In a previous paper, the author developed a method for predicting three-dimensional flow in rod bundles (or on the shell side of tube bundles) by considering the heterogeneous system of tubes and fluid as a homogeneous system with mean flow properties. A similar approach is used here to derive the general heat transport equation which includes convection, dissipation, conduction and source terms. The formulation of these terms is discussed with special consideration being given to the source term which arises from the heat transferred from the tubes to the fluid. The dependence of tube-to-fluid heat transfer on flow direction is expressed in a form which is consistent with experimental data. A simple example of low-Reynolds-number flow around a baffle in a shell-and-tube exchanger is used to illustrate the application of the fluid-flow and heat-transfer models. Predictions with and without tube-to-baffle leakage are shown to be in good agreement with experimental data.