  A fully non-dimensional correlation for the Nusselt number associated to
cooling processes in vertical storage tanks under laminar natural convection is
presented. The derived correlation depends on the average temperature and can
be used for the improvement of temperature profiles found from global methods.
A Finite Volume method is employed using a transient bi-dimensional model in
cylindrical coordinates and is experimentally validated. Forty cases of cooling
with four aspect ratios, five overall heat transfer coefficients and two
different volumes are considered. Thermal losses for the environment in all
tank walls (top, bottom and sidewalls) are allowable. The Buckingham theorem is
applied to determine the non-dimensional groups in the cooling of thermal
reservoirs and the corresponding correlations, in agreement with the numerical
results.
