Direct conversion of syngas to DME over CuO–ZnO–Al2O3/HZSM‐5 nanocatalyst synthesized via ultrasound‐assisted co‐precipitation method: New insights into the role of gas injection

In this study, direct synthesis of dimethyl ether (DME) is conducted over a bifunctional CuO–ZnO–Al₂O₃/H Zeolite Socony Mobil‐5 (HZSM‐5) nanocatalyst. A hybrid method of ultrasound‐assisted co‐precipitation is used for the synthesis of catalysts, and the effect of gas injection during sonication is investigated. The physicochemical characteristics of the catalysts are analysed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), particle size distribution (PSD), energy dispersive X‐ray (EDX), Brunauer–Emmett–Teller (BET) and Fourier‐transformed infrared (FTIR) methods. In the absence of gas injection, the acetate‐based catalysts have a better morphology and higher surface area than the nitrate‐based catalyst. Gas injection significantly changes the morphology and structural properties of the acetate‐based catalyst. High surface area, narrow PSD and better dispersion of small CuO crystals are obtained in a gas‐injected synthesized sample. DME synthesis experiments showed that the CO conversion and DME selectivity are correlated with surface area, nanocatalyst particle size and its dispersion. The gas‐injected CuO–ZnO–Al₂O₃/HZSM‐5 nanocatalyst that has the highest surface area and the smallest dispersed particles showed more than 70% DME selectivity. The gas‐injected CuO–ZnO–Al₂O₃/HZSM‐5 nanocatalyst exhibited high stability in terms of CO conversion and DME yield over 1440‐min time on a stream test at 275°C, 40 bar and 18 000 cm³ g.h^?1. Copyright © 2014 John Wiley & Sons, Ltd.     

Estimation of Nusselt number and effectiveness of double‐pipe heat exchanger with Al2O3–, CuO–, TiO2–, and ZnO–water based nanofluids

This paper deals with experimental studies carried out to analyze heat transfer characteristics of Al₂O₃–, CuO–, TiO₂–, and ZnO–water based nanofluids in a double‐pipe, counter flow heat exchanger for different volume concentrations (0.025%, 0.05%, 0.075%, and 0.1%) of the nanofluids. The fabricated double‐pipe heat exchanger is made up of two different materials, viz., copper as the inner tube and unplasticized polyvinyl chloride as the outer tube. The density, viscosity, and thermal conductivity were calculated, and were used to estimate dimensionless numbers, such as Reynolds number, Prandtl number, and Nusselt number, and also to estimate heat exchanger effectiveness. High‐energy ball milling technique was used to prepare nanoparticles and were characterized using X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. Polyvinyl alcohol (3%) was used as a surfactant for making the nanofluids stable. It was observed from the experiment that with the increase in the volume concentration, thermal conductivity, viscosity, and friction factor increase, whereas the Reynolds number decreases. The experimentally observed data for Nusselt number were formulated into a correlation that matches the data for all these nanofluids within an error of 11.4%. It was found that the highest effectiveness was obtained while using TiO₂–water nanofluids than other nanofluids.     

Enhanced performance of alpha‐Fe2O3 nanoparticles with optimized graphene coated layer as anodes for lithium‐ion batteries

A series of different α‐Fe₂O₃ nanoparticles composites containing different amounts of graphene coatings have been successfully prepared using a simple electrostatic self‐assembly (ESA) method. The structure and electrochemical properties of these α‐Fe₂O₃@graphene composites have been investigated. The α‐Fe₂O₃ nanoparticles composite containing 40 wt% graphene coating exhibits the highest specific capacity (385 mAh g^?1) under 1000 mA g^?1, resulting in superior cycle stability with no downward trend after 500 cycles. These results demonstrate that graphene coatings can be used to enhance the electrochemical properties and morphological stability of α‐Fe₂O₃ nanoparticles as anodic materials for high performance lithium‐ion batteries (LIBs). The low‐energy self‐assembly method employed in the paper has good potential for the broad‐scale preparation of other graphene‐modified materials because of its simplicity and the relatively low temperature conditions.     

