Turbulence models application on CFD simulation of hydrodynamics,heat and mass transfer in a structured packing

In this study, turbulence model applications on two-phase flow simulation in a structured packing are investigated using CFD application. Dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are studied by k–ε, RNG k–ε, k–ω and BSL turbulence models. The best results obtained by k–ω and BSL models, but k–ω is recommended because it is more robust than BSL. The mean absolute relative error (MARE) between CFD prediction of k–ω model and experimental data for dry pressure drop, irrigated pressure drop, mass transfer and heat transfer are 16.9%, 10.7%, 8.1%, 0.9%, respectively.     

Hydrogen environment embrittlement of stable austenitic steels

Seven stable austenitic steels (stable with respect to γ → α′ transformation at room temperature) of different alloy compositions (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N, 0.6C–23Mn, 1.3C–12Mn, 1C–31Mn–9Al, 18Cr–19Mn–0.8N) were tensile tested in high-pressure hydrogen atmosphere to assess the role of austenite stability on hydrogen environment embrittlement (HEE). The influence of hydrogen on tensile ductility was small in steels that are believed to have a high initial portion of dislocation cross slip (18Cr–12.5Ni, 18Cr–35Ni, 18Cr–8Ni–6Mn–0.25N), while the effects of hydrogen were significantly greater in steels with other primary deformation modes (planar slip in 18Cr–19Mn–0.8N and 1C–31Mn–9Al or mechanical twinning in 0.6C–23Mn and 1.3C–12Mn) despite comparable austenite stability at the given test conditions. It appears that initial deformation mode is one important parameter controlling susceptibility to HEE and that martensitic transformation is not a sufficient explanation for HEE of austenitic steels.     

An experimental and modelling study of a photovoltaic/proton-exchange membrane electrolyser system

An experimental model of a photovoltaic (PV) module-proton exchange membrane (PEM) electrolyser system has been built. A model has been developed for each device separately based on the experimental results. Output current–voltage (I–V) characteristics of the PV module are modelled in respect to different irradiance and temperature conditions by experimental tests. Similarly, input I–V characteristic and hydrogen formation characteristic of the PEM electrolyser are measured and modelled. After these studies, combined PV module–PEM electrolyser system model is defined. There is a good agreement between model predictions and measurements. At 18–100% irradiance interval, operating points of PEM electrolyser on the PV module are predicted with relative errors of 0.1–0.8%. Furthermore, the study shows that these simple model system devices can easily be defined in MATLAB/Simulink and used to model similar systems of different size.     

Electrodeposition of Ni–Co–Sn alloy from choline chloride-based deep eutectic solvent and characterization as cathode for hydrogen evolution in alkaline solution

The electrodeposition of Ni–Co–Sn alloy were carried out at room temperature from the chlorine chloride (ChCl)–ethylene glycol (EG) deep eutectic solvent (DES). For comparison of properties, Ni–Sn and Co–Sn alloys were also deposited using the same solvent. Deposition mechanism, microstructure, and electrochemical properties of the deposits in 1 M KOH solution were investigated. The deposition of Ni, Co, Sn, Ni–Sn, Co–Sn and Ni–Co–Sn on platinum electrode were also studied using cyclic voltammetry. Interestingly, the electrochemical stability of DES is observed to be increased in the presence of Sn²⁺ ions. The X-ray diffraction (XRD) patterns showed only Ni phases indicating that the other elements get incorporated inside the nickel matrix and the lattice constant have linear relation with Sn content in alloy. The morphologies of Ni–Sn and Ni–Co–Sn alloys were observed to be almost same with fine grains, the XRD studies confirm this. The potentiodynamic polarization measurements showed that the Ni–Co–Sn alloy exhibits the lowest corrosion current density (j_corr), noblest corrosion potential (E_corr) and highest exchange current density (j_c) value than the other two binary alloys, indicating that the ternary alloy is a good candidate for Hydrogen Evolution Reaction (HER).     

