Heat transfer coefficients measured in a 0.15 m ID bubble column are compared with similar studies in larger diameter columns to identify influence of column diameter. Gas phase used is oil free compressed air and its flow rate is varied from 0.03 to 0.35 m/s. Tap water is the liquid phase and the solid particles used are 49 mu m glass beads and their concentration is varied up to 20 vol%. The observed increase in heat transfer coefficients can be related to increase in liquid circulation velocity with column diameter which in turn is related to increase in large bubbles rise velocity. A simplified scale-up procedure is presented based on available data and suitably modified literature correlations for heat transfer coefficient. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.