Three dimensional Couette flow and heat transfer through a porousmedium with variable permeability

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Three dimensional free convection couette flow with transpiration cooling

INTRODUCTION In recent years, the subject of free convection flow has attracted the attention of a number of scholars because of its possible applications to several geophysical problems. In view of these applications, a series of investigations were made to study the flow past a vertical wall. Transpiration cooling can very effectively pro-tect certain structural elements in turbojet and rocket engines, like combustion chamber walls, exhaust nozzles or gas turbine blades from hot gases. …     

3D couette flow of dusty fluid with transpiration cooling

INTRODUCTION Transpiration cooling is a very effective process to protect certain structural elements like combustion chamber walls, exhaust nozzles, or gas turbine blades in turbojet and rocket engines, from the influence of hot gases. In view of this, Eckert (1958) obtained an exact solution of the plane couette flow with transpi-ration cooling. The problem remained 2D due to the uniform injection and suction applied at the porous plates. Flow and heat transfer along a plane wall with…     

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。     

螺旋折流片强化管壳式换热器内管束传热数值模拟

介绍了一种用于强化管壳式换热器壳侧传热和支撑管束的螺旋折流片新型结构,该结构是对换热器管子相间地套上螺旋折流片以产生旋涡流动.研究模型是在正方形布置的4个管子中的2个对角管子套上螺旋折流片后形成的通道,利用FLUENT软件对该上述四管通道模型的流场和温度分布情况进行了数值模拟;分析了四管通道模型中螺旋折流片对强化传热和流动阻力随雷诺数的变化关系的影响.算例结果显示该新型结构可比相同尺寸的光管通道中的情形传热系数提高约40%～55%,同时也将伴随较高的流动阻力.可以相信螺旋折流片式换热器将会在许多工业领域有良好的应用前景.     

Study on the heat transfer of cross flow in vertical upward tubes

INTRODUCTION Cross flow and heat transfer were widely found in oil production and chemical facilities.A detailed study of the hydrodynamic characteristics and heat transfer of cross flow is necessary for optimal design of the system and the development of new measuring techniques.Studies on the heat transfer in sin-gle-phase liquid cross flow were carried out in the past decades.Air or water was often chosen as the working fluid,in these studies commonly focused on fluids flowing across r…     

扩散吸收式制冷系统中板式换热器综合传热性能分析

在一种太阳能驱动、采用喷雾吸收器并以板式换热器作为主要换热部件的LiNO3-NH3-He三工质扩散吸收式制冷系统中,根据试验测得的运行参数,以溶液的p-t-x西方程及物性方程、传热基础理论等为依据,提出了计算溶液换热器中溶液流量的方法,并利用综合传热系数k、传热单元数N_TU与换热器效率s研究了板式换热器作为LiN03-NH3-He扩散吸收式制冷系统发生器、冷凝器、溶液热交换器、溶液冷却器时的换热性能．试验与分析表明,板式换热器的换热面积及其内部流道中的流量（流速）对其综合传热性能具有较大影响;在介质流量一定时,板式换热器不宜考虑过大的面积预留量;板式溶液换热器内部流道宜采用多流程布置形式以强化传热、提高换热效率．     

矩形管道内充分发展热流动的可视化计算

推导了求解矩形管道内充分发展流体流动和热交换的有限差分方程,编写了相应的计算机程序,借此求得了管道横截面内速度和温度的结点值,然后利用计算机图形显示算法自动生成相应的速度和温度等值线图形．最后,对管道内充分发展热流动的特性进行了讨论．     

Arrangement strategy of ground heat exchanger with groundwater

The orientation strategy of side pipe and the heat transfer performance of six ground heat exchangers(GHEs) were optimized by numerical simulation,with soil being treated as a porous medium.An experiment on the heat transfer of four GHEs was carried out in 2010.Results indicate that the velocity field is disturbed by GHEs.The optimal orientation strategy of side pipe is that the upward pipe is located upstream and the downward pipe downstream.The space between GHEs should be appropriately adjusted,depending on the direction and flow velocity.Groups of GHEs should be installed perpendicular to the mainstream in a single row,but if the acreage does not meet the requirements,GHEs should be installed in staggered multiple rows.Fewer GHEs parallel to the mainstream strengthen the heat transfer.Moreover,numerical results agree well with the test data,with the maximum relative error being less than 7.7%.     

