The effect of operating and design parameter on bubble column performance: The LOPROX case study

It is known that the performances of multi-phase reactors depend on the operating parameters (the temperature and the pressure of the system), the phase properties, and the design parameters (the aspect ratio (AR), the bubble column diameter, and the gas sparger design). Hence, the precise design and the correct operation of multi-phase reactors depends on the understanding and prediction of the fluid dynamics parameters. This paper contributes to the existing discussion on the effect of operating and design parameter on multi-phase reactors and, in particular, it considers an industrial process (e.g., the LOPROX (low pressure oxidation) case study, which is typical example of two-phase bubble columns). Based on a previously-validated set of correlations, the influence of operating and design parameter on system performances is studied and critically analyzed. First, we studied the effects of the design parameter on the liquid–gas interfacial area, by keeping constant the fluid physical–chemical properties as well as the operating conditions; subsequently, we discussed for a fixed system design, the influence of the liquid phase properties and the operating pressure. In conclusion, this paper is intended to provide guidelines for the design and scale-up of multi-phase reactors.     

Analysis of surface and interior degradation of gas diffusion layer with accelerated stress tests for polymer electrolyte membrane fuel cell

The effects of surface and interior degradation of the gas diffusion layer (GDL) on the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs) have been investigated using three freeze-thaw accelerated stress tests (ASTs). Three ASTs (ex-situ, in-situ, and new methods) are designed from freezing ?30 °C to thawing 80 °C by immersing, supplying, and bubbling, respectively. The ex-situ method is designed for surface degradation of the GDL. Change of surface morphology from hydrophobic to hydrophilic by surface degradation of GDL causes low capillary pressure which decreased PEMFC performance. The in-situ method is designed for the interior degradation of the GDL. A decrease in the ratio of the porosity to tortuosity by interior degradation of the GDL deteriorates PEMFC performance. Moreover, the new method showed combined effects for both surface and interior degradation of the GDL. It was identified that the main factor that deteriorated the fuel cell performance was the increase in mass transport resistance by interior degradation of GDL. In conclusion, this study aims to investigate the causes of degraded GDL on the PEMFC performance into the surface and interior degradation and provide the design guideline of high-durability GDL for the PEMFC.     

Co-firing hydrogen and dimethyl ether in a gas turbine model combustor: Influence of hydrogen content and comparison with methane

To promote the utilization of hydrogen (H₂) in existing gas turbines, dimethyl ether (DME) was used to co-fire with H₂ in a model combustor. The swirl combustion characteristics of DME/H₂ mixtures were measured under the varying H₂ content up to 0.7. The results show that the flow velocity elevates as the H₂ content increases, which is associated with the increased flame temperature. The OH level firstly increases and subsequently keeps nearly unchanged as the H₂ content increases. Meanwhile, the OH area nonlinearly increases with the increasing H₂ content. Moreover, the increasing H₂ content induces almost linearly decreased lean blowout limit (LBO), increased NO emission, and intensified combustion acoustics. Furthermore, the combustion characteristics of the 0.46DME/0.54H₂ mixture and CH₄ with the same volumetric heat value were compared. The 0.46DME/0.54H₂ flame displays lower LBO and higher NO emission than the CH₄ flame, which mainly results from the higher reactivity of 0.46DME/0.54H₂ mixture.     

Enable high reversibility of Fe/Cu based fluoride conversion batteries via interfacial gas release and detergency of garnet electrolytes

Garnet-type Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO) electrolyte suffers from unstable chemical passivation under air exposure, responsible for the poor interfacial wettability and conductivity with Li metal. Instead of conventional methods to remove surface contaminants by mechanical polishing, acid etching and high temperature reduction, herein we propose a simple strategy of interfacial gas release and detergency to smartly convert Li₂CO₃ passivation layer into ion-conductive Li₃PO₄ domains at mild temperature (∼200 ℃). The in-situ formation of PH₃ vapor and its phosphorization enables a dramatic decrease of Li/garnet interfacial resistance down to 2 Ω cm² at room temperature (RT). The improved interfacial wettability and conductivity endow the symmetric cells with ultra-stable galvanostatic cycling over 1500 h and high critical current density of 2.6 mA/cm². The high coulombic efficiency of Li plating enables a high reversibility of solid-state NCM811/Li cells even under a low N/P ratio (∼4) and high cut-off voltage of 4.5 V at RT. The prototype of fluoride-garnet solid-state batteries are successfully driven as rechargeable system (rather than widely known primary battery) with high conversion capacity (400 ∼ 500 mAh/g) and high-rate performance (251.2 mAh/g at 3 C). This interface infiltration-detergency approach provides a practical solution to the achievement of high-energy solid-state Li metal batteries.     

