Abstract
One of the characteristics of the microbubble is reduction of frictional pressure drop. However, the reduction mechanisms have not been completely clarified yet. In the present study, the microbubble was generated by the swirling flow method (S.F.M) and the pressurized dissolution method (P.D.M) and Reynolds number was varied from 11000 to 35000 at 10, 20, 30 °C in a horizontal channel. The frictional pressure drop, bubble diameter, mean velocity distribution and components of turbulent fluctuation were measured. The conclusions are as follows: (1) The averaged bubble diameter was about 30 μm (QG = 0 ml/min), 35 μm (QG = 40 ml/min), 43 μm (QG = 80 ml/min) in the S.F.M and it was about 30 μm in the P.D.M. (2) The frictional pressure drop of microbubble flow generated by the S.F.M decreased about 3~7 % from single phase flow, but the frictional pressure drop of the P.D.M increased in almost all experimental conditions. (3) Microbubble had no influence on mean velocity distribution during presented experiment. (4) The occurrence of increase and decrease between frictional pressure drop and turbulent fluctuation －u'v' were the same in many cases, but it is important to measure at the nearest wall. (5) The presented frictional pressure drop conditions around the boundary of the transition diagram didn't correspond to the transition diagram. It is suggested that the boundaries of transition have certain regions.
