Flow pattern change in horizontal rectangular laterally ribbed ducts through alteration of the ribs thickness and pitch

► Experiments were conducted on two-phase flow in laterally ribbed rectangular ducts. ► The effect of rib thickness and pitch on flow pattern diagrams were investigated. ► Rib arrangements were implemented with different thicknesses and different pitches. ► Increasing the rib thickness, results in different flow patterns to occur. ► Increasing the rib thickness, effects on boundary positions and shapes dramatically.