[en] An accurate prediction of the pressure drop along the flow paths is crucial in the design of advanced passive systems cooled by heavy liquid metal coolants. To date, a generic pressure drop correlation over spacer grids by Rehme has been applied extensively, which was obtained from substantial experimental data with multiple types of components. However, a few experimental studies have reported that the correlation may give large discrepancies. To provide a more reliable correlation for ring-type spacer grids, the current numerical study aims at figuring out the most critical factor among four hypothetical parameters, namely the flow area blockage ratio, number of fuel rods, type of fluid, and thickness of the spacer grid in the flow direction. Through a set of computational fluid dynamics simulations, we observed that the flow area blockage ratio dominantly influences the pressure loss characteristics, and thus its dependence should be more emphasized, whereas the other parameters have little impact. Hence, we suggest a new correlation for the drag coefficient as C_B ¼ C_v,m/ε ^2.7, where C_v,m is formulated by a nonlinear fit of simulation data such that C_v,m ¼ -11.33 ln(0.02 ln(Re_b))

[en] A micro/nano pattern was simply fabricated on the surface of a hydroxyethyl cellulose (HEC) thin film and its properties were investigated. HEC is easily dissolved in water and has excellent properties such as viscosity, transparency and stability. In this study, HEC was prepared by chemical processing with water-insoluble cellulose and water-soluble ether and was then cast as a flexible film. With the use of a micro patterned metal mold, the pattern was simply replicated on the solid-state HEC film. Micro/nano hybrid structured patterns consisting of micro-scale structures of about 10 μm and nano-scale fibrils of less than 10 nm were prepared, and the surface characteristics of the patterned HEC film were experimentally verified. Measurements showed that the micro/nano hybrid structure resulted in a higher water drop contact angle, but the contact angle decreased gradually with increasing wetting time.