Thermal transport phenomena of turbulent jet diffusion flames by means of anisotropic k–ϵ–t2–ϵt model

A numerical study is performed on transport phenomena in a turbulent jet diffusion flame of hydrogen from a vertical circular nozzle. An anisotropic k–ϵ–t² –ϵ_t model and the eddy‐dissipation model are employed to simulate thermal fluid flow and combustion phenomena, respectively. The governing boundary‐layer equations are discretized by means of a control volume finite‐difference technique and are numerically solved. The model predicts the experimental data in the existing literature. It is found from the study that (i) the model employed here can be applied to combustion phenomenon, and (ii) the presence of flame enhances the anisotropy of turbulence and causes a substantial attenuation in the turbulent kinetic energy, that is, most turbulent kinetic energy in the flame in the downstream part is laden exclusively in the streamwise fluctuation. Copyright © 1999 John Wiley & Sons, Ltd.     

Vapor–liquid equilibrium of ammonia–water–lithium nitrate solutions

Experimental results on the pressure–temperature data for the NH₃‐H₂O binary and NH₃‐H₂O‐LiNO₃ ternary solutions are reported. The pressure was varied between 100 and 800 kPa, while the mass fraction of ammonia was varied in the range 0–0.30. The lithium nitrate concentration of the solution was chosen in the range of 10–50% of mass ratio of lithium nitrate in pure water. An analytical equation for the equilibrium pressure as a function of temperature and concentration was obtained with a good fit to experimental data. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20351     

Laminar‐turbulent flow simulation for wind turbine profiles using the γ– transition model

The accurate prediction of the laminar‐turbulence transition process is fundamental in predicting the aerodynamic performance of wind turbine profiles. Fully turbulent flow simulations have been shown to over‐predict the aerodynamic performance and thereby negatively impacting the design of airfoils in flow regimes where the possible presence of laminar flow could be exploited to improve the performance of wind turbine rotors. Correlation‐based transition modelling offers a fully computational fluid dynamics compatible approach, where the model integrates completely with the existing turbulence model, allows for the prediction of various transition mechanisms, is applicable to three‐dimensional flows and compatible to adjoint‐based design optimization frameworks. The present paper addresses several modifications necessary for a robust transition model and investigates the accuracy of the model for a wide range of angles of attack and Reynolds numbers, which are necessary for a thorough validation of the correlation‐based transition model for wind turbine profiles. The transition model was employed to predict the transition locations; and an assessment of the various transition mechanisms, Reynolds number effects, sectional characteristics and aerodynamic performance for the NLF(1)‐0416 and S809 airfoils is presented with comparisons to experimental data and numerical solutions. Copyright © 2013 John Wiley & Sons, Ltd.     

A new k‐epsilon model consistent with Monin–Obukhov similarity theory

A new k‐? model is introduced that is consistent with Monin–Obukhov similarity theory (MOST). The proposed k‐? model is compared with another k‐? model that was developed in an attempt to maintain inlet profiles compatible with MOST. It is shown that the previous k‐? model is not consistent with MOST for unstable conditions, while the proposed k‐? model can maintain MOST inlet profiles over distances of 50km. Copyright © 2016 John Wiley & Sons, Ltd.     

Double‐diffusive natural convection in a partially heated enclosure using a nanofluid

This paper analyzes numerically the effect of double‐diffusive natural convection of a water–Al₂O₃ nanofluid in a partially heated enclosure with Soret and Dufour coefficients. The top horizontal wall has constant temperature T_c, while the bottom wall is partially heated T_h, with T_h > T_c . The concentration in the top wall is maintained higher than the bottom wall C_c < C_h. The remaining bottom wall and the two vertical walls are considered adiabatic. Water is considered as the base fluid. The governing equations are solved by the Penalty Finite Element Method using Galerkin's weighted residual scheme. The effect of the parameters, namely, Rayleigh number and solid volume fraction of the nanoparticles on the flow pattern and heat and mass transfer has been depicted. Comprehensive average Nusselt and Sherwood numbers, average temperature and concentration, and mid‐height horizontal and vertical velocities at the middle of the cavity are presented as functions of the governing parameters mentioned above. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21010     

Development of temperature‐change sensor by thermoelectric elements and its response evaluation on dropping into water

