The paper presents detailed numerical study of heat transfer enhancement by a spherical dimple placed on a wall in a narrow channel. RANS approach with MSST model is applied to investigate the influence of the depth to diameter ratio Delta and the Reynolds number on the flow and heat transfer. Numerical model was successfully validated using LDV measurements, pressure loss data and LES results. Special attention is paid to identification of the flow topology at different Delta and Reynolds numbers. Contribution of different heat exchanger surface parts to the heat transfer enhancement is analyzed. Application of entropy production as a criterion of heat exchanger efficiency is discussed. Detailed information gained from the present computations can be used to get a deep insight into flow physics over dimpled surfaces and as a benchmark for validation of numerical and experimental methods. (C) 2009 Elsevier Ltd. All rights reserved.