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

TL;DR

This study investigates heat and mass transfer during a sudden vacuum loss in helium-cooled tubes, extending previous nitrogen-based models to superfluid helium (He II) to improve safety design for particle accelerators.

Contribution

The paper develops and validates a modified model for gas dynamics and heat transfer in He II cooled tubes, incorporating superfluid helium's unique properties.

Findings

Successfully reproduced gas front dynamics in He II using the tuned model.

Provided reliable estimates of heat deposition in He II during vacuum loss.

Enhanced understanding of condensing gas behavior in superfluid helium environments.

Abstract

A sudden loss of vacuum can be catastrophic for particle accelerators. In such an event, air leaks into the liquid-helium-cooled accelerator beamline tube and condenses on its inner surface, causing rapid boiling of the helium and dangerous pressure build-up. Understanding the coupled heat and mass transfer processes is important for the design of beamline cryogenic systems. Our past experimental study on nitrogen gas propagating in a copper tube cooled by normal liquid helium (He I) has revealed a nearly exponential slowing down of the gas front. A theoretical model that accounts for the interplay of the gas dynamics and the condensation was developed, which successfully reproduced various key observations. However, since many accelerator beamlines are actually cooled by the superfluid phase of helium (He II) in which the heat transfer is via a non-classical thermal-counterflow mode, we need to extend our work to the He II cooled tube. This paper reports our systematic measurements using He II and the numerical simulations based on a modified model that accounts for the He II heat-transfer characteristics. By tuning the He II peak heat-flux parameter in our model, we have reproduced the observed gas dynamics in all experimental runs. The fine-tuned model is then utilized to reliably evaluate the heat deposition in He II. This work not only advances our understanding of condensing gas dynamics but also has practical implications to the design codes for beamline safety.