Comparison of electrocatalytic activity of carbon-supported Au–M (M = Fe,Co, Ni,Cu and Zn) bimetallic nanoparticles for direct borohydride fuel cells

The Au–M (M = Fe, Co, Ni, Cu and Zn) bimetallic nanoparticles supported on the Vulcan XC-72R (Au–M/C) were synthesized by a reverse micelle method. The structures and compositions of the carbon supported Au–M catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS). The electrocatalytic activity of the Au–M bimetallic nanoparticles with respect to borohydride electro-oxidation for the application of fuel cell was investigated by voltammetry, chronoamperometry and chronopotentiometry. The results showed that alloying Au with 3d transition metals Fe, Co, Ni, Cu or Zn, a metal that leads to the maximum eight-electron oxidation of BH₄⁻, not only improved the electrode kinetics of BH₄⁻ oxidation but also reduced catalyst cost. Among the various investigated Au–M/C electrocatalysts, the Au–Zn, Au–Fe and Au–Cu catalysts showed no activity of NaBH₄ hydrolysis, and Au–Zn presented an attractive catalytic activity for borohydride oxidation.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

Thermodynamic analysis of a novel absorption power/cooling combined-cycle

An absorption power/cooling combined cycle is proposed, and a thermodynamic analysis of the cycle is performed using log p–T, log p–h and T–s diagrams. Based upon two performance criteria, the overall thermal-efficiency and exergy efficiency, the cycle has been analyzed by means of a simulation. The overall thermal efficiency of the cycle is 24.2%, and the exergy efficiency is 37.3%.     

Effects of hydrothermal treatment on the catalytic activity of cobalt-doped catalysts for oxygen reduction reaction

A series of cobalt-doped catalysts (Co–PPy/BP) is synthesized by hydrothermal treatment of polypyrrole-modified BP2000 in cobalt nitride solution. The hydrothermal temperature is varied from 80 °C to 180 °C to investigate the effect of treatment temperature on the catalytic site formation for oxygen reduction reaction (ORR). Treatment temperature is found to slightly affect the structure and morphology of the synthesized catalysts. However, the catalytic activity of the synthesized Co–PPy/BP increases with increased treatment temperature up to 160 °C because higher treatment temperatures promote pyrrolic-N conversion to Co–Nx. Co–Nx catalyzes H₂O₂ electroreduction reaction, which increases the number of electrons transferred during ORR. However, the hydrothermal treatment at 180 °C leads to decreased pyrrolic-N and Co–Nx contents, which results in decreased catalytic activity of the synthesized Co–PPy/BP.     

Improved hydrogen production of the downstream bioreactor by coupling single chamber microbial fuel cells between series-connected photosynthetic biohydrogen reactors

To obtain additional hydrogen recovery from the downstream photosynthetic biohydrogen reactor (PBR), a system (PBR1–MFCs–PBR2) that combined PBRs with three single chamber microbial fuel cells (MFCs) was proposed in this study. The results revealed that the PBR2 in PBR1–MFCs–PBR2 showed a hydrogen production rate of 0.44 ± 0.22 mmol L h⁻¹, which was 15 and 4 times higher than those obtained by direct connecting the two PBRs (PBR1–PBR2) and pH regulated system (PBR1–pH regulation–PBR2), respectively. In addition, the PBR1–MFCs–PBR2 exhibited the highest glucose utilization (η_g) of 97.6 ± 2.1 %, while lower η_g values of 75.6 ± 2.2% and 70.1 ± 1.2% was obtained for PBR1–PBR2 and PBR1–pH regulation–PBR2, respectively. These improvements were due to the removal of inhibitory byproduct and H⁺ from the PBR1 effluent by the MFCs.     

HIx system thermodynamic model for hydrogen production by the Sulfur–Iodine cycle

The HI_x ternary system (H₂O–HI–I₂) is the latent source of hydrogen for the Sulfur–Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng–Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HI_x separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor–liquid, liquid–liquid, vapor–liquid–liquid and solid–liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HI_x system.     

