Liquid Nitrogen Transfer

The process of LN2 being transferred from the dewar to the MB can take 1.5-3 hours, depending on the pressure of the dewar. Once LN2 is transferred, the IVC will slowly cool to 77 K. This process can take as long as 12 hours, and is dependent on how much nitrogen exchange gas is in the IVC (hence, the importance of remembering to open the lines to the IVC when transferring exchange gas)

1. Remove the plug from the middle exhaust port at the top of the MB (this is where the over-pressurization of the MB is important! We don't want air to rush in here).
2. Insert the LN2 transfer stick into the middle exhaust port and fasten the stick to the exhaust port with the attached bolt. Lift it <1/8“ when the stick hits the transfer cone.
3. Attach one end of a long rubber hose to the end of the LN2 transfer stick jutting out of the MB.
4. Attach the \elbow” transfer stick to the nitrogen dewar.
5. Attach the other end of the long rubber hose to the elbow transfer stick. This hose will freeze when LN2 is being transferred, so position it in such a way that the hose has room to wiggle and contract during the transfer while not hitting anything. You can do this by connecting a string that is tied onto the rubber hose to one of the screws poking out on top of the platform. This will help support the hose.
6. Remove the He recovery hose from the MB.
7. Open the LN2 supply a little to let the hose cool- if you don't do this and instead open the supply completely, the hose will fly off. As the hose cools, you can actually see the LN2 flowing through the hose.
8. Once the hose is cold, open the LN2 supply more until there is a solid flow. The hose should not shake violently. Keep the valve on the LN2 tank open until the MB is full. This should take 1.5-3 hours. To know when this happens, you can use two methods:
   1. There is a rod with a pair of wires running through it located next to the cables on the rack by the DAQ computers. These wires connect together at one end to a resister that protrudes out of the rod. At the other end of the rod the two wires escape and are to be connected to a DMM. Insert this rod into the exhaust port of the MB to the right of the nitrogen transfer stick. At room temperature, resistance reads about 1 K. In LN2, resistance reads ~ 1.33 kΩ. If you read this resistance, you know you are near the end of the transfer and can end soon after if you wish .
   2. Wait for LN2 to spill out of the exhaust port.
9. Shut off the LN2 supply
10. There is a ping-pong ball plug on top of the platform. Put this on the to He recovery port where you had disconnected the line earlier. The LN2 will boil off through this port, which will keep the ping-pong ball afloat until the LN2 has been completely removed or boiled off. This device will prevent air from getting into the main bath.
11. Wait until the rubber hose has warmed up before removing it from the transfer stick and dewar. Plug the transfer stick with the stopper.