Yes the exact shape/size of the heatsink can be calculated, but none of you will like the math.
In Jnbsystems case; his worst case power dissipation would be 29V x 6A = 174 Watts. In the case of a VCCS used for anodizing, the worst case only occurs at maximum current (6A) and at startup, where the output voltage will be very low, and the VCCS has to absorb most of the 29 V. Fortunately this condition only exists for a matter of minutes, after some anodize forms, the required voltage goes up, taking some of the load off of the VCCS.
I noticed at MPJA a heatsink; 9206 HS, that is already drilled to mount three TO-220 packages, it costs about $5. TO-220 is the package that we will select for the MOSFETs. If you used this heatsink with a small 120 VAC fan; or even better, a small blower, moving air along the fins, you should be fine. MPJA has suitable fans and blowers.
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