Experimental measurements of effective diffusion coefficient of oxygen–nitrogen mixture in PEM fuel cell diffusion media

PEM fuel cells are increasingly designed to operate at high current densities. At these densities, mass transport limitations become very significant, but they are not well understood, with many modeling studies but few experimental observations. The use of accurate transport coefficients to simulate the mass transport at high current densities is crucial. In this study, experimental measurements have been carried out to determine the effective diffusion coefficient in the carbon paper gas diffusion layer that is commonly used in PEM fuel cells. It was found that almost all the existing theoretical models significantly overpredict the effective diffusion coefficient by as much as 4–5 times; thus, underestimating the transport limitations considerably. Further, the effects of temperature, Teflon treatment for hydrophobicity and porosity on the effective diffusion coefficient were investigated. It was found that temperature does not affect the overall diffusibility of the gas. The diffusibility is decreased with the increase of Teflon treatment and decrease in porosity. Further work on better understanding the diffusion process in the gas diffusion layer is under way.     

Experimental investigation of a two-stage solar humidification–dehumidification desalination process

This paper experimentally evaluates a two-stage technique to improve the humidification–dehumidification process in fresh water production from brackish water. According to modeling results of multi-stage process and on the basis of construction cost estimation, using a two-stage process is the most suitable choice that can improve important parameters such as specific energy consumption, productivity and daily production per solar collector area and thus, investment cost. A pilot plant was designed and constructed in an arid area with 80 m² solar collector area to evaluate the two-stage process. This unit was tested on cold and hot days. The effect of main parameters on fresh water production of the unit is studied. Experimental results show that two-stage HD desalination unit can increase heat recovery in condensers and hence, reduce thermal energy consumption and investment cost of the unit. Moreover, productivity can be increased by 20% compared with the single-stage unit.     

Experimental investigation of operating conditions for preparation of PVA–PEG blend membranes using supercritical CO2

Poly(vinyl alcohol)–polyethylene glycol, PVA–PEG, blended membrane were prepared using supercritical fluid assisted phase-inversion method, in which scCO₂ was used as the anti-solvent. Poly(vinyl alcohol) was utilized as the main polymer, polyethylene glycol as the additive, and dimethyl sulfoxide (DMSO) as the solvent of these polymers. Taguchi method was used to investigate the effect of some operating parameters on the morphology of the membranes. The L16 orthogonal array was selected under the following conditions: pressure (100, 135, 165 and 200 bar), temperature (40, 45, 50 and 55 °C) and PEG weight percent (0, 0.33, 0.66, and 1%). Total polymer concentration of solutions in all experiment was constant at 10% (w/w). The morphology of the obtained porous membranes was characterized by scanning electron microscopy. Through changing the conditions in each experiment, the average pore diameter changed between 3.75 and 12.2 μm. Results from analysis of variance (ANOVA) indicate that PEG concentration was the most significant factor on the average pore size of prepared membranes by 78.7%. This is the first work announcing preparation of PVA–PEG membrane using supercritical CO₂.     

Experimental investigation of green brick shrinkage behavior with Bigot’s curves

The objective of this work is to define the convenient drying parameters such that the energy consumption in the brick drying process is minimized. This is an experimental study where the challenge lies in the mechanical resistance of the dried bricks which must satisfy the quality standards despite the reduction of energy consumption and the drying time. Firstly, we run multiple drying process tests and gather experimental data, and then discover the most suitable drying conditions. Secondly, the overall drying rate is improved using a Bigot’s curve analysis on the most suitable drying conditions. The results show that the drying rate increases significantly in conjunction with shorter drying time and lower energy consumption.     

Numerical study of laminar rich hydrogen–air flames with added ethanol

The propagation of fuel-rich hydrogen–air flames with added ethanol has been studied using numerical methods. It has been shown that the inhibition by ethanol is less effective compared to propane and propylene. The addition of ethanol leads to the effect of superequilibrium temperatures, but it takes place only at ethanol concentrations above a certain value. At the flammability limit of fuel-rich mixtures of hydrogen, ethanol, and air, determined by the Le Chatelier rule, the estimated maximum flame temperature is constant. The exception is mixtures with a small addition of ethanol.     

