heat goes down

[W1UJR]

I don't see how cost is an issue

Frank, its not.

What everyone is overlooking is that this company has simply taken a page from GM's playbook.
Planned failure, assures future purchases, drives the economy, provides jobs, makes the world go around.
Now get the on the bandwagon, be a patriot, buy crappy products, and keep America working.
Remember, its "change we can believe in!" 

[Opcom]

One thing a bottom-mounted heatsink will do is warm up everything in the radio that is above it due to the heat from the top surface. Give that a few years.

[WA1GFZ]

Exactly. I ran a controlled test about 30 years ago. I bolted a power resistor to a heat sink and put a fixed voltage on the resistor. Then measured the temperature of it with the heat sink in different positions. A simple test that convinced me. Trapped air does not move heat away so you get temperature rise. The bottom line heat wants to rise so take advantage of it.
You guys left  a couple things out of the business model. Suck in investors and reward yourself with big pay as your product cooks itself. Then sell out just before the house of cards falls down. Get the government to bail you out just before elections kick out the crooks so blame is diverted to the new guy coming in. As new guy addresses the problems blame him for spending all the hard earned money forgetting the money wasted by the crooks.

[W1VD]

With vertical fins it pays to keep the bottom (and top) of the heatsink unobstructed. Had a chance to measure this a few years back on a power supply project. With the heatsink standing vertical in the middle of the bench (bottom of the heatsink in contact with the bench) there was a significant increase (10 - 15% IIRC) in temperature compared to the heatsink at the edge of the bench with clear airflow from below. Didn't try blocking the airflow above the heatsink but expect the results would be similar.     

[KA1ZGC]

You mean "hot air wants to rise".

You still haven't answered my perfectly-reasonable question. Preferably without bringing politics into it.

[W3RSW]

If the fins are horizontal and open at both ends of the cross section then air flow induced by temperature differential will be better with the fin opening facing down rather than up.  Why?  With fin openings pointing upwards, air has to flow inward from the ends towards the middle and then upwards.  With the fin opening pointing downwards, cool (more dense) air enters all along the fin "tops" where cross-sectional area is at a maximum, thus heated then flows outward along the long axis in the backing channels where radiation area is at a minimum, then out the ends of the cross section.

In reality it probably doesn't make much difference, 'up' or 'down', not nearly as much as radiation from the fins if they were 'vertical.'

Heat dissapation from the fins is by convection and radiation.  The radiation component is independet of alignment and is based on the cross sectional area of the fins, temperature differential between the metal and air, heat transfer of the metalurgy, etc.  

The convection component would probably be better if the rig were placed vertically, then air entering the bottom would 'chimny' thereby adding velocity to the metal to air heat transfer.  With no fan this, of course, would be laminar flow, not nearly as efficient in heat transfer as turbulent flow such as induced by a fan.

Concerning heating the rig above by having the heat sink and disspations system on the bottom,  recall that the heat sink is taking heat out of the rig, probably all of it by virtue of being cooler than the heat in the rig.  Heat flows from hotter to cooler.  Rig and components are warmest, heat sink collector (backplane, bottomplane, etc.) cooler, radiation fins cooler (and even they have internal temperature differences), and the air coolest.

[KA1ZGC]

I still want to see a picture, and I still want to know what the difference in surface area is. Surface area is the key to heat dissipation. That's the whole reason the fins are there.

[W3RSW]

Perhaps re-reading black body thermo., radiation and convection, specific heat of materials, fluid flow dynamics (static, laminar and turbulent flow heat transfer), etc. would refresh you.

All of this can be explained without fancy math or language.
A lot is intuitive, e.g., place just a bit of vertical component in the long axis of the fins, say your typical car installation and you get better heat transfer from the rig to the air by using the velocity increase of the cooling air by the chimney effect.

[KA1ZGC]

What makes you think those questions were aimed at you?

I'm asking Frank for a picture of the unit. Can you deal with that?

