A biobank maintained with liquid nitrogen should ensure a stable low temperature.
To your experience, how low can I expect my gas phase in a storage tank to be?
I expected to reach close -196°C when the tank is accordingly filled with N2, which does not happen (says -94°C). S
So, I wonder if I need to relocate the temperature sensor? (currently it is shortly underneath the thick isolation layer of the cloding lid)
thanks for your experience and recommendations.
That may be the case, it depends on the geometry and insulation. Also, if the tank is pressurised, the temperature will rise (the principle of pressure cooking applies), your 77 K estimate is correct at atmospheric pressure only.
It also depends on the effectiveness of isolation - I disagree with the argument of temperature rise when the tank is pressurized - if this would be the case your temperature problem is the least you have :-)
A very good place is appr. 20cm below the isolation - approximatelyr there, where the first samples are stored - this is by the way the temperature that is really of interest. Typically it should be -130°C.
Storage tanks keep semen indefinitely
at −196° C as long as any liquid nitrogen is present,
but a depth of at least 5cm of liquid nitrogen should
always be maintained as good insurance against possible
service delays. The normal field holding time or time
allowed between liquid nitrogen refills varies according
to the tank model and the number of times it is opened.
The liquid nitrogen level should be monitored weekly
with a measuring stick.
Technical advances in design and construction have
produced storage tanks with liquid nitrogen holding
times of 6 to 9 months. Although semen tanks are well
constructed, they are still susceptible to damage from
mishandling. Damage to the liquid nitrogen tank is most
likely to occur when the tank is moved, so excessive
movement of the tank should be avoided. The inner
chamber of the tank, which contains the liquid nitrogen,
is actually suspended from the outer shell by the neck
tube. Any abnormal stress on the neck tube, which can
be caused by sudden jarring or any excessive swinging
motion, can crack the neck tube, resulting in vacuum loss
and tank failure. Failure to secure the tank in a moving
vehicle can result in not only increased probability of
damage to equipment but also increased risk of injury to
the driver or passengers if liquid nitrogen is spilled inside
the passenger compartment of the vehicle.
To ensure maximum holding time, the tank should be
kept in a cool and dry location away from direct sunlight,
in a clean and well-ventilated area. The tank should be
located in an area where it can be observed frequently to
detect excessive nitrogen evaporation and development
of frost around the outside neck of the storage tank.
Drafts from milk coolers and furnaces should be avoided,
but ventilation should be sufficient to prevent possibleuser suffocation, which can be caused by too high a proportion
of nitrogen gas in the air. The tank should be protected
from corrosion by being elevated above concrete
or wet floors. A wooden dolly equipped with wheels so
that it can be moved easily is ideal for tank storage. The
tank should be located where it will be safe from children
and vandals or locked to secure and protect semen. Particular
attention must be paid to the neck and vacuum
fitting. Accumulation of frost on these fittings indicates
that the vacuum insulation has been lost and liquid
nitrogen has been evaporating rapidly. If frost build-up
is observed, a functional tank must be located and the
semen transferred to it immediately. The viability of
semen in the tank should be evaluated before extensive
use.
As with any well-managed business, an accurate inventory
of location and quantity of the semen stored in the
liquid nitrogen tank is important. This is necessary not
only for accounting and audit purposes but, more important,
to avoid any unwanted exposure of semen during
searching for the desired sire’s semen before removal for
thawing. A simple semen tank inventory log enables the
exact location and quantity of semen remaining to be
determined quickly.
See CURRENT THERAPY IN LARGE ANIMAL
THERIOGENOLOGY, SECOND EDITION ISBN 10: 0-7216-9323-7
Copyright © 2007, 1997 by Saunders, an imprint of Elsevier Inc.
P 253
thank you for your answers. apparently, we score -171°C but only if the storage towers are in place, as they conduct themperature from down to up. however, still we have a way higher N2 consumption than its supposed to be, as the automatic filling causes issues. curious where the cryo stroy takes us...
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