SUMMARYThis paper presents a numerical and experimental study of finite wall thickness on stratification during charging of soar thermal storage tanks. A numerical two-dimensional spectral-element model has been used. Predictions of the model are compared with experimental data, and with a one-dimensional plug flow model. The fluid inlet effect on the stratification is minimized in the experiments by the use of a proper diffuser design with a settling mesh. Both heat conduction in the tank wall and the developing flow in the tank have a significant effect on stratification during charging at low flow rates.The one-dimensional plug flow model is shown to be inferior to the two-dimensional model in representing the experimental data. Yet, a simple one-dimensional flow model corrected for both centreline velocity and mixing effects has given comparable results to the more expensive two-dimensional model.