Experimental investigation on particulate emissions of a direct injection diesel engine fueled with diesel–diethyl adipate blends

Euro V diesel fuel blended with 8.1%, 16.4%, 25% and 33.8% by volume of diethyl adipate (DEA), corresponding to 3%, 6%, 9% and 12% by mass of oxygen in the blended fuels, were tested on a 4-cylinder direct-injection diesel engine. Experiments were conducted under five engine loads at a steady speed of 1800 rev/min to investigate the effects of the blended fuels on combustion and particulate emission characteristics. The results indicate an increase in ignition delay and the amount of heat release in the premixed burning phase, while a decrease in both diffusive and total combustion duration with an increase in DEA in the fuel. Compared to the diesel fuel, the particulate mass concentration and the total number of particles are reduced significantly, whereas the proportion of soluble organic fraction (SOF) in the particles increases with increasing DEA in the fuel. The increase in SOF might increase the toxicity of the particles. Moreover, the geometric mean diameter (GMD) of the particles shifts towards smaller size. A diesel oxidation catalyst was used and found to further reduce both particulate mass and total number concentration. The results also show that the DOC could reduce the finer particles more effectively.     

Experimental investigation on the indentation hardness of precursor derived Si–B–C–N ceramics

The elasto-plastic response of the precursor derived Si–B–C–N ceramics upon contact loading was determined by depth sensing nanoindentation technique. The indentation response of as-thermolyzed Si–B–C–N ceramic was compared with the heat-treated counterpart. The as-thermolyzed ceramic was X-ray amorphous and the heat-treated ceramic was phase separated and crystallized. The hardness and reduced elastic modulus values of the as-thermolyzed ceramic were ～16 GPa and ～172 GPa, respectively. The reduction in hardness to ～9 GPa in the heat-treated ceramic was attributed to phase separation and crystallization of SiC and Si₃N₄. Furthermore, high elastic recovery with a plastic work ratio of ～0.3 was observed and ascribed to volume controlled deformation mechanism.     

Experimental investigation and modeling of steam cracking of Fischer–Tropsch naphtha for light olefins

The characteristics of product distribution and the kinetic model for predicting the yields of the major products from steam cracking of Fischer–Tropsch (F–T) naphtha have been investigated in a pilot plant under various conditions. An analysis of the experimental data suggests that the naphtha produced via the low-temperature slurry-phase F–T process is an excellent feedstock for the production of light olefins, especially ethylene. For steam cracking of two F–T naphthas studied, ethylene is the primary product varying from 36.89 to 41.83 wt%, and the total yield of valuable light olefins (C₂H₄, C₃H₆ and 1,3-C₄H₆) is not less than 60.34 wt% under the conditions estimated. The experimental product distributions could be satisfactorily predicted by use of a detailed molecular reaction scheme which consists of a first-order primary reaction and 37 secondary reactions.     

Experimental investigation and CFD simulation of liquid–solid–solid dispersion in a stirred reactor

For understanding the monosodium aluminate hydrate crystallization from the supersaturated aluminate solution containing red mud as the leaching liquor of bauxite, the liquid–solid–solid dispersion of a simulant system, i.e. glycerite, red mud and sand, in a stirred reactor has been experimentally investigated as well as simulated using computational fluid dynamics model (CFD) for the first time. The computational model is based on the Eulerian multi-fluid model along with RNG k–ε turbulence model, where Syamlal–obrien-symmetric drag force model (Syamlal, 1987) of the inter-phase momentum transfer between two dispersed solid phases is taken into account. A good agreement is obtained between the experimental data of solid distributions and the simulation results in the flow fields of liquid–solid–solid as well as liquid–solid systems. The solid suspension qualities of both liquid–solid and liquid–solid–solid systems in the stirred reactors with and without draft tube were also studied in detail based on mixing time, the standard deviation of solid concentration proposed by Bohnet and Niesmak (1980), the flow pattern and power number. The influence of the interaction between two dispersed solid phases on the suspension of red mud is found significantly greater than that of sand. The holdup of sand below the impeller is considerably larger than that above the impeller and the red mud dispersion approaches homogeneous in the reactor. The mixing time of liquid–solid–solid suspension is longer than that of liquid–solid suspension under the same conditions, and the mixing times of both systems in the stirred reactor with draft tube are longer than that in the reactor without draft tube. Furthermore, the distributions of sand and red mud in the reactor with draft tube were found less homogeneous than those without draft tube in most cases.     

