Coupling Of Different Processes Research Articles

Multiphase Fluid Dynamics and Mass Transport Modeling in a Porous Electrode toward Hydrogen Evolution Reaction

The intrinsic activity of hydrogen evolution reaction (HER) catalysts has been significantly improved in the past decades, and current efforts are devoted to implement these catalysts for HER applications through electrode design and fabrication. However, HER in an electrode usually involves complex processes including electrochemical reaction, ion transport, bubble behavior, and gas–liquid flow near the electrode surface. The coupling of different processes makes it difficult to accurately analyze the effect of each process on the HER performance of the electrode. In this paper, a multiphase fluid dynamics and mass transport model is proposed to decouple the HER processes and provide a deep understanding on the interactions among those processes. The results reveal a strong interaction between ion transport inside the electrode and bubble detachment/ascending outside the electrode. The surface design can effectively improve the velocity profile of the liquid and hence dominate the ion transport near the electrode, whereas the design of pore structure can remarkably enhance the ions diffusion inside the electrode. In addition, external forced electrolyte flow can further enhance the fluid convection and ion transport when the speed of forced flow is higher than that induced by bubble ascending. These results conclude that the proposed model contributes to the understanding of interactions among electrochemical reaction, ion transport, bubble behavior, and gas–liquid flow near the electrode surface, providing a guideline for HER electrode design.

Testing and scaling-up of a novel Ti/Ru0.7Ti0.3O2 mesh anode in a microfluidic flow-through reactor

This work investigates the scale-up of the electrolysis and photo-electrolysis of water polluted with clopyralid using a novel Ti/Ru0.3Ti0.7O2 mesh anode produced by CO2 laser. Two different cells were used: a mixed tank cell (MT) and a microfluidic flow-through reactor (MF-FT). The main advantages of the MF-FT reactor are the simultaneous reduction of the ohmic resistance and mass transfer limitations, which are two critical factors in electrochemical oxidation. Thus, the goal is the scale-up evaluation and the study of the effects of the kind of water matrix towards practical application of the laser-made anode in water treatment. Aqueous solutions of clopyralid and groundwater intensified with this pollutant were studied in the context of the scale-up evaluation to clarify the effects of the water matrix. Single photolysis was also studied for comparison purposes. It was demonstrated that photo-electrolysis results in a faster clopyralid and TOC removal in both the MF-FT reactor and mixed tank cells as compared to single electrolysis. This work also focuses on the synergy coefficient to evaluate the effect of the coupling of different processes on system performance. Higher synergistic effects occur on clopyralid removal in the MF-FT reactor (110% and 358%, for natural groundwater and synthetic water, respectively) and TOC (233.3% and 15396% for natural groundwater and synthetic water, respectively). The best performance was obtained in the MF-FT reactor, which was attributed to the more uniform potential/current distribution associated with the reduced interelectrode gap (few microns) in comparison with the MT cell (gap of one centimeter), which also results in reduced energy consumption.

Understanding Space Launch Vehicle Complexity: A Case Study in Combustion Instabilities

Abstract In rocket engine failures of F-1 and Titan-II, chamber combustion instabilities (CI) caused damage, reflecting behavioral complexities at the component level. Combustion chamber walls with embedded acoustic nodes self-excited by the heat released to cause amplification of acoustic oscillations, showed increases in the thermo-kinetic related pressure. Although the causes of the failed launch were determined decades after the accident, the problem-solving process identified the CI problem domain with information describing the internal representation of the problem. Rocket engine complexity may be described by the high number of component parts contained; alternatively, of the constituent processes occurring. Interactive behaviors not accounted for, occur at the interface between the parts or result from coupling of different processes within the combustion chamber. Unlike monolithic systems, rocket engines exhibit performance behaviors emergent, unpredictable and uncoordinated. Over half propulsion technologies of prospective mission competence have a Technical Readiness Level (TRL) less than 5. However, operational risk needs mitigation through increased development of technological readiness related to not only structural performance but to processes enacted of their functions. Increasingly complex propulsion technologies and the thousands of stakeholder requirements needed for analysis are important for framing problems to be solved. The purpose of this paper is to correlate complexity of propulsion technology at the subsystem level with development of technological readiness for performance reliability. Nonlinear performance behaviors connote system complexity.

Coupled chemical and mechanical processes in concrete structures with respect to aging

Accurate prognoses of the durability of concrete structures require a detailed description of the continuously running aging processes and a consideration of the complete load history. Therefore, in the framework of continuous porous media mechanics a model is developed, which allows a detailed analysis of the most important aging processes of concrete as well as a flexible coupling of different processes. An overview of the prediction model and the balance equations is given. The material dependent model equations, the consequences of coupling different processes and the solution scheme are discussed. In two case studies the aging of concrete due to hydration and chloride penetration are presented, which illustrate the capabilities and the characteristics of the developed model.

The effects of baryon physics, black holes and active galactic nucleus feedback on the mass distribution in clusters of galaxies

The spatial distribution of matter in clusters of galaxies is mainly determined by the dominant dark matter component, however, physical processes involving baryonic matter are able to modify it significantly. We analyse a set of 500 pc resolution cosmological simulations of a cluster of galaxies with mass comparable to Virgo, performed with the AMR code RAMSES. We compare the mass density profiles of the dark, stellar and gaseous matter components of the cluster that result from different assumptions for the subgrid baryonic physics and galaxy formation processes. First, the prediction of a gravity only N-body simulation is compared to that of a hydrodynamical simulation with standard galaxy formation recipes, then all results are compared to a hydrodynamical simulation which includes thermal AGN feedback from Super Massive Black Holes (SMBH). We find the usual effects of overcooling and adiabatic contraction in the run with standard galaxy formation physics, but very different results are found when implementing SMBHs and AGN feedback. Star formation is strongly quenched, producing lower stellar densities throughout the cluster, and much less cold gas is available for star formation at low redshifts. At redshift z = 0 we find a flat density core of radius 10 kpc in both of the dark and stellar matter density profiles. We specu- late on the possible formation mechanisms able to produce such cores and we conclude that they can be produced through the coupling of different processes: (I) dynamical friction from the decay of black hole orbits during galaxy mergers; (II) AGN driven gas outflows producing fluctuations of the gravitational potential causing the removal of collisionless matter from the central region of the cluster; (III) adiabatic expansion in response to the slow expulsion of gas from the central region of the cluster during the quiescent mode of AGN activity.