Fabrication of novel AlN-SiC-C refractories by nitrogen gas-pressure sintering of Al4SiC4

Novel AlN-SiC-C refractories were fabricated by nitrogen gas-pressure sintering using single Al₄SiC₄ as raw-material. The high nitrogen pressure is essential and effective for the nitridation because it contributes to the diffusion of the nitrogen atoms into the interior matrix of Al₄SiC₄ specimen. Different from traditional carbon-containing refractories and ceramic bonded carbon materials (CBCs), the resulted products possess a honeycomb microstructure consisting of interlocked structure of worm-like SiC and C particles with a AlN ceramic boundary. AlN-SiC nanoparticles and aluminum carbonitride particles (Al-C-Ns) were formed at the interface between AlN-rich and C/SiC-rich area, which acted as transition phases that make these two areas combined tightly. The as-prepared AlN-SiC-C refractories at 1700 ℃ by a 20 atm pressure showed a relative density of 75.8%, combining a bulk density of 2.20 g/cm³ with a flexural strength of 120.9 MPa. Furthermore, the potential reaction mechanism responsible for fabrication of AlN-SiC-C refractories was revealed.     

Controllable synthesis of porous Co3O4 nanorods and their ethanol-sensing performance

A simple strategy for synthesizing porous Co₃O₄ nanostructures through a hydrothermal process with subsequent thermal decomposition of the obtained Co(CO3)0·35Cl0·20(OH)1.10 precursors was introduced. To understand the growth mechanism of the Co(CO₃)_0·35Cl_0·20(OH)_1.10 precursors and realize morphology control of the resultant Co₃O₄ nanomaterials, a series of controlled experiments were carried out by varying CO(NH₂)₂ dosages, hydrothermal temperatures and time. The Co₃O₄ nanorods obtained under optimized synthesis conditions demonstrated porous structural features, which were constructed by well-connected nanograins, leaving many pores composed of the space between nanograins. The ethanol-sensing behaviors of these Co₃O₄ nanostructures were evaluated, showing the highest response (19.581) and a short response and recovery time (1 s/10 s) to 100 ppm ethanol. Moreover, the Co₃O₄ sensor demonstrated excellent anti-interference ability toward several interfering gases such as methanol, benzene hexane, and dichloromethane. The stability of the Co₃O₄ sensor was further confirmed by 14 days of continuous testing. Compared with previously reported works, this Co₃O₄ sensor still demonstrated outstanding gas sensing properties due to its unique advantages such as 1D porous nanostructures, high BET surface area, abundant oxygen vacancies, and active cobalt sites.     

Influences of hydrogen and various gas fuel addition to different liquid fuels on the performance characteristics of a spark ignition engine

This study reports the impacts of dual fuel mixtures on the theoretical performance characteristics of a spark ignition engine (SIE). The effects of addition of liquefied hydrogen, methane, butane, propane (additive fuels) into gasoline, iso-octane, benzene, toluene, hexane, ethanol and methanol fuels (primary fuels) on the variation of power, indicated mean effective pressure (IMEP), thermal efficiency, exergy efficiency, were examined by using a combustion model. The fuel additives were ranged from 10 to 50% by mass. The results exhibited that the ratios of hydrogen, methane, butane, propane noticeably affect the performance of the engine. The maximum increase ratio of power is 82.59% with 50% of toluene ratio and its maximum decrease ratio is 10.84% with 50% of methanol ratio in hydrogen mixtures. The maximum increase ratio of thermal efficiency and exergy efficiency are observed as 26.75% and 32.23% with the combustion of benzene-hydrogen mixtures. The maximum decrease ratio of thermal efficiency is 29.71% with the combustion of 50% of methanol ratio and it is 21.95% for the exergy efficieny with the combustion of 50% of ethanol ratio in hydrogen mixtures. The power, IMEP, thermal efficiency and exergy efficiency of primary fuels demonstrate different variation characteristics with respect to type and ratio of additive fuels.     

