Hi i am carrying out a natural convection analysis to find out the temperatures on a pcb , the pcb has 3 transistors on it , these also have heat sinks, and the full pcb is inside an enclosure , there is no fan , so the heat dissipation is thru natural convection only, can any one tell me the heat transfer co-efficients to be used on the pcb surface and the heat sink

Rgds Naren

Doesn't fluent calculate htc for you? Otherwise, you'll have to look for some experimental correlations for htc for some configuration sililar to yours. Try Bejan's book. They are generally in terms of nusselt number, and look like this:

Nu = 0.424 Re^0.5 Pr^0.3

Hope this helps, H.

Hi i am using ansys, for which we need to input the HTC, also we only know the power dissipation of the transistor and we dont have the temperature values by experiment. some one had sugested to use a Htc valueof 50 w/m2 k on the heat shink to air..... i am looking out for the data books for checking out wether we have any ready values like these..

I am having similar issue. I am using Cosmosworks for an LED lighting application. I have not found much that fits the values these programs are looking for. Most references suggest between 5-25 W/(m-sqrd *K). Avvid Thermalloy has a lot of info but it does not easily correlate into these applications. Good luck, if I find something. I will stop back here.

Thanks, i found in one of the books that a general value of 10 W/(m-sqrd *K). is a good approximation for metals... any way thanks for he info.