H型换热器的数值分析及优化设计

对6种特定结构的H型鳍片管换热器的传热及阻力特性进行了数值模拟研究。运用Fluent软件分别模拟H型换热器中烟气侧及水侧的流动与传热过程,实现换热器管内、金属、管外换热的耦合计算,得到换热器工作过程中的温度场和速度场。讨论H型鳍片管结构参数对鳍片管换热器换热性能的影响,为该类换热器的优化设计和制造提供了有价值的参考依据。     

阵列射流冲击冷却流场与温度场的数值模拟

采用数值模拟方法对冲击冷却的流动和传热过程进行了三维数值研究。特别研究了在冲击孔叉排方式下,相邻孔间距、冲击距离以及射流入口雷诺数对冲击表面冷却流动传热特性的影响规律。     

阵列射流冲击冷却换热系数的数值研究

采用数值模拟方法对冲击冷却的流动和传热过程进行了三维数值研究.特别研究了在冲击孔叉排方式下,相邻孔间距、冲击距离以及射流入口雷诺数对冲击表面冷却流动传热特性的影响规律.     

燃气轮机罩壳内的流动阻力和传热特性计算

为了建立具有异型结构和复杂流动过程的燃气轮机罩壳系统内部阻力和传热特性的工程计算模型,采用Fluent软件结合UDF函数对罩壳内三维流场和传热特性进行了数值模拟,并用燃机电厂实测数据进行了验证.采用数值模拟结果对异型结构通道的阻力工程计算公式和燃机本体保温层外的对流传热系数分别进行了修正.修正后的工程算法结果表明保温层...     

Cu-H_2O纳米流体流动与强化换热的数值模拟研究

模拟纳米流体在三维管道中的流动和强化传热过程,运用数值计算方法研究纳米流体的流动特性和传热机理,探究不同纳米颗粒体积分数和不同纳米颗粒大小在不同雷诺数(Re)下对纳米流体的流动和传热特性的影响。基于DPM模型对纳米流体在圆管中的对流换热进行了数值模拟研究,研究结果表明,在一定范围内,每增加0.5%的体积分数,纳米流体的传热性能平均增强7.82%。随着纳米颗粒的减小,纳米流体的传热系数不断增加。     

高功率直流电弧等离子体流动传热过程的数值模拟

金刚石薄膜在现代工业和军事中具有重要应用价值,但是其制备过程中仍然存在着诸多问题,影响了其产业化发展。本文采用数值模拟的方法对影响金刚石薄膜制备的关键因素直流电弧等离子体的流动传热过程进行了研究,获得了等离子体流动与传热过程中的流场分布、温度分布、电离度分布等有关参量的分布状况,为掌握和控制电弧等离子体流动传热过程提供了理论依据和指导。     

具有浇注缺陷的扰流柱流动与换热特性的对比分析

采用数值模拟方法对两种具有浇注缺陷的扰流柱通道的换热和流动阻力特性进行了模拟,重点研究了断裂结构和束腰结构扰流柱的影响,并与完整扰流柱通道进行了比较。结果表明所研究的扰流柱通道与完整扰流柱通道相比,其换热效果和压力损失系数相差不大。具有断裂结构和束腰结构的扰流柱减轻了叶片的重量,降低加工精度,对通道的流动和换热特性的影响不大,甚至具有一定的强化传热作用。     

孔隙率对斯特林发动机回热器影响的数值模拟

回热器作为斯特林发动机的核心部件,其工作条件极其恶劣,流动和传热过程更是复杂,迄今为止还没有一种准确描述其工作过程的方法.针对孔隙率对回热器传热及流动特性的影响,利用Fluent软件进行了三维数值模拟,通过模拟发现填料孔隙率的变化对回热器内压损及蓄热能力都有很大的影响.     

波纹管内流动与传热规律的数值计算

采用三维层流及低雷诺数湍流模型对波纹管内流动与传热性能进行了数值模拟,模拟结果与试验结果吻合良好.通过数值计算拓宽了波纹管流动与传热关联式的参数范围,发现在较大雷诺数(RP)范围内波纹管阻力系数随Re的变化趋势表现为指数规律.考察了不同波纹高度、波纹间距对流动与传热的影响,并对模型参数进行了综合性能评价,结果表明:波纹高度对波纹管内流动与传热的影响较波纹间距更显著;波纹管结构的强化传热性能只有在高Re条件下才得以体现,Re越大,波纹管综合性能因子也越高.通过数值计算得到了波纹管流动与传热的最优结构参数及最佳传热雷诺数范围.     