Surface and interface properties of monolayer graphene on hydrophobic and hydrophilic ultrananocrystalline diamond structures for hydrogen sensing applications

Here, for the first time, we synthesize hybrid hydrophilic and hydrophobic nanocarbon materials with reliable and stable gas sensing performance. The hybrid monolayer graphene (Gr)–nitrogen and argon (N₂ and Ar) gas incorporated ultra-nanocrystalline diamond (Gr/N₂@UNCD and Gr/Ar@UNCD) structures were synthesized using a microwave plasma enhanced chemical vapor deposition (MPECVD) method. The presented nanohybrid combinations have a unique morphology with diamond defects (sp³) covered by a graphene sheet (sp²). Sample sensors with metal electrodes were fabricated to study the H₂ gas sensing properties of the material. Thus, the as-fabricated Gr/N₂@UNCD exhibited higher sensor response (14.6%) than those of the as-fabricated Gr, N-UNCD and Gr/Ar@UNCD (3.6, 1.07 and 11.2%) based devices. The Gr/N₂@UNCD nanohybrid based sensor showed outstanding repeatability, selectivity and stability over ～56 days. The substantial improvement in the H₂ sensing performance of the as-fabricated Gr/N₂@UNCD nanohybrid based sensor was attributed to the modifications in surface morphology and resistance. The partial-hydrophobic surface of Gr/N₂@UNCD alters the beneficial resistivity and improved absorption, which assists in the efficient transport of electrons and H₂ gas molecules. The hybrid nanostructure of Gr-N₂@UNCD exhibits several unique properties that paves the way to future opportunities for advanced gas sensor fabrication.     

Multi-criteria analysis for screening of reversible metal hydrides in hydrogen gas storage and high pressure delivery applications

Metals and alloys forming reversible hydrides with hydrogen gas are potential building blocks for compact, solid state hydrogen storage systems. Based on the materials’ thermodynamic characteristics, their use as temperature-swing gas compression and delivery systems in the hydrogen economy is also possible. Given the wide variety of materials developed and tested at laboratory and pilot scales, a harmonized method of selecting the feasible material(s) for a particular real-life application is required. This study proposes a system selection framework based on a normalized, multi-criteria metric. Using calculated values of multi-criteria metric, multi-criteria screening and ranking of potential materials has been demonstrated for a particular use case. It is found that the alloy TiMn_1.52 having value of additive metric between 0.25 and 0.35 represents the best material for a single stage system. The alloy pair CaNi₅–Ti_1.5CrMn represents the best alternative for a two-stage system with additive metric values between 0.63 and 0.82. Energy and economic characteristics of the metal hydride gas compression and delivery systems are evaluated and compared with an equivalent mechanical compression system producing the same final effect (i.e., delivery of a given quantity of gas at a defined pressure).     

Thermomechanical stability and inelastic energy dissipation as durability criteria for fuel cell gas diffusion media with pre-assembly effects

In this article, pre-assembly hot-press pressure and thermal expansion effects in gas-diffusion layers (GDLs) are addressed to explore the practicalities of the constitutive model reported in the companion article. A facile technique is proposed to include deformation history dependent residual strain effects. The model is implemented in the numerical environment and compared with widely followed conventional models such as isotropic and orthotropic material models. With the normal and accelerated thermal expansion effects no significant variation in stresses or strains is reported with the compressible GDL model in contrast to the conventional incompressible form of the GDL model. The present work identifies the critical differences with advanced and extended variants of the model along with conventional GDL material models in terms of planar stress/strain distribution and the membrane response. Finally, the model is simulated for micro-cyclic stress loads of varying amplitudes that imitate the real working conditions of fuel cell. The inelastic energy dissipation in GDLs is predicted using the proposed model, which is utilized further to distinguish the safe (elastic) and unsafe (inelastic shakedown) operating limits. The inelastic collapse of GDLs is shown to be a active function of high amplitude micro-cyclic load with high initial clamping load.