不同边界条件下交叉三角形波纹流道传热与流动的数据处理

为准确量化交叉三角形波纹流道的强化传热性能,除了需要进行数值模拟,还需要对所获得的数据进行正确计算处理.针对两种构造不同的交叉三角形波纹流道A和流道B,在模拟时选取不同的壁面给热条件,将恒热流密度壁面与等效恒温壁面的数值模拟结果进行了对比,并借助合适的数据处理方法,得到各自条件下的平均摩擦系数fL和平均努塞尔数NuL.结果表明,高热流密度时流道B的传热强化明显,低热流密度时流道A的传热减弱明显.对任何一类流道而言,边界给热条件的变化对流动摩擦阻力影响很小,但流道内的流动和传热之间其实是具有复杂的相互关联性的.     

波形折流杆换热器的开发和工业化实验研究

The conventional heat exchanger with segmental baffles is prone to bring forth fluid-induced vibration of heat transfer tubes and increase the pressure drop of shell-side greatly at higher fluid flow velocity. In order to avoid the above defects, the ROD-baffle heat exchanger has been developed. However, its collocation of heat transfer tubes is conventionally in square, which leads to fewer heat transfer area per unit volume. Based on the ROD-baffle heat exchanger, a new type curve-ROD baffle has been developed, and an industrial investigation of the curve-ROD baffle heat exchanger with normal triangular collocation has been carried into execution. In this paper, two equations using the Reynolds number were acquired to predict the heat transfer coefficients of the shell-side and tubeside. The experimental results show that the shell-side heat transfer and pressure drop characteristics of the curve-ROD baffle heat exchanger are superior to those of the segmental baffle one.     

杆支撑换热器壳侧单元流道的三维模拟

1 Introduction The traditional segmental baffle heat exchangers(SHE) can be si mply manufactured and run reliably,but they are mainly suitable for the situation of lowerflow velocity. When fluid velocity becomes higher inthe shell side ,the pressure dropi…     

空调表冷器热工性能测试的实现及分析

介绍了一种自行研制的空调表冷器热工性能测试系统,该系统是通过对实验室现有空气调节处理过程实验台进行改造制得。在压缩机和节流阀之间装设套管式蒸发器,制得冷冻水,经水泵送入表冷器中,与空气进行换热后重新返回套管式蒸发器中。通过温控器实现表冷器入口冷冻水温度的控制,表冷器进出口冷冻水温通过布置热电偶进行测量,冷冻水流量通过转子流量计进行测量,利用原有干湿球温度计测量空气进出口干湿球温度,进而在不同工况下实现表冷器析湿系数、热交换效率、接触系数和换热量的测试。依据测试结果分析风量、风速、冷冻水流量对表冷器热工性能的影响。     

封闭方腔自然对流传热的场协同分析

文章采用有限元方法数值研究了封闭方腔自然对流传热问题,并基于场协同理论分析了速度场与温度梯度场的协同关系,进一步深层次分析了协同角场同速度场、温度场、温度梯度场之间的协同关系,展示了不同瑞利数下方腔自然对流速度场和温度梯度的协同效果,着重探讨了各物理场对封闭方腔协同角的影响规律,同时表明以协同角为评价指标,可有助于改善局部的传热效果,从而深层次理解强化自然对流传热的机理,为实际工程的传热强化提供了理论依据。     

Liquid Flow Field on Evaporator of Wiped Short Path Distillation--Experimental Results and Computer Simulation