A temperature‐change sensor by thermoelectric elements that is directly connected to a p‐type element and an n‐type element was developed. A β‐FeSi₂ thermoelectric semiconductor made by a spark plasma sintering method was used as a prototype sensor. Evaluation of this thermoelectric temperature‐change sensor was carried out by measuring its electromotive force when it was dropped into a thermostated water bath. It was confirmed that there existed a correlation between the temperature difference and the electromotive force of the sensor, i.e., approximately 5 mV of electromotive force was generated at a temperature difference of 30 K. In addition, the dependence of electromotive force on the size and properties of the thermoelectric elements was evaluated by carrying out FEM analysis. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20268     

Novel improvements in the sensitizers of dye‐sensitized solar cells for enhancement in efficiency—a review

In the present review article, we have focused our study on the novel improvements that have been brought about in the molecular design of various sensitizers for application in dye‐sensitized solar cells (DSSCs). The sensitizers based on noble metals such as ruthenium, osmium, and rhenium showed high efficiency, but their cost and complicated synthesis restrict their wide applications. Further, to reduce the cost of fabrication of DSSCs, researchers are focusing their interest in organic sensitizers. In this context, organic dyes have offered several possibilities, as by improving their molecular structure brings about improvement in the light harvesting ability of dyes, and with the help of such dyes, optimal DSSCs have been fabricated. Further, to reduce the cost of DSSCs, researchers are also focusing on natural sensitizers such as betacyanin and anthocyanin or chlorophyll, as natural sensitizers are easy to prepare, cost effective, and environmentally friendly. With the help of these natural sensitizers, eco‐friendly and more cost‐effective DSSCs can be fabricated. Thus, we found from our study that beside metal‐based sensitizers, organic and natural sensitizers also offer a vast potential for the optimization of efficiency in DSSCs. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence of tungsten loading on CO2/O2 reforming of methane over Co‐W–promoted NiO‐Al2O3 nanocatalyst designed by sol‐gel‐plasma

Co‐W–promoted NiAl₂O₄ nanocatalyst with various amount of tungsten (0, 1, 3, and 7 wt.%) was fabricated via hybrid sol‐gel‐plasma method. The nanocatalysts were evaluated by XRD, FESEM, EDX, BET, and FTIR analyses. The samples were utilized in CO₂/O₂ reforming of methane to syngas. EDX results proved the existence of all the applied elements in synthesis. FESEM and BET results illustrated that tungsten addition led to lower surface area, larger particle size, and roughly worse particles scattering. Therefore, Co‐NiAl₂O₄ (NCW0A) presented higher yield; however, yields were reduced for the other samples due to the covering impact of tungsten. As a result of time on streams performance (2880 minutes and at 750°C), the 7 wt.% tungsten promoted sample exhibited stable but lower yield (Y_H2 = 64%). Moreover, NCW1A exhibited more stable and higher yield than NCW0A. Optimum operating parameters were obtained as GHSV = 24 l/g_cat.h, CH₄/CO₂ = 1, and CH₄/CO₂/O₂ = 1/1/0.08. TG‐DTG, EDX, and FESEM analyses were applied for the used samples. TG‐DTG graphs demonstrated that by rising of tungsten loading, lighter and lower amount of coke was formed. Some agglomerations were observed in the EDX images of NCW0A and NCW1A while lower agglomeration was found for the tungsten‐rich sample. Carbon fiber formation was detected in the FESEM images of the used NCW0A while for the others, amount of the deposited coke and carbon fibers decreased.     

A BiOCl/β‐FeOOH heterojunction for HER photocatalytic performance under visible‐light illumination

