离心渗铸金属铝熔液的瞬态固化与再熔

通过分析离心力场中金属铝熔液在Al2O3短纤维多孔介质内的渗流传热，考虑了离心惯性力对铝熔液的瞬态固化与再熔的影响，建立了旋转多孔介质内的渗流传热理论模型．研究了复合管铸造工艺中不同工况下液固共融区的长度和固化率的瞬态变化规律以及流场压损的分布规律．结果表明：在Al2O3颗粒的预热温度低于铝熔化温度的条件下，当渗透前沿达到一定深度时出现液固共融，随后液固共融区随渗透过程而增长，固化率逐渐提高．随着孔隙率的减小，液固共融区的长度和固化率增大，出现共熔现象的固化率降低，复合层能达到的最大厚度减小．而随着转速的减小，液固共融区长度缩短，共熔区内的固化率水乎提高，出现共熔现象的固化率增大，复合层能达到的最大厚度减小。     

基于ANSYS软件对SiCp/A1(ZL102)复合材料铸造渗流过程多孔介质结构的有限元处理

采用统计平均的方法描述多孔介质微观结构的影响,根据多孔介质的连续介质模型及有限元方法对多孔介质内的铝液的渗流行为进行数值模拟,给出了可视化的瞬态温度场分布,并且初步预测了不同时刻的渗流有效高度.     

液氮在多孔介质体系中传热特性实验研究

为研究液氮在煤体内的传导机制,构建了基于玻璃棉的多孔介质体系,进行了液氮在多孔介质体系中的传热模拟实验。采用热电偶和数据采集器获取了多孔介质内温度场的动态分布,探讨了注液氮量对液氮传热特性的影响。结果表明,液氮在多孔介质体系中形成冷量集中区,呈现局部降温效果;冷量集中区以垂直向下移动为主,移动速度受注液氮量的影响较小。研究为液氮防灭煤火技术实践提供理论基础。     

医用冷冻实验室离心机制冷系统设计及腔体内温度场研究

依目前医用冷冻实验室离心机的研究现状,通过采用CFD方法对离心腔内的速度场进行初步的理论计算,分析了蒸发器与离心机腔体内空气之间的传热性能;根据CFD的计算结果设计与之相匹配的制冷系统,并对制冷系统各主要部件进行设计与选型计算;最后,对所设计的医用冷冻实验室离心机制冷系统进行实验研究,分别测试不同运行工况下离心腔内速度场和离心腔内温度场,并对离心腔内速度场实验值与理论计算值进行对比。结果表明,腔体内速度场计算结果可靠,根据速度场的模拟计算结果来分析蒸发器的传热性能可行,制冷系统设计合理。     

二维Al1100/Ti-6Al-4V/SiC FGM板瞬态热传导问题

引入二维Al1100/Ti-6Al-4V/SiC FGM结构进行研究,根据热传导理论,从计算传热学的角度,研究第一类加热边界条件下FGM板瞬态温度场问题的有限元算法。采用变分有限元法和有限差分法推导出瞬态热传导有限元基本方程。应用有限元方法,编写计算程序,通过数值计算和分析,研究采用二维Al1100/Ti-6Al-4V/SiC FGM的热力学物性参数时二维FGM金属/金属/陶瓷平板在第一类加热边界条件下瞬态温度场随mx的变化规律。     

化学吸附式制冷系统传热传质的数值模拟和实验研究

运用多孔介质理论分析了化学吸附式制冷系统中的吸附床,按多孔介质的质量、动量和能量传递过程建立了吸附床内流动、传热和传质耦合求解的数学模型,并根据吸附剂在吸附床内多孔介质中的流动特性,采用比经典的Darcy模型更精确的多孔介质流动模型-Ergun模型。所建立的数学模型较之现有的吸附床传热传质数学模型能更全面、准确的描述吸附床的传热传质特性。将所建立的模型对化学吸附制冷样机进行了模拟计算,计算结果和测试结果吻合得较好。数学模型和计算结果有助于深入认识吸附床的传热传质特性,并可进一步用于吸附床和系统的优化设计。     

