Band gap engineering in ruthenium‐based Heusler alloys for thermoelectric applications

In this work, systematic electronic structure calculations are performed on Ru₂TiZ alloys to examine their structural and thermoelectric related transport properties. The electronic structural properties are analyzed using the GGA and GGA+U as exchange correlational potential. The calculated lattice parameters agree very well with the existing experimental data, and the percentage of error is less than 1%. The electronic structural properties as analyzed, using the GGA exchange correlation scheme, reveal that these alloys can be semimetals. In the band structure, it is observed that ruthenium‐d and titanium‐d states are lying very close to the Fermi level. Hence, computations are performed again by including the Hubbard potential for d states of ruthenium and titanium. The calculated electronic structure in GGA+U reveals that all the 3 alloys are semiconductors with the indirect energy gap of 0.209, 0.175, and 0.259 eV, respectively, for Ru₂TiSi, Ru₂TiGe, and Ru₂TiSn. The electrical transport coefficients are calculated in both the GGA and GGA+U exchange correlational potential and reported. If experimentalists prove that these alloys are semiconductors, then all 3 alloys will be potential thermoelectric materials. If by experiment they are semimetals, only then Ru₂TiSn can be a good thermoelectric material. Doping of electron and hole for various concentrations is studied for Ru₂TiSn, and optimum doping level is reported.     

Experimental and optimization studies of hydrogen production by steam methane reforming over lanthanum strontium cobalt ferrite supported Ni catalyst

Over the years, research focused has been on the development of active and stable catalysts for hydrogen (H₂) production by steam methane reforming (SMR). However, there is less attention on the individual and interaction effect of key process parameters that influence the catalytic performance of such catalysts and how to optimize them. The main objective of this study is to investigate the individual and interaction effects of key parameters such as methane partial pressure ( (10‐30 kPa), steam partial pressure ( (10‐30 kPa), and reaction temperature (T) (750‐850°C) on H₂ yield and methane (CH₄) conversion during SMR using Box‐Behnken experimental design (BBD) and response surface methodology. The H₂ production was catalyzed using Ni/LSCF prepared by wet impregnation method. The evaluation of the Ni/LSCF using different instrument techniques revealed that the catalyst exhibited excellent physicochemical properties suitable for SMR. Response surface models showing the individual and interaction effect of each of the parameters on the H₂ yield and CH₄ conversion were obtained using the set of data obtained from the BBD matrix. The three parameters were found to have significant effects on the H₂ yield and CH₄ conversion. At the highest desirability of 0.8994, maximum H₂ yield and CH₄ conversion of 89.77% and 89.01%, respectively, were obtained at optimum conditions of 30 kPa, 28.86 kPa, and 850°C for , , and temperature, respectively. The predicted values of the responses from the response surface models were found to be in good agreement with the experimental values. At optimum conditions, the catalyst was found to be stable up to 390 minutes with time on stream. The characterization of the used catalyst using thermogravimetric analysis, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy showed some evidence deposition of a small amount of carbon on the catalyst surface.     

