Bartimaeus wrote:The screen enclosure for the liquid cooling system is almost finished, just need to mill the lexan faceplate and paint it.The top line is for the infared temperature sensor that is pointed at the outside of the motor, and the second line is for the thermistor that is inside the motor (not connected in photo). When the temperature gets above a certain level a pump gets activated and sends water inside the motor, where the heat from the motor will turn it into steam, which will escape through the side vent holes. The membrance switches on the top will eventually be for changing the settings like the emissivity coefficient used for the IR sensor and the trigger temperature for the pump. Also have some LEDS that will turn on when the pump is on, tank is empty, etc.
None of the holes I see on your motor are at the perimeter, so any water that doesn't evaporate will be stuck with no way out of the motor. Unless I just haven't seen them next time you guys have the motor open you should make at least some small holes at the extreme perimeter of the magnet backing ring.
Evaporating 1 liter of water will take over 2 million joules of heat out with it, so over a 10 minute run that's an average of over 3.7kw, which sounds about right. My only question is the temp, because 100C is pretty hot to me, not failure type hot, but a few points loss of efficiency hot.
It's a neat rig, but let's compare to air cooling with heat capacity of air of 1 joule per gram per degree C and a density of 1.29 grams per liter, a 65° delta T (ambient to stator), and again a 10 minute run. You'd have to get almost 2700 liters of air through the motor per minute for similar cooling as the water evaporation. That seems like a lot, but it's only 95 cubic feet per minute and little 120mm computer fans can move that much air with just 4 watts, so a well designed centrifugal fan approach on a 30hp several krpm outrunner motor should easily get double or triple that through the motor. Plus the benefits of cooling are 100% of the time. There's also the active fan approach like Toolman2 took. He uses an 80W leaf blower to blast air through the motor...sure a lot more noise but nice and easy and you get 300-400 cfm without being dependent upon motor rpm. He calculated his 80W blower was reducing copper losses by 1000W.
The heat capacity and latent heat of water are always attractive for cooling, but with our electrics we have neither the delta T's nor the overall heat to dissipate to make it worthwhile IMHO. Look at my near silent unoptimized approach which keeping stator temps below 85°C on a 22km ride of mixed riding, and with some changes I expect to get that in the 70's with no sensors or switches or electronics of any kind to fail. That's with a hubmotor, so much lower rpm than your mid-drive, and pushing a much heavier load too, so imagine your higher rpm motor. I prefer to keep liquids away from electronics anyway.