Mixed convection in a narrow rectangular cavity with bottom inlet and outlet

摘要

A model describing the heat transfer in horizontal mantle heat exchangers used in solar water heaters has been developed by approximating a narrow horizontal annulus to an equivalent rectangular cavity. Particle tracking velocimetry (PTV) and compu- tational fluid dynamics (CFD) simulations were used to determine the flow field. The flow is in the mixed-convection regime, where buoyancy locally affects the flow field and heat flux. The effect of the heat-transfer wall temperature distribution on the net heat- transfer rate has been quantified by the introduction of a stratification correction parameter. A mean Nusselt number, defined by using the difference between the inlet temperature and mean heat-transfer wall temperature, is shown to be independent of buoyancy forces when the stratification correction parameter is taken into account. A correlation has been developed for the mean Nusselt number for a range of geometries and boundary conditions. This correlation predicts the net heat-transfer rate to within 10/100.