What might be even more interesting is mineral oil immersion cooling. You would still need a heatsink to conduct heat away from the PA device(s) but the advantage to oil immersion cooling is that it can also efficiently cool all the other parts such as Low pass filter coils, Voltage regulators, power supply etc.
It's becoming a thing in High performance computing for servers http://www.datacenterknowledge.com/archives/2012/09/04/intel-explores-mineral-oil-cooling/ I guess one of the questions at RF is how much the dielectric constant of the oil will change things and if it's enough that it needs to be taken into account at the design phase. For our application the thermal mass of the oil combined with our duty cycles would also help keep the radiator requirements reasonable I love the idea of having a silent High power Amplifier. On Tue, 2014-12-16 at 12:06 -0700, Doug Person via Elecraft wrote: > This is really a fascinating idea. I have noticed that there are water > cooling kits made for computer CPU's. Some of the bigger CPU's run over > 225 watts of power. I wonder how applicable one those CPU kits might > be. They include a heat sink, pump and radiator. > 73, Doug -- K0DXV > > On 12/16/2014 11:10 AM, David Cutter wrote: > > Hi Dick > > > > Start from the LDMOS data sheet and work out the temperature you wish > > to keep within at the junction. Because water cooling is so good, you > > can choose either to run the device cooler than you would with air > > cooling to improve reliability, or stick to the same temperature and > > get more power / use a smaller cooling plate / use less water. There's > > a direct relationship between reliability and temperature, but it's > > not linear. Then use the temperature rise per W rating of the device > > to get to the surface temperature. > > > > In work I did >10 years ago all devices were directly bolted to the > > liquid-cooled plate without an intermediate spreader, however, these > > LDMOS devices are so small (ie very high heat density) there is a good > > reason to spread the heat out first before cooling proper takes place, > > I'm somewhat hazy what thickness, but you must achieve good flatness > > of contact against the plate. Some very large devices eg IGBTs and > > rectifiers the size of your open hand are supplied curved and the > > bolting-down process achieves the flatness with the correct torque > > setting on the bolts. > > Then you do the same sums as you do with air cooling ie temperature > > rise v watts dissipated from the heat sink data. > > > > Say you want to dissipate 1kW of heat continuously (eg in a data > > contest) then a small 2 pass model would give you around 90 to 100K > > rise at the surface of the plate with 1 US gallon per minute, whereas > > a 4 pass model would give you around 20K rise on a 152mm length plate. > > This of course assumes that the heat is being delivered into the plate > > evenly over the whole surface, ie using a spreader. Heat sink paste > > adds a little to the thermal gradient and is needed in very small > > amounts, evenly spread. > > > > Do the sums several times with different criteria until you get to the > > one you feel comfortable with. If you live in a cold climate you can > > dump the heat into a small central heating radiator to keep the shack > > warm and no fans required just an aquarian pump to run it; if you live > > in a hot place, then put the radiator on the shade side of the house > > or even bury it. If water is abundant, eg river water or a pond, you > > can re-cycle it back to the source. > > > > You can make your own water cooling plate, see here a small example > > cooling a dozen TO-220 devices: > > https://www.youtube.com/watch?v=WGpau-raMho > > Somebody here will check my sums I'm sure. > > 73 > > David > > G3UNA > > > > ----- Original Message ----- From: "Richard Solomon" > > <w1...@earthlink.net> > > To: <elecraft@mailman.qth.net> > > Sent: Tuesday, December 16, 2014 4:44 PM > > Subject: Re: [Elecraft] LDMOS for QRO [OT] > > > > > >> If one wanted to use one of these to cool an LDMOS VHF KW, where would > >> one find the design info to calculate which cold plate would provide > >> sufficient > >> cooling ? > >> > >> I envision a stack something like this: > >> > >> LDMOS PC Board > >> Copper Heatsink (thickness need be determined) > >> Cold Plate > >> Aluminum Heat Sink (is this really necessary ?). > >> > >> 73 es HH, Dick, W1KSZ > >> > >> > >> On 12/14/2014 4:32 PM, David Cutter wrote: > >>> I'm a little surprised that folks in this group haven't suggested > >>> liquid cooling for this modest application. Semiconductor cold > >>> plates have been around for a long time, are economical to use and > >>> in my view a much better solution than forced air cooling. They are > >>> compact, quiet, require far less cabinet space, keep junctions > >>> cooler and more stable than air could ever and enable higher > >>> reliability. > >>> > >>> Look at Aavid for instance, whose devices I used on many occasions: > >>> http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf > >>> > >>> > >>> > >>> If you play your cards right, you can cool the amplifier and the > >>> power supply on a short 4-pass plate. Put the heat somewhere > >>> convenient, not in your shack. > >>> > >>> 73 > >>> > >>> David > >>> G3UNA > >>> > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:Elecraft@mailman.qth.net > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to k0...@aol.com > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to ei6iz.bren...@gmail.com -- 73 Brendan EI6IZ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