Modeling,simulation, and optimization of a microalgae biomass drying process

The aim of the present work was to develop a transient mathematical model focused on microalgae biomass drying, considering two phases: solid (wet biomass) and gas (drying air). Mass and thermal energy balances were written for each phase producing a system of ordinary differential equations (ODE). The solution of the ODE set delivers the temperature and air humidity ratio and biomass profiles with respect to time. The numerical results were directly compared with temperature experimental measurements—for both phases—and with the biomass humidity content. Data from experiment 1 were used to carry out the mathematical model adjustment, whereas data from experiment 2 were used for the experimental validation of the model. The model was adjusted by proposing a new correlation for the mass transfer coefficient and by calibrating the heat transfer coefficient. The transient numerical results were in good quantitative and qualitative agreement with the experimental results, ie, within the experimental error bars. Then the experimentally validated mathematical model was utilized to optimize the following parameters: (i) the electric heater power ( ) and the dry air mass flow rate ( ) and (ii) the convection oven length to width ratio (L/W). The goal was to minimize system energy consumption (objective function). The optimization procedure was subject to the following physical constraints: (i) fixed convection oven total volume and (ii) fixed biomass and drying air contact surface area. For the oven original geometry,  = 3.0 kW and  = 9 g s^?1 were numerically found for minimum energy consumption, so that 36.9% and 43.5% energy consumption decreases were obtained, respectively, in comparison with the measurements of experiment 1. Next, the numerical geometric optimization found (L/W)_opt = 9, with and , which was capable to reach a 51.6% energy consumption reduction in comparison with the original system tested in experiment 1. The novelty of this work consists of the development and experimental validation of a physically based microalgae biomass drying mathematical model, ie, instead of using empirical correlations to predict the drying time and temperature profiles and then minimize system energy consumption. Therefore, the results show that it is reasonable to state that the model could be used to design, control, and optimize drying systems with configurations similar to the one analyzed in this study.     

Cost‐competitive methane steam reforming in a membrane reactor for H2 production: Technical and economic evaluation with a window of a H2 selectivity

Techno‐economic viability studies of employing a membrane reactor (MR) equipped with H₂ separation membranes for methane steam reforming (MSR) were carried out for H₂ production in Korea using HYSYS®, a well‐known chemical process simulator, including economic analysis based on itemized cost estimation and sensitivity analysis (SA). With the reaction kinetics for MSR reported by Xu and Froment, the effect of a wide range of H₂ selectivity (10‐10,000) on the performance in an MR was investigated in this study. Because of the equilibrium shift owing to the Le Chatelier's principle, great performance of enhancement of methane conversion ( ) and H₂ yield and reaction temperature reduction was observed in an MR compared with a packed‐bed reactor (PBR). A window of a H₂ selectivity from 100 to 300 is proposed as a new criterion for better MR performance of MSR depending on potential applications from in‐depth analysis of and H₂ yield enhancements, a H₂ purity, and temperature reduction. In addition, economic analysis to evaluate the feasibility of an MR technology for MSR was carried out focusing on a levelized cost of H₂ based on itemized cost estimation of capital and operating costs as well as SA. Techno‐economic assessment showed 36.7% cost reduction in an MR compared with a PBR and revealed that this MR technology can be possibly opted for a cost‐competitive H₂ production process for MSR.     

Investigation of Zr-doped ceria for solar thermochemical valorization of CO2

This study belongs to the estimation of the CO₂ conversion ability of Ce_1−xZr _xO₂ (CZ) materials performing multiple thermogravimetric CO₂ splitting (CDS) cycles. By varying the molar concentrations of Zr in the range of 0.05 to 0.5, the CZ materials were prepared by using co-precipitation method. By employing various analytical methods, the physical properties such as phase and elemental composition, crystallite size, and particle morphology of the as-synthesized CZ materials were recognized. The systematic estimation of the reactivity of each CZ material was performed by conducting multiple cycles in a thermogravimetric analyzer (TGA). Obtained findings indicated that Ce_0.7Zr_0.3O₂ (CZ30) and Ce_0.85Zr_0.15O₂ (CZ15) were proficient towards producing maximum amounts of O₂ () and CO ( n_CO ) than other CZ materials. It was further understood that, to achieve higher and n_CO as compared with CeO₂, the molar concentration of the Zr should be in the range of 15% to 35%.     

