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100 C is only 212 degrees F; I would think the valve filled with sodium would have excellent thermal properties due to convection heat transfer via the sodium. Not sure what the vibration would do to the convection patterns though, I guess that is why I am an electronic tech instead of a fluid dynamics engineer! Stephen J. Jackson Commissioning Engineer, Petron Industries, Inc. SJackson@petronworld.com -----Original Message----- From: Jim Adney [mailto:jadney@vwtype3.org] Sent: Wednesday, November 16, 2005 8:40 AM To: type3@vwtype3.org Subject: Re: [T3] Stretching valve stems? On 16 Nov 2005 at 0:37, Dave Hall wrote: > > The sodium valves are mostly empty, with just a bit of solid sodium in them. > At > > operating temps, the sodium boils and carries heat very effectively to the top > > (stem end) of the valve, where it condenses. It then runs back down to the > head > > end by gravity and the shaking of the valve. > > Ah, ISTR doing some calculations on such heat pipes with water inside, to > calculate the thermal 'conductivity' of the system. Can't remember if it worked > out better than solid or not, though. Steam transfers a lot of heat, so I guess > it's probably better. If the liquid can return quickly to the heat source, it's an incredibly effective technique. As you know, it's all in the heat of vaporization, which is huge compared to other heat transfer methods. Okay, I just looked up sodium's melting and boiling points, which turn out to be about 100 and 900 C, respectively. The melting point looks to me like it might be too high to be useful here, but I really don't know what temp a valve head sees. I'll ask around here and see what kind of opinions I come up with. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~