Interaction between (La,Sr)MnO3 cathode and Ni–Mo–Cr metallic interconnect with suppressed chromium vaporization for solid oxide fuel cells

Interaction between (La_0.8Sr_0.2)_0.90MnO₃ (LSM) cathode and newly developed Ni–Mo–Cr metallic interconnect is investigated at 900 °C under operation conditions of solid oxide fuel cells (SOFCs). The results show that chromium deposition on the LSM cathodes in the presence of Ni–Mo–Cr interconnect is remarkably reduced as compared to that in the presence of a conventional Fe–Cr metallic interconnect (RA446). In contact with the Ni–Mo-Cr interconnect the overpotential, η, for the O₂ reduction reaction on LSM cathode decreased from 529 to 111 mV during the 1200 min current passage at 200 mA/cm². In contrast, η increased from 464 to 561 mV for the reaction in the presence of a RA446 interconnect. The decrease in η clearly indicates that chromium poisoning effect of the Ni–Mo–Cr interconnect is also significantly suppressed as compared to that with conventional Fe–Cr interconnect materials. The suppressed Cr deposition and poisoning effects observed on the LSM cathodes demonstrate promising potential of the Ni–Mo–Cr alloy as new interconnect materials with significant suppressed chromium vaporization and deposition for SOFCs.     

Hydrogen production from ethanol steam reforming over core–shell structured NixOy–, FexOy–, and CoxOy–Pd catalysts

The present work focused on the investigation of the hydrogen generation through the ethanol steam reforming over the core–shell structured Ni_xO_y–, Fe_xO_y–, and Co_xO_y–Pd loaded Zeolite Y catalysts. The transmission electron microscopy (TEM) image of Ni_xO_y–Pd represented a very clear core–shell structure, but the other two catalysts, Co_xO_y– and Fe_xO_y–Pd, were irregular and non-uniform. The catalytic performances differed according to the added core metal and the support. The core–shell structured Co_xO_y–Pd/Zeolite Y provided a significantly higher reforming reactivity compared to the other catalysts. The H₂ production was maximized to 98% over Co_xO_y–Pd(50.0 wt%)/Zeolite Y at the conditions of reaction temperature 600 °C, CH₃CH₂OH:H₂O = 1:3, and GHSV (gas hourly space velocity) 8400 h⁻¹. In the mechanism that was suggested in this work, the cobalt component played an important role in the partial oxidation and the CO activation for acetaldehyde and CO₂ respectively, and eventually, cobalt increased the hydrogen yield and suppressed the CO generation.     

A study of the development of bio-energy resources and the status of eco-society in China

Industrialization of bio-energy relies on the supply of resources on a large scale. The theoretical biomass resources could reach 2.61–3.51 billion tce (tons of coal equivalent)/a in China, while the available feedstock is about 440–640 million tce/a, however, among this only 1.5–2.5% has been transferred into energy at present. Marginal land utilization has great prospects of supplying bio-energy resources in China, with co-benefits, such as carbon sequestration, water/soil conservation, and wind erosion protection. There is a large area of marginal land in China, especially in northern China, including about 263 million ha of desertification land, 173 million ha of sand-land, and 17 million ha of salinizatin land. The plant species suitable to be grown in marginal lands, including some species in Salix, Hippophae, Tamarix, Caragana, and Prunus is also abundant Biomass feedstock in marginal lands would be 100 million tce/a in 2020, and 200 million tce/a in 2050. As a result, a win–win situation of eco-society and bio-energy development could be realized, with an expected 4–5% reduction of total CO₂ emission in China in 2020–2050. Although much progress has been made in the field of bio-energy research in China, yet significant efforts should be taken in the future to fulfill large-scale industrialization of bio-energy.     

Improvement of hydrogen yield of lba-transgenic Chlamydomonas reinhardtii caused by increasing respiration and impairing photosynthesis

The transgenic alga lba of Chlamydomonas reinhardtii yielded H₂ with 50%–180% higher than the control strain. Further experiments showed that photosynthetic rates and photosynthetic reaction center II's photochemical capacities of the transgenic algae obviously decreased 33.4%–85.9% and 30.0%–51.7%, respectively, compared with those of the control. On the contrary, respiration rates of the transgenic algae significantly increased, with 40.0%–200.0% higher than those of the control. Furthermore, starch contents of the transgenic algae were also improved significantly by 79.1%–592.8% compared with the control. Therefore, the reason of H₂ yield improvement of the transgenic alga lba is not only due to its decrease of photosynthetic capacity and increase of the respiration rate, but also due to the metabolic changes related to starch metabolism, photosynthesis and respiration which is possibly caused by hetero-expression of lba gene in chloroplasts of C. reinhardtii, indicating the potential of utilization of lba gene to improve hydrogen yield of micro-green algae.     