Synthesised spirobichroman-based polyimide functionalized by pyridine: Effects of substituent position on gas separation and thermal properties

Spirobichroman - based polymers have garnered considerable attention as promising gas separation membrane materials. Herein, two spirobichroman-based diamines were synthesised using a pyridine heterocyclic ring with methyl substituents at different positions. The diamines were reacted with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and bis-(3-phthalyl anhydride) ether (ODPA) to achieve four polyimides functionalised by pyridine. The polymers performances were characterised by experimentally and molecular dynamics simulations. They showed high molecular weights of M_n = 9.4 to 14.0 × 10⁴, excellent thermal stability, good solubility in a series of common organic solvents, and easy processability to form membranes. The membrane showed high gas pair selectivities of and , which were attributed to turnstile-like rotary motions of the methyl and basic group of pyridine. The gas permeability results suggested that the substituents position of the methyl has little effect on the rigid molecular chain, unlike the densely packed flexible molecules chains.     

Sensitivity analysis of the effects of the thermal parameters of exhaust gases on the output of a thermoelectric generator

Recovering the dissipated heat from exhaust is a useful means of reducing the energy consumption level as well as cutting down on environmental pollution. An efficient technique for recovering this lost heat is the use of thermoelectric generators, which directly convert the dissipated heat into useful electrical energy. In this paper, a whole thermoelectric generator system installed on the exhaust pipe of a vehicle has been modeled, and the effects of thermal parameters on the output of this thermoelectric generator have been measured and evaluated by means of sensitivity analysis. The E‐Fast sensitivity analysis method has been used in this study. The sensitivity analysis results indicate that, among the thermal parameters examined, the temperature of gases entering the heat sink installed at exhaust pipe outlet () has the greatest influence (37%) and the flow rate of fluid entering the heatsink installed on the cold side of thermoelectric modules () has the second greatest influence (17%) on the output power of the considered thermoelectric generator. By using these results, the best cases of hot exhaust gases from various industries and vehicles with the highest potential of recovering the dissipated energy and heat from them by thermoelectric generators can be identified.     

Significance of the nonlinear radiative flow of micropolar nanoparticles over porous surface with a gyrotactic microorganism,activation energy,and Nield's condition

Current continuation presents the numerical study regarding stretched flow micropolar nanofluid over moving the sheet in the existence of activation energy and microorganisms. Furthermore, nonlinear aspects of thermal radiation are also utilized in the energy equation which results in the energy equation becomes highly nonlinear. This investigation has been performed by using convective Nield boundary conditions. First, useful dimensionless variables are implemented to reduce the partial differential into ordinary ones. Later on, the approximate solution of the transformed physical problem is computed by using the shooting scheme. A detailed physical interpretation of obtained results is also presented for velocity, temperature, motile microorganisms density, and mass concentration profiles. A detailed graphical explanation for each engineering parameter has been discussed for some specified range like , and The theoretical computations based presented here can be more proficient to attain the maximum efficiency of various thermal extrusion systems and microbial fuel cells.     

Unconditional nonlinear stability for double‐diffusive convection in a porous medium with temperature‐dependent viscosity and density

In this study, fluid flow in a porous medium is analyzed using a Forchheimer model. The problem of double‐diffusive convection is addressed in such a porous medium. We utilize a higher‐order approximation for viscosity‐temperature and density‐temperature, such that the perturbation equations contain more nonlinear terms. For unconditional stability, nonlinear stability has been achieved for all initial data by utilizing the or norms. It also shows that the theory of is not sufficient for such unconditional stability. Both linear instability and nonlinear energy stability thresholds are tested using three‐dimensional (3D) simlations. If the layer is salted above and salted below then stationary convection is dominant. Thus the critical value of the linear instability thresholds occurs at a real eigenvalue , and our results show that the linear theory produces the actual threshold. Moreover, it is known that with the increase of the salt Rayleigh number, R_c, the onset of convection is more likely to be via oscillatory convection as opposed to steady convection. The 3D simulation results show that as the value of R_c increases, the actual threshold moves towards the nonlinear stability threshold, and the behavior of the perturbation of the solutions becomes more oscillatory.     

