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Numerical and experimental analyses of velocity and temperature fields inside a tank submitted to internal natural and mixed convection are presented in this paper. The numerical analyses were performed with two approaches: one using a two-dimensional model in cylindrical coordinates through the finite volume method and another using a one-dimensional model. A turbulence model for low Reynolds numbers was added to the two-dimensional model in mixed convection regime. The two-dimensional model was experimentally validated and then adopted as reference. Its results were compared to those obtained with one-dimensional models (combined with certain computational artifices described in this work) with a good agreement. [Copyright &y& Elsevier]

A numerical and an experimental analysis of velocity and temperature fields inside a storage tank submitted to natural convection is presented. The analysis was performed in two stages. In the first stage, the temperature profile along the vertical axis of the storage tank was obtained experimentally and numerically, for cooling time ranging from 45 to 60 h. The numerical analysis was carried out using a transient bi-dimensional model in cylindrical co-ordinates. In the second stage, after the numerical code validation, 40 cases of cooling with four aspect ratios, five insulation thicknesses, and two different volumes were simulated. In all simulations, thermal losses for the environment in all tank walls (side, top and bottom) were considered. Two correlations for the Nusselt number, encompassing all the forty cases, were obtained with these results. [Copyright &y& Elsevier]

Abstract: A numerical analysis of the three-dimensional temperature and velocity fields in horizontal cylindrical storage tanks was performed. The phenomena of laminar natural convection and vertical stratification of temperature were considered. The developed three-dimensional transient computing code solves the equations of energy and momentum through the finite volume method. The simulation of fluid cooling process inside the tank showed the formation of stratified temperature profiles that matched those obtained experimentally. Based on several simulations, a correlation was proposed for determining the degree of thermal stratification inside the tank regarding thermal and geometrical parameters. From this correlation, an expression was proposed to predict the fluid temperature profiles along the time. This information is very important in many applications, such as in thermosiphon solar water heating systems, where the global efficiency of the system increases with the thermal stratification degree of the working fluid. Another case studied considered that the tank was connected to solar collectors, aiming at investigating the influence of the inlet jet position with and without a baffle plate on the preservation of the thermal stratification. Results showed that the baffle plate modified the velocity and temperature fields close to the inlet jet, allowing a better thermal stratification. Also the suitable choice of the inlet jet position allowed the formation of a more effective thermal stratification. Some other aspects of the internal dynamics of this kind of storage tank are presented and discussed. For the cases studied, the inlet jet next to the top led to a greater thermal stratification. However, it was verified that when the inlet jet temperature remains constant for a long period of time, and thus its temperature approaches the temperature of the water inside the tank, for the same height, the temperature profiles obtained become similar to the case of the inlet located at usual height of 2/3 of the diameter. [Copyright &y& Elsevier]