Melting heat transfer with radiative effects and homogeneous–heterogeneous reaction in thermally stratified stagnation flow embedded in porous medium

The present article deals with thermally stratified stagnation-point flow saturated in porous medium on surface of variable thickness along with more convincing and reliable surface condition termed as melting heat transfer.Homogeneous–heterogeneous reaction and radiative effects have been further taken into account to reconnoiterproperties of heat transfer.Melting heat transfer and phenomenon of homogeneous–heterogeneous reaction have engrossed widespread utilization in purification of metals,welding process,electroslag melting,biochemical systems,catalysis and several industrial developments.Suitable transformations are utilized to attain a scheme of ordinary differential equations possessing exceedingly nonlinear nature.Homotopic process is employed to develop convergent solutions of the resulting problem.Discussion regarding velocity,thermal field and concentration distribution for several involved parameters is pivotal part.Graphical behaviors of skin friction coefficient and Nusselt number are also portrayed.Concentration of the reactants is found to depreciate as a result of strength of both heterogeneous and homogeneous reaction parameters.With existence of melting phenomenon,declining attitude of fluid temperature is observed for higher radiation parameter.

A modified model for isothermal homogeneous and heterogeneous reactions in the boundary-layer flow of a nanofluid

The homogeneous and heterogeneous reactions in the boundary-layer of a flat surface are considered. The autocatalysts are assumed to be of regular sizes, while the solution is a dilute nanofluid. The heat release due to the chemical reactions is taken into account. The Buongiorno’s model is used to describe the behaviors of this reaction system. This configuration makes the current model be different from all previous publications. Multiple solutions are given numerically to the rescaled nonlinear system, whose stability is verified. The results show that the strength coefficients of the homogeneous and heterogeneous reactions are key factors to cause the appearance of the multiple solutions in the distribution of the chemical reactions. Nanofluids enhance the diffusion of heat and help maintain the stability of chemical reactions.

Multiscale Homogenization Analysis of Alkali–Silica Reaction (ASR) Effect in Concrete

The alkali silica reaction (ASR) is one of the major long-term deterioration mechanisms occurring in con- crete structures subjected to high humidity levels, such as bridges and dams. ASR is a chemical reaction between the silica existing inside the aggregate pieces and the alkali ions from the cement paste. This chemical reaction produces ASR gel, which imbibes additional water, leading to gel swelling. Damage and cracking are subsequently generated in concrete, resulting in degradation of its mechanical proper- ties. In this study, ASR damage in concrete is considered within the lattice discrete particle model (LDPM), a mesoscale mechanical model that simulates concrete at the scale of the coarse aggregate pieces. The authors have already modeled successfully ASR within the LDPM framework and they have calibrated and validated the resulting model, entitled ASR-LDPM, against several experimental data sets. In the pre- sent work, a recently developed multiscale homogenization framework is employed to simulate the macroscale effects of ASR, while ASR-LDPM is utilized as the mesoscale model. First, the homogenized behavior of the representative volume element (RVE) of concrete simulated by ASR-LDPM is studied under both tension and compression, and the degradation of effective mechanical properties due to ASR over time is investigated. Next, the developed homogenization framework is utilized to reproduce experimental data reported on the free volumetric expansion of concrete prisms. Finally, the strength degradation of prisms in compression and four-point bending beams is evaluated by both the mesoscale model and the proposed multiscale approach in order to analyze the accuracy and computational ef - ciency of the latter. In all the numerical analyses, different RVE sizes with different inner particle realiza- tions are considered in order to explore their effects on the homogenized response.

Melting heat transfer in Cu-water and Ag-water nanofluids flow with homogeneous-heterogeneous reactions

This article addresses melting heat transfer in magnetohydrodynamics(MHD)nanofluid flows by a rotating disk. The analysis is performed in Cu-water and Ag-water nanofluids. Thermal radiation, viscous dissipation, and chemical reactions impacts are added in the nanofluid model. Appropriate transformations lead to the nondimensionalized boundary layer equations. Series solutions for the resulting equations are computed.The role of pertinent parameters on the velocity, temperature, and concentration is analyzed in the outputs. It is revealed that the larger melting parameter enhances the velocity profile while the temperature profile decreases. The surface drag force and heat transfer rate are computed under the influence of pertinent parameters. Furthermore, the homogeneous reaction parameter serves to decrease the surface concentration.

