Re: Heat Sink Colour.
I read in !emc-pstc that Chris Maxwell chris.maxw...@nettest.com wrote (in 83d652574e7af740873674f9fc12dbaaf7e...@utexh1w2.gnnettest.com) about 'Heat Sink Colour.' on Mon, 12 May 2003: We radiate heat through our skin, not our clothes. We don't cool by radiation much, but by evaporation of perspiration. Dark skin radiates better, hence the dark coloring of people with African ancestry. The dark skin is more for protection against UV. -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Interested in professional sound reinforcement and distribution? Then go to http://www.isce.org.uk PLEASE do NOT copy news posts to me by E-MAIL! This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Heat Sink Colour, Thermal imagers etc
-Original Message- From: Wan Juang Foo [SMTP:f...@np.edu.sg] Sent: Tuesday, May 13, 2003 3:09 AM To: emc-p...@majordomo.ieee.org Subject: RE: Heat Sink Colour. (IR scanners a little O.T.) I was thinking about those far end IR scanners used to monitor travelers for 'fever'. So this may be a little O.T. A prctical 'blackbody' radiates more heat. A good reflector is a poor emitter. I just read more about it from a Physics text (Sears, Zemansky and Young). :-) Tim et al *Commercial warning*- my employer is a leading player in the SARS ( fever) imager market. The favoured technique is to monitor the temperature of the eyes. A typical thermal image of a face will show these to be the hotspots. Hence skin colour, facial hair, surface chilling etc are not an issue. Assuming no transmission then Emissivity + Reflectivity = 1 so as you said, the key to a good emitter is to think of a bad reflector. To increase Emissivity, the surface should be as black as possible -at the wavelength of interest. As others have pointed out, there is not necessarily any correlation between being optically black at visible wavelengths and being black in the infrared. In our products we use different grades of black anodized finish. The finest for cosmetic finishes is smooth and quite shiny. The coarsest grade used on internal components is sand blasted before anodizing and gives a very matt finish, almost like a blackboard (chalk board). It gives the same sensation if you run your finger nails along it! When a similar thread arose previously, there seemed to be some confusion as to how airflow affects the radiated energy. W= SB x A x (T^4 - Tamb^4) where W =power radiated in Watts, SB=Stefan Boltzmans constant 5.67E-8, A=area in m^2, T is temp of body in K, Tamb is temp of ambient in K. If I take an example of a surface of 0.0058m^2 ( approx 3inch x 3 inch) at a temperature of 95C (368K) in an ambient of 25C (298K) Then a black body surface would radiate 3.5W. It doesn't matter whether this surface is in a vacuum or a blowing hurricane. At 368K it radiates 3.5W. For black anodised aluminium assume Emissivity is 0.95, so it radiates 3.3W For oxidised aluminium, assume Emissivity is 0.35. It then radiates 1.2W For shiny unoxidised aluminium, assume Emissivity is 0.025. It then radiates 0.09W. If this surface was a simple heatsink, it might be dissipating 10W for this 70C rise above ambient. In this case 35% of the energy would be lost via radiation for a black surface. If by good design and increased conduction and forced air cooling etc, this heatsink was dissipating 1kW for the 70C rise: the surface would still be radiating 3.5W, but this would now represent only 0.35% of the total. Hence, the designer will probably decide that the additional cost of anodising etc is not worth while. (Note that the total physical surface area is not same as the effective area for radiation loss. eg for two parallel sheets of metal there are four surfaces available for heat loss via convection. For the two inner surfaces there would be no net loss of radiated energy to the environment, they would simply exchange energy with each other. Therefore complicated profiles with lots of fins etc help greatly with convection loss but make little difference to radiated loss) Also for a large high power heatsink, the radiated energy (although small as a percentage of the total dissipation) may be large enough to interfere with nearby components. In this case it would be better to have low radiation so that the energy can be taken away to the safe area and not leak to nearby components. I am not a heatsink designer, but from my experience of measuring infrared radiation, it makes sense that most small heatsinks I have seen are black while most large high power heatsinks are not. Regards Andy Wood Land Infrared division of Land Instruments International Dronfield England www.Landinst.com This e-mail and its contents may be confidential, privileged and protected by law. Access is only authorised by the intended recipient. The contents of this e-mail may not be disclosed to, or used by, anyone other than the intended recipient, or stored or copied in any medium. If you are not the intended recipient, please advise the sender immediately. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald
RE: Heat Sink Colour. (IR scanners a little O.T.)
