In the present work, two different models (micro-scale and meso-scale) were developed to investigate the heat transfer between the gas and liquid phases in the trickle flow regime of a packed bed reactor. In the micro-scale model, a simplified description of bed geometry, known as the double-slit model, was implemented to study the effects of different operating parameters, in terms of gas and liquid Reynolds, Prandtl and Eotvos numbers, on the interfacial Nusselt number. In the meso-scale model, the Volume-of-Fluid (VOF) approach was used to simulate trilobe, cylindrical and spherical catalyst shapes and accurately predict the effects of interface morphology and bed geometry on interfacial heat transfer. To validate the implemented methods, a simple packed bed reactor with spherical catalysts was developed to experimentally investigate the interfacial heat transfer of co-current, downward gas-liquid film flows. The results obtained from CFD simulations and experimental data were in agreement and accurately predicted bed reactor temperature profiles with a mean relative error of 2.15%. In both the micro- and meso-scale models, an increase in the Reynolds and Prandtl numbers increased the interfacial Nusselt number; whereas, an increase in dimensionless groups of the liquid phase or the Eotvos number caused the opposite effect. Finally, a new correlation was proposed that evaluated the gas-liquid Nusselt number in the trickle flow regime with a standard deviation of 7.19% compared to results acquired using the micro-scale model. (C) 2013 Elsevier Ltd. All rights reserved.