RML;
I work in a small shop which uses extensive RF Induction Heating in the manufacture of product. We have about 75kW of total RF available in a about a dozen distributed systems which range from 2-5kW output, 10-500kHz. Since the end of life for one of these units is generally catastrophic, we use very cheap Chinese imports which are really intended for low duty cycle brazing and welding operations. We run them flat out in 6 hour long continuous runs, 18 hours a day, and because of this, we generally have to beef up the cooling before they go into service.
Solid State RF Induction Heating units share many of the problems a transmitter or linear have, and many components need to be cooled including tuning caps, large ferrite load transformers, work coils, and power supply. The real killer is keeping the switching transistors cool. Most of these units come with very flimsy liquid cooled heat sinks, and I have been replacing them with this:
http://www.mcmaster.com/#catalog/119/535/=nw4vigThis is a simple off-the-shelf solution for liquid cooling solid state components. It's McM so it is overpriced, but I have no doubt that similar units can be found online for cheaper, or you could DIY for cheaper still.
It's pretty easy to liquid cool anything; the problem and expense come from getting rid of the waste heat. We use a number of methods at work:
1) Water to air (pump, radiator, fan)
2) Water to water (pump, heat exchanger, process chiller)
3) Pump 'n Dump (city water through the units then down the drain) in emergencies
Water to air is the easiest for portable operation, and would likely work if you carefully shop components (the costs can mount quickly) or if you have a shotgun full of nickels you can shoot at the problem. It all depends on the device temperature you need to maintain at anticipated power output and the ambient temperature.
A couple of years ago I was looking at using Peltier devices for cooling parts of the product that were getting too hot in the RF field. (I have since dropped that ball.) They have come a long way, and I was impressed by the Qmax figures (max heat transfer for the device) for some of these guys; up to 120 Watts in a small package. Maybe an alternative?