Experimental and numerical investigation of the chemical reaction kinetics in H<Subscript>2</Subscript>/CO syngas flame at a pressure of 1–10 atm

The structure of a premixed stoichiometric flame of syngas (H₂/CO/O₂/Ar = 0.0667/0.0667/0.0667/0.8) stabilized on a flat burner at a pressure of 5 atm was studied experimentally and by numerical simulation. The mole fraction profiles of the reactants (H₂, CO, and O₂) and the major (H₂O and CO₂) and intermediate (O, OH, HO₂, and H₂O₂) combustion products were measured by molecular beam mass spectrometry. The experimental data were compared with those calculated using three detailed chemical-kinetic mechanisms proposed in the literature for oxidation of a H₂/CO mixture. Good agreement was found between the results of the experiment and simulation. Calculations of the structure of the flame of the same composition at a pressure of 1 and 10 atm were performed to establish the effect of the pressure on the chemical reaction kinetics in the syngas flame. The results were explained by kinetic analysis of the mechanisms.     

Experimental investigation of liquid–liquid flow in an inclined pipe using dimensionless numbers

Two-phase flow is a common phenomenon in the energy industry, where flow patterns significantly affect heat transfer and pressure drop in different systems. However, there is no unique or comparable flow map because of its dependency on dimensional parameters. Therefore, an analysis using dimensionless numbers makes the results comprehensive. To do so, a series of liquid–liquid flow experiments (1296 experiments) were conducted in a transparent pipe at the different velocities of the phases. The flow patterns were captured using a high-speed camera. The experiments were performed at eight different inclinations within the range of −20 to +20 degrees. Six flow patterns are observed at different inclinations; stratified flow with mixing at the interface (STMI), dispersion of water in oil (Dw/o), dispersion of oil in water (Do/w), dual continuous (DC), slug, and wavy stratified (WST), where the first five flow patterns are presented in the upward flow and the two last flow patterns disappear in some of the downward flow. The pattern of boundaries for each flow pattern in the upward flow shows dependency on inclination, while in the downward flow condition, a rather general format can be applied to most of the patterns. The analysis illustrates that gravity and buoyancy forces are the dominating forces in the system compared to other forces, such as viscous, inertia, and interfacial tension, which are due to the inclination of the pipe.     

Structure analysis of cBN films prepared by DC jet plasma CVD from an Ar–N2–BF3–H2 gas system

The structure of the cBN films deposited by DC jet plasma CVD from an Ar-N₂-BF₃-H₂ gas system was investigated by transmission electron microscopy and electron-energy-loss spectroscopy. A sequent layered-structure of Si/amorphous /hexagonal/cubic BN was revealed, which was also confirmed by the confocal Raman technique. For comparison, the phase composition, crystal size and crystallinity of cBN films deposited for different times at initial growth stage were studied by infrared spectroscopy, Raman spectroscopy and glancing-angle X-ray diffraction. A columnar growth of the cBN grains with the average column width of approximately 0.2 μm was observed. The columns were proved to be cBN single crystals elongated from the nucleation sites on the hexagonal BN to the film surface. High-density twins and stacking faults were observed on the {111} planes of the cBN crystals, which subdivided the crystals into many lamellae of several to about 20 nm in thickness.     

Phenomena and mechanism of local oxidation microlithography of 4H–SiC via electrochemical jet anodisation

Local oxidation microlithography (LOM) of 4H–SiC wafers based on the spatial confinement of electrochemical oxidation inside a microelectrolyte jet, namely, electrochemical jet anodisation (EJA), is presented. EJA enables selective growth of the oxide layer on a micro-scale local area with no masks because the anodic reaction occurs exclusively in the jet-substrate interaction area. The shape and height profile of the oxide layer were highly dependent on the anodising conditions. The change in the current density resulted in two distinct oxidation regimes, leading to the formation of either Gaussian-type or doughnut-shaped oxide spots. The oxide growth mechanism was revealed by SEM, AFM and XTEM characterisation of the oxide at the micro/nanoscale. A flat oxide layer with uniform thickness was obtained by applying parametric control. Following a chemical etching process, microstructures were readily created at the patterned oxide locations, demonstrating EJA as a potential lithography technique for microfabrication.     

