传热传质分离的绝热吸收过程实验研究

根据传热传质分离的吸收形式,设计加工了一台溴化锂绝热降膜吸收的实验装置,对溴化锂水溶液在倾斜平板上对水蒸气的吸收特性进行了实验研究,分析了预冷却温差、溶液流量及平板倾角对吸收过程的影响。实验结果表明:预冷却温差、溶液流量及平板倾角越大,溴化锂溶液对水蒸气的吸收效果越好,并认为吸收过程可以分成三个步骤,另外就热质分离吸收器的设计过程中的溴化锂溶液的最小速度提出建议。     

Stable gem-trifluoromethyl anionic σ-complexes based on 1,3,5-tris(sulfonyl)benzene derivatives and their transformations

A convenient synthetic procedures is described to obtain gem-trifluoromethyl anionic σ-complexes of 1,3,5-tris(fluorosulfonyl)benzene, 1,3,5-tris(β,β,β-trifluoroethoxysulfonyl)benzene, 1,3,5-tris(trifluoromethylsulfonyl)benzene as well as of 1,3,5-trinotrobenzene. Conditions for easy oxidation of these adducts into corresponding 2,4,6-tris(substituted)benzotrifluorides have been found. It is shown that the latter add trifluoromethyl anion to the 1 and 3 positions of the aromatic ring forming new anionic σ-complexes in different ratio. Structures and relative stabilities of the anionic adducts are discussed based on RI-MP2 quantum chemical calculations.     

从证据推理视角对“离子反应”教学案例的分析及其启示*

证据推理是学生以其经验为基础、问题为起点,根据教师提供的一个或几个学习材料(已知判断),得出目标概念(新判断)的深度思维过程。通过梳理和界定证据推理的概念、证据类型、证据推理过程及核心要素,建构出实验探究教学中以“问题、解释、假设、证据、推理、结论”为要素及其之间关系的证据推理线形模型和循环模型,以此分析视角及其框架对“离子反应”教学中证据推理的过程进行了分析,并基于证据推理的6要素得出培养学生证据推理能力的启示与建议,达到证据推理过程中基本思想方法的外显,落实证据推理与模型认知的化学学科核心素养,也为今后的教学实践提供核心推理思路及教学建议。     

贫困地区高中化学课堂教学行为现状调查——以甘肃省某中学为例

以甘肃省某高级中学为例,将高中化学课分为化学概念与化学用语课、化学理论与化学计算课、元素化合物课、实验课、习题课等5类,分类抽取不同化学教师的课堂进行观察和量化,并对化学教师进行访谈调查。调查发现,在化学概念与化学用语课堂中,教师以“问-讲”的教学方式为主,学生主动参与程度较低;化学理论与化学计算课堂中,教师一讲到底,严重弱化学生的自主思考、自主练习和交流;元素化合物课堂中,教师以自问自答和师问-生答-师讲的模式为主,学生课堂参与度较大,但主动性和自主性不高;实验课堂中教师重在讲实验,学生重在背实验,实验操作以机械模仿为主;习题课堂中教师自问自答、一讲到底,学生多书写和记录,无思考和交流。最后总结了产生上述现象的主要原因。     

在大转角透平叶栅中叶片反弯曲对通道涡及静压场的影响

本文采用微型球头五孔探针对低展弦比大转角透平直叶片栅和反弯曲叶片栅栅内外流场进行了详尽测量,并开设静压孔测取了叶栅端壁和叶片表面的静压分布。根据实验结果,作者全面分析了叶片反弯曲对通道涡及静压场的影响,并明确提出：在大转角透平叶栅中,叶片反弯曲后,由叶片力在吸力面前部产生的沿叶高方向的反“Ｃ”型静压分布是控制通道涡减弱的关键,这也是叶片反弯曲作用的本质所在。     

Discrete simulation and micromechanical analysis of two-dimensional saturated granular media

In this study, a novel approach to incorporate the pore water pressure in the discrete element method (DEM) to comprehensively model saturated granular media was developed. A numerical model was constructed based on the DEM by implanting additional routines in the basic DEM code; pore water pressure calculations were used with a two-dimensional (2D) model to simulate the undrained behavior of saturated granular media. This model coupled the interaction of solid particles and the pore fluid in saturated granular media. Finally, several 2D undrained shear tests were simulated. The test results showed that the model could predict the response of the saturated granular soil to shear loading. The effect of initial compaction was investigated. Biaxial tests on dense and loose specimens were conducted, and the effect of the initial density on the change in shear strength and the volume change of the system was investigated. The overall behavior of loose and dense specimens was phenomenologically similar to the real granular material. Constant volume tests were simulated, and the results were compared to those from the coupled model. Induced anisotropy was micromechanically investigated by studying the contact force orientation. The change in anisotropy depended on the modeling scheme. However, the overall responses of the media obtained using the coupled and constant volume methods were similar.     

