Two-phase flow and maldistribution in gas channels of a polymer electrolyte fuel cell

Liquid water transport in a polymer electrolyte fuel cell (PEFC) is a major issue for automotive applications. Mist flow with tiny droplets suspended in gas has been commonly assumed for channel flow while two-phase flow has been modeled in other cell components. However, experimental studies have found that two-phase flow in the channels has a profound effect on PEFC performance, stability and durability. Therefore, a complete two-phase flow model is developed in this work for PEFC including two-phase flow in both anode and cathode channels. The model is validated against experimental data of the wetted area ratio and pressure drop in the cathode side. Due to the intrusion of soft gas diffusion layer (GDL) material in the channels, flow resistance is higher in some channels than in others. The resulting flow maldistribution among PEFC channels is of great concern because non-uniform distributions of fuel and oxidizer result in non-uniform reaction rates and thus adversely affect PEFC performance and durability. The two-phase flow maldistribution among the parallel channels in an operating PEFC is explored in detail.     

Effects of kiwifruit and mixed dietary fibre on faecal properties and microbiota in rats: a dose–response analysis

In this study, a rat model was used to explore the interaction of kiwifruit with co‐consumed mixed dietary fibre. Rats were used in three consecutive trials in which faecal properties and composition, and bacterial populations were examined. In trial 1 diets, content of a dietary fibre mixture (DFM; Raftiline–citrus fibre–wheat fibre) was increased from 0% to 20%. In trial 2, dried kiwifruit pulp (KFP) content was increased from 0% to 20%. In trial 3, KFP was increased from 0% to 20% in a diet containing a 20% basal content of the DFM. The KFP caused a small dose‐dependent increase in faecal bulk and water‐holding capacity and had much less effect than the DFM. Faecal bacterial populations examined were stable across all diets and intakes of DFM and KFP. The disappearance of fermentable fibre during hind gut passage was not reduced with increasing KFP. Therefore, kiwifruit may not only have the beneficial effect of extending fermentation distally in the colon through gut activation, but may do so without disrupting the bacterial ecosystem and its functions.     

Metal oxide nanomaterials in seawater: linking physicochemical characteristics with biological response in sea urchin development

The fate and behavior of nanomaterials (NMs) in environmental media has important consequences for toxicity. The majority of aquatic research to date has focused on NM behavior in freshwater systems. However, pH and salinity differences of seawater affect dissolution and aggregation of NMs. In this study, physical characteristics of metal oxide NMs in seawater were linked with their toxicity to developing sea urchins. The metal oxide NMs TiO₂ and CeO₂ up to 10 mg/L were not toxic to the embryos of the white sea urchin (Lytechinus pictus). In contrast, ZnO NM was highly toxic to these embryos (EC₅₀ = 99.5 μg/L). The toxicity of ZnO NM was not significantly different from bulk ZnO or soluble Zn²⁺ (from ZnSO₄·7H₂O), suggesting that the toxicity of ZnO NM can be attributed to soluble Zn²⁺. Furthermore, solubility data indicate that at the concentrations used in our sea urchin embryo experiments, ZnO NM was rapidly and completely solubilized in seawater. The present study also demonstrated that Fe-doped NMs were less soluble in seawater compared to pure ZnO NMs, but there was no concomitant reduction in toxicity.     

Impedance analysis of Pb<Subscript>2</Subscript>Sb<Subscript>3</Subscript>LaTi<Subscript>5</Subscript>O<Subscript>18</Subscript> ceramic

Polycrystalline sample of Pb₂Sb₃LaTi₅O₁₈, a member of tungsten- bronze (TB family, was prepared using a high temperature solid- state reaction technique. XRD analysis indicated the formation of a single-phase orthorhombic structure. The dielectric studies revealed the diffuse phase transition and the transition temperature was found to be at 52° C. Impedance plots were used as tools to analyse the sample behaviour as a function of frequency. Cole-Cole plots showed Debye relaxation. The activation energy was estimated to be 0·634 eV from the temperature variation of d.c. conductivity. The nature of variation of d.c. conductivity with temperature suggested NTCR behaviour.     

Performance of Dye-Sensitized Solar Cells (DSSCs) Fabricated with Zinc Oxide (ZnO) Nanpowders and Nanorods

Due to their high efficiencies, along with lower production costs, many researchers are working on dye-sensitized solar cells (DSSCs) over last few decades as a substitute technology for nonconventional energy. Nanostructured ZnO has got many interesting properties such as wide band gap, large exciton binding energy, good exciton stability, and high breakdown strength, which are applicable as DSSC electrodes. This present work compares the device properties of DSSC fabricated using ZnO nanorods on a ZnO film and ZnO nanopowders. Different types of ZnO photoanode and dye combinations are used to study the stability and photovoltaic properties of the DSSC cell. The photovoltaic properties of the ZnO-based DSSC samples were systematically investigated. The photovoltaic properties of fabricated cell obtained are discussed in the light of band structure and density of states of different types of ZnO nanolayers. The ZnO nanorods fabricated through the sol–gel route have more uniform thickness resulting in enhanced photovoltaic properties of the fabricated device.