As a self educational project, I'm working on a thermal model of a multiple segment vacuum jacketed pipe system we use at work. I'm running into several roadblocks that I need help with. The system starts at ambient conditions before crogenic temperature gas is introduced. I'm modeling performance once it is at stable temperature under flow. I know the ambient vacuum of each line segment, but not the vacuum at stable operating conditions. I have inlet and outlet temperatures, so know the overall performace of the system. When in use, the system is flowing cold helium at roughly LN2 temperatures. For my initial model, I used the vendor spec data on the VJ heat leak, bayonet heat leak, etc and my model predicts significantly better thermal performance that we currently achieve. I suspect this is because the operating vacuum is not as low as the vendor used when he came up with the spec values.
1. Although I don't yet have data on the apparent conductivity vs. vacuum level for the pipe segments used, I do understand the curve has a characteristic shape. Can I make any generizalations on this curve if I can't get this data from the vendor? Any good sources of generalized curves for various line diameters, etc?
2. How do I make an accurate conversion from ambient vacuum conditions to operating temperature vacuum conditions. I know the ideal gas law should be accurate, but I don't know what operating temperature to use. Should it be commodity temperature, average temperature, something else? I've been unable to find any good references.
3. I have vendor data for heat leak at each bayonet joint, but I have been unable to find what heat leak to use for several non-insulated tubing connections into the VJ pipe. Any suggestions?
1. Although I don't yet have data on the apparent conductivity vs. vacuum level for the pipe segments used, I do understand the curve has a characteristic shape. Can I make any generizalations on this curve if I can't get this data from the vendor? Any good sources of generalized curves for various line diameters, etc?
2. How do I make an accurate conversion from ambient vacuum conditions to operating temperature vacuum conditions. I know the ideal gas law should be accurate, but I don't know what operating temperature to use. Should it be commodity temperature, average temperature, something else? I've been unable to find any good references.
3. I have vendor data for heat leak at each bayonet joint, but I have been unable to find what heat leak to use for several non-insulated tubing connections into the VJ pipe. Any suggestions?