I was thinking about those far end IR scanners used to monitor travelers for 'fever'. So this may be a little O.T. A prctical 'blackbody' radiates more heat. A good reflector is a poor emitter. I just read more about it from a Physics text (Sears, Zemansky and Young). :-) Chris Maxwell chris.maxw...@nettest.com wrote on 05/13/03 01:35 AM Dark skin radiates better, hence the dark coloring of people with African ancestry. The text did mention that the radiating charateristic of the human body ( any skin pignentation, I supppose) is a very good approximation to a 'blackbody' as far as the far-end IR for body heat is concerned. That is of course, provided that it's temperature is not so high that it became self-luminous! For what it matters, the 'Agfans' seem to favour wearing black. I suppose apart from the practical reason of not needing frequent washing ;-), I suppose these black 'clolors' radiate better under the shade and thus are 'cooler'. Since it can be so, would anybody go for black equipment housing operating in hot areas (scorching, 100°F ( high 30s°C) summerdays, or housing that are close to heat sources like car engines and water heaters)? Or for that matter using black bedsheets. I suppose it can be more than a cosmetic/fashion statement. Just my 2 ¢ worth. Tim Foo This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
RE: Heat Sink Colour.
Heatsinks always bring up disagreement; but I believe that most of the disagreements are based on availability of materials being traded off against optimum performance. Let's talk basics. For heat sinking, you need to consider conduction, radiation and convection. The heat must conduct through the heatsink. Metals have excellent thermal conduction properties; so metal is the bulk material of choice. Any coatings or paint on the metal would usually be an insulator (usually either an organic material or an oxide), so they tend to hurt performance. As for radiation, materials with black coloring abosorb and radiate faster. So black is optimum. Increasing surface area with ribs, or roughening also increases radiation. As for convection, anything that increases surface area or turbulance at the surface helps transfer heat to the air. So, rough, ribbed, wavy surfaces are ideal. Forcing an air flow over the surface with a fan also maximizes convection. Of the three heat transfer methods conduction works the fastest. So do all that you can to maximize conduction first. So, use a metal heatsink, thermal grease (or a gap pad) and smooth surfaces to mate the item that you are cooling to your heatsink. Microscopic air gaps prevent conduction and kill performance. Once you have maximized conduction, then you need to design your heatsink for maximum radiation and convection. For these purposes, you would ideally like a solid, black, metal heatsink with a rough, ribbed wavy outer surface with no coatings whatsoever. This type of heatsink is rare, if not impossible to make. For instance, there aren't many black metals; and there aren't many machining, extruding or molding processes which produce a rough surface. So, here is where the tradeoffs (and confusion) begins. Note that I'm using Aluminum as the example; but other metals may work. A cheap heatsink would be an Aluminum block. A little more money gets you some thermal grease to help transfer heat from the item to be cooled to the Aluminum block. For a little more money, you can have ribs put in your Aluminum block. A little more money gets an Aluminum form with ribs and sandblasting to roughen it. A little more money gets an Aluminum form with ribs, sandblasted roughing and black anodize. Note that the black anodize is an oxide coating, which hurts conduction at the surface a little bit; but the black color helps radiation. Black anodize also helps with cosmetics (covers up scratches); and it helps to prevent corrosion. A little more money gets you a fan to blow over your heatsink. This also costs a power penalty because the fan needs power. So, be an engineer, do some calculations, experiments or educated guesswork to figure out how much money you want to spend to get the job done. By the way, light clothes are worn in the summer to reflect the sun's heat. The light clothes are very poor at radiating our own heat away. That doesn't matter anyway. We radiate heat through our skin, not our clothes. Dark skin radiates better, hence the dark coloring of people with African ancestry. I hope that I've helped you. Chris Maxwell | Design Engineer - Optical Division email chris.maxw...@nettest.com | dir +1 315 266 5128 | fax +1 315 797 8024 NetTest | 6 Rhoads Drive, Utica, NY 13502 | USA web www.nettest.com | tel +1 315 797 4449 | This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Heat Sink Colour.