Discrete simulation and micromechanical analysis of two-dimensional saturated granular media

In this study, a novel approach to incorporate the pore water pressure in the discrete element method （DEM） to comprehensively model saturated granular media was developed. A numerical model was constructed based on the DEM by implanting additional routines in the basic DEM code; pore water pressure calculations were used with a two-dimensional （2D） model to simulate the undrained behavior of satu- rated granular media. This model coupled the interaction of solid particles and the pore fluid in saturated granular media. Finally, several 2D undrained shear tests were simulated. The test results showed that the model could predict the response of the saturated granular soil to shear loading. The effect of initial compaction was investigated. Biaxial tests on dense and loose specimens were conducted, and the effect of the initial density on the change in shear strength and the volume change of the system was inves- tigated. The overall behavior of loose and dense specimens was phenomenologically similar to the real granular material. Constant volume tests were simulated, and the results were compared to those from the coupled model. Induced anisotropy was micromechanically investigated by studying the contact force orientation. The change in anisotropy depended on the modeling scheme. However, the overall responses of the media obtained usinz the couoled and constant volume methods were similar.     

Experimental Investigation of Opposing Mixed Convection in a Channel with an open Cavity Below

Abstract

In this article, mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The heated wall is on the opposite side of the forced inflow. The results are reported in terms of wall temperature profiles of the heated wall and flow visualization. The range of pertinent parameters used in this experiment are Reynolds numbers (Re) from 100 to 2,000 and Richardson numbers (Ri) from 4.3 to 6,400. Also, the ratio between the length and the height of cavity (L/D) ranges from 0.5–2.0, and the ratio between the channel and cavity height (H/D) is equal to 1.0. The lack of experimental results on mixed convection in a channel with an open cavity below was an impetus for investigating this configuration when one cavity vertical wall is heated at uniform heat flux. The present results show that at the lowest investigated Reynolds number, the surface temperatures are lower than the corresponding surface temperatures for Re = 2,000 at the same ohmic heat flux. The flow visualization shows that for Re = 1,000, there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100, the effect of a stronger buoyancy determines a penetration of thermal plumes from the heated plate wall into the upper channel. Moreover, the flow visualization shows that for lower Reynolds numbers, the forced motion penetrates inside the cavity, and a vortex structure is adjacent to the unheated vertical plate. At higher Reynolds numbers, the vortex structure has a larger extension while L/D is held constant.     

Die Frontenmarkierung mit radioaktiven Isotopen bei der Untersuchung technischer Ionenauschprozesse

Der Einsatz radioaktiver Isotoper bewährt sich bei der Untersuchung von Ionenaustauschprozessen auβerordentlich, da hierdurch eine unmittelbare Kontrolle des Konzentrationsverlaufes der Komponenten im Eluat, zugleich aber auch in der Säule mögl;ich ist. Bei technischen Versuchen bereitet aber die Anwendung radioaktiver Isotope insofern unter Umständen gewisse Schwierigkeiten, als relativ groβe Lösungsmengen radioaktiv markiert werden mūssen. Es wäre sehr mützlich, wenn sich die zur Markierung benötigte Menge eines Radionuklids ohne Einbuβe an Aussagewert des Versuchs wesentlich senken lieβe, indem nur die Front des betreffenden Elements markiert wird. Die Theorie des Ionenaustauschs legte eine solche Möglichkeit nahe, und wie ein mit ⁶⁰Co durchgeführter Versuch zeigt, ergibt sich für das aktive Co innerhalb der Front inaktiven Kobalts tatsächlich nahezu der von der Theorie geforderte Verlauf. Von dieser Möglichkeit wurde in einem technischen Versuch zur Reinigung einer Platin-Rhodium-Lösung an einem Kationenaustauscher mit Erfolg Gebrauch gemacht.     

Investigation of the ferroelectric–relaxor crossover in Ce-doped BaTiO3 ceramics by impedance spectroscopy and Raman study

BaCe _x Ti_{1? x} O₃ (x?=?0.06, 0.10, and 0.20) solid solutions were prepared via conventional the solid-state reaction and sintered at 1500°C for 4?h, resulting in dense single phase ceramics with homogeneous microstructures. The electric field dependence of permittivity of the BaCe _x Ti_{1? x} O₃ ceramics was investigated in detail, together with the ferroelectric–paraelectric phase transition features. A transformation from normal to relaxor ferroelectrics was observed by increasing the Ce concentration. For low-Ce content, a substitution of Ce on both A and B site positions was proposed from the dielectric study and confirmed by Raman analysis.