About the LHe Vessel
A kind of the LHe Vessel
The LHe vessel comes with many different
kinds. A practical thing is divided into
two of the following with those containers
roughly by an insulation method.Now a super
insulation method becomes the mainstream.
The using most frequent material at the
beginning was glass.Lately,the using metal
materials are an aluminum and a stainless
steel.Metal becomes the mainstream aluminum,
stainless steel recently.In addition, in
these days,,sometimes using FRP at neck part
on the liquid tank because of well insulation.
A Vacuum Pull of an Insulation Tank(Re-exhaust)
To vacuum pull of an insulation our vessel,
that belongs to cryogenic lab(Re-exhaust)please
talk to us first.
The most of the vessel of the insulation
vacuum tank loses vacuum degree by using
longtime.It needs to vacuum pull(re-exhaust)
The time of vacuum pull is varies by individuality
and condition. There is no certain time to
do it, but from our experience ,we do the
vacuum pull as listed bellow.
-
The evaporation volume had increased or frost
covers outside of vessel.(These cases obesely
has a bad insulation. It need to vacuum pull
as soon as possible.)
The liquid tank had kept as room temperature
for long time, it loses vacuum degree. It
also need re-exhaust.
-
Bring up the liquid tank's temperature as
room temperature,even it's short time the
insulation quality of the Air Liquid vessel
goes down.It needs to re- exhaust. Messier,CryoFab
and its vessel are need to decide as follow
as below.
A general vessel is, put the Liquid Nitrogen to around 30% of the container
capacity in a liquid helium container and weigh it.(Because nitrogen is
heavier than helium) After that, to see the evaporation volume, measure
the volume at least once a day.
In many cases, a volume change calms down the next day of put the Liquid
Nitrogen. Afterwards,the evaporation volume is under 0.1〜0.2kg/day, it
doesn't need re -exhaust.So it pre-cool with liquid nitrogen and then put
the liquid helium. If it's over than 0.1〜0.2kg/day ,generally,it might
have decreased vacuum degree of insulation tank. So it need to re-exhaust.
There is a situation that is able to put the Helium,even though ,evaporate
over 0.1〜0.2kg/day,very rarely.(It assume a gas in an insulation vacuum
tank gets cold when putting the Helium in liquid tank, and it is thought
that absorption of an active carbon in an insulation vacuum tank can increases.)
There is the reverse,too.
※It is general story as things mentioned above,It has to add it to judgment
of evaporation rates when adding the volume and liquid helium. Basically,
The evaporation rate of liquid nitrogen exceeds evaporation rate when adding
the Liquid Helium. It is thought that an insulation vacuum is poor.
A vacuum pull goes in the following procedures.
About Pre-Cool Down
At the liquefy room, liquid helium container
cools it in liquid nitrogen and then put
liquid helium in it. In nitrogen being heavier
than helium, please make it around 30% of
container capacity. Doing the pre-cool down
is about one week. in the mean time, do the
weight measurement and measure volume of
evaporation of liquid nitrogen.The evaporation
volume is under 0.1〜0.2kg/day, then fill
the liquid helium,but if over than readings
do the vacuum pull again.
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