Simulation of two-phase flows of a droplet impacting on a liquid film with an improved lattice Boltzmann model

Based on the lattice Boltzmann method (LBM), an improved pseudo-potential model, combined with a method of adding force term, is used to simulate the two-phase flows caused by a liquid droplet impacting on a liquid film. In this model, the different phases are treated as one fluid, and the interfaces between the vapor and liquid phases can be obtained by density value of the fluid. This variant of the LBM allows one to obtain the densities of vapor and liquid with high accuracy. The model is validated by an example of phase separation. The early stage of the impact of droplet on liquid film is simulated, and the results are qualitatively consistent with physical phenomena.     

不互溶液体内泡滴的直接接触传热模型(英文)

研究垂直管内两不互溶液体——正戊烷 -水系统的直接接触传热 ,管内易汽化的液体从管底用氮气压入形成分散泡滴 ,不易汽化的连续相液体在加热到一定温度后 ,以并流形式流过 .在考虑气泡被连续相流体破碎的情况下 ,借助于平均体积传热系数模型 ,在理论分析基础上通过实验研究建立了单个气泡的传热系数模型 ,模型参数有较好的关联性     

Analysis of streamwise conduction in forced convection of microchannels using fin approach

The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been studied. By employing the fin approach in the first law of analysis, models with and without streamwise conduction term in the energy equation were developed for hydrodynamically and thermally fully-developed flow under local thermal non-equilibrium for the solid and fluid phases. These two models were solved to obtain closed form analytical solutions for the fluid and solid temperature distributions and the analysis emphasized details of the variations induced by the streamwise conduction on the fluid temperature distributions. The effects of the Peclet number, aspect ratio, and thermal conductivity ratio on the thermal characteristics of forced convection in microchannel heat sinks were analyzed and discussed. This study reveals the conditions under which the effect of streamwise conduction is significant and should not be neglected in the forced convective heat transfer analysis of microchannel heat sinks.     

油气在竖直管内湍流流动时冷凝的数值模拟

为了探索油气在冷凝回收过程中的冷凝规律,采用气液两相流模型描述了油气在竖直管内湍流流动时的冷凝过程.采用有效传质系数描述了油气组分的质量传递.模拟了油气在管内冷凝时的温度、管内压力、液膜厚度和Nusselt数的变化,得到了入口油气和管壁的温差、雷诺数对冷凝率和Nusselt数的影响.结果显示：增大入口雷诺数能显著增强传热和冷凝,但是增大入口油气和管壁的温差对冷凝率的影响较小;另外,还发现传质阻力对油气冷凝率有较大影响.此模型的计算结果与先前的实验数据能够很好地符合.     

Numerical simulation of interaction between laminar flow and elastic sheet

A numerical simulation of the interaction between laminar flow with low Reynolds number and a highly flexible elastic sheet is presented. The mathematical model for the simulation includes a three-dimensional finitevolume based fluid solver for incompressible viscous flow and a combined finite-discrete element method for the three-dimensional deformation of solid. An immersed boundary method is used to couple the simulation of fluid and solid. It is implemented through a set of immersed boundary points scattered on the solid surface. These points provide a deformable solid wall boundary for the fluid by adding body force to Navier-Stokes equations. The force from the fluid is also obtained for each point and then applied on the boundary nodes of the solid. The vortex-induced vibration of the highly flexible elastic sheet is simulated with the established mathematical model. The simulated results for both swing pattern and oscillation frequency of the elastic sheet in low Reynolds number flow agree well with experimental data.     

双液滴垂直冲击薄液膜的数值模

The normal impingement process of two water droplets upon a thin film on the solid surface was numerically investigated. The numerical treatment was based on the finite volume solution of the Navier-Stokes （N-S） equations combined with the volume of fluid method （VOF）. Physically reasonable results for the process of two droplets impacting on the thin film were obtained. The effects of the droplet velocity, the fihn thickness and the spacing between the two droplets on the splash and spread process of the impact were examined.     

Influence of baffle position on liquid sloshing during braking and turning of a tank truck

The influence of baffle position on liquid sloshing during the braking and turning of a tank truck was studied using a volume of fluid (VOF) model. The forces,their positions and weight distribution during braking and the forces and rolling moment during turning were calculated. The reliability of the calculation method was validated by comparisons with experimental results. The results showed that during braking,liquid splashes in the tank and the maximum forces and G (the ratio of weight acting on the front axle to the rear axle) are large when A (the ratio of the arch area above the baffle to the area of cross section)≤0.1. When A≥0.2,as the position of the baffle is lowered,the maximum of Fx (the force in direction x) first decreases then increases,and the maximum of Fy (the force in direction y) and G increase. During turning,liquid splashes in the tank and the maximum forces and M (the rolling moment) are large when D (the ratio of the arch area above the baffle to the area of cross section)≤0.2. When D≥0.3,as the position of the baffle is lowered,the maximums of Fy,Fz (the force in direction z) and M increase.     