地热对井系统裂隙岩体三维渗流传热耦合的等效模拟方法

研究地热对井系统中的裂隙岩体渗流传热问题对于开采深层地热能和发展可再生清洁能源利用技术具有重要价值。基于渗流传热耦合理论和离散裂隙网络模型,提出了裂隙岩体三维热流耦合的等效模拟方法:考虑由岩块基质及复杂离散裂隙网络组成的双重介质,采用无厚度单元模拟裂隙、线单元模拟对井,通过裂隙、对井和岩块三者之间的流量和热量交换实现渗流和传热过程耦合分析。通过与解析方法和精细模拟方法相比较,验证了等效模拟方法的有效性;并将其应用于含大规模裂隙岩体地热对井系统热采过程的数值模拟,获取了储层内温度场的分布规律,评价了裂隙开度对储层平均温度和整体开采率的影响。结果表明:该文方法能够对裂隙及井筒中的渗流传热行为进行细致模拟,在保证精度的前提下,可大幅减小计算量和计算时长;裂隙网络的非均匀及各向异性分布导致岩体温度场分布呈现高度不均匀性,反映了热流耦合的早期热突破和长尾效应等特点;裂隙内水的对流传热作用明显,冷锋面沿储层内的主要贯通裂隙网络移动,裂隙开度是影响岩体温度场分布的重要因素。     

饱和多孔介质一维瞬态波动问题的解析分析

采用基于混合物理论的多孔介质模型,提出了饱和多孔介质一维动力响应的初边值问题。利用拉氏变换和卷积定理,分别得到了边界自由排水时在任意应力边界条件和任意位移边界条件下瞬态波动过程的解析表达。几种典型的数值算例同时给出了两类边界条件下瞬态波动过程中多孔固体的位移场、应力场和孔隙流体的速度场、压力场。结果表明,饱和多孔介质的波动过程是多孔固体和孔隙流体中以同一速度传播的两种波动的耦合过程,时效特性分析也揭示了饱和多孔介质固有的表观粘弹性性质。     

多孔介质材料在低温下的传热特性实验研究

对多孔介质材料在低温下的传热特性进行了实验研究,在填充液氮以后其低温维持时间明显增加,主要原因是由于多孔材料的参与改变了传热特性;采用连续介质管束模型,用有限元分析软件对其整体温度场分布进行了数值模拟计算,计算结果和实验数据吻合。     

高温铝熔液在旋转多孔介质内的渗透与瞬态固化和再熔过程

针对离心渗铸板材工艺中金属铝熔液在旋转的Al₂O₃预型体内的充型过程,考虑离心惯性力对金属铝熔液的瞬态固化与再熔过程的影响,研究了伴随有瞬态固化和再熔现象的流场温度分布以及熔融区长度和固化率瞬态变化规律,推导了渗透界面和再熔界面移动速度计算公式,建立了界面速度与温度的耦合关系。结果表明:当Al₂O₃颗粒预热温度低于铝熔化温度时,渗透过程出现了瞬态固化和再熔现象,液固共熔区随渗透过程不断向前推进,共熔区长度和固化率随渗透过程而增长。随着孔隙率和转速的减小,共熔区内固化率提高,渗透前沿和再熔前沿界面移动速度减小。但孔隙率的减小使两种界面移动速度差值增大,液固共熔区长度增长;而转速的减小使两种界面移动速度差值缩小,液固共熔区长度缩短。     

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.     

Film stacking impregnation model for a novel net shape thermoplastic composite preforming process

An impregnation model has been developed to evaluate the infiltration phenomena that occur during a novel near net shape preforming method. This process comprises automated deposition of thermoplastic resin and unidirectional (UD) carbon fibres to a pre-programmed stacking sequence, thereby forming tailored preforms for subsequent stamp-forming. Infiltration kinetics have been simulated to study the effect of different stacking scenarios, materials, and pre-consolidation routes on the novel preforming process. Isothermal infiltration of a liquid thermoplastic polymer into a compressed UD fibre bed has been examined and the experimental results have been used to validate an infiltration model based on local fluid flow in compressible porous media. This enables simulation of infiltration in alternating matrix film and fibre layers, relating pressure, time, and temperature with the local fibre volume fraction, pressure, and liquid and solid velocities in the stacked material. For a given set of processing conditions, the model fibre volume fraction distribution prediction enables the optimum matrix stacking layer thicknesses to be determined. It was shown that infiltration is inhibited above a limiting pressure which leads to increased fibre bed compaction and hence decreased permeability.     