[ka3zlr]

Well some of us think this is pretty interesting, I do,..We're all friends here, Besides Thinking on the order of Solid State as compared to Hollow state was a good composition by Don, there's alot to learn here for the new guys...come on...

73
Jack.
 

[W1AEX]

Frank, I've noticed quite frequently that hot air is pushed outward from the receiver's speaker when listening to AM.

Rob W1AEX

[W3RSW]

Just got back from an Easter egg hunt for the kids down over the hill.
It's just so neat to watch the lit' cuties snatch up those eggs.
One little girl looked so forlorn when she couldn't find any.  A boy rushed in a direction that she spied in the last minute.  She then took off, Jeckle turned into Hyde.. (or other away around?) and she ebowed the bigger boy aside, pony tail flying and got her eggs.

Someone also made chocolate covered marshmellow eggs, tooth-picked to a big piece of foam covered in white icing made to look like a bunny.  Couldn't stay away from them.

************************

uh, ok, back to the topic.
Perhaps one really good reason for putting fins on the bottem, particularly in mobile rigs is just plain old dirt. Can you imagine the uglies, reports, papers, cigar ashes, coffee grounds.....double whoppers  'n stuff place on top the fins if they were top mounted?

Dust, any particulates, grease or other contaminent stops heat flow both conductive and radiative... just another layer, another heat insulator for the design to deal with.

Come to think of it, that might be the main reason for putting the heat exchanger on the bottom, just to keep it clear.

...smoke em if ya got em.

[WA1GFZ]

Jay,
I measured the same thing. You want air flow around every surface. Also don't want to trap air between the fins near the bottom of the heat sink.

Vertical fins do not collect dust but fins facing up sure will. Maybe I should check the 160 meter rig since it has not been dusted in 13 years.

It took about 5 minutes of operation with fins down on the SDR set up to convince me to prop up the heat sink so the fins were vertical.

[W3RSW]

Were the bottom mounted fins sitting on a flat surface or exposed to lots of air underneath, similar to a car installation?

If not, then I was wrong, 

[W3SLK]

Let me tickle this discussion here with maybe a reason for the mounting of the 'heat sink in question.' One of the things taught in our fire fighting classes is that heat tends to seek, (convect, radiate, migrate, etc) toward cooler surfaces. By placing it on the bottom, it will use the surface it is sitting on to sink heat away from the unit. Could that be the reason??? (scratches un-mentionable body parts)

[WA1GFZ]

Tom,
I don't know the answer to your question because the number of uncontrolled variables. I think you are looking for a ratio of area in different configurations.
The rule of thumb is 1 watt will heat 1 square inch of area 130 degrees C. My issue is getting that heat coupled to the air and away from the heat sink.
I just don't remember the actual temperatures I measured 30 years ago. Only the best configuration was worth storing in gray sludge.
From my many years of using a coal and wood stove.  It is always more effective getting the fire going at the bottom of the pile not the top. Why, The raising heat heats the fuel.

[KA1ZGC]

Okay, I got the impression that you saw this online? Can you provide a link, or at least a manufacturer and model? Then we can all see for ourselves. At the moment, we've only got your description to go by (not that you aren't a very descriptive guy  ).

Off-topic, did you work out where your signal cutout was happening?

[WA1GFZ]

Tom,
There is not a lot of good reading material out there. I was lucky to work with some real experts.  One guy showed me a test he ran on copper heat spreaders that made a lot of sense. But the bottom line is heat wants to rise and the easier you make that happen the more heat you can dissipate. We have a class A 200w 10 KHz to 1 GHz SS amp at work that has fins up. It runs at around 1 KW input.
I found my problem with HPSDR. I set a buffer size too small. It worked fine for RX but TX had drop outs. I just loaded McAfee on that machine which may have something to do with it. The smaller the buffer you run the smaller the processing delay.

[KA1ZGC]

Nope, that's not what I meant. In your original post, you wrote:

I was looking at a new transceiver that will sell for $1600 and see the heat sink fins face down.

That's what I'm interested in a picture of: the actual unit you saw that started this thread.