SURFACE TEMPERATURE PATTERNS IN THERMOCAPILLARY CONVECTION IN A RECTANGULAR CAVITY - AN EXPERIMENTAL STUDY

摘要

Critical conditions for the onset of oscillatory thermocapillary flow, its structure and temperature distribution have been experimentally investigated in horizontal silicone oil (0.65, 1 and 2 cSt) layers with Prandtl numbers of 7.8, 13.9 and 27 in a rectangular cavity (10, 15 and 30 mm long and 50 mm wide). The liquid layer thickness ranged from 0.5 up to 4 mm and a horizontal temperature gradient was applied along the shorter side. The onset of oscillatory convection was detected using three different methods, and the changes in the surface temperature distribution have been monitored with an infrared imager. On the liquid layer surface, hydrothermal waves, obliquely travelling waves and standing waves were observed depending on the Prandtl and dynamic Bond numbers. For Pr = 7.8, wavy isotherms with perturbations traveling at a certain angle from the applied temperature gradient were seen at all aspect ratios investigated, while for Pr = 13.9 and 27, the surface isotherms exhibited possibly an interaction of obliquely travelling waves at larger aspect ratios. The present data are also compared with previous experimental data available for Pr= 13.9.