Fractionation is one of the pivotal unit operations in refineries and gas processing industries which is single largest energy-degrading processing unit utilized to separate mixtures into individual products A reliable design method for sizing tray fractionators must take into account of foaming which is a major consideration in many process systems The aim of this study is to develop simple predictive tool, which is simpler to use than current available techniques avoiding large number of parameters requiring less complicated and shorter computations, for accurate determination of downcomer velocity and vapor capacity factor as a function of tray spacing and density The results can be used in follow-up design calculations to size fractionators without foaming formation for tray spacing up to 1.2 m, vapor densities up to 100 kg/m(3) and liquid and vapor density differences up to 950 kg/m(3) The accuracy of the proposed equations was tested and found to be in excellent agreement with the reported data for the wide range of conditions, wherein the average absolute deviation percent of proposed equations are 077% and 2.35% for downcomer design velocity and vapor capacity factor respectively. The proposed predictive tool detailed in the paper can be very helpful for design engineers to handle sizing calculations for tray fractionators (C) 2010 Elsevier Lid All rights reserved.