Short path distillation (SPD) is a kind of high vacuum distillation method, which is suitable for the separation of high boiling, heat sensitivity and viscidity products.In this paper,through measuring the phase-averaged velocity distributions with a conditional sampling method of the particle imaging velocimetry (PIV), the liquid flow field that affects the heat and mass transfer of evaporating thin-film in an SPD evaporator is investigated.Measured results show that the flow velocities decrease rapidly apart from the wiper at different wiper velocities, the maximum velocity appears before wipers, and the quicker the wiping, the larger the flow velocity. Meanwhile, the evaluation of numerical calculations is carried out.The measured velocity distributions indicate clearly the effect of the wiper both on the flow field along its moving direction and on the vortices behind the wiper.Simulation data show that the performance of liquid flow field on the heating surface not only agrees with the experimental results well,but also can give further more information, such as the distribution of turbulent kinetic energy.In this study,turbulent kinetic energy mainly distributes before wipers and laminar flow appears far away from the wipers.     

Liquid Flow Field on Evaporator of Wiped Short Path Distillation——Experimental Results and Computer Simulation

Short path distillation (SPD) is a kind of high vacuum distillation method, which is suitable for the separation of high boiling, heat sensitivity and viscidity products. In this paper ,through measuring the phase-averaged velocity distributions with a conditional sampling method of the particle imaging velocimetry ( PIV), the liquid flow field that affects the heat and mass transfer of evaporating thin-film in an SPD evaporator is investigated. Measured results show that the flow velocities decrease rapidly apart from the wiper at different wiper velocities, the maximum velocity appears before wipers, and the quicker the wiping, the larger the flow velocity. Meanwhile, the evaluation of numerical calculations is carried out. The measured velocity distributions indicate clearly the effect of the wiper both on the flow field along its moving direction and on the vortices behind the wiper. Simulation data show that the performance of liquid flow field on the heating surface not only agrees with the experimental results well, but also can give further more information, such as the distribution of turbulent kinetic energy. In this study ,turbulent kinetic energy mainly distributes before wipers and laminar flow appears far away from the wipers.     

Numerical study of the melting of nano-enhanced phase change material in a square cavity

A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles. A paraffin-based nanofluid containing various volume fractions of Cu was applied. The governing equations were solved on a non-uniform mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid-liquid interface. The effects of nanoparticle dispersion in a pure fluid and of some significant parameters, namely nanoparticle volume fraction, cavity size and hot wall temperature, on the fluid flow, heat transfer features and melting time were studied. The results are presented in terms of temperature and velocity profiles, streamlines, isotherms, moving interface position, solid fraction and dimensionless heat flux. The suspended nanoparticles caused an increase in thermal conductivity of nano-enhanced phase change material (NEPCM) compared to conventional PCM, resulting in heat transfer enhancement and a higher melting rate. In addition, the nanofluid heat transfer rate increased and the melting time decreased as the volume fraction of nanoparticles increased. The higher temperature difference between the melting temperature and the hot wall temperature expedited the melting process of NEPCM.     

不同密实度网衣周围流场数值模拟

将网衣进简化为平面透空薄板,应用有限体积法求解湍流模型,计算了不同密实度网衣与流场的耦合作用。结果表明,当流速和冲角一定时,密实度越大流速衰减越明显,并且网衣背流区上下两侧的流速增加也越大。随着冲角增大流速衰减越明显,并且阻力系数也随之增大,举力系数先增大后减小,在冲角45°时举力系数最大,在冲角为90度时,举力系数减小为0。     

Evaluation of the heat transfer performance of helical coils of non-circular tubes

This study addresses heat transfer performance of various configurations of coiled non-circular tubes, e.g., in-plane spiral ducts, helical spiral ducts, and conical spiral ducts. The laminar flow of a Newtonian fluid in helical coils made of square cross section tubes is simulated using the computational fluid dynamic approach. The effects of tube Reynolds number, fluid Prandtl number, coil diameter, etc., are quantified and discussed. Both constant wall temperature and constant heat flux conditions are simulated. The effect of in-plane coil versus a cylindrical design of constant coil, as well as a conical coil design is discussed. Results are compared with those for a straight square tube of the same length as that used to form the coils. Advantages and limitations of using coiled tubes are discussed in light of the numerical results.     

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).