This study summarizes experimental investigations of the flow field characteristics in the cross-flow planes of a 5×5 rod bundle with spacer grid and split-type mixing vanes. Under the isothermal and atmospheric conditions, the velocity fields in the cross-flow planes are obtained by applying the matched-index-of-refraction and time-resolved particle image velocimetry (TR-PIV) techniques for Reynolds numbers of Re1=14,000 and Re2=28,000. The cross-flow planes axially start from the tips of the mixing vanes of the spacer grid and end at 11.73Dh (Dh is the hydraulic diameter of the rod bundle). From the acquired TR-PIV velocity fields, flow statistics such as the in-plane mean velocity and vorticity, turbulent kinetic energy and Reynolds stress are computed and presented for four cross-flow planes of interest axially located at 0,2Dh,5Dh, and 11Dh. Two counter rotating vortices are observed near the spacer grid. After a change in elevation to z/Dh=5, the vortices merge into a single vortex centered in the middle of the subchannel. In addition, the turbulence flow characteristics at the elevations of interest are discussed through calculations of integral length scales and spectral analysis. No dominant frequency is observed, and the turbulence characteristics are strongly influenced by the proximity to the spacer grid. The mass transfer between the subchannels and the associated turbulent mixing flow rate is calculated for all elevations; hence, this study is a step toward improving the correlations currently used in subchannel codes. Results for secondary flow intensities, lateral velocity profiles and velocity contours are compared with large-eddy simulation results from the literature for Re1=14,000, and a reasonable agreement is observed.

Objectives: Face masks are an important component of personal protection equipment employed in preventing the spread of diseases such as COVID-19. As the supply of mass-produced masks has decreased, the use of homemade masks has become more prevalent. It is important to quantify the effectiveness of different types of materials to provide useful information, which should be considered for homemade masks. Methods: Filtration effects of different types of common materials were studied by measuring the aerosol droplet concentrations in the upstream and downstream regions. Flow-field characteristics of surrounding regions of tested materials were investigated using a laser-diagnostics technique, i.e., particle image velocimetry. The pressure difference across the tested materials was measured. Results: Measured aerosol concentrations indicated a breakup of large-size particles into smaller particles. Tested materials had higher filtration efficiency for large particles. Single-layer materials were less efficient, but they had a low pressure-drop. Multilayer materials could produce greater filtering efficiency with an increased pressure drop, which is an indicator of comfort level and breathability. The obtained flow-fields indicated a flow disruption downstream of the tested materials as the velocity magnitude noticeably decreased. Conclusions: The obtained results provide an insight into flow-field characteristics and filtration efficiency of different types of household materials commonly used for homemade masks. This study allows comparison with mass-produced masks under consistent test conditions while employing several well-established techniques.

Pressurized water reactors (PWRs) are the most common types of electricity generating nuclear reactors. Within their cores, fuel rods generate heat by fission and the high-pressure water is used as a coolant. The heated water is then used as a heat source in a steam generator that boils water in the secondary loop. The steam is used to spin a turbine and generate electricity. Spacer grids are key components of a PWR's core. Their objectives are to maintain the fuel rods at their positions and enhance the coolant mixing and heat exchange. Over the past decades, numerous experimental and numerical studies have been performed, to characterize the flow induced by different types of spacer grids. The recent advancements of the computational description of the above-mentioned flows, led to a shift to higher resolution models for turbulence like Large Eddy Simulations. Therefore, highly spatially resolved experimental data is needed for code validation. The comparison and usage of the data about the flow in rod bundles with spacer grids obtained by different research groups is challenging. One major reason comes from the fact that the majority of the spacer grids studied are proprietary, and their geometries cannot be disclosed. The data required for some purposes like numerical code validation do not necessarily have to originate from one specific type of spacer grid. It is important to provide a detailed overview of the geometry tested and the experimental conditions. Equally crucial is to possess high spatial resolution and well-quantified and low relative uncertainty. In this study, a new, non-proprietary spacer grid is designed and 3D-printed. The flow induced by the spacer grid is characterized in a 5 x 5 rod bundle facility with Matching of Index of Refraction (MIR) at a Reynolds number Re = 27,390 using particle image velocimetry techniques. A complete uncertainty analysis is performed accounting for a variety of uncertainty sources. A low relative uncertainty is obtained. Eight middle-of-subchannel planes are selected as the domain of interest for this paper. Highly spatially resolved statistical results for the velocities, root-mean-square (RMS) fluctuating velocities, and Reynolds stresses are obtained along the span-wise direction of the flow, starting at the edge of the spacer grid up to 4.3 hydraulic diameters. The cross-flow between subchannels induced by the spacer grid is sustained for all the domain assessed. The turbulence induced by the spacer grid is assessed with the use of two-points cross-correlations and with the comparison of the RMS fluctuating velocities at different elevations. An increase of the size of the turbulent vortices along the span-wise direction is related to the decrease in the rms fluctuating velocities to evidence the turbulent dissipation. Differences between the size of the turbulent structures found with integral length scale calculations in the stream-wise and span-wise directions are attributed to the turbulence anisotropy. The full dataset and spacer grid geometry design will be available on the research group website of the authors. The data obtained can be used by other groups according to their interests.