Helium properties important for experiments

The typical helium property at a temperature lower than 2.17 K is a drop in viscosity. Superfluid helium features extra high thermal conductivity. Variations are given of the vapour pressure above liquid helium in a range of 0.01 to 1,000 torr with temperatures in a range of 0 to 3.5 K. The coefficient of heat transfer between the cryogenic liquid and the heat transfer surface grows from 300 to 15,000 Wm-2K-1. A single-phase flow may only be considered for the supercritical state helium. Helium density and thus also the intensity of cooling is significantly higher than for vapour of the same temperature under normal pressure. (J.B.)