封闭腔内Al_2O_3-EG纳米流体自然对流传热特性的数值研究

对梯形封闭腔内Al2O3-EG纳米流体自然对流传热进行了数值模拟,讨论了封闭腔尺寸比、瑞利数、纳米颗粒体积分数以及布朗运动对自然对流流动与传热特性的影响。数值模拟结果表明在考虑布朗运动时,腔体尺寸比与瑞利数对流动传热均有很大影响,且尺寸比为0.5时,对流换热平均Nusselt数达到最大值。随着纳米颗粒体积分数的增加,纳米流体换热效果逐渐增强;但当忽略布朗运动时,添加纳米颗粒削弱了换热效果。     

Modeling and simulation of heat transfer phenomena during investment casting

Determining the heat transfer phenomena during casting processes is an important parameter for measuring the overall performance of process. It gives information about the properties of the metal being casted and its possible behavior in the mold during casting process. Improper determination of heat transfer phenomena and use of improper molding materials and casting conditions leads to defects such as misruns, cold shuts, shrinkage, pin holes, air holes and porosity in final product. A mathematical model was developed using standard transport equations incorporating all heat transfer coefficients to calculate the time for solidification of metal in casting and computer simulation of the model was carried out in C++ to validate the model. The metal used was pure iron casted in investment molds of silica sand with zircon coating. It was shown that airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. So, the changes in heat transfer coefficient also contribute towards time of solidification. The time calculated was found to be in good agreement with experimental values.     

NUMERICAL SIMULATIONS OF ELECTRO-SLAG REMELTING PROCESS

Flow and heat transfer characteristics in the electro-slag remelting process (ESR) are important in manufacturing steel of good quality. An integrated numerical model is developed to compute the flow field and the temperature distribution inside ESR units with a metal pool profile which is solved simultaneously. In addition to the conservative equations of mass, momentum, energy, and turbulent properties, Maxwell's equations are employed to obtain the electromagnetic field by either AC or DC power supply. The results include the effects of power supply type, current amplitude, casting rate, and flow field patterns (laminar or turbulent) on flow and heat transfer characteristics. Different flow patterns and turbulent properties have been predicted using a pool profile close to the real one for AC and DC power supplies. The present model concludes that the casting rate and current amplitude are very effective in affecting the pool shape.     

Direct numerical simulation of interphase heat and mass transfer in multicomponent vapour–liquid flows

A Volume-of-Fluid methodology for direct numerical simulation of interface dynamics and simultaneous interphase heat and mass transfer in systems with multiple chemical species is presented. This approach is broadly applicable to many industrially important applications, where coupled interphase heat and mass transfer occurs, including distillation. Volume-of-Fluid interface tracking allows investigation of systems with arbitrarily complex interface dynamics. Further, the present method incorporates the full interface species and energy jump conditions for vapour–liquid interphase heat and mass transfer, thus, making it applicable to systems with multiple phase changing species. The model was validated using the ethanol–water system for the cases of wetted-wall vapour–liquid contacting and vapour flow over a smooth, stationary liquid. Good agreement was observed between empirical correlations, experimental data and numerical predictions for vapour and liquid phase mass transfer coefficients. Direct numerical simulation of interphase heat and mass transfer offers the clear advantage of providing detailed information about local heat and mass transfer rates. This local information can be used to develop accurate heat and mass transfer models that may be integrated into large scale process simulation tools and used for equipment design and optimization.     

