Some aspects concerning modelling the flow and heat transfer in horizontalmantle heat exchangers in solar water heaters

An experimental and numerical investigation has been undertaken to study th e heat transfer process in horizontal mantle heat exchangers used in solar water heaters. A rectangular cavity has been used as a simplified geometry. With the aid of particle image velocimetry (PIV) the how held in the centr e-plane of the rectangular cavity has been visualized. Three-dimensional ho w simulations were performed using a commercial CFD package. The impinging jet formed by the inlet flow directed towards the opposite wall was found t o produce localised turbulence in the cavity, with an inlet Reynolds number as low as 360. This turbulence was found to effect the flow field and heat transfer in the cavity when the inlet Reynolds number was above 1200. It i s shown that, with the boundary conditions used in this study, most of the heat transferred was in the bottom half of the cavity. This is not the idea l situation for optimization of solar water heating systems. Copyright (C) 1999 John Wiley & Sons, Ltd.