March 10, 2016 | International Cryogenic Engineering Conference-26, New Delhi, India Nitrogen gas propagation following a sudden vacuum loss in a tube cooled by liquid helium Ram C. Dhuley Steven W. Van Sciver National High Magnetic Field Laboratory, Tallahassee, FL 32310, USA Mechanical Engineering Department, FAMU-FSU College of Engineering, Tallahassee, FL 32310, USA Research supported by US Department of Energy grant DE-FG02-96ER40952

Loss of vacuum in a SRF beam-line Cryomodule environment atmosphere more cryomodules LHe vacuum beam-line How does air propagate in a LHe cooled vacuum channel?

Conceptual picture of the propagation vacuum Air LHe front channel wall (cold) Atmosphere (~ 295 K) channel wall, warm due to air condensation LHe Vacuum Air Channel wall Gas front in the vacuum space Heat wave in the tube wall

Experimental setup Mass flow generation and measurement Ram C. Dhuley and Steven W. Van Sciver, IEEE Trans. Appl. Supercond. 25(3), 9000305, (2015) R. C. Dhuley and S. W. Van Sciver, Cryogenics (under review) Mass flow generation and measurement Propagation speed measurement

The gas front decelerates along the vacuum tube! Direction of propagation T1 T11 T12 pstart = 50 kPa Deceleration observed during experiments with pstart = 50, 100, and 150 kPa in the gas tank

Empirical analysis of the front arrival data R. C. Dhuley and S. W. Van Sciver, Int. J. Heat Mass Transfer 96, 573-581, (2016) Three experiments: pstart = 50 kPa, 100 kPa, 150 kPa Front speed decreases nearly exponentially along the tube b = speed decay length-scale

Analytical model of the gas front speed R. C. Dhuley and S. W. Van Sciver, Int. J. Heat Mass Transfer 96, 573-581, (2016) constant if choked Conservation of mass in the gas phase: the propagation speed should decrease along the tube : constant : will grow with x

Reducing the empirical and analytical models Empirical fit Analytical model constant with x

vs. location How do b’ and b compare? b’ = mdep decay length-scale R. C. Dhuley and S. W. Van Sciver, Int. J. Heat Mass Transfer (under review) Local for the three experiments b’ = mdep decay length-scale How do b’ and b compare?

Comparison of the decay length-scales The two independent analyses agree reasonably

Our contribution A simple analytical model to explain the front deceleration Experimental evidence of the exponential decrease in the front speed

Thank you

Extra slide: Estimation of R. C. Dhuley and S. W. Van Sciver, IOP Conf. Proc.: Mater. Sci. Eng. 101, 012006, (2015) Locally, Temperature vs. time data at the twelve locations Local condensation heat transfer rate, qdep (energy balance at the tube wall)

Extra slide: Estimation of : exists ‘exactly’ at the front, extremely difficult to measure/quantify Approximation: , mass deposition rate behind the front

Extra slide: Effect of He II coolant Preliminary result (same N2 mass in-flow rate) The front travels slower when the tube is cooled by He II He II bath size (heat capacity) will influence the front speed

Extra slide: Effect of the decreasing mass in-flow pstart (kPa) min start* (g/s) min end** % change 50 9.2 7.4 20 100 19.1 17.6 8 150 28.4 27 5 pstart (kPa) b (m) % (v0-v)/v0 50 0.46 96 100 0.63 91 150 0.95 80 Over the travel length,