I'm confused about the entire copper vs aluminum debate. I hear that copper is superior to aluminum when it comes to drawing heat away from the transistor, but not as good as aluminum at getting rid of it. How is this possible?
Thermal Conductivity
@ 0 - 100°C
Al 237 W m-1 K-1
Cu 401 W m-1 K-1
Specific Heat @ 25°C
Al 900 J K-1 kg-1
Cu 385 J K-1 kg-1
From what I see, copper conducts better but it can't hold as much heat as aluminum. Regardless of capacity, wouldn't you care more about conductivict of heat?
Thermal Conductivity
@ 0 - 100°C
Al 237 W m-1 K-1
Cu 401 W m-1 K-1
Specific Heat @ 25°C
Al 900 J K-1 kg-1
Cu 385 J K-1 kg-1
From what I see, copper conducts better but it can't hold as much heat as aluminum. Regardless of capacity, wouldn't you care more about conductivict of heat?
True, aluminum would slow temperature rise but would also hold the temperature longer after the source of heat is removed.
Aluminum is popular because it is cheap and easily extruded.
When I can afford it, and can chose between the two , copper is what I use. For CPU cooling systems, copper is available, for power audio aluminum is very available.
Aluminum is popular because it is cheap and easily extruded.
When I can afford it, and can chose between the two , copper is what I use. For CPU cooling systems, copper is available, for power audio aluminum is very available.
The ability to radiate heat away into an environment
is a function of the shape and size, the thermal conductivity
of the material, and the color of the surface. All other things
being equal, superior thermal conductivity = 'better ability to
get rid of it".
is a function of the shape and size, the thermal conductivity
of the material, and the color of the surface. All other things
being equal, superior thermal conductivity = 'better ability to
get rid of it".
So would it be a good idea to get a very thin sheet of copper from www.onlinemetals.com, corrugate it and mount transistors to it?
For heatsink types and information try
http://www.wakefield.com/
or
http://www.aavid.com/
There are lots of technical papers listed at:
http://www.aavidthermalloy.com/technical/index.shtml
and probably a few at wakefield as well.
http://www.wakefield.com/
or
http://www.aavid.com/
There are lots of technical papers listed at:
http://www.aavidthermalloy.com/technical/index.shtml
and probably a few at wakefield as well.
Not necessarily. Thin sheet has surface area, but not much conductivity, probably less SA than you'd want given the cond.
The best solution would be to take a slab of copper (or silver, for that extra-cool reduction in microphonics and flattening of frequency response ...sorry), braze Cu wires to its backside, and coat those with aluminum, which is then anodized black (black is most emissive to radiation). The aluminum can probably be skipped altogether if a fan is used.
Me, I'd just cut up some styrofoam, glue it together in the shape of a heatsink, bury it in sand, and pour aluminum all over it! 😉
Tim (been doing a lot of lost-foam casting lately 🙂 🙂 )
The best solution would be to take a slab of copper (or silver, for that extra-cool reduction in microphonics and flattening of frequency response ...sorry), braze Cu wires to its backside, and coat those with aluminum, which is then anodized black (black is most emissive to radiation). The aluminum can probably be skipped altogether if a fan is used.
Me, I'd just cut up some styrofoam, glue it together in the shape of a heatsink, bury it in sand, and pour aluminum all over it! 😉
Tim (been doing a lot of lost-foam casting lately 🙂 🙂 )
So you mean that the last few fins are too far away from the transistor to pull much heat away from it? A corrugated design would be easiest, but wouldn't a thinner metal do a better job since it's surface area to mass ratio is a lot bigger?
Thermal resistance in C/W means that for every watt of power dissipated by the device, it and the heatsink get "C" degrees hotter right?
Hi Solid,
Although Nelson answered your original question, I thought I’d provide a link to some threads that “debated” around this topic. You can see some more viewpoints on the subject.
http://www.diyaudio.com/forums/sear...d=153769&sortby=lastpost&sortorder=descending
Rodd Yamashita
Although Nelson answered your original question, I thought I’d provide a link to some threads that “debated” around this topic. You can see some more viewpoints on the subject.
http://www.diyaudio.com/forums/sear...d=153769&sortby=lastpost&sortorder=descending
Rodd Yamashita
Thanks for the link. On another note, what was it I saw in that thread about heatsinks making noise?!? One guy said he clapped and the fins rang! Someone else said even while driving a dummy load, the heatsink made a ringing noise. How is this possible?
It's very possible that hand clapping or the hum (vibration) from the power supply excited a resonance in the thin fins of the heatsink. If you plan to use this type of thin heatsink, you should also start thinking about how you're going to deal with this issues should it arise.Solid Snake said:
Rodd Yamashita
Emissivity
If you care to read the other links, note the stuff about emissivity which is yet anothe factor to take into account in addition to colour and surface area. Aluminium has higher emissivity than Cu.
Also consider the weight. Cu is very heavy compared to Alu, and it cannot be anodized.
