Flow rate instabilities under self-sustained cooling

• Published in: Cryogenics (Guildford) 1994, Vol.34 (7), p.555-562
• Main Author: Rudman, I.Kh
• Format: Article
• Language: English
• Subjects: Applied sciences; Cryogenics; Energy; Energy. Thermal use of fuels; Exact sciences and technology; flow rate instabilities; heat influx; Refrigerating engineering. Cryogenics. Food conservation; self-sustained cooling
• ISSN: 0011-2275; 1879-2235
• DOI: 10.1016/0011-2275(94)90181-3

A new explanation for the phenomenon of flow rate instabilities appearing under self-sustained cooling of cryostat elements with large temperature gradients is proposed. This explanation takes into consideration the presence of a reciprocal inverse connection (feedback) between the fluctuations of gas flow rate and the heat influx along a solid element in a liquid at the liquid-vapour boundary. Conditions under which these flow rate instabilities occur are determined. By analysing and solving the heat conductivity equation for solids and the set of equations of energy, impulse and mass conservation for gas with adequate initial and boundary conditions, we achieve two things: 1, the generalized parameters defining the stability boundary are derived; and 2, the stability boundaries of helium flow rate into the channels of the cryostat construction elements made of copper and austenitic stainless steel are computed. The calculated stability boundaries are in agreement with published experimental data. Some measures that prevent the development of flow rate instabilities are also suggested.