[Amps] 20kw Dummy load?

[peter.chadwick at Zarlink.Com]

Robin was asking about water cooling resistors. The old metal film ones 
from Electrosil in the UK which were 50 watts in air were used 
professionally at 30kW. If I remember correctly (and it was 40 years ago!) 
we ran several hundred gallons per minute over them. If you got an air 
bubble that stuck to it, it went in a flash - literally! A rough 
calculation suggests that at 20kW, you need around 200gallons/minute to 
get a 50 degree C rise between water temp in and water temp out. That's 
imperial gallons, not US gallons.

You can do a lot better by vapour phase cooling, and boiling the water off 
as steam. However, you still need to be careful,. because as the water 
boils, a sheath of steam bubbles surrounds the resistor and can lead to 
the rate of heat conduction falling, leading to a rise in temperature and 
a run away condition. See Nagaiyoka (spelling??) curves. If that happens 
with straight water cooling, because of too low a water flow, again, in a 
flash - pfft!

Hope this helps

73

Peter SM/G3RZP