A new dimensionless correlation for the Nusselt number and high Prandtl number is presented. It can be used to correct the temperature profiles obtained through a global method. The mathematical model is transient two-dimensional, assuming laminar flow. Thermal losses are considered for all tank walls. Several cooling cases are simulated varying the aspect ratio, the cooling rate and the volume of the tank. The temperature fields are used to obtain the internal coefficient of heat transfer. It was use the Buckingham theorem to determine the dimensionless groups that represent the cooling process. The correlation is checked with numerical simulations results with good agreement. (C) 2012 Elsevier Ltd. All rights reserved.