Tangent hyperbolic nanofluid with mixed convection flow: An application of improved Fourier and Fick's diffusion model

This article presents a tangent hyperbolic fluid with the effect of the combination of forced and natural convection flow of nanoparticle past a bidirectional extending surface. Modified Fick's and Fourier's diffusion theories are incorporated into concentration and energy equations, respectively. Convective boundary conditions and second‐order slip flow are taken in the boundary condition. Nonlinear partial differential equations result after boundary layer approximations of the mathematical formulation of the flow problem. Nonlinear high order ordinary differential equations (ODEs) are formed by applying similarity transformation on the nonlinear partial differential equations. The transformed equations are solved with the bvp4c algorithm from Matlab. The numerical solution of ODEs was obtained and the effect of interesting parameters, dimensionless velocity component along x‐ and y‐axis, temperature, and concentration particle, Re_x, Re_y, , and , were presented through tables and graphs and discussed thoroughly. The results indicated that a decrease in velocity along with the y‐axis results from the increasing behavior of S, M, and n. Decrease in both temperature and concentration results in an increase of but their elongation is a result of increase in Bi. An increase in concentration results in decrease of N and S but a decrease in concentration results in the widening of Sc, Nb, and . Furthermore, enlargement of and results in increase of and modules and elongation of both and results in increase of and (Sc and Nb), respectively. A comparison with previously published literature was performed and a good agreement was found.     

Numerical simulation of nanoparticle shape and thermal ray on a CuO/C2H6O2–H2O hybrid base nanofluid inside a porous enclosure using Darcy's law

In this study, the physical aspects of magnetohydrodynamic flow and heat transfer of a hybrid base nanofluid in a porous medium under the effect of the shape, thermal radiation, and Lorentz force have been examined using the finite element method. Copper oxide (CuO) of various shapes was dispersed into ethylene glycol 50%‐water 50% (likewise for Fe₃O₄). The Darcy model is chosen because of the porous medium. The effect of changeable, diverse parameters, for example, Hartmann number (Ha), volume fraction (), radiation parameter (), and buoyancy force (Ra), on the streamlines, temperature gradient, and Nusselt number are shown through contours. Outputs show that the Fe₃O₄ nanoparticles have a smaller temperature gradient than that of CuO nanoparticles. The Nusselt number decreases for a larger (Ha) number, but increases for a larger Ra, Rd. The blade shaped nanoparticle has a larger impact on increasing compared with that of other shapes.     

Analysis of a boundary layer flow over moving an exponentially stretching surface with variable viscosity and Prandtl number

Boundary layer flow phenomenons on a stretching sheet find numerous applications in industrial processes such as manufacture and extraction of rubber and polymer sheets. The current study focuses on two‐dimensional water boundary layer flow on exponential stretching surface with a vertical plate for variable physical properties of fluid such as viscosity and Prandtl number. The Quasilinearization technique has been used on governing equations to transform nonlinear to linear equations and these equations are discretized by finite difference techniques to get numerical solutions. The effect of buoyancy parameters (λ), velocity ratio parameter () and streamwise coordinator (ξ) on velocity profiles (F), temperature profiles (θ), local skin‐friction coefficient (C_fx(Re_Lξexp(ξ)^)1/2) and the local Nusselt number (Nu_x(Re_Lξexp(ξ)^)?1/2) has been analyzed graphically based on numerical outcome. The magnitude of velocity profiles increases and temperature profile decreases approximately by 4% and 16% with increases the buoyancy parameter from λ = 1 to λ = 3 at = 0.5 and ξ = 1.0. The skinfriction and heat transfer coefficient increases approximately by 22% and 27% with an increase in ξ from 0.5 to 1.0 at fixed = 0.5 and λ = 1.0. The variations of velocity profiles and temperature profiles have more impact with as compared to ξ and λ. The benchmark studies were carried out to validate the current results with previously published work and found to be in excellent agreement.     

