I need to choose a heatsink and a fan for cooling a three phase rectifier. Let's say that the total power dissipation is 1.8kW and that the rectifier is made of three half bridge IGBT/diode modules where each switch dissipates 300W.
With Rth,jc (junction to case) for the IGBT and diode and Rth,cs (case to sink) I have calculated Rth,sa (sink to ambient) thermal resistance of a heatsink that should be used.
However, since there are six IGBT/diode modules I was wondering if I need to divide the final Rth,sa by 6. If I do this I get unreasonably (in-my-not-a-big-expert opinion) low Rth,sa of 0.015K/W and would require a heatsink of 240x120x300mm size with forced air cooling in which case the air velocity should be 20m/s.
This particular heatsink weighs 9kg and this air velocity on a Beaufort wind scale corresponds to number 9 for which the land conditions are: Twigs break off trees; generally impedes progress according to Wikipedia. So I have strong doubts about this...
Is this value of Rth unreasonable or I should stick to 0.9K/W ?