铝熔体在多孔介质中的渗流过程

在流体流动相似原理的基础上，提出了铝熔体在多孔介质间隙（简称多孔介质）中渗流模拟的原理和方法．设计建造了用于铝液和模拟液在外加压力下进行单向渗流的两套试验装置模拟试验揭示渗流时铝液在多孔介质中渗流的若干规律实践表明理论模型与试验吻合良好．     

颗粒分散技术在真空液相浸渗制备Cf/Al复合材料中的应用

采用真空反压液相浸渗工艺,以碳纤维增强铝为研究对象,探讨了M40J纤维增强AlMg10复合材料制备工艺中,SiC及淀粉分散颗粒对复合材料微观组织及性能的影响。结果表明,碳化硅可以减少铝液在束内的浸渗阻力,并使纤维分布均匀,从而提高复合材料构件的成型性和力学性能。经过5%SiC+3%淀粉溶液的分散后,复合材料的体积分数由72%降低到51%,而复合材料的拉伸强度提高了131MPa,达到498MPa。     

Production and properties of SiCp-reinforced aluminium alloy composites

A vacuum infiltration process was developed to produce aluminium alloy composites containing various volume fractions of ceramic particles. The matrix composites of aluminium with 9.42 wt%Si and 0.36 wt%Mg containing up to 55 vol% SiCp were successfully infiltrated and the effect of infiltration temperature and volume fraction of particle on infiltration behaviour was investigated. In addition to aluminium powder, magnesium was used to improve the wetting of SiC particles by the molten aluminium alloy. The infiltration rate increased with increasing infiltration time, temperature and volume fraction of particle, but full infiltration appeared at the optimum process parameters for the various volumes of fraction composite compacts. In addition, the microstructure, hardness, density, porosity and wear resistance of the composites were also examined. It is observed that the distribution of SiC particles was uniform. The hardness and density of the composite increased with increasing reinforcement volume fraction and porosity decreased with increasing particle content. Moreover, the wear rate of the composite increased with increasing load and decreased with increasing particle content.     

Numerical simulation of hydrodynamic characteristics in a gas–solid fluidized bed

The fluidization of quartz particles as bed materials in the fluidized bed has significant influences on the combustion and gasification of refused derived fuels. Three-dimensional (3-D) simulations and analyses are performed for Geldart B particles using the computational fluid dynamics (CFD) method based on the kinetic theory of granular flows (KTGF) to investigate the hydrodynamic behavior. The drag models of Syamlal–O’Brien, Gidaspow, and Wen and Yu are selected to analyze the applicability of the kinetic model. The pressure drop, velocity distribution and solid volume fraction are studied numerically when the gas inlet velocity is changed. The results show that the increase of superficial gas velocity would lead to heterogeneous expansion of solid volume fraction and velocity distributions in both the dense phase zone and free board with a similar distribution pattern. The near wall particles form a dense phase structure with the solid volume fraction being greater than 0.3.     

Fabrication of alumina short fibre reinforced aluminium alloy via centrifugal force infiltration

Abstract

A new casting process for fabricating short fibre reinforced metal matrix composites via the centrifugal force infiltration of fibre preforms with molten aluminium alloys is described. The effect of processing variables, such as pouring temperature, preheated mould temperature, and time of application of centrifugal force, on the infiltration kinetics and resultant microstructure is discussed. Composites having fibre volume fractions of 4·5, 8·0, 12, and 16% were obtained via this method. Comparisons with existing infiltration technology and the mechanical properties of the composite are presented.

MST/2000     

考虑离心作用的螺杆挤出机固体输送理论分析

应用前文考虑离心作用和物料可压缩性建立的模型,考察了离心力对物料运动速度和加速度的影响,并分析讨论了固体输送段输送角、压力分布和固体输送段的长度,并和实验值作了对比。在固体输送段开始处牵引角最大,最大牵引角和螺纹升角是互补关系,此处压力最小,螺杆的离心作用最小,在固体输送结束处,牵引角最小,压力最大,螺杆的离心作用最强。物料与螺杆、机筒的摩擦热正比于局部压力,界面温度也密切服从于局部压力。压力温度关系对形成很高压力是一内在安全机理,挤出机自己可调节固体输送段中形成的极限压力。