竖直通道内降膜流动数值模拟研究

降膜蒸发是一种高效的传热技术,平均液膜厚度是考察降膜蒸发传热性能的一个重要影响因素。本文基于VOF算法,建立了水和空气沿二维竖直通道降膜流动的CFD模型,模拟研究了液膜速度、工质种类、同向和逆向气流对平均液膜厚度的影响。结果表明:提高液膜速度会增大平均液膜厚度;气相工质对液膜厚度影响不大,而液相工质对液膜厚度影响较大,液膜厚度随液相黏度增大而增大;同向气流对入口段和发展段的液膜厚度影响不大,稳定段液膜厚度会随着同向气流速度的增大而减小;平均液膜厚度随逆向气流速度增大而降低,当逆向气流速度达到2.5 m/s后,气流速度对液膜厚度的影响减小。     

立式降膜蒸发器的机理研究

研究了立式降膜蒸发机理,得知蒸发管路底部的未蒸发制冷剂流量与管子单位面积制冷量成反比,需要采用循环喷淋设备;制冷剂入口初始速度随管子单位面积换热量增大和管长增大而减小,初始液膜总厚度随液膜主流区初始速度增大而减小。采用射流泵作为循环喷淋设备后,可以节省液体循环泵的耗功。     

内翅板蒸发式冷凝器降膜流动与传热特性

为了增强蒸发式冷凝器板外气液两相流动与传热,基于数值模拟方法对比分析了几种新型的板片结构,研究了板片构型、喷淋水喷淋密度、空气入口速度等因素对气液两相流流体流动及传热性能的影响。结果表明:半圆波纹板有较长的水膜稳定时间和较大的换热面积,换热性能较好;不同板片结构的蒸发式冷凝器具有不同的最佳喷淋水喷淋密度,最佳喷淋密度区间范围为0.48~0.93 kg/(m·s);空气入口速度一定时,半圆波纹板的壁面温度随喷淋密度增大而增大,气液界面温度随喷淋密度增大而减小;当空气入口速度小于2.5 m/s时,空气入口速度的适当增大能够有效减薄半圆波纹板板外水膜厚度,强化换热。     

热管式溶液吸收器传热传质过程的数值模拟

本文首次利用水重力热管，以溴经锂水溶液为工质，对在这外壁面上溶液降膜吸收水蒸气并移出吸收热的传热传质过程进行了数值模拟。结果表明，在一定条件下，所需热管加热段长度随膜雷诺数的增加而增加，随输出热温度的提高而减小，并且降膜平均传热和传质系数随膜雷诺数的增加而降低；利用热管作为吸收器的传热传质元件，其传热温差很小，但大较大浓差和较大雷诺数下，所需热管加热段长度太长。     

低雷诺数下溴化锂溶液降膜吸收热质传递的数值研究

溴化锂溶液降膜吸收是吸收式空调系统中常见的热质传递形式之一。本文对溶液降膜吸收过程的热质耦合传递分析,建立了溴化锂溶液垂直降膜吸收热质传递的二维数学物理模型,采用CFD-Fluent对模型进行求解。计算得到不同Re下的液膜界面温度、液膜内浓度分布、传热传质通量及传热传质系数等。分析了Re对降膜吸收过程中热质传递的影响。结果表明:当液膜Re150时,液膜界面平均温度与平均传质系数随着Re的增大而增大,而平均传热系数随着Re的增大而减少;平均传热传质通量均是随着Re的增大而先增大后减小,存在一个最佳液膜Re使降膜吸收过程的传热传质通量达到最大,即Re=50时,平均传热和传质通量分别达到最大值7.2 k W/m~2与2.9×10~(-3)kg/(m~2·s)。     

