I need to get final power consumption values for HF or CT but Fluorinert has a critical heat flux of ~20W/cm2.  Originally it looked like HF was going to use an integrated heat spreader like KNC does but they have gone w/ "naked" dies so some sort of heat sink will be needed.   It remains to be seen if CT will use an integrated heat spreader and if the heat flux will be below the critical heat flux of fluorinert.

KNC package size and integrated heat spreader may be large enough to avoid needing a heatsink.  Still given the cost of the immersion fluid I believe HF and CT are the best choices at this point.  Still the heatsinks don't need to be particularly large.  Lets assume HF uses 250W per chip (4 dies).  Even a flat plate heat spreader would only need a surface area of 250/20 = 12.5 cm2 to keep the heat flux below the CHF.  Obviously we would want a margin of safety, so lets say 25 cm2.  That is ~5cm x 5cm flat surface and would be less for a "3D" heatsink as it increases the surface area beyond the linear dimensions.  The nice thing about HF design (the company itself is pretty scammy but they have some nicely designed hardware) is there is a large open space around the die and it uses standard Intel CPU cooler mounting holes so finding a low profile heat sink which lowers the heat flux shouldn't be difficult.  I have looked at a couple low profile server heatsinks which should do the trick but am hoping to find a cheaper solution.