TRANSPORT CHARACTERISTICS OF TWO-PHASE FLOW IN ROD BUNDLE CHANNELS WITH A SPACER GRID

The variation of void fraction and interfacial area concentration can affect the heat transfer, mass transfer, and interfacial drags. This study investigates the air-water two-phase flow in 5x5 Rod Bundle Channels with a spacer grid. The four-sensor conductivity probe was used to measure the distribution of local two-phase flow parameters (void fraction, interfacial area concentration, bubble Sauter mean diameter, bubble frequency, and bubble velocity) across channels cross-sections at 36.5, 56, 65.2, 77, and 87.6 hydraulic diameters. The experimental data was used to analyze the development characteristics of two-phase flow parameters across the channel cross-section and along the flow direction, the effect of spacer grid and gas-phase superficial velocities, and the one-dimensional transport of the averaged two-phase flow parameters. The results show that the distribution of the local interfacial structure is mainly affected by the combined effects of the radial forces, such as the lift force, the wall lubrication force, and the turbulent dispersion force. The spacer grid mainly affects the distribution characteristics of interfacial parameters through turbulent vortex aggregation and grid shear fracture, with opposite effects; There is a spacer grid influence zone downstream of the spacer grid, and the distribution of interfacial parameters inside it undergoes drastic changes.