Active Chemical Sampling Using Jet Discharge Inspired by Crayfish: CFD Simulations of the Flow Fields Generated by the Jet Discharge Device

Here, we report on computational fluid dynamics (CFD) simulations conducted to develop a chemical sample collection device inspired by crayfish. The sensitivity of chemical sensors can be improved when used with a sniffing device. By collecting fluid samples from the surroundings, all solute species are also collected for the sensor. Crayfish generate jet-like water currents for this purpose. Compared to simply sucking water, food smells dissolved in the surrounding water can be more efficiently collected using the inflow induced by the jet discharge because of the smaller decay of the inflow velocity with the distance. Moreover, the angular range of water sample collection can be adjusted by changing the directions of the jet discharge. In our previous work, a chemical sample collection device that mimics the jet discharge of crayfish has been proposed. Here, we report CFD simulations of the flow fields generated by the device. By carefully configuring the simulation setups, we have obtained simulation results in which the angular ranges of the chemical sample collection in real experiments is well reproduced. Although there are still some discrepancies between the simulation and experimental results, such simulations will facilitate the process of designing such devices.

Refitting of Zirconia Toughening into Open-Cellular Alumina Foams by Infiltration with Zirconyl Nitrate

The present work describes the combination of the well-established dispersion infiltration of the hollow struts in reticulated porous ceramics (RPCs) and the salt solution infiltration of the remaining strut porosity. This approach is applied on alumina foams, which are loaded subsequently with a dispersion of sub-micrometer alumina particles and a ZrO(NO3)2 solution. The zirconyl nitrate is converted into a ZrO2 transformation toughening phase during the final sintering step. As a consequence of the complex microstructure evolution during the consecutive infiltration cycles, the reinforcement phase concentrates selectively at the weak spots of RPC structures—namely, the hollow strut cavities and longitudinal cracks along the struts. As a consequence, a severe improvement of the compressive strength is observed: The average compressive strength, normalized to a porosity of 91.6 vol.%, is 1.47 MPa for the Al2O3/ZrO2 infiltrated foams, which is an improvement by 40% with respect to alumina-only loaded foams (1.05 MPa) or by 206% compared to uninfiltrated alumina RPCs (0.48 MPa). The compressive strength results are correlated to infiltration parameters and the properties of the infiltration fluids, for example the rheological behavior and the size of the Zr solute species in the respective ZrO(NO3)2 solution.

Patterned surface charges coupled with thermal gradients may create giant augmentations of solute dispersion in electro-osmosis of viscoelastic fluids

Augmenting the dispersion of a solute species and fluidic mixing remains a challenging proposition in electrically actuated microfluidic devices, primarily due to an inherent plug-like nature of the velocity profile under uniform surface charge conditions. While a judicious patterning of surface charges may obviate some of the concerning challenges, the consequent improvement in solute dispersion may turn out to be marginal. Here, we show that by exploiting a unique coupling of patterned surface charges with intrinsically induced thermal gradients, it may be possible to realize giant augmentations in solute dispersion in electro-osmotic flows. This is effectively mediated by the phenomena of Joule heating and surface heat dissipation, so as to induce local variations in electrical properties. Combined with the rheological premises of a viscoelastic fluid that are typically reminiscent of common biofluids handled in lab-on-a-chip-based micro-devices, our results demonstrate that the consequent electro-hydrodynamic forcing may open up favourable windows for augmented hydrodynamic dispersion, which has not yet been unveiled.

Radiation-Induced Electrolytic Corrosion of LWRS: (Part 1) — Basic Mechanism and Implications in Degradation Phenomena

The author recently found that there should exist a “radiation-induced electrolytic (RIE)” mechanism in the reactor water inducing severe interaction between structural materials and their environments in aged LWRs. This mechanism was identified while trying to theoretically reconstruct the potential differences observed in two in-pile test loops; NRI-Rez in Czech Republic and INCA Loop in Sweden. These results are indicating that the in-core potential is approximately 0.1/0.4volt higher, in BWR(NWC)/PWR water chemistry respectively, when compared to the out-core regions. Through modeling studies, it was found that the concentrations of (DH)/(DO) for PWR/BWR(NWC) are higher/lower respectively, in the in-core region compared with the out-of-core region. These solute species in high concentrations should spontaneously decompose at the out-of-core region, enabling control of their water chemistry. This mode of corrosion cell has been dismissed in the nuclear community considering that the transport of ions with flow is insignificant due to high purity of reactor water. Part 1 of this paper focuses on how the RIE phenomena are prompted although the reactor water is kept in high purity. The stable molecular species in the reactor water flow transport the valence electrons. They are released at the cathodic in-core region and are recovered at the anodic out-of-core region. Thus estimated potential differences have been benchmarked with the published in-pile test results for both PWR- and BWR water chemistry environments as explained in Part 2 of this series (1).

Correlation between the Local Melt Structure and the Dynamical Properties of Mn, Zn and Si in Liquid Al: An Ab Initio Molecular Dynamics Study

In this study, Mn, Zn and Si elements which are the most common alloying elements in Al, were chosen as solute atoms to be analyzed. The structure of molten Al, local structure around solute atoms and diffusion of the solute atoms are studied using ab initio molecular dynamics simulations. The results show that minimum addition of a solute (1 atom) does not significantly influence the structure of liquid Al as a whole. However, the local structure around foreign atoms varies dramatically for the different solute species. The local structure around Mn is the most compact and stable among the three types of solute atoms, leading to its lower diffusion coefficient. Conversely, Si possess the highest diffusion coefficient among those three kinds of elements derive from the local structure around Si is the most relaxed structure. In summary, the close packing and stable spherical shell around the solute atoms affect their diffusion behaviors in the melt. In addition, it is suggested that more alloying elements should be investigated to corroborate the results of this study.

Alloying-related trends in thermal properties of ternary TiN-based nitrides

The thermal properties of TiN -based nitrides are studied using first-principles calculations. Bulk modulus, thermal expansion, heat capacity, vibrational entropy and melting point for TiN –X compounds are computed, considering all possible transition-metal solute species X. The calculated properties show clear trends as a function of d-band filling. The results indicate that the largest increase of melting point of TiN is caused by alloying element W. Computed thermal properties for pure TiN are in good agreement with the available experimental and theoretical data.

Modeling of reactant concentration in electrocatalytic processes at conducting polymer modified electrodes

This research presents a mathematical model analyzing of electrochemical processes occurring at electrodes covered with a thin film of a conducting polymer. The model takes into account the diffusion of solution species into a polymer film, diffusion of charge carriers within the film, and a chemical redox reaction within the film. The aim of this work was to find the location of a mean reaction zone that is of a great practical interest related to optimization of the parameters of electrocatalytic system for its best performance. It has been shown that electrocatalysis of solute species at conducting polymer modified electrodes proceeds within the polymer film rather than at he outer polymer/solution interface.