Experimental study of cross flow and lateral pressure drop in a 5 × 5 rod bundle with mixing vane spacer grid

Abstract

Cross flow and lateral pressure drop downstream a split-type mixing vane spacer grid in a 5 × 5 rod bundle were experimentally measured by particle image velocimetry (PIV) and differential pressure transmitter at the sub-channel Reynolds number (Re) of 13200. The geometrical parameters of the 5 × 5 rod bundle is as the same diameter (D = 9.5 mm) and pitch (P = 12.6 mm) as the real fuel rods of a typical pressurized water reactor (PWR), with sub-channel hydraulic diameter (Dh) 11.78 mm. With the aid of matched index of refraction (MIR) technique of transparent fluorinated ethylene propylene (FEP) tubes and water, the PIV measurements of cross flow covering all sixteen inner-sub-channels were conducted for cross sections at 1Dh, 4Dh, 8Dh and 16Dh downstream the spacer grid. With detailed error and uncertainty analysis, the uncertainty of the turbulent statistics is mainly determined by the out of plane error and sampling number error. The maximum standard uncertainty of statistical quantities normalized by the bulk velocity is less than 1%. The characteristics of cross flow were mainly determined by the mixing vanes of spacer grid in rod bundle. The mixing vanes generate strong cross flow and drastic turbulence flow downstream the spacer grid, enhancing the cross flow mixing and turbulent mixing between sub-channels. The lateral pressure drop was measured at 1Dh, 2Dh, 3Dh, 4Dh, 5Dh, 6Dh, 8Dh, 10Dh, 12Dh, 14Dh, 16Dh, 18Dh and 20Dh. The relative uncertainty level of lateral pressure drop is between 0.7% and 7.0%. Downstream the spacer grid, the lateral pressure drop increases from 1Dh to 2Dh. After 3Dh, the lateral pressure drop decays in exponential way with distance from spacer grid. After 16Dh, the lateral pressure drop almost keeps constant.