PT410 Helium Re-liquefier:
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PT410 Helium Re-liquefier
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The Cryomech PT410 Helium Re-liquefier is designed to recondense the boil off from liquid helium dewar/cryostats, and then return the liquid helium to the dewar/cryostat establishing a closed helium loop. It can be installed into dewars already full of liquid helium or be utilized to liquefy helium gas from gas cylinder to fill a dewar.
A 4K pulse tube cryorefrigerator, Cryomech Model PT410, supplies the cryorefrigeration necessary to condense the helium inside the re-liquefier. The cryorefrigerator is the most complicated component in the complete system.
It has been standard practice in the design of liquid helium dewars/cryostats to use the liquid helium boil off to cool the cryostat neck, intermediate radiation shield, current leads, insert assembly, and other components of the cryostat that connect room temperature to the liquid helium. This practice is necessary to the overall efficiency of the Dewar. The re-liquefier condenses the helium boil off after it leaves the cryostat and then re-fills the cryostat through the existing fill port, turning the open cycle cryostat into a closed cycle system with no helium leaving the system.
The PT410 Pulse Tube Cryorefrigerator supplies the cooling to liquefy the helium. The complete cryorefrigerator consists of two major components: the CP2880 Compressor Package and the PT410 Cold Head. The CP2880 supplies high and low pressure helium gas to the PT410 Cold Head. The high pressure helium is expanded inside the cold head to the low pressure, dropping in temperature to below 4K. Heat can then be transferred into the PT410 4K heat exchanger and returned to the CP2880, where it is removed into the cooling water. Two flexible stainless steel lines and a motor cord connect the PT410 and the CP2880.
The PT410 Cold Head is mounted into a vacuum insulated condensing chamber, referred to as the Re-liquefier ‘Main Assembly', as shown in Figure A-1. The room temperature helium gas/vapor returning from the cryostat Dewar enters into the condensing chamber through the KF16 flange on the ‘main assembly.' As the warm helium comes in contact with the Cold Head, its heat is absorbed into the heat exchangers on the PT410 cold head. This reduces its temperature, increasing its density, dropping it lower inside the condensing chamber; until it contacts the 4K condensing surface, where it condenses.
The liquid helium is funneled into the liquid helium return line which connects the bottom of the condensing chamber to the cryostat Dewar. The return line is delicate and must be handled with care.
The complete PT410 Helium Re-liquefier also includes a temperature controller, electrical feed through, silicon diode, and heater assembly as well as a pressure relief valve and a vacuum port.
Cryomech offers an optional stand to customers. The stand allows the Re-Liquefier to be easily raised and lowered into the Dewar/cryostat. Lockable castors are mounted to the stand for adjustment in the horizontal plane. A level is included on the stand for installation purposes. All these features decrease the chances of damaging the delicate PT410 Re-Liquefier liquid helium drain leg by centering it onto the Dewar/cryostats fill port.