CzSi晶体生长传热特性的数值研究

在提拉法晶体生长中,坩埚内的熔体受到多种驱动力的作用,主要包括:由熔体内部温差驱动的浮力、自由表面温度梯度导致的热毛细力、坩埚和晶体旋转产生的离心力和科里奥力,因而坩埚内的熔体流动表现出复杂的非线性流动状态.通过数值计算,模拟熔体内的对流流动、温度分布及晶体生长界面的形态,研究了晶体生长过程中,热质传输从对称到非对称的演化以及对流对固液面表面造成的影响.     

Numerical Simulation of Unsteady-State Flowsin Bubble Column Reactors

Thebubblecolumnreactor (BCR) ,withbatchfeedandcontinuousgasaerated ,hasobtainedwideapplica tionsinbiochemicalengineering ,chemicalengineeringandwastewatertreatment ,etc .OneimportantfeatureofBCRisthattheconversionandtheyieldofthereactioncanbehighlyincreasedundertheunsteady stateopera tion .Sincethemassandtheheattransferpropertiesinaprocessmainlydependontheflowbehavior ,itisstronglydesirabletoinvestigatetheunsteady stateflowstructurebeforethedesignandscale upofBCRwithhighreactiveconversionsa…     

对流传热系数测定的探讨

测定了不同流速下的各种传热数据,用实验法和理论计算法给出管内热膜系数α测、α计、Nu测、Nu计及总传热系数K测、K计的值,分析了实际法和理论法得到的传热系数的区别.在传热管中加入螺旋弹簧作为强化元件后,对各种数据的计算及与理论值之间的差别进行了分析.     

Studies on solar flat plate collector evaporation systems for tannery effluent （soak liquor）

INTRODUCTION The tannery effluent (soak liquor) spewed out by tanneries to the surroundings has been polluting the land and water bodies in and around the tanneries and is evaporated over a period of time. The rate of evaporation over this period is small in the natural evaporative ponds and so large area is required. But land in urban and semi-urban sectors is scarce and very costly. Hence, it is required to augment the evaporation rate by adopting some suitable techniques. The rate of e…     

Aerobasics — An introduction to aeronautics

A study of air flow past simple bodies provides a background for the understanding and interpretation of aerodynamic forces on airplanes. In this article some simple flows are studied by treating air as a viscous and compressible fluid subject to the laws of mechanics. The importance of two dimensionless parameters, the Reynolds number and the Mach number, respectively representing the viscous and compressibility effects is clearly brought out. The different flow phenomena associated with specific ranges of the Reynolds and Mach numbers are indicated and explained.     

Numerical investigation of the influence of companion drops on drop-on-demand ink jetting

In this study we characterized and investigated the specific phenomenon of ??companion drops?? in the drop-on-demand (DOD) ink jetting process. A series of simulations based on a piezoelectric DOD printhead system is presented, adapting the volume-of-fluid (VOF) interface-capturing method to track the boundary evolution and model the interfacial physics. The results illustrate the causality between the generation of companion drops and droplet deviation behavior, as well as their close correlations with ink jetting straightness and printing accuracy. The characteristics of companion drops are summarized and compared with those of satellite drops. Also, a theoretical mechanism for the generation of companion drops is presented, and their effects and behaviors are analyzed and discussed. Finally, the effects of critical factors on the generation of companion drops are investigated and characterized based on variations in the printable pressure range. Recommendations are given for the suppression of companion drops and for the improvement of printing accuracy.     

Numerical study of heat transfer characteristics of downward supercritical kerosene flow inside circular tubes

The heat transfer characteristics of China RP-3 aviation kerosene flowing in a vertical downward tube with an inner diameter of 4 mm under supercritical pressures are numerically studied. A ten-species surrogate model is used to calculate the thermophysical properties of kerosene and the re-normalization group (RNG) k-ε turbulent model with the enhanced wall treatment is adopted to consider the turbulent effect. The effects of mass flow rate, wall heat flux, inlet temperature, and pressure on heat transfer are investigated. The numerical results show that three types of heat transfer deterioration exist for the aviation kerosene flow. The first type of deterioration occurred at the tube inlet region and is caused by the development of the thermal boundary layer, while the other two types are observed when the inner wall temperature or the bulk fuel temperature approaches the pseudo-critical temperature. The heat transfer coefficient increases with the increasing mass flow rate and the decreasing wall heat flux, while the inlet bulk fluid temperature only influences the starting point of the heat transfer coefficient curve plotted against the bulk fluid temperature. The increase of inlet pressure can effectively eliminate the deterioration due to the small variations of properties near the pseudo-critical point at relatively high pressure. The numerical heat transfer coefficients fit well with the empirical correlations, especially at higher pressures (about 5 MPa).     