β‐iron oxide hydroxide (β‐FeOOH) had been proven to be an effective co‐catalyst during H₂ evolution reaction (HER) process. In this research, a BiOCl/β‐FeOOH heterojunction was successfully synthesized by a solid‐state doping method. Then, the structure, composition, and photo‐electrochemical properties of the prepared photocatalysts were studied. For the superior HER photocatalytic activity of ultrasmall β‐FeOOH nanoparticles (NPs) and the formation of the BiOCl/β‐FeOOH heterojunction, this heterojunction photocatalyst exhibited very superior photocatalytic performance in the HER process. Especially, when the amount of incorporated β‐FeOOH NPs was appropriate, the BFOH‐2 possessed the highest photocatalytic activity in HER process, and the HER rate was about 16.64 mmol·g^?1·h^?1 during illuminated time of 6 hours under visible light. When appropriate, ultrasmall β‐FeOOH NPs were implanted into the structure of BiOCl, the BiOCl/β‐FeOOH heterojunction interfaces would form for the existence of interfacial interactions. Therefore, this BiOCl/β‐FeOOH heterojunction exhibited superior visible‐light response, fast photo‐carrier migration, and high‐efficient separation of photo‐carriers, so that the BFOH‐2 heterojunction possessed high‐efficient hydrogen evolution reaction (HER) photocatalytic activity.     

A study on thermal conductivity of a quasi‐ordered liquid layer on a solid substrate

In the present paper, a study on thermal conductivity of a quasi‐ordered liquid layer on a solid surface was performed by molecular dynamic simulation. Results showed that the motion of the molecules and their radial distribution function in the quasi‐ordered liquid layer were similar to those of solid molecules. By using the Green–Kubo formula, the thermal conductivity of the layer was calculated. It was found that it increased with the increase of the parameters of ordering. The size effect and the influence of the boundary condition were also discussed. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 429–434, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20171     

Numerical investigation of non‐Newtonian nanofluid mixed convection in a two‐opposite direction lid‐driven cavity with variable properties

The mixed convection fluid flow in a square cavity filled with AL₂O₃‐water non‐Newtonian nanofluid is numerically analyzed. The left and right vertical boundaries of the enclosure have been kept in the constant temperature. Remaining walls of the cavity have been considered to have adiabatic boundary condition. Two different cases have been considered. In the first case, left and right side walls have been moved vertically with constant speed V_b in opposite directions. In the second case, the directions of their motions have been reversed. The transport equations, written in terms of the primitive variables for the non‐Newtonian nanofluid, have been solved numerically using the finite volume method. The shear stresses were calculated using the Ostwald‐de Waele model for the shear‐thinning nanofluid. The model introduced by Patel et al was used to obtain the thermal conductivity of the nanofluid. The variation of the fluid flow with respect to the Richardson number and volume fraction of the nanoparticles was investigated through a parametric study. Even though increasing the volume fraction of nanoparticles leads to heat transfer enhancement, for the second case of this study, for Ri = 1, the average Nusselt number initially drops sharply by increasing the volume fraction of nanoparticles, then remains constant.     

The k‐ϵ‐fP model applied to wind farms

The recently developed k‐?‐f_P eddy‐viscosity model is applied to one on‐shore and two off‐shore wind farms. The results are compared with power measurements and results of the standard k‐? eddy‐viscosity model. In addition, the wind direction uncertainty of the measurements is used to correct the model results with a Gaussian filter. The standard k‐? eddy‐viscosity model underpredicts the power deficit of the first downstream wind turbines, whereas the k‐?‐f_P eddy‐viscosity model shows a good agreement with the measurements. However, the difference in the power deficit predicted by the turbulence models becomes smaller for wind turbines that are located further downstream. Moreover, the difference between the capability of the turbulence models to estimate the wind farm efficiency reduces with increasing wind farm size and wind turbine spacing. Copyright © 2014 John Wiley & Sons, Ltd.     

β‐molybdenum carbide/carbon nanofibers as a shuttle inhibitor for lithium‐sulfur battery with high sulfur loading

We report the synthesis of β‐molybdenum carbide/carbon nanofibers (β‐Mo₂C/CNFs) by electrospinning and annealing process, when exploited as an interlayer in Li‐S batteries, demonstrating significantly improved electrochemical behaviors. The synthesized β‐Mo₂C/CNFs with 3D network structure and high surface area are not only conducive to ion transport and electrolyte penetration but also effectively intercept the shuttle of lithium polysulfide by polar surface interaction. Moreover, the reaction kinetics of the batteries enhanced is due to the presence of β‐Mo₂C, promoting the solid‐state polysulfide conversion reaction in the charge‐discharge process. Compared with the batteries with CNF interlayer and without interlayer, the batteries using a β‐Mo₂C/CNFs interlayer with a sulfur loading of 4.2 mg cm^‐2 delivered excellent electrochemical performance because of a facile redox reaction during cycling. The discharge capacity at the first cycle at 0.7 mA cm^?2 was 1360 mAh g^?1, maintaining a specific capacity of 974 mAh g^?1 after 160 cycles. Furthermore, it showed a high‐rate capacity of 700 mAh g^?1 at 14 mA cm^?2. This work demonstrates the β‐Mo₂C/CNFs as a promising interlayer to exploit Li‐S battery commercialization.     