Petter
If you care to read the other links, note the stuff about emissivity which is yet anothe factor to take into account in addition to colour and surface area. Aluminium has higher emissivity than Cu.
Also consider the weight. Cu is very heavy compared to Alu, and it cannot be anodized.
Petter
Emissivity is nice, but at 50 deg c, radiant heat is a small component compaired to convection heat. after spending money to anodize my sinks, I found that color isn't that big of a factor in dissapation at the temps we need for semiconductors. Well, it wasn't wasted; it looks cool.
Copper would be better because the fins could be skinny-er and carry the same heat away.
Copper would be better because the fins could be skinny-er and carry the same heat away.
Solid Snake said:
No, not necessarily. Thinner copper (or anything else) will have a lower conductance (as opposed to conductivity). If the sheet has a small cross-sectional area, you'll inhibit the ability of heat to flow. You play off volume to surface versus bulk thermal resistance in a heat sink design. Normally, engineers at places like Wakefield do a pretty good job of maximizing dissipation for a given volume of heat sink.
The best of all, of course, would be a heat sink with air (or other cooling fluid) flowing over it. And make the heat sink out of diamond.
Hi,
Al bare metals have nearly no thermal radiation. This has to do with the free electrons at the surface. For this phenomenon look for a good textbook about the physics of thermal radiation. For improved radiation you need to coat the surface with a non-conductive layer, whether the material is copper or aluminium. The colour is not that important. A white surface radiates nearly as much heat as a black surface. Although black does slightly more. With regard to this aluminium is easier because it can be anodised black cheap and easy. But the bulk of the heat is transferred to the air by convection. You can see this also in the graphs of thermal resistance of the manufacturer. Making the heat sink higher than app. 15cm to 20 cm does not lower the thermal resistance much.
About the lower specific heat of copper take into account that the specific mass of copper is much higher than that of aluminium.
What counts is the total thermal resistance of the heat sink. This depends mainly on the surface area and the layout. There is not much difference between copper and aluminium with regard to this. Thermal conductivity of both is more than high enough compared to the thermal conductivity of the mica or silicon rubber isolation sheet usually used.
The advantage of copper can be that it is softer and as such it will resonate less mechanically. But is this a real advantage? I doubt.
Regarding to the above, aluminium is good enough for cooling audio amps. At least for me 😉
Al bare metals have nearly no thermal radiation. This has to do with the free electrons at the surface. For this phenomenon look for a good textbook about the physics of thermal radiation. For improved radiation you need to coat the surface with a non-conductive layer, whether the material is copper or aluminium. The colour is not that important. A white surface radiates nearly as much heat as a black surface. Although black does slightly more. With regard to this aluminium is easier because it can be anodised black cheap and easy. But the bulk of the heat is transferred to the air by convection. You can see this also in the graphs of thermal resistance of the manufacturer. Making the heat sink higher than app. 15cm to 20 cm does not lower the thermal resistance much.
About the lower specific heat of copper take into account that the specific mass of copper is much higher than that of aluminium.
What counts is the total thermal resistance of the heat sink. This depends mainly on the surface area and the layout. There is not much difference between copper and aluminium with regard to this. Thermal conductivity of both is more than high enough compared to the thermal conductivity of the mica or silicon rubber isolation sheet usually used.
The advantage of copper can be that it is softer and as such it will resonate less mechanically. But is this a real advantage? I doubt.
Regarding to the above, aluminium is good enough for cooling audio amps. At least for me 😉
OK let's get real nitty gritty ...
This is slightlu off topic, but if you look at the magnetic properties of these materials, Alu is diamagnetic -- the least worrysome magnetic effect out of the three known types of magnetism, whereas Cu is not magnetic at all. Some report that Cu enclosures sound better than Alu ones, and magnetic properties may be part in this equation if it is indeed correct 🙂
Petter
This is slightlu off topic, but if you look at the magnetic properties of these materials, Alu is diamagnetic -- the least worrysome magnetic effect out of the three known types of magnetism, whereas Cu is not magnetic at all. Some report that Cu enclosures sound better than Alu ones, and magnetic properties may be part in this equation if it is indeed correct 🙂
Petter
Peter Daniel said:
Well, aluminum (6061-T6) is a bit harder than copper (UNS C11000). Aluminum is far less dense however. Both will readily resonate, just that copper will resonate at a lower frequency, which arguably would be worse seeing as the lower the frequency the more difficult it is to damp any resonances.
But realistically, they'd both resonate at a high enough frequency that it wouldn't be terribly difficult to effectively damp either.
se
Steve Eddy said:
That is strange indeed. I have to replace my drill bits and saw blades much more often when I work with a copper.😉
Petter said:
Copper is also diamagnetic.
But even the most diamagnetic material, bismuth, is so weakly diamagnetic that the far far far weaker diamagnetic properties of aluminum and copper are for all intents and purposes, non-existent, which is why they're considered paramagnetic materials.
se
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