Bubble Wake Interaction with Convective flow from a heated vertical flat plate

Time-synchronised flow velocity, temperature, and heat flux measurements were preformed to characterise the interaction of a single rising ellipsoidal bubble with the free convection flow from a heated vertical flat surface. The heat transfer measurements from the surface were provided by a hot film heat flux sensor calibrated using a pre-calibrated microfoil heat flux sensor. Two thermocouples were used to measure the temperature difference between the solid surface and the adjacent fluid layer and the velocity flow was mapped by a time-resolved digital particle image velocimetry technique (DPIV). Heat flux fluctuations, preceding and following the bubble passage, were shown to correlate with variation in both local flow velocities and fluid temperatures. The bubble induced swirling flow was shown, for example, either to assist or to hinder the heat transfer process by assisting or opposing the free convection flow (see velocity plot below). Vortices, shed by the free rising bubble and convected within its wake, were also linked to the transport of colder fluid into contact with the heated surface. When both flow and temperature effects combined to enhance the convective cooling process a magnification larger than 5 was measured from the sample test selected for the present analysis, while the bubble effect was shown to last beyond the 4.4s duration of the test records.