HOMOGENEOUS CATALYTIC REACTION(EC')AT GENERATION/COLLECTION MICROELECIRODE

A new type of macro-micro-macro triple electrode is fabricated. The kinetic equation is obtained by using the decrease in collection current to determine the kinetic constant of homogeneous catalytic reaction, the method can be used to study homogeneous chemical reaction with any magnitude of kinetic constant, and overcomes the disadvantages that the microelectrode is only suitable for fast catalytic reaction.

Mechanistic insights into homogeneous electrocatalytic reaction for energy storage using finite element simulation

The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts.In this paper,homogeneous electrocatalytic reaction between hydroxymethylferrocene(HMF)and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which,the secondorder rate constant(k_(ec))of the chemical reaction between HMF^(+)and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation.The corresponding k_(ec)(1.1(mol·m^(-3))^(-1)·s^(-1))is further verified by linear sweep voltammograms under the same model.Square wave voltammetry parameters including potential frequency(f),increment(Estep)and amplitude(ESW)have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction.Specifically,the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon.Moreover,the proposed methodology of k_(ec)prediction is examined by hydroxyethylferrocene(HEF)and L-cysteine.The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose,especially in terms of electrochemical kinetics extraction and flow battery design.

Effect of Homogenizing Procedures on the Properties of Reaction Sialon Suspension

Homogeneous, high concentrated ceramic suspensions wi th low viscosity are the key controlling factors for the production of ceramic c omponents through colloidal processing. A well-dispersed suspension can be obta ined by choosing suitable dispersant, solvent, particle size distribution etc. B esides these factors, the homogenizing procedure is also a key step. In this paper, reaction sialon suspensions were prepared using 3-wt% KD1 as dis persant in organic media composed of 60-vol% methyletheylketone and 40-vol% et hanol. Different homogenizing procedures have been used and compared, including planetary milling, low energy ball milling and ultrasonic disaggregation. The ef fects of different homogenizing routes and mixing times on the rheology and stab ility of suspensions, and on the microstructure of slip casting green bodies, ha ve been studied. The varying dispersion efficiencies observed could be attribute d to differences in deagglomeration degrees achieved and in adsorption amount of dispersant onto the surface of reaction sialon powders.

Note on characteristics of homogeneous-heterogeneous reaction in flow of Jeffrey fluid

This letter describes the characteristics of homogeneous-heterogeneous re- action in the boundary layer flow of a Jeffrey fluid due to an impermeable horizontal stretching sheet. An analysis is carried out through the similar values of reactant and auto catalyst diffusion coefficients. Heat released by the reaction is not accounted. The exact solution for the flow of the Jeffrey fluid is constructed. The series solution for the concentration equation is derived. The velocity and concentration fields reflecting the impact of interesting parameters are plotted and examined.

基于空间分辨中子衍射方法的锂离子电池电化学反应均匀性研究

锂离子电池作为一种具有复杂组成的电化学器件,其电化学反应的均匀性受多种因素影响,包括正负极材料成分、电池结构和制备工艺等。电池的局部电化学反应不均匀性将导致局部失效加剧,进而影响其电化学性能、循环稳定性和安全性。鉴于电池拆解分析不但会破坏其电芯结构,改变电极材料的化学性质,进而影响分析结果的准确性,本工作介绍并应用无损的空间分辨飞行时间中子衍射方法,对大尺寸软包锂离子电池电化学反应分布的均匀性展开研究。通过采集和分析毫米尺度测试区域的中子衍射数据,获得了全电池在初始状态和失效状态下锂离子嵌入石墨负极过程中的相变信息,并构建了全电池不同位置处的石墨负极多相含量分布和归一化后负极中的锂浓度分布图。此外,结合高精度三维X射线断层扫描方法,从电池厚度、电流密度和电解质浓度等多个角度,分析和探讨了这些因素对锂离子电池电化学反应均匀性的影响。空间分辨中子粉末衍射方法可以对不同类型和不同形状的金属离子电池中的电化学反应均匀性进行快速直接的检测,为电池结构性能优化和技术改进提供强有力的技术支持。

Experimental and numerical investigations on micromixing performance of multi-orifice cross-flow jet mixers

