Wettability effect on the flow pattern of air-water two-phase flows in a vertical circular pipe

Synopsis : The flow pattern of air-water two-phase flows in a vertical, cir cular pipe was experimentally investigated. The wettability of the pipe was changed by surface treatment. The original acrylic pipe had a contact angl e theta(c) of 77 degrees, while two pipes after the surface treatment had t heta(c) of 36 degrees and 104 degrees, respectively. The flow patterns in t he pipes having theta(c) of 36 degrees and 77 degrees were the same and agr eed favourably with previously published results for pipes of good wettabil ity (theta(c)<90 degrees). On the other hand different types of bubbly and slug flows appeared in the pipe of theta(c)=104 degrees, being caused by at tachment of bubbles and slugs to the wall of the pipe. The bubbly flows for theta(c) of 104 degrees were classified into two categories and slug flows for the same contact angle were classified into three categories. The boun dary between the bubbly and slug flows, however, was hardly dependent on th e wettability of the pipe.