金属泡沫内石蜡固液相变蓄热/放热实验

针对解决太阳能热利用过程中所面临的辐射强度不稳定、不连续和不均匀等关键问题,相变蓄热技术常与太阳能热利用系统耦合协同匹配,以实现稳定连续的热量输出.为了强化固液相变蓄热/放热过程、提高系统热储能效率,对金属泡沫内石蜡类相变材料(PCMs)在不同蓄热流体温度下的固液相变蓄热/放热特性开展了实验研究.设计并搭建了相界面可视...     

固液两相流泵的研究现状及展望

重点阐述了固液两相流泵的研究现状及其进展.在内部流动特性方面介绍了固体颗粒在叶轮内部的流动规律,研究了泵内部过流部件的磨损规律及抗磨措施;外部特性主要介绍了泵的几何参数对泵性能的影响.介绍了四种固液两相流泵的水力设计方法,并进行了分析,指出了四种设计方法对固液两相流理论发展的影响.从理论、试验研究和实际应用等方面分析了固液两相流泵性能优化的方向,并对固液相流泵的设计和应用作出了展望.     

相变材料相变点温度热物性的测试及误差分析

固-液相变过程中移动的相界面曲线与两相热物性如比热、密度、导热系数以及相变潜热是密切相关的。本文提出通过测定相界面的移动速率来确定相变材料固-液相变温度点导热系数等多个热物性参数的方法,并设计了相应的测试装置。对测试系统的测量误差进行了定量分析,发现采用数值计算与实验相结合的方法测试的系统误差不超过3％。利用研制的测试系统对几种材料的导热系数和热扩散系数进行了测定,得到了满意的结果,表明本文所提出的测试方法是可信的。     

填充开孔泡沫铝的固液相变蓄冷器设计与实验研究

为进一步满足固液相变蓄冷器需求,在计算固液相变蓄冷器漏热的基础上进行了相应优化,使用开孔泡沫铝作为固液相变蓄冷器填充材料,搭建实验台进行不同负载功率下的液氮固体蓄冷系统性能实验研究。实验结果表明：所设计的固体蓄冷系统能够在0.5 W的热负载下工作4.23 h;2 W热负载实验条件下,固体蓄冷系统能够在温度小于65 K条件下工作1 h。     

离心泵输送气液固多相流时性能指标的计算

对离心泵输送固液、气液 、气液固混合物时性能指标的计算问题进行了具体的研究，认为在气液固多相流的泵性能指标计算中必须考虑流型及各相的具体表现，扬程的计算要以“单位重量”为基础，论文重点进行了多相流动分析和扬程公式的推导，给出了泵使用和测试的相关计算方法和公式，参9。     

污泥湿式氧化试验研究及经济性分析

为优选污泥湿式氧化处理的反应条件并考察反应效果,在反应釜试验装置上通过正交试验研究了温度、过量空气系数和停留时间等因素对处理效果的影响;对产物中的固、液、气三相分别展开了热重分析、元素分析、化学需氧量测试和气体成分分析,并对固相和液相产物中重金属的质量分数进行了分析.结果表明:在优选条件下,污泥的有机质分解率可达90%以上;固相产物残渣的热失重率小于10%,液相产物有一定的化学需氧量,可返回市政污水处理厂进行处理;气相产物无SO_2和NO_x;重金属富集于残渣中;初步经济性分析发现,污泥湿式氧化的综合处理成本约为130元/t.     

固定PCM在热球体外表面上接触融解时液膜厚度变化规律的研究

基于润滑近似理论和Ｎｕｓｓｅｌｔ液膜流动理论建立了一个描述固体相变材料在热球体外表面上接触融解的数理模型。由于更准确地应用了固液两相界面处能量平衡关系式，所在求解所得的融解液液膜厚度分布更合理。据此模型，还指出了文献中模型存在的问题及其得到错误液膜厚度分布的原因。     

液固比对生物质水热炭化产物结构演变的影响

为了研究水量的添加对生物质水热炭化反应过程和目标产物水热焦特性的影响,以草坪草、麦秆和梧桐树叶为原料,利用高温高压反应釜,对3种生物质分别在不同反应温度、液固比(水与生物质原料干基质量比)为10~50的条件下,进行水热炭化实验,并对实验所得水热焦的组成与结构和液体产物中还原糖产量的变化进行分析。研究发现,随着液固比的增加,草坪草、麦秆和梧桐树叶水热焦产率均有所下降,但当液固比超过30以后,变化幅度均不大,在液固比10~50范围内,水热焦产率是液固比的函数,均可用单指数衰减函数进行拟合,这有利于水热焦产率的预测;3种水热焦的碳含量和液体产物中还原糖产量随液固比的增加而增加,而糖类化合物特征峰的红外吸收强度有所减弱;由傅里叶红外光谱分析可知,随着温度的升高及液固比的增加,水热炭化反应的影响逐渐减弱,在反应温度200~240℃,液固比从10增加到50时,主要增加水的溶解性能,对化学反应的影响较小,从水热焦的理化特性演变发现温度较高时,可选择相对较低的液固比。     

