LN use by the UC Bekeley Microlab is currently averaging 750 slpm. This
is supplied to the laboratory as gaseous N2 at 120 psi and delivered
through stainless tubing. We reduce from 120 psi to 85 psi in our laboratory.
Swagelock fittings were used for this installation; however, orbital welded
tubing would be our preference. Our storage vessel was increased from a
1500 gallon vessel to a 3000 gallon vessel in 1986.
A second, 1500 gallon, low pressure LN vessel was added in 1988 to supply
LN for two molecular beam epitaxies (MBE's). The MBE's require low pressure
LN for their Meisner traps which is delivered by vacuum jacketed piping.
Using a low pressure LN tank delivering LN at ~30 psi significantly
reduces the "flash" loss inevitable if we deliverered from our 120 psi vessel.
(As a courtesy to adjacent departments we allow 160 liter liquid pressurized
gas cylinder fills from this low pressure tank. These "lpg160" tanks operate
at 27 psi and are best filled from a low pressure tank). LN usage from
1500 gallon tank is predicated by the frequency of MBE runs.
We are currently planning an upgrade to a 9000 gallon vessel to
accommodate increased N2 demand. The use of dry mechanical pumps
and additional equipment is taxing our 3000 gallon LN supply. Our current
750 slpm N2 use rate is already based on conservation. If we ran
equipment at vendor specifications we would greatly increase N2 useage.
The price of a 6000 gallon tank may not be much less than a 9000 gallon
tank. A recent price quote for the Microlab on a 9000 gallon vessel was
$84k without install. A semiconductor research lab is a plumb for an
LN vendor. You may find your vendor will work on a better "package" price
than buying and installing your own vessel. Your vendor may also discount a
larger vessel to reduce deliveries. The major difference in the size of
a 6k vs. 9k will be the vessel height.
Sincerely,
Bob Hamilton
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| University of California at Berkeley |
| Department of Electrical Engineering and Computer Sciences |
| Bob Hamilton bob@eecs.berkeley.edu |
| Senior Development Engineer fax: 510 642-2916 |
| Microlab Manager phone: 510 642-2716 |
| EECS/ERL Microfabrication Laboratory |
| 406 Cory Hall # 1770 preference: e-mail |
| Berkeley, CA 94720-1770 |
| http://www-microlab.eecs.berkeley.edu:8080/ |
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