Hi The tip it and listen to it slam test is a standard way of checking out a triple point of water cell for basically the same reason (you check the vacuum. Of course since a TWP cell is thin glass and not a nice metal pipe, you *may* break the seal by testing it ....
Bob On Dec 27, 2009, at 9:33 AM, Joe Gwinn wrote: > At 12:00 PM +0000 12/27/09, [email protected] wrote: >> >> Date: Sat, 26 Dec 2009 17:04:46 -0700 >> From: Robert Darlington <[email protected]> >> Subject: Re: [time-nuts] Cheap Rubidium (heatpipe cooling for) >> To: Discussion of precise time and frequency measurement >> <[email protected]> >> >> My comments are in-line, below.... >> >> On Fri, Dec 25, 2009 at 4:38 PM, Joe Gwinn <[email protected]> wrote: >> >>> At 12:45 AM +0000 12/25/09, [email protected] wrote: >>> >>>> >>>> Date: Thu, 24 Dec 2009 17:14:38 -0700 >>>> From: Robert Darlington <[email protected]> >>>> Subject: Re: [time-nuts] Cheap Rubidium (heatpipe cooling for) >>>> To: Discussion of precise time and frequency measurement >>>> <[email protected]> >>>> >>>> >>>> On Thu, Dec 24, 2009 at 1:32 PM, Bob Camp <[email protected]> wrote: >>>> >>>> Hi >>>>> >>>>> A heat pipe might work if the fluid had a sufficiently low boiling >>>>> point. >>>>> >>>> >>>> >>>> The working fluid in a heat pipe will boil at every temperature above its >>>> melting point. >>>> >>> >>> Well, I've been thinking about this, and I used the term "heat pipe" too >>> loosely. Both the one- and two-pipe systems mentioned here have no wicks, >>> and so technically are two-phase thermosyphons, which depend on gravity to >>> circulate vapor and condensate. A true heat pipe has a wick, and will work >> > in zero gravity. >>> >>> One gets significant heat transfer by phase change so long as the vapor >>> pressure in the heat input end is high enough to generate enough vapor to >>> carry the thermal power flow, and this makes the pipe isothermal. However >>> the temperature (although constant along the pipe) varies with the thermal >>> power flow (in thermal watts) being carried. >>> >>> What I'm looking for is related but different: A device where the heat >>> transfer capacity varies sharply with temperature, so that there is a range >>> of heat transfer rates over which the input-end temperature will be >>> substantially constant. This is why I envision the fluid boiling (versus >>> evaporating), which is actually out of the operating regime of a true heat >>> pipe. >>> >> > >>>> I tend to use water because it's cheap, but have made them >> >> with 3M "engineered fluids", Fluorinert, and denatured alcohol. >> > >>> Fluorinert. I think that's what the expensive commercial CPU-cooling >>> heatpipes use. >>> >> $1000 a gallon! Or $5 a drum when you buy it at a salvage auction. > > That explains why low-end heatpipes use alcohol or acetone. > > Actually, one ought to be able to use the freon intended for automobile air > conditioners, for a whole lot less money, even new. > > >> >> I've found >>>> that ordinary solder works just fine. A trick to make these things easy >>>> to build is to use a ball valve at the top (I'm assuming there is a top and >>>> we're going with gravity return because it's simple). I've got a few that >>>> are still under vacuum for several years now in this configuration. My >>>> giant heat pipe of doom is a 10 foot stick of 1/2" copper with a ball valve >>>> at one end and an end cap at the other. There is perhaps 100ml water in >>>> there total, and no air. You can either boil the liquid until it builds up >>>> a nice head of steam, or go the easy way and pull a vacuum with a pump and >> >> just close the valve. >> > >>> I wouldn't have thought that an ordinary ball valve would be tight enough, >>> allowing the water to escape and the air enter, slowly, although I suppose >> > one can replace the water if it comes to that. >> > >> Mine have been running for a few years with no sign of needing to be pumped >> down again. They just work. >> >> > But I think people want to build this exactly once, so I followed >>> refrigeration practice. A properly made hermetically sealed refrigeration >>> system keeps its working fluid essentially forever. I suppose one can use a >>> refrigeration fill valve, say from an automobile air conditioning system, >>> but these all leak to some degree. >>> >>> Is the ball valve anything special? >> > >> Nope, just whatever was on the shelf at the local hardware store. >> Stainless ball with brass valve body. Teflon bearing surface. > > Ahh. A quarter-turn ball valve, used as a cutoff. The term "ball valve" > isn't quite precise in plumbing parlance. > > These are very good, but still they are not hermetic, and will over decades > (if not a few years) lose their working fluid. I bet that while water will > be contained, freon will diffuse right through the teflon seal of the ball > valve. So, there's the tradeoff. > > >> >> These things are incredible. If you pack snow around >>>> the end of this thing, the other end that is ten feet away gets cold almost >>>> immediately. They want to stay isothermal and the heat transfer is at the >>>> speed of sound through the working fluid. Delays are introduced because >>>> you're dealing with a thermal mass of copper pipe that needs to change >> >> temperature along with the working fluid so it's not quite instant, but >>>> still about 10,000 times faster heat transfer than copper by itself. They >>>> are certainly handy for getting heat out of confined spaces. >> >> >>> >> > What is the purpose of the heatpipe of doom? Education? >> > >> Education, fun, and then later a demonstration piece. It's fun to rapidly >> move the thing along its axis, upward and then stop. The slug of water >> moves up and then slams back down to the bottom and sounds like a steel ball >> in the pipe. It makes a satisfying clang sound. A couple of years back >> when I did a demo, people were convinced I had a metal part in there that >> was loose. I opened the valve and out came a 100ml water and nothing >> else. Too cool, and you can make them at home for next to nothing. > > This definitely sounds like a good physics demo for school use. > > >> Before >> I started using vacuum pumps to pump them down, I'd use a blowtorch to boil >> the water and use the valve to throttle the steam coming out. Once the >> steam is coming out really fast you basically just quickly close the valve >> and remove from the heat source. That's it! For smaller diameter pipes I >> use other methods and other working fluids because heating tends to just >> eject the sometimes very expensive fluid. > > What sizes, what fluids, what purposes? > > > Joe > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