液层厚度比对环形腔内双层液体的热毛细对流稳定性的影响

为了了解微重力条件下、水平温度梯度作用时,上部为固壁的环形腔内双层流体系统中液层厚度比对流动稳定性的影响,采用隐式重启Arnoldi方法(IRAM)对环形池内5cSt硅油/HT-70双层流体的热对流过程进行了线性稳定性分析,获得了不同液层厚度比下的临界Marangoni数、临界波数、临界相速度,并通过计算特征向量,得到了临界Marangoni数附近液-液界面的热流体波形态。     

椭圆管矩形翅片清洗影响因素的数值分析与优化

对电站空冷凝汽器椭圆管矩形翅片空气侧进行了液固两相流清洗的数值模拟,分析了清洗流速、固相颗粒粒径、固相体积分数对壁面平均剪切应力及流动阻力的影响。确定最优清洗流速、固相颗粒粒径、固相体积分数的组合形式。结果表明:随着清洗流速、固相颗粒粒径、固相体积分数的增加,壁面平均剪切应力和流动阻力均持续增大并呈单调增加趋势;综合考虑清洗效果和节水节能,采用正交试验法分析确定清洗椭圆管矩形翅片的最优组合为入口流速14m/s,固相颗粒粒径0.4mm,固相体积分数0.06。结果为椭圆管矩形翅片的优化清洗提供理论基础。     

流化床密相区流动特性的数值模拟

流化床内气固两相流动一直是实验研究和数值模拟的热点。基于Eulerian双流体模型,本文建立了流化床内的气固两相流动模型,采用FLUENT软件对流化床密相区两相流动特性、床内气泡的产生运动和爆裂等特性进行了数值模拟。模型中,将颗粒相看作是连续介质,建立与气相相同形式的数学模型;采用了离散介质动力理论,引入颗粒温度来描述固相粘性应力,并用气固曳力进行气固两相耦合。模拟得到了气泡产生、运动和爆裂的变化过程,与实验结果相一致。采用不同的曳力模型对流化床稠密两相流动进行了模拟,与Kuipers实验对比,结果表明采用Gidaspow曳力模型描述流化床稠密两相流动特性更准确。     

A three-fluid model of two-phase dispersed-annular flow

A three-fluid model of the dispersed-annular regime of two-phase flow is suggested. The model is based on the conservation equations of mass, momentum, and energy for the gas phase, the dispersed phase (droplets), and the film. Additionally, this model includes the equation for the number density of particles of the dispersed phase, which is used to determine the mean particle size. Calculations are compared with experimental data on the entrainment coefficient, film and droplet flow rates, film thickness, pressure drop, and droplet size.     

温度对喷动流化床煤气化影响的数值模拟

建立了基于CFD的三维非稳态的喷动流化床煤气化动力学模型,考察了温度对喷动流化床煤气化影响。此模型包含了以下子模型：气固流动模型,煤的挥发分析出模型,焦炭气化反应模型,气相间的均相反应模型。焦炭的非均相反应的速率由气体的扩散和化学反应动力学共同控制,气体的均相反应可以作为二级反应来处理。试验结果和模拟的计算结果进行了对比,验证的结果表明了此CFD模型可以用来预测煤气化的反应过程。     

相变蓄热同心套管传热模型和性能分析

建立了一种简便的相变蓄热同心套管传热模型,用来求解相变材料在相变过程中流体温度和相变界面随时间和向位置的变化规律,模型中考虑了相变材料导热热阻和有效传热面积随时间和位置的变化,适用于流体入口温度和流量随时间变化的情况,计算值与有关文献值吻合,验证了模型的正确性。藉此模型对文献「７」中相变贮能换热器的储、放热性能进行了模拟分析。     

A comprehensive mathematical model of a serial composite process for biomass and coal Co-gasification

A comprehensive mathematical model to simulate a serial composite process for biomass and coal co-gasification has been built. The process is divided into combustion stage and gasification stage in the same gasifier, it is a new process for the co-gasification of biomass and coal. The model is based on reaction kinetic, hydrodynamics, mass and energy balances, it is a one-dimensional, K-L three-phase, unsteady state model. The model is divided into two sub-models, one is the combustion sub-model, the other is the coal-biomass serial gasification sub-model. Combustion sub-model includes coal pyrolysis, dense phase combustion, and dilute phase combustion model. Gasification sub-model includes biomass pyrolysis, dense phase coal gasification, dense phase biomass gasification, and dilute phase gasification model. The model studies the effects of key parameters on gasification properties, including gasification temperature, S/B, B/C, and predicts the composition of product gas and gas calorific value along the reactor's axis at different time. The model predictions agree well with experimental results and can be used to study and optimize the operation of the process.     

