碱式碳酸铜制备实验的教学设计

针对传统实验教学中存在的"教师讲授-学生实验"的验证模仿式教学模式的弊端,以实验教学目标的多维化和建构主义学习理论为教学设计的理念指导,设计了碱式碳酸铜的制备实验的教学过程:通过创设碱式碳酸铜及其应用的相关情境,激发学生学习兴趣;进而围绕制备路线的确定、反应条件的控制和实验方案的设计提出5个问题,启发学生积极思考和交流讨论;在此基础上引导学生自主完成实验方案的设计;最后,提供拓展性实验资源,促进知识的迁移应用。该教学设计有利于教师从单纯注重知识传授转变为引导学生学会学习,全面提高实验素养。     

基于泛在学习的SPOC翻转实验教学探讨——以极化曲线的测定为例

以物理化学实验“碳钢在碳酸氢铵溶液中极化曲线的测定”实验为例,探索构建了基于泛在学习的SPOC的线上线下的翻转实验教学模式,其教学设计基本思路为：课前实验与理论相联系,培养学生基本技能;课中实验与专业相衔接,培养学生创新思维;课后实验与生产相融合,培养学生应用能力。实践表明,该教学模式不仅拓展了实验内容,而且极大地激发了学生的探究热情和创新思维,培养了学生的实际应用能力。     

基于建构主义理论的有机化学实验混合式教学设计与实践*

基于建构主义理论和支架式教学思想,以“北京大学有机化学实验在线学习与测试平台”为依托,探索了混合教学模式在有机化学实验课程中的应用。以薄层色谱和柱色谱实验为例,通过确立目标、分析学情、分解任务、搭建支架、教学实施、评估反馈的教学设计和实践,帮助学生掌握实验知识与技术,培养学生解决实际问题的能力,增强其实验信心。     

医学院校无机化学实验课程考核评价体系的探索与实践

针对当前无机化学实验教学中存在的问题,改革了无机化学实验课程的考核办法和评分标准,提出了"多元化实验考核模式",并进行实践应用。教学实践证明:通过完善实验考核办法和评价体系,对学生的实验成绩有一个公平、准确的评价,可以激发学生的实验兴趣,提高学生的实验动手能力和分析、解决问题的能力。     

基于生态教育理念的高职分析化学教学设计与实践

针对当前高职分析化学“保姆式”教学模式、学生学习无积极性等问题,依据生态教育理念,以酸碱滴定实验内容为例,从课前准备,课中渗透生态思想,课后学生反思、自查和总结等3个方面进行教学设计,并运用于实践教学中,提升了学生的实验兴趣和应用创新能力,培养了学生的工作责任心,实现了真正的和谐生态课堂。     

化工基础实验课改革的思考与实践

本文论述了化工基础实验课在高师院校教学中的作用及其应达到的目的要求。提出了对化工基础实验课改革的一些想法和尝试 ,即增加应用和综合实验内容 ,通过实验培养学生应用实验技能和分析解决问题的能力     

比较教学法在仪器分析实验教学中的应用

仪器分析实验是化学及相关专业的重要实验课程。结合课程特点和培养目标,提出了将比较教学法融入课堂的教学方法,指出了意义和作用,介绍了教学中开展比较教学的实践与应用。该方法加强了学生对仪器功能特点的掌握,激发其实验兴趣和创新精神,学生的认知能力在比较过程中不断建构、丰富、提高和发展,取得了较好的效果。     

物理化学教学中理论与实验相互渗透的方法探究

针对物理化学课程的特点和教学中存在的一些问题,结合实例探讨了理论与实验相互渗透的教学模式在物理化学教学中的应用。实践证明在理论教学中设计实验和在实验教学中强调理论分析的做法可以有效地提高学生的学习兴趣和参与教学的积极性,从而取得较好的教学效果。     

矿物基环境修复材料制备及应用的综合性实验设计

为促进“研学结合”,增强学生实际操作能力,依托于化学实验平台设计了“矿物基环境修复材料制备及应用”的化学综合实验。实验内容包括改性沸石材料的制备、表征和应用探索。实验由教师科研成果转化而成,已在本校环境化学综合实验课中进行教学实践,该实验可以使学生掌握文献调研、材料制备与表征、性能分析、数据处理等重要技能,锻炼学生综合实验设计和思维创新的能力,激发了学生探索环境修复材料前沿知识的兴趣。     

归类比较教学法在元素性质实验课中的应用

将归类法和比较法原理应用到无机化学的元素性质实验教学过程,在实验步骤中加入了归类比较内容,这不但能够帮助学生记忆,提高学生学习兴趣,而且能使学生带着更加明确的实验目的完成实验过程。实践结果表明,在元素性质实验中,归类比较教学法的引入确实增强了学生对理论课知识的理解和掌握,教学效果得到显著改善,是一项值得推广的教学经验。     

