CFD Simulation and Performance Investigation on a Novel Bionic Spider-Web-Type Flow Field for PEM Fuel Cells

The products generated by the electrochemical reaction in the PEM fuel cell (PEMFC) are mainly concentrated in the flow field on the cathode side of the bipolar plate, and the oxygen introduced on the cathode has higher requirements to improve its diffusion performance by using the flow field structure. For this reason, the optimization of the cathode flow field of the PEMFC is essential. Inspired by the structure of a spider web, this paper proposes a novel spider-web-type flow field. In this kind of flow field, the shape of a polygonal structure and the number of layers of spiral flow channels are the two most crucial variables. In order to explore the impact of these two variables on the cathode flow field, complete three-dimensional PEMFC models with different values of the two variables were established, and the models were simulated by the method of CFD. By observing the results of oxygen distribution, the water removal performance and fuel cell output performance of different schemes, the optimal scheme of the polygonal structure and layer number are determined. Compared with the traditional flow field, it is proved that the optimization scheme is desirable in improving the performance of the cathode flow field in PEMFC.

Novel polygonal structure Mn4+ activated In3+-based Elpasolite-type hexafluorides red phosphor for warm white light-emitting diodes (WLEDs)

Red phosphors (NH4)2NaInF6:Mn4+ with controllable morphology were synthesized via different synthetic methods, which can be fabricated for warm white LEDs.

Lead seals with tetrarchic busts from the imperial palace in Sirmium

In the course of archaeological excavations of the north section of the imperial palace in Sirmium (locality 85), conducted in 2015, as many as 39 lead seals were found to the south of column IV of the polygonal structure encountered in 2014. Nine specimens of imperial seals with a representation of four busts, i.e. images of the tetrarchs, are particularly interesting in this group. These seals appear in three iconographic variants (a-c) depending on whether the four busts are positioned in two rows or in a single row and whether they are of identical size. The discovery of imperial lead seals with the busts of tetrarchs bears witness to the importance of Sirmium at the time of the tetrarchy, not only as an army base for Diocletian?s wars against the Sarmatians, but also as a commercial centre where the deliveries of various products also arrived. They were, among other things, intended for building and decorating the polygonal structure used for celebrating the imperial cult.

Effects of Ca and RE Additions on the Precipitation and Microstructure of As-Cast AZ91 Alloy

The effect of Ca and RE metal additions on the precipitation and microstructure of as-cast AZ91 alloy was systematically investigated. It was found that Ca and RE additions could result in phase and microstructure changes. The XRD pattern showed the crystallite phase of as-cast AZ91 alloys consists of α-Mg matrix and β-Mg17Al12, however, after adding 1.5wt. % Ca and 0.8wt. % RE (0.5wt. % Sm and 0.3wt. % La), peaks coincident with Al2Ca, Al2Sm and Al11La3 intermetallic compounds were found, suggesting the generation of relative precipitates. The SEM images indicated that in as-cast alloys, the Al2Ca intermetallic compound was located at grain boundaries with a lamellar structure, and the Al2Sm intermetallic compound was homogeneously distributed in the α-Mg matrix or near the grain boundaries with a polygonal structure, and the Al11La3 intermetallic compound was located at grain boundaries with a needlelike structure. These intermetallic compounds could reduce the amount of β-Mg17Al12 and refine the microstructure of as-cast AZ91 alloy.

Observations of Plants with Tubular Stems with Possible Biomimetic Implications

Two plants having tubular stems were examined. Water lily belongs to nymphaeaceae, while butterbur belongs to asteraceae. These plants are not relatives; however both have large leaves with lacinia. Furthermore, these plants have tubular long stems. Observations of leaf surface are described. Water lily leaf has an inside layer consisting of a network polygonal structure. The leaf has three layers at the microscopic level including small transparent skin tissue, and a middle layer showing a polygonal green structure where photosynthesis can be performed. The bottom layer shows fine tubular tissues. Stomas are observed on the surface of the leaf, with transparent tissue on the top layer and the stem of the butterbur with honeycomb (polygonal) structures in the leaves and stems. Plants are of interest for technology because their remarkable functional structure may provide clues for applications in materials science. In this study, the fine structures of the two plants were observed to learn their functional structure.