Quote:
Originally posted by Graystar
1)I'm sorry, but I just can't figure out what those charts are showing me. I don't know what "30x10x1.1mm" means.
2) The calculation for Convection Coefficient considers area only. 3)What's that third dimension? Is that the channel height? Is that implying that my channel should be taller?
4)Also, as Convection Coefficient is a property of the boundary, it is unaffected by base thickness, and can be considered a constant when trying to calculate the effects of base thickness. Therefore, I am confused by its appearance in the charts.
5)Finally, there is absolutely no explanation whatsoever as to how the C/W is calculated. "C/W" is Thermal Resistance. The thermal resistance through a solid increases with the length of the solid. That is a fundamental. In the matter at hand, base thickness is the length. For any given area, it is impossible for a solid with a longer length to have a lower thermal resistance than a solid with a shorter length. So I simply don't understand what that first chart is demonstrating.
6)I also have no idea what the second chart is showing, or why it's there.
Les, can you explain the charts and how you arrived at these numbers?
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1) "30x10x1.1mm" is a reference to the water chamber dimensions(lenght x width x height) of your wb.
2) The Convection Coefficient is calculated by Kryotherm*. Kryotherm uses the Sieder-Tate relationship. Have calculated at various flow rates for two Channel sizes(10x1.1mm and 40x0.8mm).It is plotted against flow-rate(LPM)
3) Third dimension ( "1.1mm and 0.8mm"?) is channel height. Not syuggestions on channel height made. Used 0.8mm for larger bp area(ed) wb since had calculations to hand.
4) Only plotted Convection Coefficient against flow-rate.
5) C/W(for 10x10mm heat-die) is calculated by equating the Thermal Conductance at the bp/water interface with the Film Coefficient in a Waterloo Spreading Resistance calculator** . The Thermal Conductance through the bp/water interface(Edit****) is taken as the reciprical of dimensionally corrected "Kryotherm K/W" for a 0.1mm bp. The "Total Resistance" from Waterloo is added to an estimate(0.1C/W)*** of the TIM Thermal Resistance to give a C/W value.
6) The second chart shows the predicted Pressure Drop(dP Total)) v Flow-rate (LPM) for the two considered wbs and th P/Q curves for three pumps. The intercepts of the pump and wb curves gives the predicted flow-rates - from which graph1 gives the predicted C/W for the different different pumps.
*
http://www.kryotherm.ru/soft.htm
**
http://www.mhtl.uwaterloo.ca/old/onl...ce/strip2.html
*** From Billa [url}
http://www.overclockers.com/articles654/index02.asp[/url] making an allowance of 0.05 C/W for die RTD offset.
**** EDIT: "through the bp/water interface" did read "of the wb".