Thermal Conduction in Rotating Liquid Helium II

When a heat current flows in a wide channel filled with liquid helium II, the resulting temperature gradient is approximately proportional to the cube of the heat current density. The establishment of this gradient requires a time $\tau$ which is a function of heat current, temperature, and past history of the helium. The present experiments concern the effect of uniform slow rotation, about an axis normal to the direction of heat flow, upon $\mathrm{grad}T$ and $\tau$. $\mathrm{Grad}T$ was measured at 0 and 1.3 rad/sec, the highest angular velocity at which this measurement could conveniently be carried out. No effect of rotation could be observed; however, an approximate calculation suggests that $\mathrm{grad}T$ might increase detectably at somewhat higher rates of rotation. $\tau$ was measured at a number of angular velocities between 0 and 4 rad/sec; it was found that $\tau$ was appreciably reduced by rotation, the effect being greatest at small heat currents and high angular velocities. These results can be explained on the assumption that mutual friction results from turbulence in the superfluid component, taking the form of a tangled mass of vortex line. The delay time $\tau$ characterizes the rate of growth of this turbulence when a heat current is switched on; rotation reduces $\tau$ by introducing an initial length of vortex line which accelerates this growth.