Hi Vanarian
One must take these data sheet values seen from a technically theoretical point.
They are of course correct, but to achieve the values is not quite as straightforward as it may seem.
Your idea of a thermal chamber filled with oil is not a bad one at all, indeed this is done in some applications.
The problem we have though is size and weight. If the size is to be kept relatively small then a system must be made where the oil would circulate, taking the heat from the chip to a point where it can cool. Lets assume a small sump with cooling fins.because of low volume the flow would have to be reasonably fast, this means a pump of some form. Heat pipes like one knows from a PC microprocessor would not be fast enough. The junction within a MOSFET where the heat occurs is very small, this then spreads to the case, which is not very large either. At large currents the heat is very substantial and must be carried away immediately.
That all being said, I realise you do not wish to achieve the 240A continious current and a small enclosure, with cooling fins and open to ambient air flow would definitely increase the power one could draw.
Not sure if this is practical on a skateboard but for other applications, such as you mention, definitely a possibility.
Personally though I think, taking space, cost and manufacture into consideration, a heat sink with a small fan would be an easier solution to achieve similar results.
(But hey, that would be the easy way - go ahead, push boundaries, make one)
