1. 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

2. 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?

3. 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

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

5. 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

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

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

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

9. 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?

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

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

12. Thank you

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

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

15. 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

16. 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,