Wettability effects on bubble characteristics in a bubbling wall jet along a vertical flat plate

Experimental investigation was carried out to reveal the effect of the wettability of a vertical flat plate on a bubbling jet rising along the plate. Two flat plates with different contact angles of theta = 62 degrees and 104 degrees were used, being classified into a good and a poor wettability plate, respectively. Bubble frequency, gas holdup, mean bubble rising velocity and mean bubble chord length were measured with a two-needle electroresistivity probe. When the wettability of a plate was poor, bubbles were likely to rise in the close vicinity of the plate and some of them attached to the plate. As a result, the mean bubble rising velocity and mean bubble chord length thus measured in the close vicinity of the plate were dependent significantly on the wettabilily of the plate. The horizontal distributions of the bubble frequency were similar in an axial region where the buoyancy force acting on bubbles governs the flow field. The same was true for the horizontal distributions of the gas holdup.