As a general rule of thumb, use polished aluminum fins (no finish) for high velocity forced air cooling (maximum thermal transfer to the airstream). Black anodized works well with more gentle airflow, and you would want a rough cast or sandblasted blackened finish when relying solely on natural convection. The rough surface increases both surface area and turbulence. scott Lacey On 9 May 2003 at 9:50, LEUNG YAT WAH DEREK wrote: Could anyone tell me about the heatsink is really in lighter colour can release heat faster ( similar to we wearing lighter clothes in summer), but why people always painted the heatsink in black or very dark colour, and the material of the coating on heatsink will affect their performance? Thanks. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Heat Sink Colour.
To efficiently radiate heat, the radiator needs to appear black at the wavelength of the radiation. For electronic devices, the wavelength of radiation is well into the infrared region. It turns out that almost any organic coating will work well. Paints are organic coatings. The color of the paint really doesn't make much difference, though you do want to avoid metalic paints. Don Borowski Schweitzer Engineering Labs Pullman, Washington hansm hans.mellb...@baclcorp.com@majordomo.ieee.org on 05/08/2003 07:31:24 PM Please respond to hansm hans.mellb...@baclcorp.com Sent by:owner-emc-p...@majordomo.ieee.org To:LEUNG YAT WAH DEREK ywle...@vtc.edu.hk, EMC- PSTC emc-p...@majordomo.ieee.org cc: Subject:Re: Heat Sink Colour. Only in static or radiant mode. Otherwise surface finish has more effect in forced or convection mode. But, in any event, black seems to be the the most radiant in black body radiation mode. There are more details than than but this is just a thumbnail synopsis. Hans Mellberg Engineering Manager BACL 230 Commercial Street Sunnyvale CA 94085 USA 408-732-9162 x38 408-732-9164 fax From: LEUNG YAT WAH DEREK ywle...@vtc.edu.hk To: EMC- PSTC emc-p...@majordomo.ieee.org Sent: Thursday, May 08, 2003 6:50 PM Subject: Heat Sink Colour. Could anyone tell me about the heatsink is really in lighter colour can release heat faster ( similar to we wearing lighter clothes in summer), but why people always painted the heatsink in black or very dark colour, and the material of the coating on heatsink will affect their performance? Thanks. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Heat Sink Colour.
Very simply, dark colors pass radiated energy. Light colors reflect radiated energy. The human body radiates very little energy but the sun contains huge amounts of radiated energy. Therefore white clothes are cooler because they reflect the sun's energy. Fred Townsend LEUNG YAT WAH DEREK wrote: Could anyone tell me about the heatsink is really in lighter colour can release heat faster ( similar to we wearing lighter clothes in summer), but why people always painted the heatsink in black or very dark colour, and the material of the coating on heatsink will affect their performance? Thanks. --- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Re: Heat Sink Colour.
Only in static or radiant mode. Otherwise surface finish has more effect in forced or convection mode. But, in any event, black seems to be the the most radiant in black body radiation mode. There are more details than than but this is just a thumbnail synopsis. Hans Mellberg Engineering Manager BACL 230 Commercial Street Sunnyvale CA 94085 USA 408-732-9162 x38 408-732-9164 fax - Original Message - From: LEUNG YAT WAH DEREK ywle...@vtc.edu.hk To: EMC- PSTC emc-p...@majordomo.ieee.org Sent: Thursday, May 08, 2003 6:50 PM Subject: Heat Sink Colour. Could anyone tell me about the heatsink is really in lighter colour can release heat faster ( similar to we wearing lighter clothes in summer), but why people always painted the heatsink in black or very dark colour, and the material of the coating on heatsink will affect their performance? Thanks. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
Heat Sink Colour.
Could anyone tell me about the heatsink is really in lighter colour can release heat faster ( similar to we wearing lighter clothes in summer), but why people always painted the heatsink in black or very dark colour, and the material of the coating on heatsink will affect their performance? Thanks. This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org Archive is being moved, we will announce when it is back on-line. All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