Nonequilibrium entropy. Characterization of stationary states

A generalization of the Gibbs entropy postulate is proposed based on the BBGKY [Born–Bogoliubov–Green–Kirkwood–Yvon] hierarchy as the nonequilibrium entropy for a system of N interacting particles. By using this entropy and the methods of nonequilibrium thermodynamics, a master equation for the evolution of the distribution vector is derived. In addition, after neglecting correlations in this master equation the Boltzmann equation is obtained. Moreover, our theory enables us to characterize the nonequilibrium stationary states as the states of constant entropy avoiding divergences in the entropy. Nonequilibrium Green–Kubo type relations are also derived.     

Ni/MgO–Al2O3 and Ni–Mg–O catalyzed SiC foam absorbers for high temperature solar reforming of methane

Ni catalyst supported on MgO–Al₂O₃ (Ni/MgO–Al₂O₃) prepared from hydrotalcite, and Ni–Mg–O catalyst are studied in regard to their activity in the CO₂ reforming of methane at high temperatures in order to develop a catalytically activated foam receiver–absorber for use in solar reforming. First, the activity of their powder catalysts is examined. Ni/MgO–Al₂O₃ powder catalyst exhibits a remarkable degree of high activity and thermal stability as compared with Ni–Mg–O powder catalyst. Secondly, a new type of catalytically activated ceramic foam absorber – Ni/MgO–Al₂O₃/SiC – and Ni–Mg–O catalyzed SiC foam absorber are prepared and their activity is evaluated using a laboratory-scale receiver–reactor with a transparent quartz window and a sun-simulator. The present Ni-based catalytic absorbers are more cost effective than conventional Rh/γ-Al₂O₃ catalyzed alumina and SiC foam absorbers and the alternative Ru/γ-Al₂O₃ catalyzed SiC foam absorbers. Ni/MgO–Al₂O₃ catalyzed SiC foam absorber, in particular, exhibits superior reforming performance that provides results comparable to that of Rh/γ-Al₂O₃ catalyzed alumina foam absorber under a high flux condition or at high temperatures above 1000 °C. Ni/MgO–Al₂O₃ catalyzed SiC foam absorber will be desirable for use in solar receiver–reactor systems to convert concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures.     

Electrocatalysts for bifunctional oxygen/air electrodes

Oxygen reduction and evolution have been studied with respect to the development of bifunctional air/oxygen electrode (BFE). Three groups of catalysts have been prepared: (i) Cu_xCo_3−xO₄ by thermal decomposition of mixed nitrate and carbonate precursors; (ii) thin films of Co–Ni–Te–O and Co–Te–O were deposited by vacuum co-evaporation of Co, Ni and TeO₂ and (iii) Co_xO_v/ZrO₂ films were obtained by electrochemical deposition.     

Nanoporous Ni-based catalysts for hydrogen generation from hydrolysis of ammonia borane

We report nanoporous Ni, Ni–Fe, and Ni–Pt as catalysts for hydrogen generation from hydrolytic dehydrogenation of ammonia borane (NH₃BH₃, AB). The Ni and Ni–Fe nanoparticles with diameters of 20–25 nm were synthesized by a colloidal method in starch-containing aqueous solution. They exhibited considerable in situ catalytic performance but severely lost activity after separating from the reaction solution. Nanoporous Ni_1−xPt_x (x = 0.01, 0.08 and 0.19) with particle size below 5 nm was prepared from the isolated Ni nanoparticles through a replacement reaction. After centrifugation, drying, washing, and annealing, the obtained nanoporous Ni–Pt could attain remarkable activity, high hydrogen generation rate and efficiency, and low activation energy.