Heat conduction by liquid helium II in capilliary tubes. I: Transition to supercritical conduction

Abstract

Measurements have been made of the heat conduction by liquid helium II in capillary tubes of diameter 52.0 microns, 107.6 microns and 366 microns. The results on subcritical flow have been described previously, and the present paper is concerned with observations in the transition region to supercritical conduction. Outstanding features of the transition are (i) spontaneous fluctuations in the thermal resistance; (ii) very large hysteresis effects in the resistance at low temperatures in the wide tubes, which decrease as the lambda point is approached, and which depend on the previous history of the helium; and (iii) sensitivity of the thermal resistance to mechanical shock or vibration, including permanent changes from one branch of the hysteresis loop to the other. The observations, which include measurements of the critical velocity as a function of tube size and temperature', are discussed in terms of the vortex line theory of Feynman and its development by Vinen, which are found to give good agreement with the experiments.