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VBC is the world
leading manufacturer of "dynamic vacuum" LN2
piping systems supplied to the Semiconductor industry.VBC
developed the Closed Loop Delivery System for cryoshroud
cooling in MBE systems(Molecular Beam Epitaxy).The Triax/Phase
Separator system supplies instant low pressure, gas free
LN2 to cryopanels and cold traps.For applications requiring
higher rates, SEMIFLEX ® piping in sizes ranging from
1/2'~ 2' ID supplies more efficiently than any other system
available.Because of the hydrostatic head of liquid at
that point, the liquid is slightly subcooled.As the liquid
passes through the shroud and picks up heat, the density
changes and the lighter LN2 is returned to the separator
from the shroud vent via a two-conductor return line.Any
returning gas is vented to atmosphere through the separator.The
difference in the density of the LN2 between the feed
and return lines ensures continuous circulation of liquid.This
system eliminates pocket of gas, and the cryopanel is
at constant LN2 temperature and completed wetted.There
is no need to shut the system down except during bake-out.A
close-loop LN2 system provides 100% wetted surface.Outgassing
is minimized and more constant shroud temperatures maintain.LN2
consumption is drastically reduced and a continuous uninterrupted
supply became available.
Advantages of Closed-Loop LN2
Circulation for MBE
| 1. |
Triaxial feed
lines and hydrostatic head pressure allow only pure,
sub-cooled liquid to enter the cryopanel. This eliminates
the need for the MBE to vent huge amounts of gas
generated by the flash loss from the supply tank,
and heat loss of the piping system.
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| 2. |
Cryopanel
surfaces remain fully wetted. Natural benefit of
closed-loop circulation is the self-compensating
effect when heat levels change. The resulting lower
density liquid in the return line accelerates circulation
of liquid in the cryopanel. |
| 3. |
Gas
is vented from the phase separator, while liquid
is recovered, resulting in safe, efficient, and
completely reliable circulation. |
| 4. |
No measurable
difference in pumping speed or “sticking coefficient”
as compared to an “integral phase separator” MBE.
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| 5. |
Piping in clean-room
is flexible, allowing for ease of disconnection
prior to bake out. |
| 6. |
Mating bayonets
on many MBE’s LN2 feed-thru’s allow for completely
vacuum jacketed connections, eliminating ice-balls
and condensation. |
| 7. |
Vacuum-jacketed
temperature probe is available to monitor the temperature
of the gas and liquid in the return line, ensuring
the operating of good circulation. |
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