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<blockquote data-quote="Tony Stewart" data-source="post: 955536" data-attributes="member: 135953"><p>Surface finish of heatsinks need to get like that of HDD platters for optimal low Rth. This is not easy, that means coplanarity error and surface roughness. Of course any hard specks of solids in the paste will ruin the Rth. Ideally the silver grease needs to only fill the gap. Smaller gaps mean better Rth.</p><p> </p><p>Typical is 20'C rise per 50 Watts for core to heatsink interface</p><p>or Rth = 0.4'C/W, ( of heatsink compund interface )</p><p>Better is 10'C per 75W</p><p>or Rth= 0.13'C/W</p><p>and awesome is Rth< 0.05'C/W.</p><p> </p><p>This gives you the headroom to OC and OV the system and not get too hot and makes passive cooling possible but not easy.</p><p>OC= overclock, OV = overvoltage to switch CMOS faster. OC is not recommended unless you know how test for margin. No margin means ....{ random BSOD or random shutdown or freezes or CPU runs >60C if CPU > 70'C fix it..) If CPU runs @ 40'C all the time, you are lucky or good. ( keep in mind heat reduction methods are used in mobile CPU's when near idle e.g underclock FSB to get CPU/2 etc and undervoltage -10, -15%)</p><p> </p><p>The grease thermal resistance degrades the performance of most heatsinks due to these factors, ( excess thickness, poor grade, excess coplanarity & surface roughness and debris on surface. Since most people cannot measure the heatsink temperature accurately or the grease thermal resistance a rule of thumb, is, if there is a no fan and the heatsink feels just warm while the Speedfan or everest.exe or equiv reports the CPU is burning hot ( > 60'C) then your grease, surface mating job is poor. Lapping a heatsink is not recommended unless you are a skill machinist, but is recommded if you are better than the OEM who mass produced the heatsink.</p><p> </p><p>A thick low RPM fan will move the air velocity enough to optimize the heat sink resistance Rth, high RPM fans just generate more noise with high eddy current noise. Then construct a plenum to remove the heat directly out of the case rather than circulate the warm air which just raises the internal amibient temp and then the CPU adds to that...</p><p> </p><p>In the end. for a 23'C room temp, Mobo temp ought to be < 10'C rise and CPU < 10'C rise above mobo or 43'C If MOBO is too high you are not removing the heat directly from the CPU. Make it a plenum like most GFX cards using any thermal insulating materials you can find. ( plastic etc)</p><p> </p><p>Just my two cents worth.. but the copper pipe system ought to perform well, but not as well as liquid heat exchangers with moving air..</p><p> </p><p><strong>You can use the same heatsinks for 10W~100W LED arrays using similar principles.</strong></p></blockquote><p></p>
[QUOTE="Tony Stewart, post: 955536, member: 135953"] Surface finish of heatsinks need to get like that of HDD platters for optimal low Rth. This is not easy, that means coplanarity error and surface roughness. Of course any hard specks of solids in the paste will ruin the Rth. Ideally the silver grease needs to only fill the gap. Smaller gaps mean better Rth. Typical is 20'C rise per 50 Watts for core to heatsink interface or Rth = 0.4'C/W, ( of heatsink compund interface ) Better is 10'C per 75W or Rth= 0.13'C/W and awesome is Rth< 0.05'C/W. This gives you the headroom to OC and OV the system and not get too hot and makes passive cooling possible but not easy. OC= overclock, OV = overvoltage to switch CMOS faster. OC is not recommended unless you know how test for margin. No margin means ....{ random BSOD or random shutdown or freezes or CPU runs >60C if CPU > 70'C fix it..) If CPU runs @ 40'C all the time, you are lucky or good. ( keep in mind heat reduction methods are used in mobile CPU's when near idle e.g underclock FSB to get CPU/2 etc and undervoltage -10, -15%) The grease thermal resistance degrades the performance of most heatsinks due to these factors, ( excess thickness, poor grade, excess coplanarity & surface roughness and debris on surface. Since most people cannot measure the heatsink temperature accurately or the grease thermal resistance a rule of thumb, is, if there is a no fan and the heatsink feels just warm while the Speedfan or everest.exe or equiv reports the CPU is burning hot ( > 60'C) then your grease, surface mating job is poor. Lapping a heatsink is not recommended unless you are a skill machinist, but is recommded if you are better than the OEM who mass produced the heatsink. A thick low RPM fan will move the air velocity enough to optimize the heat sink resistance Rth, high RPM fans just generate more noise with high eddy current noise. Then construct a plenum to remove the heat directly out of the case rather than circulate the warm air which just raises the internal amibient temp and then the CPU adds to that... In the end. for a 23'C room temp, Mobo temp ought to be < 10'C rise and CPU < 10'C rise above mobo or 43'C If MOBO is too high you are not removing the heat directly from the CPU. Make it a plenum like most GFX cards using any thermal insulating materials you can find. ( plastic etc) Just my two cents worth.. but the copper pipe system ought to perform well, but not as well as liquid heat exchangers with moving air.. [B]You can use the same heatsinks for 10W~100W LED arrays using similar principles.[/B] [/QUOTE]
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