Chapter III Rayleigh Disks in Liquid Helium II

Abstract

Publisher Summary The thermal Rayleigh disk provides a direct method for detecting and measuring second sound waves by purely mechanical means, dependent solely upon such fundamentals as kinetic energy density and the geometry. While not necessarily confirming the two-fluid hypothesis, the operation of the disk is consistent with the conditions based on that model. The Rayleigh disk responds to the kinetic energy density of a mechanical wave, without regard to the direction of particle migration, such that the counter flowing natures of the mass transport within liquid helium II in no way affects its performance. It is interesting that this device, developed by Rayleigh in the century before the advent of microphones, is capable of detecting the internal counter flow of quantum hydrodynamics to which microphones are insensitive. Future applications of the Rayleigh disk include such possibilities as observing the torque exerted by superfluid alone. This could be accomplished by suspending the disk within a region of steady-state flow of pure superfluid through a background of stationary normal fluid, produced by combining a heat source with a suitable combination of semi-permeable barriers.