directions to improve the marginal cooling just
that tiny bit to prevent the thermal protection tripping. Looked damn
ugly but did the trick.

Yes I can believe that. It would help cause the 'turbulent airflow' effect. I first
learnt about this around 30 years ago from data supplied by the IERC heatsink company
and have widely used the technique ever since with measurable success.

You see with purely vertical or horizontal fins widely spaced, the air going 'up the
middle' between them never actually extracts much useful heat. You need to get the
airflow to 'mix' to get the best effect.


What works best Graham, a thick ally heatsink with many thick fins, or a
thick ally plate with many convoluted thin sheet fins?

Within reason, the fins don't need to be that thick at all. Their minimum width is
normally a limitation of the extrusion technique. What's best it have lots of them,
consistent with not creating a dust trap by having them pitched too fine..

Don't make the fins TOO convoluted as this will actually impede airflow. I have my
own 'proprietary' technique that avoids any need to twist the fins which most people
would find counter-intuitive but in a calibrated test produced a 20% improvement in
thermal resistance with a lower weight of aluminium in 2 (superficially to the casual
viewer) identical designs.

As it seems no-one has yet twigged my method, I'm reluctant to give away my 'secret'.

As for the 'plate' its needs to be thickest near the devices and can taper further
out. Thermal resistance calculation are little different to electrical resistance
after all.

Graham