Measurements of the Heat of Transport of Liquid Helium II

The heat of transport of helium II has been measured accurately from 1.15°k to 2.1°k in order to compare it with the calorimetric entropy data. The measurements were made with a thermally isolated glass vessel, which was connected to an isothermal liquid helium bath by a tube packed with fine powder. The heat of transport was determined (i) from the temperature and hydrostatic pressure changes in the vessel during thermomechanical flow, and (ii) from the heat input necessary to produce a measured flow rate. The results agree well with the indirect measurements of the fountain effect by van den Meydenberg, Taconis, Beenakker and Wansink and with the calorimetric data of Kramers, Wasscher and Gorter. The agreement with Kramers et al. is within the experimental error up to 1.8°k but at higher temperatures the present measurements are slightly higher. Oscillations in the temperature of the vessel were observed even during thermomechanical flow, provided that the rate was subcritical. As expected, the oscillations were damped out above the critical rate. When the flow was just critical, a pronounced peak in the temperature-time graph was observed at the beginning of the flow, which appears to be due to an unexplained irreversible process.