Hi Cold traps and vac-ion pumps were very common on precision crystal seal setups 50 years ago. They have gotten better since then….
Bob > On Jun 9, 2017, at 9:13 AM, jimlux <jim...@earthlink.net> wrote: > > On 6/8/17 1:19 PM, Bob kb8tq wrote: >> Hi >> >> If you look at the thermal conductivity vs very low pressures, the >> conductivity >> comes up pretty quickly from a hard vacuum. There is essentially no impact >> on Q. >> > > basically, when the mean free path gets to be shorter than the distance to > the wall, the thermal conductivity drops off. > > MFP = 65 nm at 1013 hPa = 760 torr > > So at 10-4 Pa/0.75E-3 micron (start of very high vacuum) the MFP is 65 cm > > High vacuum usually starts around 0.1 Pa (close to 1 micron), where the MFP > is 65 mm - this is where the MFP is comparable to the size of the stuff > you're pumping down, and where you can't use a "pump", but rather you need > something that flings the air molecules toward the exit (diffusion or turbo > molecular pump) or something that is like flypaper for molecules (sorption, > cold finger, etc.) > > > If you've got a "refrigeration" vacuum pump, they pull down to about 30-40 > microns - MFP is a few millimeters > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.