An experimental study of boiling two-phase flow in a vertical rod bundle with a spacer grid-Part 2: Effects of vane angle

We performed boiling flow experiments and measured the void fraction in a 3 x 3 rod bundle including a spacer grid with split type vanes using X-ray computed tomography, which provides high-resolution time-averaged void data without disturbing the flow. We studied the effects of mixing vanes with different vane angles, namely, 20°, 29° and 40°, for a mass flux between 535 and 1950 kg/m2 s and the central rod being heated giving a heat flux of 85.7 kW/m2. The presence of vanes leads to an increase of the cross-sectional averaged void fraction up to an axial position of Z≈〖0.8D〗_h. After that, the void fraction decreases until 3D_h