Research On The High Speed Fluid Flow In Pebble-bed Porous Channel

In order to study the hydraulics of pebble-bed water-cooled nuclear reactor, experiments of water flowing through circular tube packed with same glass balls were carried out. The inner diameter of stainless tube is 50mm, and the diameter of the balls covers 2, 3, 5 and 8mm, which porosities are 0.379,0.39,0.397 and 0.408, respectively. Tests were performed for a flow rate of 0.6~10m3/h at air pressure.The Ergun equation is more commonly used in the Porous media. Compared with the experimental data , the traditional Ergun equation and Macdonal equation are better able to predict fluid pressure drop in porous media in the Forchheimer zone, especially the porosity is relatively small experimental values match very well with the empirical formula , and as the Reynolds number increases the value of the experimental data fit better with the experience. In the turbulent zone experience traditional Ergun formula and Macdonald empirical formula compared with the experimental data show great deviation, so turbulent zone can not use empirical formula to predict.In this paper, based on the experimental data have been re-fitted the constant coefficients of the Ergun-type empirical formula to be a more reasonable formula in the turbulent zone . And in the turbulent zone flow mechanism were analyzed, with the Reynolds number increased viscous part is decreases continuously, inertial part is increased as the Reynolds number is increasing, and in the turbulent zone is only 2mm viscous part and inertial part have a certain cross-cutting, other smaller inertial part is always higher than the viscous share.At last, fractal theory is used in the Forchheimer areas and turbulent areas respectively. The results show that the theoretical value of fractal theory is better than traditional Ergun-type empirical formula in the Forchheimer and turbulent area,and more accurate physical meaning. From the fractal theory can be seen, not only with the velocity, porosity, but also pore size, fractal dimension, tortuosity fractal dimension have an irreplaceable impact in the degree of pressure loss.