THERMAL COUNTERFLOW IN THE HELIUM FILM-VAPOR SYSTEM

The well-known experiment on the thermal conductance of the film-vapou r system has been used to collect extensive sets of data on the superf luid onset, the flow resistance and the thermal-boundary resistance of very thin helium films on glass. In the temperature range from 1.0 to 2.1 K the onset thickness is found to increase smoothly, but rather s teeply, from 2 to 15 atomic layers. The dependence of the flow resista nce on heat input exhibits the expected power law, the exponent rising with increasing film thickness from the value two near onset, be it w ith a slope significantly steeper that expected on the basis of simila r experiments by others. Thirdly, the film-substrate thermal boundary resistance is found to increase gradually with decreasing film thickne ss.