Characterization of the dissipation of elbow effects in bubbly two-phase flows

This study develops a method to characterize the elbow-region for vertical-upward-to-horizontal air-water bubbly two-phase flows through a 90° elbow with a non-dimensional centerline radius of curvature, R_C/. D, of three. The dissipation of the elbow-effects in the horizontal region downstream of the elbow is characterized by the change in the local void fraction distribution. To quantify the dissipation characteristics, the elbow-strength, S, is defined as the inverse of the second moment of the local void fraction distribution. It is found that the elbow-strength decreases exponentially with increasing development length in the elbow-region. The slope of decrease of the elbow-strength in the elbow-region is determined by the dissipation parameter, β. The dissipation parameter determines the development length required for the elbow-effects on the two-phase flow parameters to become negligible. It is found that the dissipation parameter is a linear function of the mixture Reynolds number for the flow conditions investigated in the present study.