Multi-orifice cross-flow jet mixers(MOCJMs)are used in various industrial applications due to their excellent mixing efficiency,but few studies have focused on the micromixing performance of MOCJMs.Herein,the flow characteristics and micromixing performance inside the MOCJM were investigated using experiments and computational fluid dynamics(CFD)simulations based on the Villermaux/Dushman system and the finite-rate/modified eddy-dissipation model.The optimal A value was correlated with the characteristic parameters of MOCJMs to develop a CFD calculation method applicable to the study of the micromixing performance of the MOCJMs.Then the micromixing efficiency was evaluated using the segregation index XS,and the effects of operational and geometric parameters such as mixing flow Reynolds number(ReM),flow ratio(RF),total jet area(ST),the number of jet orifices(n),and outlet configuration on the micromixing efficiency were investigated.It was found that the intensive turbulent region generated by interactions between jets,as well as between jets and crossflows,facilitated rapid reactions.XS decreased with increasing ReM and decreasing RF.Furthermore,MOCJMs with lower ST,four jet orifices,and the narrower outlet configuration demonstrated a better micromixing efficiency.This study contributes to a deeper understanding of the micromixing performance of MOCJMs and provides valuable guidance for their design,optimization,and industrial application.

Chemically Radiative MHD Flow of a Micropolar Nanofluid over a Stretching/ Shrinking Sheet with a Heat Source or Sink

This study examines the behavior of a micropolar nanofluidflowing over a sheet in the presence of a transverse magneticfield and thermal effects.In addition,chemical(first-order homogeneous)reactions are taken into account.A similarity transformation is used to reduce the system of governing coupled non-linear partial differ-ential equations(PDEs),which account for the transport of mass,momentum,angular momentum,energy and species,to a set of non-linear ordinary differential equations(ODEs).The Runge-Kutta method along with shoot-ing method is used to solve them.The impact of several parameters is evaluated.It is shown that the micro-rota-tional velocity of thefluid rises with the micropolar factor.Moreover,the radiation parameter can have a remarkable influence on theflow and temperature profiles and on the angular momentum distribution.

少水/DMSO反应体系制备聚丙烯腈动力学研究

以过硫酸铵(APS)为引发剂,丙烯腈(AN)与衣康酸(IA)为聚合反应单体,采用少量水(不超过10%)和二甲基亚砜(DMSO)作为混合溶剂,进行均相溶液聚合制备聚丙烯腈(PAN)共聚物。研究了AN与IA共聚反应动力学规律,绘制了转化率-时间曲线,建立了聚合反应速率方程,探究了温度对聚合速率的影响。结果表明:随着引发剂浓度和总单体浓度升高,聚合反应转化率增加;随着共聚单体IA含量的增多,聚合反应转化率下降;随水含量的增多,转化率先升高后降低;随温度升高,聚合反应速率常数增大,计算得到反应活化能为127.61kJ/mol;该聚合反应速率方程为:R p∝[APS]^(0.924)[M]^(1.35)。

酯交换合成碳酸二甲酯反应动力学研究

研究了离子交换树脂催化碳酸乙烯酯(EC)和甲醇(MeOH)酯交换合成碳酸二甲酯(DMC)的反应动力学。在间歇搅拌釜式反应器中研究了催化剂的种类、搅拌速率、醇酯摩尔比、催化剂用量和反应温度对酯交换过程的影响;采用拟均相动力学模型对实验数据进行关联。结果表明,估算的动力学参数使计算结果和实验数据吻合较好,建立了离子交换树脂催化酯交换反应的动力学模型,为反应精馏过程中的模拟计算以及工业化生产提供了一定的理论支持。

固载型席夫碱金属配合物对醇催化氧化研究进展

席夫碱过渡金属配合物因其易制备及特殊性能被广泛应用,但作为均相催化剂使用时,不易于与产物分离及在反应过程中易发生聚合而失去活性等问题。在分离技术的发展情况下,固载型席夫碱金属配合物作为一种极具潜力的多相催化剂而被广泛应用于各种氧化反应中,尤其苯甲醇的选择性催化氧化是研究的热点。本文综述近十年固体载体固载席夫碱过渡金属配合物对苯甲醇的选择性催化氧化性能的研究。本综述主要对磁性纳米颗粒作为载体对苯甲醇的选择性催化氧化反应进行评述。

AUTO-DARBOUX TRANSFORMATION AND EXACT SOLUTIONS OF THE BRUSSELATOR REACTION DIFFUSION MODEL

Firstly, using the improved homogeneous balance method, an auto-Darboux transformation (ADT) for the Brusselator reaction diffusion model is found. Based on the ADT, several exact solutions are obtained which contain some authors' results known. Secondly, by using a series of transformations, the model is reduced into a nonlinear reaction diffusion equation and then through using sine-cosine method, more exact solutions are found which contain soliton solutions.