Natural convection boundary layer flow of nanofluids around different stations of the sphere and into the plume above the sphere

The main intent of the present study is to investigate the natural convection boundary layer flow of nanofluids around different stations of the sphere and eruption of the fluid from the boundary layer in to the plume above the sphere. It is pertinent to point out that in this study heated sphere is treated as point source. The system of transport boundary layer equations is based on the effects of Brownian motion and thermophoresis. The system of dimensioned boundary layer equations is transformed into nondimensional form. Later, the nondimensional form of the mathematical model is solved numerically by using implicit finite difference method. The solution of the problem depends on a controlling parameters Prandtl number P_r, Lewis number , thermophoresis parameter , and Brownian motion parameter . Particularly, it is observed that for Lewis number , Prandtl number P_r, Brownian motion parameter , and thermophoresis parameter the velocity profile is maximum at station and minimum at station . On the other hand temperature distribution is uniform at each station around the sphere and slightly reduced for . It is also observed that nanoparticles concentration is maximum at station and minimum at station We also established the result that with the increase of skin friction is reduced while the heat and mass flux are increased in the plume region‐III.     

Extensive investigation of structural,electronic, optical,and thermoelectric properties of hybrid perovskite (CH3NH3PbBr3) with mechanical stability constants

Recently, Organometallic halide based perovskites have emanated as an auspicious candidate as a solar cell absorber layer. In this article, we have explored the fundamental properties such as structural, electronic, optical, elastic, and thermoelectric parameters of CH₃NH₃PbBr₃ through first-principles calculations, because it has accomplished the entire criterion to use in photovoltaic and thermoelectric applications. We have used full-potential linearized augmented plane wave method (FP-LAPW) within DFT and implemented in Wien2k. The generalized gradient approximation (GGA) parameterized by Wu-Cohen (WC) has been used to optimize the lattice parameter, while for band gap calculations different exchange-correlation potentials (LDA/GGA) have been used. The band gap up to 2.26 eV has been achieved by doing some appropriate changes in the parameter of TB-mBJ exchange-correlation potential. The nature of band gap is direct and exist at R (0.5 0.5 0.5) symmetry point of the Brillouin zone. All the optical spectral response between 2 and 5 eV is due to the transition of Br 5p with little contribution Pb 5s orbital electrons of VBM to Pb 6p orbitals in CBM and a minor contribution of second band gap components also incorporate. As well as, a high absorption coefficient shows that it may be strongly applied in photovoltaic devices. The orientation of organic cations (CH₃NH₃)⁺ has no considerable impact on the band structure formation. To render a solid foundation about the application in the thermoelectric device up to the high-temperature region, the thermoelectric parameters have been discussed at optimal carrier concentration and definite temperature range. The measurement of elastic constants, B/G and Poisson's ratio indicates the ductile nature of CH₃NH₃PbBr₃. To the best of my knowledge, most of the investigations have been discussed first time for this material.     

Graphitic carbon nitride‐chitosan composites–anchored palladium nanoparticles as high‐performance catalyst for ammonia borane hydrolysis

The novel composites consisting of graphitic carbon nitride and chitosan (denoted as g‐C₃N₄‐CS) is synthesized for anchoring palladium nanoparticles. The results reveal that the resultant catalysts possess superior catalytic activity for ammonia borane (AB) hydrolysis. The corresponding turnover frequency reaches up to 27.7 at 30.0°C, and the activation energy is as low as 35.3 kJ mol^?1. Kinetics study reveals that the hydrolysis reaction is 0.50 and 0.68 orders with AB concentration and palladium concentration, respectively. In addition, the catalytic activity of the resultant Pd(0)/g‐C₃N₄‐CS catalysts is stable even after 10 runs. The result will be helpful for the development of hydrogen generation and functional materials.     

