Thanks for the clear description, it sounds like a great solution. Is it basically relying on a centrifugal fan to draw air up from the base and expel it from the holes in the ring at the top?
With such a system, it sounds like if you needed extra cooling you could have a small mister with just a few mL of water. Water’s latent heat of evaporation is enormous-- 500 times higher than its specific heat-- so a very fine aerosol mist (like from a ultrasonic humidifier) could have a possibly decisive cooling potential. If you had the motor running at 100C and needed to cool it down urgently, 1g @25C would suck up (.001 * 4186 * 75) = 314J + (.001 * 2256000 = 2256J) = 2570J. So if the motor is 90% efficient, and you’re running a full 15kW, you have 1500J/s of waste heat. That’s a little more than half a gram per second of water cooling.
With batteries running at 10C for max power, that’s only 360 seconds of runtime. The upshot is that 180g of water would theoretically supply all cooling needs for an entire flight.
Did you get efficiency numbers beyond the ones published on the above-linked pages?