Experimental study of the SnO2–ZrO2 phase diagram

The study of the SnO₂–ZrO₂ phase diagram in the 1230–1750 °C temperature range has shown the existence of an immiscibility gap, leading to two (Zr_1−xSn_x)O₂ and (Sn_1−yZr_y)O₂ limited solid solutions. Four compositions were synthesised for each solid solution, leading to pure phases, which were characterised by room-temperature and high-temperature X-ray diffraction. The unit-cell parameters of tetragonal (Sn_1−yZr_y)O₂, monoclinic (Zr_1−xSn_x)O₂ and tetragonal (Zr_1−xSn_x)O₂ were determined and correlated with the content of the substituted atom. The monoclinic to tetragonal and reverse reactions for the (Zr_1−xSn_x)O₂ series were also characterised (transition temperatures) when varying the tin mole fraction.     

Effect of C/B ratio in reactants on low-pressure CVD boron-doped carbon deposited from a BCl3–C3H6–H2 mixture

Propylene was used to fabricate boron-doped carbon coatings by low-pressure chemical vapor deposition. The effects of carbon/boron (C/B) ratio in reactants on the deposition rate, morphologies, and bonding states of the deposits were investigated. Deposition rate increased with increasing C/B ratio, when C/B ratio was less than 4.0. Then, deposition rate decreased with increasing C/B ratio. The maximum rate was 500 nm/h. SEM results showed that cross section morphologies and thickness of deposits were influenced by C/B ratio. Morphologies were compact and not-delaminated with a low C/B ratio, however nanoscale delamination occurred in the deposits with a high C/B ratio. The infiltration characteristic was also influenced by the C/B ratio. The suitable C/B ratio was 1.0–2.0 for infiltration in a T300 carbon bundle. XPS results showed that carbon content is major in the deposits with all C/B ratios. The boron contents decreased and carbon contents increased with increasing C/B ratio. B-sub-C and BC₂O were main bonding states. The total contents of B-sub-C and BC₂O were above 60.0 at.% with all C/B ratios.     

Experimental investigation on high temperature wettability and structural behaviour of SAW fluxes using MgO–TiO2–SiO2 and Al2O3–MgO–SiO2 flux system

To establish the relationship between wettability and structure with the change in SAW flux composition, the contact angle measurement study was performed at 1700 K. For MgO–TiO₂–SiO₂ and Al₂O₃–MgO–SiO₂ flux system the wetting behaviour was studied by evaluating the contact angle as well as surface tension properties. Sessile drop method was used to determine the wetting properties of SAW fluxes. Twenty-one SAW fluxes were designed & developed by applying mixture design approach of design of experiments. Chemical, phase and structural properties of SAW fluxes were measured using modern techniques such as X-ray fluorescence (XRF), X-ray diffraction (XRD) & Fourier Transform Infra-red spectroscopy (FTIR). As per the calculated contact angle value, different surface tension values for MgO–TiO₂–SiO₂ and Al₂O₃–MgO–SiO₂ flux system was calculated using Young's & Boni's equations. Using Dupre's equation the adhesion energy for twenty-one basic fluxes was also calculated. Measured contact angle value increased with increase in the TiO₂/MgO & TiO₂/Al₂O₃ flux ratio. Lower contact angle gives higher wettability between the flux and the heating substrate. With increase of TiO₂/SiO₂ ratio up to 1.5 to 2.0 the calculated surface tension value is decreasing while after that it is increased with increase in TiO₂/SiO₂ ratio.     

Experimental investigation and thermodynamic simulation of the uranium oxide–zirconium oxide–iron oxide system in air

The behavior of melts and the phase composition of crystallization products of six compositions in the uranium oxide-zirconium oxide-iron oxide system in air have been investigated. It has been revealed that crystallized samples containing 20–50 wt % uranium oxide and 25–80 wt % iron oxide (the rest is zirconium oxide) consist of five crystalline phases and involve two types of eutectic structures. The possible factors responsible for this phenomenon have been considered.     

Synthesis of TiO2–Ag nanocomposite with sol–gel method and investigation of its antibacterial activity against E. coli

TiO₂–Ag nanocomposite was prepared by the sol–gel method and an azeotropic distillation with benzene was used for dehydration of the gel. Because of gel dehydration by distillation method a nanopowder with a surface area of 230 m²/g was produced which decreased to 80 m²/g after calcination. TEM micrographs and XRD patterns showed that spherical nanosized Ag particles (≈ 10 nm) were deposited among TiO₂ particles. The antibacterial activity of calcined powder at 300 and 500 °C was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The antibacterial tests confirmed the powder calcined at 300 °C possessed more antibacterial activity than the pure TiO₂, amorphous powder and the powder calcined at 500 °C under UV irradiation. In the absence of UV, the reduction in viable cells was observed only with calcinated powder at 300 °C.