Thermal analysis of a fluidized bed drying process for crops. Part I: Mathematical modeling

Development of a comprehensive mathematical model to simulate the simultaneous heat and mass transfer processes in a bubbling fluidized bed is described. Although the model is applicable to a wide range of particles, wheat is chosen as an example. In the development of the model, the commonly used two‐phase theory is not used because of its insensitivity to the particle group used in the bed. Instead, a new hydrodynamic model is developed for each specific particle group. The behaviour of bubbles in a bed of group D particles (wheat) is modelled with the consideration that they grow in size as they rise in the bed, but are of the same size at any height in the bed. The voidage of bubbles, particles and interstitial gas is modelled separately. A newly developed expression to determine the minimum fluidization velocity of wet particles is used. The model considers the presence of different phases inside the bed, and their physical variation along the bed. The interstitial gas phase, the bubble phase, and the solid phase are modelled separately. The drying mechanism for the solid phase is considered in two stages: the falling rate, and the constant rate, with appropriate temperature and moisture diffusion coefficients and wall effects. The simultaneous heat and mass transfer processes during the drying process including the internal and external effects are modelled for each phase. A set of coupled nonlinear partial differential equations is employed to accurately model the drying process without using any adjustable parameters. A numerical code is developed to solve the governing partial differential equations using a control volume‐based discretization approach. Piecewise profiles expressing the variation of dependent variables between the grid points are used to evaluate the required integrals. Copyright © 2000 John Wiley & Sons, Ltd.     

加压喷动流化床煤气化数值模拟

建立了基于CFD的三维非稳态喷动流化床煤气化动力学模型.此模型包含气固流动模型,煤的挥发分析出模型,焦炭气化反应模型和气相间的均相反应模型等子模型.焦炭的非均相反应速率由气体扩散和化学反应动力学共同控制.气体均相反应可以作为二级反应来处理.将试验结果和模拟的计算结果进行了对比,结果表明,入口中心喷动区的温度最高,温度场沿床高方向逐渐降低.煤气质量在加压后有了明显提高.验证的结果表明此CFD模型可以用来预测煤气化的反应过程.     

An axisymmetric bioheat transfer analysis through a unified model

A unified model is developed for the analysis of heat transfer (radiation and non-Fourier conduction) in an axisymmetric participating medium. The proposed model includes three different variants of hyperbolic–parabolic heat conduction models, that is, the single phase lag model, dual phase lag model, and the Fourier (no phase lag) model. The radiating-conducting medium is radiatively absorbing, emitting, and isotropically scattering. Significance of all the above mentioned models on the heat transfer characteristics is investigated in a two-dimensional axisymmetric geometry. The equation of transfer and the coupled non-Fourier conduction-radiation equation are solved via finite volume method. A fully implicit scheme is used to resolve the transient terms in the energy equation. For spatial resolution of radiation information, the STEP scheme is applied. Tri-diagonal-matrix-algorithm is used to solve the resulting set of linear discrete equations. Effects of two important influencing parameters: the scattering albedo and the radiation- conduction parameter are studied on the temporal evolution of temperature field in the radiatively participating medium. The non-Fourier effect of heat transport captured well with the proposed unified model. A good agreement can be found between the proposed model predictions and those available in the literature. It is also found that when the phase lag of the temperature gradient and the heat flux are the same, it reduces to conventional Fourier conduction-radiation and the wave behavior diminishes. However, the reduction to this Fourier model fails in the presence of constant blood perfusion and metabolic heat generation.     

A molecular dynamics simulation investigation of fuel droplet in evolving ambient conditions

Molecular dynamics simulations are applied to model fuel droplet surrounded by air in a spatially and temporally evolving environment. A numerical procedure is developed to include chemical reactions into molecular dynamics. The model reaction is chosen to allow investigation of the position of chemical reactions (gas phase, surface, liquid phase) and the behavior of typical products (alcohols and aldehydes). A liquid droplet at molecular scale is seen as a network of fuel molecules interacting with oxygen, nitrogen, and products of chemical fuel breakdown. A molecule is evaporating when it loosens from the network and diffuses into the air. Naturally, fuel molecules from the gas phase, oxygen and nitrogen molecules can also be adsorbed in the reverse process into the liquid phase. Thus, in the presented simulations the time and length scales of transport processes – oxygen adsorption, diffusion, and fuel evaporation are directly determined by molecular level processes and not by model constants. In addition, using ab initio calculations it is proven that the reaction barriers in liquid and gas phases are similar.     

A model of the two-phase turbulent jetUn modele du jet turbulent diphasiqueEin modell für den turbulenten zweiphasenstrahlMo;дe;ля двy;чфa;знo;и тy;p;бy;лe;нтнo;и c;тp;y;и

A model of the two-phase turbulent jet is presented. Consideration is given to cases in which the primary fluid phase contains a secondary phase of rigid particles. The mass fraction of the secondary phase is at most of order unity while its volume fraction is much less than unity. A set of model differential equations is developed for cases in which the mean velocities of the phases are sensibly equal. A first-order closure scheme for the axisymmetric jet is devised and the resulting equations solved numerically. This scheme accounts for momentum transfer between the phases and the imperfect response of the particles to the fluid turbulence. Satisfactory agreement with published experimental data is obtained for computed values of the mean velocity, and the mean mass flux of the particles.