VISUALIZATION STUDY ON THE THERMOHYDRODYNAMIC PHENOMENA INDUCED BY PULSATIVE HEATING IN HE-II BY THE USE OF A LASER HOLOGRAPHIC INTERFEROMETER

A visualization method for cryogenic thermo-hydrodynamic phenomena is established by using a laser holographic interferometer. The technique is applied to the study of some transient heat transfer, that is the thermal shock wave propagation and onset of boiling in He II. All thes e phenomena are induced by a pulsative heating from a thin-film planar heater. The evolution of an initial trapezoidal thermal pulse into a thermal shock wave and the subsequent propagation is visualized at var ious temperatures. The temperature rise due to diffusive process cause d by the action of high density vortices, that is the formation of a t hermal boundary layer adjacent to the heater, and subsequent boiling a re observed. The finite-amplitude pressure wave is found to be generat ed in response to the onset of pulsative heating. Further, a visualiza tion of evaporation from an He II free surface caused by the incidence of a thermal shock wave is made and the propagating speed of the vapo r front is measured from visualization photos. (C) 1996 Elsevier Scien ce Limited