An analytical experimental investigation into the temperature field inside the hot water storage tank of a solar collector was carried out. A transient two-dimensional semi-infinite cylindrical length model with time-and-space boundary-conditions dependency was selected. Conduction and convection heat-transfer modes in the axial direction together with conduction in the radial direction were neglected, since these were considered to be small in comparison with the axial conduction and convection diffusion terms, which in turn were considered small relative to the energy stored. Good agreement between theoretical and experimental prediction was verified. The radial direction temperature dependency disappeared for axial lengths greater than one quarter of the tank depth for most practical operating conditions especially for low inflow velocities and low inlet to outlet temperature ratios. The axial conduction term in the governing equation can be dropped out for inflow velocities greater than a certain critical value without distorting the theoretical consequences. Temperature profiles in the axial direction of a cylindrical storage tank can be assumed to be linear especially for high inflow velocities as well as low temperature differences at inlet and outlet of the storage tank.

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