Turbulence and cooling effect in adiabatic flow of HeII

Investigations are reported on the thermal effect which occurs when superfluid HeII is forced to flow through a system consisting of a superleak, a chamber and a capillary in series. Varying the flow velocity in the capillary, it is found that there is a rather sharp transition in the behavior of the thermal effect. An estimation of the Reynolds number suggests that this transition corresponds to the classical laminar-turbulent transition in the capillary. This turbulent state is essential for the cooling effect in this device.