AbstractData on liquid entrainment are reported for rectangular‐cap bubble trays on 24‐in. tray spacing for an air‐water system. Several tray variations were studied, and entrainment is given for trays containing eight, twelve, and sixteen caps a tray. Some hydraulic characteristics (pressure drop, liquid backup, minimum vapor velocity, and downflow froth height) are also reported. It was found in this study that decreasing liquid path lenght increased the entrainment from a bubble‐cap tray and increasing tray bubbling area decreased entrainment. It was also found that decreasing slot area generally had no effect on liquid entrainment over the range inves