Unsteady natural convection cooling of a water storage tank with an internal gas flue

The cooling process by natural convection in cylindrical cavities is a phenomenon which takes place in several applications such as solar energy systems. In the present work a storage tank with an internal gas flue is studied experimentally and numerically during its long-term cooling process. The computational domain includes two fluids, i.e. water in the store and air in the chimney, and two external and internal layers of steel separated by polyurethane insulation material. In this paper, the numerical and the experimental analysis of the temperature field inside the tank submitted to an external convection cooling process with a constant convection heat transfer coefficient is presented. The air and the water temperature profiles along the vertical lines are obtained experimentally and numerically, for a cooling period of 90 h. The numerical analysis is carried out using a specific CFD code developed for the present work; an axisymmetric domain has been considered. Finally, a detailed description of the phenomena that occur inside the water part of the domain during the cooling process is also provided.