A summary concerning LHe purity:
Although a couple of us have heard of using ultra high purity bottled
gas, It was pointed out by several people that the impurities in the
LHe are likely frozen and will probably remain on the bottom of the
dewar during a fill especially if the LHe transfer line doesn't get
close to the bottom of the tank (ca. no less than 1 cm).
Steve Sieber at Texas A&M wrote:
"Purity grades for LHe...[might] refer to the gas purity that was
liquified. Normally,
impurities in the inlet gas to a liquifier are cleaned and trapped
before liquification is complete. Too much impurity causes icing
and plugs in the liquifier. It may be more expensive to start
with 99.999% gas, but I doubt that the result is any better (marketing
hype?)."
He also did a "back-of the envelope" calculation for me:
"Assuming 10L/month as a 'normal' boil off, you are looking at
adding 120L/year, or 1200L per decade to the magnet. 0.005% of
1200L is .06L of impurity you are adding over 10 years, versus
.012L with the 99.999%. I can't believe that this is meaningful."
A few ammrls wrote to say that they are purchasing LHe at about
$4-$5.50 per liter (cheaper may be the result up bulk shipments.
Thanks for all the replys,
Brian
--
Brian Myers, Ph.D.
Assistant Professor
Department of Chemistry and Biochemistry
Meyer Hall of Science (rm 258)
Ohio Northern University
525 South Main Street
Ada, OH 45810
419-772-2350 (voice)
419-772-2985 (fax)
b-myers_at_onu.edu
http://www2.onu.edu/~b-myers/
Received on Fri Nov 05 2004 - 14:51:22 MST