Experimental Observations on average pulse velocity and frequency in concurrent gas-liquid (down) flow through randomly packed beds are used to extract constitutive relations for the gas-liquid interaction and mean curvature terms that appear in a recently proposed volume-averaged two-fluid model for bubbly flow. The proposed closures lead to a reasonably quantitative prediction of the average pressure drop and liquid saturation under bubbly flow conditions and in the near pulse regime. In addition, the proposed closures provide realistic estimates for the location of the bubble-to-pulse transition in microgravity and in 1g down-flow and predict the disappearance of the bubbly flow pattern at low liquid fluxes in 1g down-flow. (c) 2016 American Institute of Chemical Engineers AIChE J, 63: 812-822, 2017