Visualization Study of Highly Transient Thermo-Fluid Dynamic Phenomena in He II

A laser holographic interferometer is applied to the study of the thermo-fluid dynamic phenomena in superfluid helium. A pressure wave accompanied by a thermal wave and a vapor wave by a thermal wave incidence to a liquid-vapor interface are investigated, all excited by pulse heating from a plane heater under the saturated vapor pressure condition. A new technique for interfcrometry — finite-fringe method — is introduced in order to observe the above phenomena not only visually but also quantitatively. It is understood from the visualized photos that a finite amplitude pressure wave of the first sound origin propagates with a speed of sound, corresponding to the local Mach number of unity in He II, in immediate response to the onset of heating, being ahead of a thermal shock wave. The density variation and propagating speed of the vapor wave with the variable heat flux from the heater are measured from the visualized photos. It is found that the two have their own limits with applied heat flux.