Propagation of nitrogen gas in a liquid helium cooled vacuum tube following sudden vacuum loss – Part II: Analysis of the propagation speed

Abstract

The propagation of near-atmospheric nitrogen gas entering a liquid helium (LHe) cooled vacuum tube following an accidental loss of vacuum will be strongly influenced by condensation of the gas on the tube wall. Our previous experimental study revealed that in presence of condensation, the propagation speed of the gas front decreases nearly exponentially as the front advances in the tube. In the present paper the exponential decrease is studied analytically. We reduce the analytical model of the front speed, using assumptions, to show its derivative in the direction of propagation to be proportional to the mass deposition rate near the front. The deposition rate is then calculated at discreet locations along the tube from the condensation heat transfer rate at these locations. We find the deposition rate to diminish nearly exponentially along the tube so that the spatial derivative of the speed will show the same effect. In this special case the front speed will also fall exponentially along the tube. Within the experimental and procedural uncertainty, the exponential decay coefficient of the mass deposition rate also agrees reasonably with the empirically determined exponential decay coefficient of the propagation speed.

Epoxy encapsulation of the Cernox™ SD thermometer for measuring the temperature of surfaces in liquid helium

“…The sensitivities agree very well with those documented in [2]. These encapsulates were then used in a series of experiments [6,7] (column B of Table 1), which involved several thermal cycles between 295 K and 4.2 K. After these experiments, we performed systematic tests to study the shift in calibration due to potting. Columns from C to F of Table 1 show the chronology of these thermal tests.…”

Heat and mass transfer during a sudden loss of vacuum in a liquid helium cooled tube -- Part III

“…In order to better understand the complex coupled heat and mass transfer processes involved in a beamline vacuum break event, pioneering work has been carried out in our cryogenics lab by Dhuley and Van Sciver via venting room-temperature nitrogen (N 2 ) gas from a buffer tank to a LHe cooled vacuum tube [9,10]. Their experiments with normal liquid helium (He I) showed that the gas-front propagation slowed down nearly * Corresponding: wguo@magnet.fsu.edu exponentially.…”

“…Their experiments with normal liquid helium (He I) showed that the gas-front propagation slowed down nearly * Corresponding: wguo@magnet.fsu.edu exponentially. This deceleration was attributed to gas condensation to the tube wall [10], but a quantitative analysis on how the condensation leads to the observed exponential slowing down was not provided. Another limitation in these early experiments is that the tube system was not suitable for measurements with the superfluid phase of liquid helium (He II).…”