[Amps] PowerGenius XL - Others

[John Lyles]

I've been using water cooled pulsed RF amplifiers since 1995 at work. 
The first uses were DMOS MRF151G variants running @28 VDC. In the last 3 
years we have moved those out and gone to 48 volt LDMOS, far less 
devices to get 5500 watts peak at 200 MHz.

> I know water-cooling has been discussed here before, but I agree that a
> well designed water-cooled SSPA has the potential to gain some traction in
> the amateur market if the $ make sense. That said, I think it is
> unrealistic to expect one of our ham radio manufacturers to offer an
> "inexpensive" water-cooled SSPA for amateur use. The added complexity and
> potential maintenance might be enough to put the water-cooling concept on
> "ice" from a ham radio manufacturing point of view.
.....
> So far, this is about the closest I have seen to getting to where the
> water-cooling needs to go (at least from another ham). I suspect in the
> ISM/radar/broadcast world, water-cooling SSPA's is fairly straightforward.
.....

In addition to solid state RF for driver stages, we use a number of 
different tubes in plain water cooled and hypovaportron cooled.
The difference is that we have already got a huge deionized water plant, 
so air cooling is generally avoided for all stages. The amplifiers are 
cleaner inside.
John K5PRO
>
> A big difference between vapor-phase and liquid-water cooling is that vapor
> cooling is much more efficient per volume unit of water passing through the
> system.   From the Dick Ehrhorn's description on cooling efficiency:
>
> "In typical closed-loop liquid-water-cooled systems, the maximum outlet
> (hot) water temp must be held well below 100 deg C to avoid hot-spot boiling
>
> on the anode surface, which can and does create steam bubbles, which in
> turn "insulate" the hot spot from the water so the hot spot gets even
> hotter. This typically creates a temperature runaway and may lead to
> destruction of tube and/or cooling components. Typical inlet (cool) water
> from the chiller may be specified as </= say, 45 deg C, and maximum outlet
> water temp as 80 deg C to avoid spot boiling.
>
> Anyway, in this example each gram of cooling water passing through the
> tube's water jacket can absorb not more than (80-45) = 35 calories of heat.
> Conversely, each gram of 45 deg C water entering a vapor-cooled tube's
> boiler absorbs approximately [540 + (100-45)] = 595 cal/gm while
> vaporizing. So, vapor cooling requires passing only about 35/595 = 1/17 as
> much water
> volume through the system as does water cooling."
>
> Paul, W9AC