Measurement of the Two-Phase Flow Void Fraction Downstream Of Spacer Grids in Tight Lattice Bundles Using Wire-Mesh Sensor

The tight lattice fuel assemblies (P/D < 1.1) have huge application potential in the new generation of the nuclear reactor systems, which possesses the advantage of higher power density and higher fuel conversion ratios, etc. Spacer grids can fix the fuel rod position and enhance the heat transfer performance. However, the two-phase flow characteristics downstream of spacer grids in the tight lattice are still not clarified. In this paper, a gas-liquid two-phase flow experiment study measuring the void fraction distribution downstream of spacer grids without mixing vanes (SGWMVs) in a double subchannels tight lattice bundle was conducted using a double-layer wire-mesh sensor. The experiment channel and the SGWMVs were both up-scaled (1:2.7) considering the difference between the experimental flow conditions and the prototype flow conditions. The phase distributions for a series of flow conditions (0.07 m/s < jg < 1.04 m/s, 0.93 m/s < jl < 1.86 m/s) were measured at Z/Dh = 115.81 of the bare rod channel as the flow data upstream of the spacer grid. Whereafter, the SGWMVs was installed at the position of Z/Dh = 145.92. The phase distributions 45mm downstream of SGWMVs were measured successively for the same flow conditions. Three types of flow patterns were obtained, including the bubbly flow, the cap-bubbly flow, and the slug flow. And the effects of SGWMVs on different flow patterns were described and analyzed. The newly obtained data established the reliability database contributing to the development of the computational fluid dynamics codes and the interfacial area transport equation.