Effect of particle loading on heat transfer enhancement in a gas-solid suspension cross flow

Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the case of very low solid loading ratio (M _s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number was derived from experimental data. In addition, thek-∈ two-equation model and the Fluctuation-Spectrum-Random-Trajectory Model (FSRT Model) are used to simulate the flow field and heat transfer of the gasphase and the solid-phase, respectively. Through coupling of the two phases the model can predict the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement due to particles loading the model predictions agreed well with experimental data. Project supported by National Natural Science Foundation for Distinguished Young Scholars (No. 50025618)     

逆流降膜除湿器除湿过程的数值研究

建立了模拟逆流降膜除湿过程传热传质的数学模型,给出了传热传质的控制方程和适当的边界条件和气液界面条件.采用氯化钙作为除湿剂,运用控制容积法对降膜除湿溶液与被处理空气之间的除湿过程进行了分析和计算.获得了相应的除湿溶液与被处理空气的速度场、温度分布和出口参数.计算结果表明:沿着除湿器高度方向溶液和空气的温度、溶液的浓度、空气的湿度在入口区域变化较快而在出口区域变化较慢.可分别通过增加竖壁的高度、溶液的入口浓度和溶液的流速来改善除湿过程;同样,也可通过降低空气的流速或空气入口湿度达到改善除湿过程的目的.研究结果有利于改进除湿器的性能,为太阳能液体除湿、空调系统的优化设计和运行调节提供了理论依据.     

过冷流动沸腾热传递的分形模型

提出过冷流动沸腾热传递的分形模型,根据加热表面活化点的分形分布得到了过冷流动沸腾热流密度的表达式。从该模型中发现过冷流动沸腾热流密度是壁面过热度、流体的过冷度、流体的主流速度与流体的接触角、流体物理特性的函数关系,并且没有增加新的经验常数。模型预测的结果与实验数据进行了比较,两者是极好的吻合。     

超临界流体萃取模型在土壤修复中的应用

针对超临界流体萃取土壤污染物的传质过程数据的缺失,分析了当前超临界流体萃取模型的优缺点,并在超临界流体萃取土壤污染物的过程是内扩散控制过程的基础之上,建立起基于微分床单元的质量守恒模型,再对模型进行求解与分析从而来模拟超临界流体萃取土壤污染物的传质过程。     

Hydrodynamics and oxygen transfer in a novel extra-loop fluidized bed bioreactor

In this paper, the characteristics of fluid mixing time in a novel extra-loop fluidized bed were studied. The results showed that the mixing time was shortened with the increase of fluid velocity. All the discrete numbers of the reactor were above 0.2. The serial number n was 2.5 -3.0. It was judged accordingly that the reactor fluid state was continous stirred tank reactor （CSTR） mainly. When the inspiratory capacity increased the mixing time of the reactor was shortened. Thus the air input was beneficial for the fluid mixing. During the three phases mixing process, the mixing time of the reactor could be decreased by the n increase of carrier and air loading together, but the change was not significant. The parameters affecting the reactor fluid state were fluid velocity, inspiratory capacity and carrier. KLa could be increased with the air loading increase, and at the same gas/liquid ratio when the pressure drop was high, KL~ value was increased. The amount of carrier complex influence on KLa. As the carrier loading continued to increase, its value had been dropped but the changes was not significant, and optimization condition was found at above 800 1 000 g carrier loading （pouzzolane） or 600 g PVC. Under gas/liquid ratio of 0.8% -5.2%, KLa was （0.62-1.37）×10^-2· s^-1.     

波纹板表面凝结传热的数学模型与计算

基于波纹板表面与液膜之间的表面张力作用能减薄液膜厚度而强化传热的机理，建立了竖直波纹板表面的凝结过程的数学模型．计算了波纹板对应于当量平板的凝结传热增强系数．分析了波纹的主要几何参数如波纹节距、波纹板高度、波纹角、波纹倾斜角、波纹圆角半径等对强化传热的影响效应以指导波纹结构的优化．提出了一种能兼顾强化传热效果和适当的流动截面积的双尺度波纹，其凝结传热系数可比当量平板增强1～2倍．