A bubble breakage model for finite Reynolds number flows

The breakage frequency of bubbles in turbulent liquid flows is modeled as the inverse of the breakage time by Martinez-Bazan et al. [J. Fluid Mech. 401: 157–182; 1999]. In this definition of the breakage frequency, it is assumed that the breakage probability is unity and hence all bubbles will break. This assumption is reasonable in turbulent flows at extremely high Reynolds numbers in which the turbulence energy dissipation is very high. For systems characterized by finite Reynolds numbers the energy dissipation rate decreases rapidly and the breakage probability is reduced significantly. In the present study, the breakage frequency model by Martinez-Bazan et al. has been extended to include the effect that only a fraction of the bubbles breaks at finite Reynolds numbers. For this model extension, an adjusted version of the breakage probability formula proposed by Coulaloglou and Tavlarides [Chem. Eng. Sci. 32: 1289–1297; 1977] was employed. The extended breakage frequency model for finite Reynolds number flows has been evaluated by comparison to recent experimental single bubble breakage data. It can be concluded that extensive experimental analyses are required to gather sufficient experimental data for improved understanding of the physical phenomena and for model validation. In particular, the bubble breakage analysis must be performed simultaneously with the characterization of the local turbulence properties in the flow.     

A Correlation of the Drag Force Coefficient on a Sphere with Interface Slip at Low and Intermediate Reynolds Numbers

The hydrodynamics of a sphere with interface slip has been numerically investigated for flows of Reynolds number ranging 0 < Re ≤ 75. A simple correlation of the drag force coefficient in the present of interface slip has been derived based on our numerical simulations. The correlation takes the slip coefficient and Reynolds number as two input parameters. By comparing results found in the literature, we believe that the present correlation is more accurate; it provides a source for future experiment study and for numerical simulations of large multi-particle system where the interface slip is important.     

Numerical simulation of nanofluids for improved cooling efficiency in a 3D copper microchannel heat sink (MCHS)

In this paper, laminar nanofluid flow in 3D copper microchannel heat sink (MCHS) with rectangular cross section, and a constant heat flux, has been treated numerically using the computational fluid dynamics software (FLUENT). Results for the temperature and velocity distributions in the investigated MCHS are presented. In addition, experimental and numerical values are compared in terms of friction factors, convective heat transfer coefficients, wall temperature and pressure drops, for various particle volume concentrations and Reynolds numbers. The numerical results show that enhancing the heat flux has a very weak effect on the heat transfer coefficient for pure water, but an appreciable effect for the case of a nanofluid. For all considered volume fractions, the sink friction factor decreases by increasing the Reynolds number and slightly increases by increasing the volume fractions, and, with increasing the volume fractions and the Reynolds number, the pressure drop increases.     

Observation and modelling of clamshell droplets on vertical fibres subjected to gravitational and drag forces

Extensive experimental investigation of the wetting processes of fibre-liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment of drops from fibres as airflow velocity increases, and also movement or flow of droplets along fibres. A detailed experimental study of the processes was conducted using stainless steel filter fibres and H2O aerosol, which coalesce on the fibre to form clamshell droplets. The droplets were predominantly observed in the Reynolds transition flow region, since this is the region where most of the above features occur. The droplet oscillation is believed to be induced by the onset of the transition from laminar to turbulent flow as the increasing droplet size increases Reynolds number for the flow around the droplet. Two-dimensional flow in this region is usually modelled using the classical Karman vortex street, however there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and preventing such oscillation. The agreement between the model and experimental results is very good for both the radial and transverse oscillations.     

Observation and modelling of barrel droplets on vertical fibres subjected to gravitational and drag forces

Extensive experimental investigation of the wetting processes of fibre/liquid systems during air filtration (when drag and gravitational forces are acting) has shown many important features, including droplet extension, oscillatory motion, and detachment or flow of drops from fibres as airflow velocity increases. A detailed experimental study of the aforementioned processes was conducted using glass filter fibres and H(2)O aerosol, which coalesce on the fibre to form barrel droplets with small contact angles. The droplets were predominantly observed in the Reynolds transition (or unsteady laminar) flow region. The droplet oscillation appears to be induced by the onset of vortexes in the flow field around the droplet as the increasing droplet size increases the Reynolds number. Flow in this region is usually modelled using the classical two-dimensional Karman vortex street, and there exist no 3D equivalents. Therefore to model such oscillation it was necessary to create a new conceptual model to account for the forces both inducing and inhibiting such oscillation. The agreement between the model and experimental results is acceptable for both the radial and transverse oscillations.     

