I was wondering if there is any reference to calculate the C/W ratings for PI48, PI49 and PI51 heat sinks? Just for reference, I am referring to these devices:


I am not even sure if PI48, PI49 and PI51 are standard terms. Also, I think the C/W values would change for different lengths.

Thanks! Abhishek

  • \$\begingroup\$ There is no standard rating, even for similar heatsinks, because minute details can make differences in the 1% to 10% range. A manufacturer should tell you. Else you need some aerodynamic properties, surface area and emissivity of the coating to calculate for passive airflow and forced flow. For the coating and for uncoated smooth aluminium good average values can be used, no doubt, but aerodynamic properties and surface area depend on the exact shape. Given the picture and size one could make "an educate guess" towards the minimum expected, but they don't even offer a size, AFAIK. \$\endgroup\$ – Asmyldof Jul 13 '15 at 7:29
  • \$\begingroup\$ Well yes, but I was wondering if PI48, PI49 and PI51 are even "standard" heat sinks? I was hoping if typical C/W values for these heat sinks can be found in literature? \$\endgroup\$ – Abhishek Jul 13 '15 at 9:41
  • \$\begingroup\$ I don't recognise the numbers, but it's possible I have just accidentally never specced a "PI**" type heatsink in my work. What the statistical chances are of that I'm not going to calculate, but small I think. Or put differently, if they were industry standard, would they not give at least a smidgeon of info on that page? \$\endgroup\$ – Asmyldof Jul 13 '15 at 9:56
  • \$\begingroup\$ Your best bet is to go with a supplier who markets to engineers. or with the manufacturer of the heatsink. you'll then find a link to a datashhet and to engineering drawings of the heatsink. \$\endgroup\$ – Jasen Jul 13 '15 at 10:08

I think you're approaching this the wrong way. Here's one way of going about it...

  • First, decide the "thermal resistance" (in C/W) you're looking for. (Note - values are usually given for unobstructed still air. Obstruction will increase thermal resistance, airflow will reduce it)
  • Then, go to a competent supplier such as Farnell (there are others) and look at their range of heatsinks.
  • Enter minimum and maximum thermal resistance values in the search menu ... such as 5C/W and 10C/W ... 213 results found.
  • Each heatsink has its manufacturer and full data listed, including dimensions and thermal resistance, so you know what you're getting. ("Multicomp" is an own-brand where this supplier doesn't want to reveal the source, or maybe they buy from several sources).
  • If you find an exact match for your own supplier's part there, now you at least have better specifications for it, and can buy it from whichever supplier you prefer.
  • If you'd rather go direct to the manufacturer, now at least you know who they are.

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