Characteristics of Flow and Heat Transfer in a Tube Bundle Evaporator with a Vapour-Liquid-Solid Flow

In this paper, a tube bundle experimental evaporator with a specific vapour-liquid-solid (V-L-S) flow boiling system with external natural circulating is established to imitate and investigate a typical three-phase flow and boiling heat-transfer characteristics in order to reveal the mechanism of this apparatus. It is shown that under the ranges of the experimental parameters tested, the average heat transfer film coefficient hfb increases with increasing of temperature difference between the inside surface of tube wall and the boiling fluid. Lowering holdup of the solid particles enhances the heat transfer process. Meanwhile, the average heat transfer film coefficient h in each tube was found to be quite different for different tubes. The addition of solid particles enlarges this difference. The circulating velocity in the tube in V-L-S flow boiling was found to increase with the increase of the overall driving force of heat transfer or temperature difference between the steam and the boiling fluid, and it is higher than that of the V-L flow boiling. Opposite is true for the pressure drop in the tube in V-L-S flow boiling. There is no obvious effect of circulating velocity but there is a clear distinction in the pressure drops when varying the solid holdups. These results may offer some useful data sets to design, scale-up of this type of evaporators.