低温流体在竖直通道中降膜蒸发研究进展

降膜蒸发作为一种高效传热传质技术,已经在空分领域得到了应用。本文介绍了空分膜式主冷凝蒸发器的原理和特点,从波状特性和破断特性方面阐述了下降液膜的动态特性,总结了入口流量、壁面结构、工质组分和热流密度因素对传热传质的影响,重点介绍了低温液氮在大空间平板上降膜过程的临界热流密度规律和过热壁面再湿润动态特性,并对现有竖直通道内降膜蒸发过程换热关联式进行了归纳。由于低温工质物性和通道结构的特殊性,已有的常温工质换热关联式应用于空分膜式主冷凝蒸发器的传热设计还存在较大差距。最后指出小传热温差条件下,复杂狭窄通道内低温流体降膜蒸发过程需要进一步研究。     

具有微米级内外径CTA中空纤维膜制备与表征

利用干湿法通过改变纺膜条件来调控中空纤维膜尺寸制备具有微米级内外径的三醋酸纤维素(CTA)中空纤维膜.结果表明,中空纤维膜的内外径随铸膜液流量和芯液流量的增加而增加,随收丝速度的增加而减小;内外径随空气段高度的增大而略微减小;其中铸膜液和芯液流量对膜尺寸的影响最为显著.此外,考察了这些因素对膜微观结构及纯水通量性能的影响,结果表明,本研究中这些因素对膜结构的影响较小,所有膜都具有海绵状孔;纯水通量随着铸膜液和芯液流量的增加而显著增加,随空气段高度和收丝速度的增加而稍有增加.     

非圆管管外降膜流动和换热特性分析

利用VOF方法,对圆管、椭圆管和扁管进行水平管外降膜流动二维数值模拟分析,研究Re数在1 278~3 406范围内3种管形对管外降膜传热和流动的影响。计算结果表明:在顶部冲击区和尾流区,管的曲率及其变化对流动和换热的影响很复杂,曲率较小会导致顶部冲击区的扰动面积增加和液膜厚度增加;相比圆管,椭圆管和扁管平均液膜厚度更小,传热性能更优;从平均液膜厚度上看,椭圆管最小,扁管次之;从平均传热系数上看,扁管最大,椭圆管次之。之所以椭圆管和扁管的平均液膜厚度和平均传热系数存在不一致,本文认为是由顶部冲击区对扁管的扰动影响要远大于椭圆管,且Re数取值较大,椭圆管的平均液膜厚度较小的优势无法凸显导致的。     

低温热管传热特性的实验研究

搭建了一套低温热管传热性能测试实验台,基于一种新型矩形内翅片低温热管,首次在-60℃至-40℃的温度下探究了冷凝温度和加热功率对热管稳态等温特性的影响,以及蒸发段和冷凝段长度变化对蒸发传热系数、总热阻值和当量导热系数的影响。研究结果表明:相同工况下,热管的轴向温差随着冷凝温度的降低而减小,随着加热功率的增大而增大;蒸发段长度越大,加热功率越高,蒸发传热系数越大;冷凝段长度越小热管热阻值越低,蒸发段长度越小热阻值越大;当量导热系数随冷凝段长度的减少而增大,随蒸发段长度的减少而减小。     

气力输送中PVC粉体静电带电影响因素

为了研究工业中常用的聚氯乙烯(PVC)粉体在气力输送过程中的静电影响因素，以PVC粉体为输送对象，以荷质比为指标，研究PVC粉体的下料质量流量、气流速度、气单位体积的气体中所含粉体的质量和球阀开度对粉体带电的影响。结果表明：当下料质量流量一定时，PVC粉体的荷质比会随气流速度增大而增大，随球阀开度减小而减小；当气流速度一定时，PVC粉体的荷质比会随下料质量流量增大而减小，输送颗粒的荷质比存在临界值为0.2μC/kg;当单位体积的气体中所含粉体的质量一定时，下料质量流量对PVC粉体荷质比影响要大于气流速度对其的影响；当下料质量流量一定时，PVC粉体的荷质比会随球阀开度的减小而减小。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.