The AM Forum

as most know heat rises. I was looking at a new transceiver that will sell for $1600 and see the heat sink fins face down. It set off my POS detector

Maybe it was designed in the south of the equator so the heat can.. hmm... nevermind.

HI Frank!

Apparently the designers took "heat Sink" literally.

Frank,

Get with Obama's program of change.

If forced air cooling is employed, I don't think it matters as much.

As far as New SSB PHONE/CW MFG'd, that even grabs my interest is the New Elecraft, of course I like alot of what those guys are doing, Second wud be Ten-Tec..

No, it doesn't.

Hot air rises over cold air. Hot water rises over cold water. The molecular density of a substance is inversely proportional to its temperature, with the exception of ice. Heat itself doesn't rise, hot matter rises over cold matter. Heat itself merely radiates and disperses.

Heat as a form of energy has no concept of gravity. A heat sink with the fins pointed down still draws heat away from the device in question. That's all it needs to do.

Actually, "heat" doesn't radiate.  What radiates is infra-red light.  Heat is the effect the radiation has on matter that absorbs the light's energy.  The warmth we feel from the sun is not from "heat" directly radiated from the sun.  Most of it is from the visible light that falls on our skin, or on whatever we perceive as "hot". The light that is not reflected off the surface gives up its energy to the matter that absorbs it, and raises its temperature.

"Radiant heat" or infra-red given off by a heater is exactly the same thing as the visible light given off by a lamp, and has exactly the same effect on temperature of surrounding objects, except that it is invisible to the eye.

Hot air given off by a heated object such as cooling fans on a tube is air in which the temperature has risen due to energy absorbed from the infra-red and visible light emitted by the tube.  Because of its higher temperature, the air feels warm because it, too is now releasing energy, until it reaches the ambient temperature of its surroundings.

Yep... fair enough.

how cum you guys no so much?  ???  :D

never ceases to amaze me the amount of knowledge in the brains inside the heads;
on top of teh necks that sit on the shoulders of the people here.

(Jumps up, raises hand) Ooh! Ooh! I know this one! I know this one!

Because I payed attention when they taught me this stuff in my 5th grade science class.

Can I be excused now? My pimp's here.

Dog in heat
Packing heat
Police
Throwing some heat
Heat of the night
Final heat
Dead heat

(http://ia.media-imdb.com/images/M/MV5BMjE3NTg3MjQ1MV5BMl5BanBnXkFtZTcwNTI2MTgxMg@@._V1._CR78,0,580,580_SS100_.jpg)

That's the worst haiku I've ever read.

haiku ? ???

Haiku is a poetic form and a type of poetry from the Japanese culture. Haiku combines form, content, and language in a meaningful, yet compact form. Haiku poets write about everyday things. Many themes include nature, feelings, or experiences. Usually they use simple words and grammar. The most common form for Haiku is three short lines. The first line usually contains five (5) syllables, the second line seven (7) syllables, and the third line contains five (5) syllables. Haiku doesn't rhyme. A Haiku must "paint" a mental image in the reader's mind. This is the challenge of Haiku - to put the poem's meaning and imagery in the reader's mind in ONLY 17 syllables over just three (3) lines of poetry!

This is clearly a hot topic, promoting a heated discussion.

Well, as long as we're being technically correct (this is the technical forum, after all) and clarifying just about everything under the sun, Pete's description more accurately depicts Senryu.

Having said that, Haiku is merely Senryu which contains a seasonal reference.

For example, Haiku:

Autumn leaves descend
onto Irwin Richardt's grave
then yelp "Okay FINE!"

...with the requisite seasonal reference appearing in the first line.

Senryu, on the other hand, is the same format without a seasonal reference:

Joseph Coors is dead.
Rot in Hell you nazi prick,
your beer tastes like piss*

Minus that one tiny (and seldom asserted) detail, Pete's description was quite accurate, eloquent, and very well-written.

Spend a few decades in talk.bizarre and you'll feel inclined to point out the difference, too. Knowing the difference was sort of a rite of passage.

Right... as you were, Gentlemen!

--Thom
*This Senryu was originally posted to talk.bizarre when Joe Coors finally died. I honestly don't remember who posted it, only laughing my ass off when I read it. Those of you offended by it would do well to look into how the man spent his spare time.

Fins down are almost as useless as horizontal fins

-warning- this is boring talk about heat transfer.

Heat sinks predominantly use two of the heat transfer types, conduction and convection.  Heat is directly conducted into the aluminum heat sink through physical contact with the device.  Aluminum has a very good coefficient for conductive heat transfer (a low resistance), so heat is effectively transferred from the device into the solid aluminum heat sink.  Conductive heat transfer from the aluminum to the air surrounding it is very poor, due to the poor heat conduction coefficient of air (think of a series circuit, a low resistance to heat conduction thru the aluminum heat sink, and a high resistance in the air surrounding it).  However, convective heat transfer occurs when the air in contact with the aluminum is warmed, and then moved away (and replaced) by colder air due to either forced air circulation or the normal circulation(rising) of warm air.  Convective heat transfer depends on the mixing of the air in contact with the surface.   The air in contact with the surface of the aluminum is heated, absorbing its heat, and is continuously replaced by colder air.  This convective heat transfer is not as effective as conduction, and that’s why there are fins on heat sinks, because more surface area is required to transfer the heat.  The upward flow of air that occurs when air is heated increases the convective heat transfer from the fins of a heat sink, and that’s why heat sinks work better with vertical fins vs. horizontal.
A warm heat sink certainly looses heat via radiation, but that is very minimal compared to the heat transfer described above.

Frank is right, upside-down heat sinks don’t make sense, because you want the best air flow possible, and with no fan the only force is that of rising warm air.

73, Karl

  Maybe the idea was having an easy way to mount the, at extra cost of course,  'optional' fan after the naive user overheated the rig when running AM into a high SWR.

Bill, KB3DKS in 1 Land

I don't see how cost is an issue

Mebbe twas the only way it'd fit into the chassis?  ::)

I have noticed in the past that some very good electrical engineers don't know a lot about the mechanical side of the house...  though they may think differently.

Or its just, build-it-fast, build-it-cheap, sell-a-lot, then go-out-of-business-business plan  :P

How could it not fit in a chassis if everything is flipped fins up.
Actually vertical fins gives the best heat transfer. Fins up is second best for moving heat. Fins up does tend to make all the components the same temperature so good when you have a number of devices in parallel. Trapped air flow hurts efficiency.  I guess during space travel it doesn't matter.

Perhaps this is when hot air doesn't rise and convectively remove heat!

Sure, but the fins themselves are still vertical. They're just on the bottom of the unit instead of the back.

The convective airflow that a heatsink needs still happens. It's not as effective as vertical fins protruding from the rear of the unit, but it still happens. The heat sink doesn't stop being a heat sink just because it's on the bottom of the unit. If it's sufficiently overbuilt, it shouldn't be a problem.

In fact, you've got far more surface area on the bottom of any radio than you have on the back, unless the fins on the back are themselves the same length as the chassis (certain Motorola radios come to mind). Surface area is the key to heat transfer, that's the whole idea behind having the fins.

So now I wonder what the surface area comparison would be between the heatsink they're using (a pic or link would sure come in handy right about now) and a heatsink mounted on the rear of the unit? How large would a rear-mounted heatsink have to be to have the same surface area as the heatsink they're using?

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!"  ;)

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.

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.

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.     

You mean "hot air wants to rise".

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

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.

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.

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.

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?

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.
 

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

Rob W1AEX

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. ;D

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.

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,  ;D

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) ???

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.

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?

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.

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


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