Natural convection from a horizontal tube heat exchanger immersed in a tilted enclosure

Heat transfer rates of a single horizontal tube immersed in a water-filled enclosure tilted at 30 deg are measured. The results serve as a baseline case for a solar water heating system with a heat exchanger immersed in an integral collector storage. Experiments are conducted for isothermal and stratified enclosures with both adiabatic and uniform heat flux boundary conditions. Natural convection flow in the enclosure is interpreted from measured water temperature distributions. Formation of an appropriate temperature difference that drives natural convection is determined. Correlations for the overall heat transfer coefficient in terms of the Nusselt and Rayleigh numbers are reduced to the form Nu_D=0.675Ra_D^0.25 for 9 × 10⁵ ≤ Ra_D ≤ 4 × 10⁷.