POLYMERIZATION MECHANISM OF DIENES WITH HOMOGENEOUS RARE EARTH CATALYSTS

The reaction mechanisms of diene polymerization with homogeneous rare earth catalyst are studied by means of the spectra of ~1H-NMR, one-and two-dimensions ^(13)C-NMR. Based on the data of above NMR spectra, it is proposed that the polymerization reaction proceeds according to the following mechanism: η~4-diene (cis-trans-)and η~3-allyl (syn-anti-).

H13钢表面同质激光熔覆中WC微合金化行为及摩擦学性能研究

采用激光熔覆技术在H13钢基体上制备了不同碳化物含量的同质熔覆层,研究了同质熔覆层的微观结构特征及摩擦学性能。借助X射线衍射仪、扫描电镜分析了同质熔覆层的物相变化规律和微观组织形貌特征,采用显微硬度计、摩擦磨损实验机和激光共聚焦显微镜研究了熔覆层的硬度变化特征及摩擦磨损性能,并阐明了微结构与摩擦学性能之间的相关性。结果表明,同质激光熔覆层与基体实现优良的冶金结合,同质粉末与WC产生微合金化反应,从原铁素体改变为奥氏体相,并生成以网络状弥散分布的新硬质相,细化晶粒的同时进一步强化晶界。网络状分布的硬质相产生“鹅卵石”效应,可使熔覆层硬度高达1104HV,摩擦系数低于0.51,比磨损率低于2.24×10-8 mm^(3)/(N·m),耐磨损性能较基体提升17.62倍。

有机废水处理中芬顿氧化反应机制研究进展

芬顿反应工艺是目前公认处理有机废水最有效的方法之一,而探索其反应机理对于高效芬顿催化反应体系的开发和应用至关重要。芬顿反应的复杂性导致其反应机理仍未得到完整的解释。该文综述了目前较受认可的均相芬顿、光助芬顿、电助芬顿和多相芬顿的反应机制,旨在帮助研究者比较全面及深入地认识不同体系中芬顿反应的机理,为芬顿反应的发展提供理论支撑。最后对芬顿过程的未来发展方向进行了展望。

具有对流项的Biochemical reactions方程粘性解的Cauchy问题

研究一类特殊的具有对流项的Biochemical reactions方程粘性解的Cauchy问题.利用对应的线性齐次方程的基本解和齐次化原理,给出非齐次方程Cauchy问题的积分形式的解.通过皮卡迭代构造出近似解序列,并证明它的极限就是原Cauchy问题的局部解.并利用极值原理通过构造辅助函数,得到了解的L∞估计,从而证明了原Cauchy问题解的整体存在性.

半固化匀浆膳在高龄鼻饲病人中的应用

目的:探讨添加食物增稠剂的半固化匀浆膳在高龄鼻饲病人中的应用效果。方法:选择2021年10月—2022年3月在上海爱以德护理院接受长期护理的262例高龄鼻饲病人,随机分为研究组和对照组各131例,对照组给予3个月膳食匀浆膳,研究组给予3个月半固化匀浆膳,比较两组病人的营养指标及肠内不耐受情况;其中20例轻度糖尿病鼻饲病人分别给予膳食匀浆膳和半固化匀浆膳1周,比较血糖水平变化。结果:研究组病人的血清清蛋白<35 g/L的比例(18.32%)低于对照组(39.69%),肠内不耐受发生率低于对照组,摄入量未达标率(3.82%)低于对照组(15.27%);20例轻度糖尿病鼻饲病人使用半固化匀浆膳时血糖水平低于使用膳食匀浆膳时,差异有统计学意义(P<0.05)。结论:半固化匀浆膳能改善鼻饲病人的营养状态,可以减少胃食道反流或呕吐、腹泻发生率,且有助于病人早期达到管饲营养目标摄入量,且对于老年糖尿病人血糖控制有一定帮助。