Electrohydrostatically driven flow and instability in a vertical hele-shaw cell

The electrohydrostatic capillary-driven flow of a viscous poorly conducting Newtonian fluid rising between conducting parallel plates is studied both theoretically and experimentally. By scaling the problem with a pressure and time derived by considering Maxwell stresses along the interface, it is determined that the dimensionless parameters governing the flow are the hydrostatic bond (Bo(H)), electrostatic bond (Bo(E)) and electrostatic Reynolds (Re(E)) numbers. A lubrication theory analysis, in the limit Re(E) --> 0, of the momentum balance leads to an analytical solution for the elapsed time versus interface position that is analogous to one derived by Washburn (1921) for the capillary pressure-driven flow of a fluid in cylindrical capillaries (Washburn, E. W. Phys. Rev. 1921, 17 (3), 273-283). Experiments are performed using silicone and castor oil at gap spacing less than the capillary length for two ranges of electrostatic Reynolds numbers 0.001 < Re(E) < 0.01 and 10 < Re(E) < 1000. The experimental results for the interface displacement as a function of elapsed time are compared with the theoretical predictions. At large electrostatic Reynolds numbers (>1), a convective instability is observed in plots of the interface position as a function of time. The propagating front also reveals an interfacial instability for large electrostatic Reynolds numbers coupled with large fluid displacements. The theory and experiments for the static rise height show good agreement with theory while the flow dynamics show good qualitative agreement in the applicable limits at low electrostatic Reynolds numbers.     

An optimised split-and-recombine micro-mixer with uniform chaotic mixing

A second generation micro-mixer, being a further optimised version of a first prototype, relying on the consequent utilisation of the split-and-recombine principle is presented. We show that the mixing can be characterized by a positive finite-time Lyapunov exponent although being highly regular and uniform. Using computational fluid dynamics (CFD) we investigate the mixing performance for Reynolds numbers in the range of about 1 to about 100. In particular for low Reynolds numbers (Re < 15) the CFD results predict an almost ideal multi-lamination. Thus, the developed mixer is especially suited for efficient mixing of highly viscous fluids. Furthermore, the numerical results are experimentally validated by investigations of mixing of water-glycerol solutions. The experimental results are found to be in excellent agreement with the numerical data and prove the high mixing efficiency.     

Three minimum wet thickness regions of slot die coating

An experimental study was carried out to determine the minimum wet thickness of slot die coating for low-viscosity solutions. There exist three distinct coating regions (I, II, and III), depending on the physical properties of the coating fluid, die geometry, and flow conditions. A critical Reynolds number was found, below which viscous and surface tension effects are important. In Region I, the minimum wet thickness increases with increasing capillary number and becomes independent of capillary number in Region II. Region III exists above the critical Reynolds number where fluid inertia is dominant. In this region, the minimum wet thickness decreases as Reynolds number increases. Flow visualization on the coating bead reveals that the position of the downstream meniscus of the coating bead determines the types of coating region, whereas the shape and position of the upstream meniscus determine the type of coating defects. It was also observed that the downstream meniscus was not located at the die lip corner and both the static and dynamic contact angles varied under different conditions. These findings are critical for realistic theoretical study of slot die coating.     

Effect of the adsorption component of the disjoining pressure on foam film drainage

The present work is trying to explain a discrepancy between experimental observations of the drainage of foam films from aqueous solutions of sodium dodecylsulfate and the theoretical DLVO-accomplished Reynolds model. It is shown that, due to overlap of the film adsorption layers, an adsorption component of the disjoining pressure is important for the present system. The pre-exponential factor of this adsorption component was obtained by fitting to the experimental drainage curves. It corresponds to a slight repulsion, which reduces not only the thinning velocity as observed experimentally but corrects also the film equilibrium thickness.     

Non-aqueous phase liquid drop formation within a water saturated fracture

This work focuses on the mechanisms of non-aqueous phase liquid (NAPL) drop formation within a single fracture fed from a NAPL reservoir by way of a circular orifice, such as a pore. The fracture is assumed to be fully saturated, the relative wettability of the system is assumed water-wet, and the water velocity profile within the fracture is described by a Poiseuille flow. The size of the NAPL drops is investigated for various water flow velocities and NAPL entrance diameters. A force balancing method was used to determine the radii of detached drops. The drop sizes calculated from the model developed here are shown to be in agreement with available experimental drop size data. It is shown that at low Reynolds numbers the buoyancy force is the dominant force acting on the drop during the formation process and at high Reynolds numbers the viscous forces dominate. A simplified expression relating the geometry of the fractured system to the drop radii is developed from the model equations, and it is shown to predict drop radii that match well with both the model simulations and the available experimental data.