pdimage wrote: > On 14/3/09 02:32, "Wallace Adrian D'Alessio" <[email protected]> wrote: > >> Overclockers who are set on defeating heat to preserve costly CPUs yet >> squeeze >> extreme clock counts out of them have been known to polish the CPU and >> heatsink with ever finer grades of wet or dry paper starting with 1000 grit. >> And even going to finer grits of polishing compound. Some may even " lap : >> the >> surfaces together with a polishing compound. >> >> Then they apply the thermal paste after all of that. >> >> In theory the more closely the parts surfaces match and the thinner the paste >> needed to >> make up the difference the faster and therefore the more successful the heat >> transfer will be. >> > > Seems strange - the laws of physics would suggest that a coarse finish - > rather than a polished surface - would provide a much greater surface area > for a face to face contact - with the compound filling the pits in the > coarse finish...
For conductive heat transfer as in this case you ideally want perfectly flat surfaces. They wouldn't need any heat transfer compound between them as there would be no gap. But ideal and perfect are on back order so you fill the thin gap with heat transfer compound which displaces the air. Heat transfer compounds have relatively poor thermal conductivity compared to the metals they are used with. But they have much better thermal conductivity than air which they replace in the gap. This is why you want just a very thin layer. A rough surface with a larger surface area is good when using convection cooling, i.e. air or a liquid flowing over the surface. -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting "I'm a designated driver on the Information Super Highway" --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed Low End Mac's G3-5 List, a group for those using G3, G4, and G5 desktop Macs - with a particular focus on Power Macs. The list FAQ is at http://lowendmac.com/lists/g-list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/g3-5-list?hl=en Low End Mac RSS feed at feed://lowendmac.com/feed.xml -~----------~----~----~----~------~----~------~--~---
