Abstract

Simultaneous measurements of surface temperature and the underlying velocity field are presented for a thick horizontal layer evaporatively cooled from above. The convection is characterized by meandering, descending sheet-like plumes which form where cool fluid at the surface collects and plunges into the warmer bulk fluid below. Previous studies have documented the temperature field at the cooled surface and a few have provided point measurements of velocity in the fluid below the surface, but simultaneous measurements of surface temperature and the velocity field were lacking. In the present study, the instantaneous, free surface temperature field has been documented with an infrared (IR) sensing camera. Simultaneous two-dimensional velocity measurements in planes perpendicular and parallel to the free surface were acquired using digital particle image velocimetry (DPIV). Data from cases using room temperature water with Ra* = 1.3 × 109, and heated water with Ra* = 8.5 × 109 are presented. In planes perpendicular to the free surface, velocities were quantified in the convective plumes and the surrounding fluid. The plumes were correlated with the low temperature lines in the free surface temperature field. The velocities in the plumes were about ten times those in the surrounding fluid. In planes parallel to the free surface, horizontal motions toward the descending sheets were observed and quantified. The present measurements provide needed documentation of the relationship between the surface temperature and the underlying hydrodynamics, that is, the velocity fields associated with the convective plumes.

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