Numerical study of conjugated heat transfer in metal foam filled double-pipe

The two equation numerical model has been applied for parallel flow double-pipe heat exchanger filled with open cell metal foams. The model fully considered solid–fluid conjugated heat transfer process coupling heat conduction and convection in open cell metal foam solid matrix, interface wall and fluid in both inner and annular space in heat exchanger. The non-Darcy effect and the wall thickness are also taken into account. The interface wall heat flux distribution along the axial direction is predicted. The numerical model is firstly verified and then the influences of solid heat conductivity, metal foam porosity, pore density, relative heat conductivity and inner tube radius of the heat exchanger on dimensionless temperature distribution and heat transfer performance of heat exchanger are numerically studied. It is revealed that the proposed numerical model can effectively display the real physical heat transfer process in the double pipe heat exchanger. It is expected to provide useful information for the design of metal foam filled heat exchanger.     

Air-cooled micro-porous heat exchangers for thermal management of fuel cells

This paper presents 3D numerical simulation of an air-cooled metal foam heat exchanger with potential application in thermal management of fuel cell systems in general and Proton Exchange Membrane Fuel Cells, PEMFCs, in particular. It has been shown that the new design can lead to a uniform temperature distribution for the heated plate especially at higher air flow speeds. The heat transfer enhancement because of the foams leads to an increase in the pressure drop which is, interestingly, comparable to that of water-cooled PEMFCs. Other potential benefits of the application of metal foams for fuel cell thermal management are briefly discussed and estimated.     

A novel multilayer fin structure for heat transfer enhancement in hydride‐based hydrogen storage reactor

Metal hydrides are promising means for compact hydrogen storage. However, the poor heat transfer in the tank packed with metal hydride powders often hinders the system from charging or discharging hydrogen effectively. In this investigation, a tube‐fin heat exchanger is supposed to be inserted to the tank, and an optimization problem accounting for both heat transfer enhancement and cost is formulated. We solve the problem with approximate analytical methods, and the influences of fin geometry are discussed. The comparison results support using quadratic curve‐shaped fins, whose effectiveness is also proved by the numerical simulation results. Furthermore, a novel multilayer fin structure with varying width is proposed, and the key parameters of it are discussed, including the number and the arrangement of fins. This paper is expected to provide new insights for the heat transfer enhancement design of hydride‐based hydrogen storage system.     

圆形铝熔炼炉内非稳态热工过程数值模拟

针对铝熔铸过程中常用的圆形铝熔炼炉,利用FLUENT软件,根据能量守恒方程、动量方程建立铝熔炼炉内热工过程数学模型,采用标准k-ε湍流模型、P-1辐射模型对铝熔炼炉内非稳态传热及流动过程进行数值模拟研究。考虑到铝料熔化过程会消耗一部分能量,采用等效比热法将铝料的熔化潜热转换为相应的比热值进行计算。通过数值模拟得到了炉内流场、炉膛及铝料温度场分布情况。模拟结果与实际情况相符,为铝熔炼炉的设计与优化研究提供了理论依据。     

Identifying heat and mass transfer characteristics of metal hydride reactor during adsorption: Improved formulation about parameter analysis

Transport process affects the performance of a metal hydride reactor significantly. Therefore in a former paper presented by the same authors, two parameters, which are known as heat transfer controlled reaction rate and mass transfer controlled reaction rate, were defined to account for this effect and assist the design of the reactors. However, a few simplifications were adopted in that article, which may result in some errors. In order to achieve better accuracy and clarity, more factors such as the external convection heat transfer and propagation of reaction front were considered here in the formulation of the parameters. Then numerical simulations for the adsorption in a tubular reactor were carried out and the situation under which parameter analysis can be applied was discussed. More characteristics in the process were revealed by the newly formulated parameters, which could be seen from the comparison of the results by parameter analysis and numerical simulation.     

直接空冷枝状排汽管道系统内导流装置的优化设计

对德国基伊埃(GEA)公司发明专利——枝状直接空冷排汽管道系统进行研究。建立某2×600MW机组直接空冷排汽管道内湿蒸气两相流动和传热的数学模型;利用数值传热学软件Fluent对典型汽轮机工况下的排汽状况进行了数值模拟;对二维管道内湿蒸气速度场、温度场和两相场的模拟、分析和研究。模拟结果表明:专利提出的简单几何原则分流方法,无法实现排汽的均匀分配。针对不同形式的直接空冷枝状排汽管道系统应进行详细的优化设计,并提出了枝状排汽管道系统导流装置的基本设计原则。