Studies of thermal effect in vortex cooler

Investigations on thermal effect which occurs when superfluid HeII is forced to flow through a system consisting of a superleak, chamber and a capillary in series (so-called vortex cooler) are reported. It is shown that in order to have a cooling effect in this device, both the temperature and the flow velocity in the capillary are important. The lowest limiting temperature of this cooling machine depends strongly on the size of the capillary and their pressure dependence can be fitted very well with constant-roton-density curves. (orig.)