Nuclear Technology / Volume 180 / Number 2 / November 2012 / Pages 159-173
Technical Paper / Fission Reactors
Pressure drops over a packed bed of a pebble bed reactor were investigated. Measurements of porosity and pressure drop over the bed were carried out in a cylindrical packed-bed facility. Air and water were used for the working fluids. There are several parameters influencing the pressure drop in packed beds. One of the most important factors is the wall effect. The inhomogeneous porosity distribution in the bed and the additional wetted surface introduced by the wall cause variation of the pressure drop. The importance of wall effects and porosity can be explained by using different bed-to-particle-diameter ratios. Four different bed-to-particle-diameter ratios were used in these experiments (D/dp = 19, 9.5, 6.33, and 3.65). A comparison is made between the predictions by a number of empirical correlations including the Ergun equation (1952) and that of the Nuclear Safety Standards Commission (KTA) in the literature. Analysis of the data indicates the importance of the bed-to-particle-size ratio on the pressure drop. The comparison between the present and the existing correlations showed that the pressure drop of large bed-to-particle-diameter ratios (D/dp = 19, 9.5, and 6.33) matched very well with the original KTA correlation. However, the published correlations cannot be expected to predict accurate pressure drop for certain conditions, especially for pebble beds with D/dp 5. An improved correlation was obtained for a small bed-to-particle-diameter ratio by fitting the coefficients of that equation to experimental databases.