Sounds neat! Glad it is working well. I assume you slipped a decimal point on your temperatures though, -1950C would be well below absolute zero! If the wobble at room temperature is too great you might try a spring loaded bushing. Do you have a good reference for materials for cryogenic use? I, a EE sonar and firmware guy, have recently been tasked with designing a LN2 recirculation system for another part of the company testing cryogenic gear. I am fumbling with where to start, other than getting my boss a new psychiatrist. Sherpa Doug > -----Original Message----- > From: Lawrence Lile [mailto:llile@TOASTMASTER.COM] > Sent: Monday, October 01, 2001 10:21 AM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [OT]: Coefficient of Thermal Expansion > > > Well, I started this mess ... ah.. thread. Here's the results: Last > Saturday we sis a shakedown cruise of our cryogenic > processor. As you may > recall, I have some fans on Stainless Steel shafts, with the > motors outside > the 'fridge, the fan blades inside the 'fridge, and HDPE > bearing blocks. > The fans would run until the system reached about -600C, then > the fans would > run slow, stop, motors overheat, and so on. So the problem > is to find the > coeefficients of expansion of Stainless and HDPE, and compute > the cleaqrance > required so the bearings will not sieze at -1950C. > > I settled on 1/16" clearance at room temperature, and this > squeezes down to > a few tens of thousanths at cryogenic temperatures. Fans > kind of wobble at > room temperatures, but behave nicely once the bearings > squeeze down. No > observable leakage of LN past the bearing blocks, for some reason. > > We ran the system all the way down, without having any fans > sieze up. It > was (pun intended) pretty cool. Also got to goof around with > a bucket of > Liquid Nitrogen. When I got done testing the calibration of > my sensors in > it, and then testing the brittleness of several plastics in > it (I was plased > to find Nylon 66 was quite flexible at -1950C - this was not > what I had read > in books.) > > We also discovered that immersing a can of root beer (opened, > to let off any > pressure) will result in a pleasing root beer float, almost > instantly. The > carbonated beverage also foams up, the foam spilling out of > the can, which > makes a kind of instant ice cream when it hits the LN. Quite > tasty, once it > warmed up to freezing. Don't try this at home. Dumping a > cup of LN into a > bucket of water freezes the water 2" thick in a minute. We were using > distilled water/ice slush as a calibration standard, so we > happily had to do > this a couple of times to make more ice. > > All quite a lot of fun. They pay us to do this kind of stuff? > > --Lawrence Lile > > > ----- Original Message ----- > From: "Sean H. Breheny" > To: > Sent: Friday, September 28, 2001 3:13 PM > Subject: Re: [OT]: Coefficient of Thermal Expansion > > > > Hi again Michael, > > > > Unfortunately, I haven't been following this thread. Did > the original > > poster want to know how to compute area expansion from > linear expansion, > or > > did they want to know what the relationship between the > defined linear and > > area coefficients of expansion? I had guessed (perhaps > incorrectly) that > it > > was the former that they wanted. In other words, they had a > practical > > application where they knew alpha for a material and wanted > to know how > > much it would expand in area. (I admit, though, that in > most circumstances > > this is splitting hairs since the alpha^2 term would be so small). > > > > Sean > > > > At 01:00 PM 9/28/01 -0700, you wrote: > > By definition, all the coefficients of thermal expansion > (whether for > > >length, area, or volume) are for linear changes. Same idea as > > >resistance, where the definition is V = I R, whether or not the > > >potential actually varies linearly with the current; in cases where > > >the variation *is* (to a good enough approximation) linear, R is a > > >constant and is called the resistance. The derivation I gave is > > >correct, because the coefficients are *defined* for the > linear regime > > >(in which change in size is proportional to change in temperature). > > >In that regime, the coefficient of area expansion is > exactly 2 times > > >the coefficient of length expansion. > > > > > >Nonlinear effects can also be treated, of course, to as high an > > >order as you need to go to get the precision that you need. > > > > > >Michael > > > > > >Thank you for reading my little posting. > > > > > > > > >_________________________________________________________________ > > >Get your FREE download of MSN Explorer at > http://explorer.msn.com/intl.asp > > > > > >-- > > >http://www.piclist.com hint: To leave the PICList > > >mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > > > > --------------------------------------------------------------- > > NetZero Platinum > > Only $9.95 per month! > > Sign up in September to win one of 30 Hawaiian Vacations for 2! > > http://my.netzero.net/s/signup?r=platinum&refcd=PT97 > > > > -- > > http://www.piclist.com hint: To leave the PICList > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.