[en] A small-scale circular tube was modeled with the CFD software ANSYS CFX to study the impact of roughness on the resistance characteristics. The calculated pressure drop was compared with the experimental data. By comparison, it was found that the calculated pressure drop was in accordance with the experimental data. Also it was in agreement with the pressure drop that arrived based on the Moody figure. But it had a large difference with the results calculated by the Blasius equation. At last, it was concluded that the roughness had an important impact on the pressure drop characteristics for the small flow path in reactor, such as fuel assembly, heat transfer tube of steam generator and so on. So the roughness must be take into account when make a numerical simulation of a small-scale pipe. But for the engineering pipe, the roughness effect can be ignored. (authors)

[en] Highlights: ► Ba_1−xEu_xWO₄ red phosphors are synthesized by coprecipitation/calcination method. ► The obtained powders are identified by X-ray diffraction, scanning electron microscope (SEM) and fluorescence spectrometer. ► Spectroscopic study of Eu³⁺ ions was made at room temperature. The optimal doping concentration and concentration quenching mechanism are discussed. - Abstract: In this paper, we report on the series of novel red phosphors (Ba_1−xEu_x)WO₄ were synthesized by coprecipitation/calcination method. The morphology and structure were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Photoluminescence (PL) excitation and emission spectra were also used to characterize the (Ba_1−xEu_x)WO₄. The results showed that all phosphors present a scheelite-type tetragonal structure with space group (I4₁/a). The SEM images showed that the grains were like shuttles with sizes ranging from 3.0 to 7.0 μm. The obtained (Ba_1−xEu_x)WO₄ phosphor emitted red emission centered at 612 nm corresponding to the ⁵D₀ → ⁷F₂ transition of Eu³⁺ when was excited by 394 nm and 465 nm which well matched with near-ultraviolet and blue chips. The optimized concentration of Eu³⁺ was 20 mol.% for the highest PL emission intensity which was excited at 534 nm. The concentration quenching occurred when the Eu³⁺ concentration was beyond 20 mol.%.