Syngas production via CO2 reforming of methane over plasma assisted synthesized Ni‐Co/Al2O3‐ZrO2 nanocatalysts with different Ni‐loadings

Ni‐Co/Al₂O₃‐ZrO₂ nanocatalysts with 5, 10 and 15 wt.% nominal Ni content have been prepared by impregnation followed by a non‐thermal plasma treatment, characterized and tested for dry reforming of methane. For nanocatalysts characterization the following techniques have been used: XRD, FESEM, TEM, EDX dot‐mapping, BET, FTIR and XPS. The dry reforming of methane was carried out at different temperatures (550‐850 °C) using a feed mixture of CH₄:CO₂ (1:1). Among the nanocatalysts studied, the catalyst with the medium Ni content (10 wt.%) was the most active in dry reforming of methane. This higher activity exhibited by Ni‐Co/Al₂O₃‐ZrO₂ catalyst with medium Ni content (10 wt.% ) can be attributed to small and well dispersed particles of Ni within the catalyst. Apart from the narrow surface particle size distribution in the case of Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂, the presence of small active components with average size of 7.5 nm is proposed to be the reason for the superior performance of the catalyst. Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst had maximum surface area and the lower surface area was observed in the case of Ni(5 wt.%)‐Co/Al₂O₃‐ZrO₂ and Ni(15 wt.%)‐Co/Al₂O₃‐ZrO₂ due to the formation of the larger agglomeration and higher mean particle size of nickel particles, respectively. Although, GHSV enhancment had inverse effect on product yield but yield reduction for Ni‐Co/Al₂O₃‐ZrO₂ catalyst with 10 wt.% Ni was less drastic at high GHSVs. According to XRD and XPS, existence of NiAl₂O₄ confirms strong interaction between Ni and support but higher loadings of Ni resulted in less NiAl₂O₄; loser interaction between support and active phase. Small particles of active components and well‐defined dispersion of them in Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst resulted in stability of the catalyst for either feed conversion or H₂/CO molar ratio. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluation of redox performance of silver and transition metal‐doped ternary ceria oxides for thermochemical splitting of CO2

Synthesis of Ce_0.9M_0.05Ag_0.05O_2‐δ materials (where, M = Ni, Zn, Mn, Fe, Cu, Cr, Co, Zr) via coprecipitation of hydroxide method and examination of these materials toward multiple thermochemical CO₂ splitting (CS) cycles is reported in this paper. Physical properties of the derived Ce_0.9M_0.05Ag_0.05O_2‐δ materials were estimated by analyzing the calcined powder using a powder X‐ray diffractometer (PXRD) and scanning electron microscope (SEM). The redox reactivity (RR) of each Ce_0.9M_0.05Ag_0.05O_2‐δ material was also evaluated by conducting high‐temperature thermogravimetric experiments. The inclusion of Ag as an active dopant has improved the RR of all the Ce_0.9M_0.05Ag_0.05O_2‐δ materials as compared with the Ce_0.9M_0.1O_2‐δ materials. Among all the Ce_0.9M_0.05Ag_0.05O_2‐δ materials, Zn5Ag5Ce material was capable of releasing highest amount of O₂ 84.1 μmol O₂/g·cycle and the Cr5Ag5Ce material indicated maximum CO production (151.6 μmol CO/g·cycle). The uppermost CO/O₂ molar ratio equal to 1.89 was observed in case of Cr5Ag5Ce material. The quantity of O₂ released and CO produced by Cr5Ag5Ce material was superior as compared with CeO₂¹ by 30.7 μmol O₂/g·cycle and 62.8 μmol CO/g·cycle, respectively.