A numerical approach for MHD Al2O3–TiO2/H2O hybrid nanofluids over a stretching cylinder under the impact of shape factor

In this research, the heat transfer and magnetohydrodynamic stagnation point flow of a (Al₂O₃–TiO₂/H₂O) hybrid nanofluid past a stretching cylinder under the impact of heat generation, nonlinear thermal radiation, and nanoparticles shape factor has been analyzed using the Runge‐Kutta‐Fehlberg fifth order numerically method. The impact of changing diverse parameters, such as nanoparticles shape factor, named hexahedron and lamina, on temperature and velocity profiles and induced magnetic field, has been explored. The main motivation of this article is using hybrid nanoparticles to improve heat transfer. The novel findings of the current research illustrate that the Lorentz force produced by increasing magnetic field parameter () causes a decline in velocity profile; also increasing solar radiation, shape factor and the use of hybrid nanoparticles caused increment in the temperature profile. Furthermore, the lamina nanoparticle shape has more impact on Nusselt number () compared with hexahedron‐shaped nanoparticle.     

Evaluation method of the energy conversion efficiency of coal gasification and related applications

Traditional gasification parameters, such as cold gas efficiency, hot gas efficiency, or thermal efficiency, only evaluate the heat energy utilisation efficiency of gasifiers and do not take into account the gasification processes expending electricity and other types of energies. Therefore, the energy conversion efficiency cannot be assessed using these parameters. The calculation process on the energy conversion efficiency of underground coal gasification (UCG) is the basis for obtaining quantitative data of carbon emission reduction and establishing the carbon trading methodology of UCG. Moreover, the energy conversion efficiency both for surface coal gasification and UCG is a key research topic because it directly affects the economic and environmental benefits of gasification projects. This study proposed that two parameters, the integrated gasification efficiency (h_com) and the hot gas integrated gasification efficiency ( ), should be included into the coal gasification parameters and used to evaluate the energy conversion efficiency of coal gasification. In addition, the calculation methods of these two parameters for both surface gasification and UCG were established. Using the method, h_com and , of the UCG and Texaco gasification under the same scale was compared and that of various UCG processes was calculated. The results proved the necessity and reasonability of the two parameters and suggested that a certain amount of CO₂ was favourable to improve h_com and of UCG. However, a certain amount of pure O₂ can improve h_com of UCG without direct influences on . Under the condition of each process, to maximise h_com and , there must be an optimal steam (CO₂) to O₂ rate. Copyright © 2015 John Wiley & Sons, Ltd.     

High photoresponse and fast carrier mobility: Two-dimensional rGO-AgBr/Ag composite based on Z-scheme heterointerface with plasma for hydrogen evolution

With the improvement of people's living standard, energy shortage is increasingly severe. Photocatalysis technology is one of the most effective means to solve this problem. Generally, poor visible-light response and fast combination of photo-induced carriers are the main limiting factors to traditional photocatalysts. Aiming at this problem, in this paper, AgBr was used as the photosensitizer to immobilize on the surface of reduced graphene oxide (rGO) for the complexation of Ag⁺ ions and carboxyl groups of precursor graphene oxide (GO), then the two-dimensional rGO-AgBr/Ag composites (2D rGAA-α, α = 1, 2 and 3) were synthesized by solvothermal method. The structures, morphologies, chemical bonding states and photoelectrochemical properties of the samples were analyzed to study the samples, and the corresponding visible-light-driven (VLD) catalytic performances were studied by hydrogen evolution reaction (HER). Compared with pure rGO, the light absorption of rGAA-α was almost extended to full spectral range for the Z-scheme heterointerface (rGO-AgBr) construction, and the separation of photo-induced carriers can be promoted effectively. The HER results showed that the average hydrogen evolution rate ( ) of rGAA-α was significantly increased, and the rGAA-2 catalyst presented the highest (72.71 μmol h^-1g^-1). After six recycling experiments, the very faint activity decrease and unobvious structure change suggested the high photostability. Accordingly, the enhanced catalytic activity of rGAA-α catalysts was attributed to the formation of Z-scheme heterointerface and generation of Ag plasmas, so this study will provide a simple, effective and promising method for hydrogen energy development.