THE GALERKIN METHOD FOR TWO-PASS CROSSFLOW HEAT EXCHANGER PROBLEM

The Galerkin method is applied to solve the two-pass crossflow heat exchanger problem in the case of neither fluid mixed throughout. Four variants of flow arrangements differing in identical and/or inverted order of coupling the passes in an overall counter-current scheme are considered. The passes are not necessarily equal with respect to the number of heat transfer units. The power of the method presented can be seen in the fact that the exchanger effectiveness can be predicted with less than 0.1% error even in the case of the first order approximation. The convergence toward the exact results by carrying out the computations to higher order terms is demonstrated. Four-significant-figure effectiveness tables based on the first order approximation are given for each type of flow arrangement for N_tu up to 10. The effectiveness deterioration caused by unequal N_tu's per pass (due to different heat transfer coefficients, different fining, different core length, etc.) is presented in the form of charts.     

Derivation of Charts for the Approximate Determination of the Area Requirements of Heat Exchangers Using Plain and Low‐Finned Tube Bundles (Part A)

Heat exchangers can be made more compact by either enhancing the heat transfer coefficient or by increasing the amount of area per unit volume. The use of low‐finned tubes is an effective means of achieving the latter. The extent to which the equipment size can be reduced using such means is problem‐dependent. Decisions of whether or not to employ process intensification have to be made at the conceptual stage of design. There is, therefore, a need for sizing procedures that avoid the recourse to full detailed design. Such a procedure is reported here. The key to the procedure is a relationship between the shell‐side pressure drop, shell‐side heat transfer coefficient and overall exchanger surface area. The procedure has been applied to a number of ‘typical’ fluids. The results are presented in a series of charts relating exchanger size and duty. It is shown how individual duties can be ‘normalized’ in the form of a ‘duty factor’ that relates shell‐side pressure drop, mass flow rate, stream temperature change and exchanger temperature driving force. So, the charts are independent of duty.     

高粘度流质下管壳式折流板开孔换热器换热性能的数值模拟

通过数值模拟计算研究了4块弓形折流板管壳式折流板开孔换热器在高粘度流质下的强化换热性能。模拟结果表明,在高粘度流质中折流板开后换热器压力分布比未开孔前分布均匀些,温度分布同样遵循相似规律,未开孔折流板背根部会产生滞留区,并且滞留区随着速度的增大而增大,折流板开孔后会对流体产生扰动作用,从而改善滞留区,有助于强化传热。     

自由降膜传热传质数值模拟技术应用进展

自由降膜过程在许多工业领域,特别是在石油化工工业中有着非常广泛的应用。近年来,随着计算机技术的发展,研究人员采用理论分析、数值模拟和实验相结合的技术手段,对降膜传热传质过程进行了深入的研究,为优化降膜传热传质过程和新型设备的开发提供了理论基础。     

HEAT TRANSFER IN A SUBCOOLED WATER FILM FALLING ACROSS A HORIZONTAL HEATED TUBE

A numerical simulation and an experimental study were carried out for sensible heat transfer for a subcooled water film falling across a horizontal heated tube. A laminar model and a turbulent model were adopted to calculate the heat transfer coefficient. The whole wetting zone on the tube surface was divided into two zones: the top stagnation zone and the lateral free film flow zone. The initial boundary conditions for the free film flow zone were determined by calculating the fluid and the temperature fields in the stagnation zone. A modified wall function method was used for the turbulent model. The comparisons between the experimental data and the numerical solutions show that the experimental data agree reasonably well with the laminar model solutions. Finally, two simple correlations were proposed for predicting the convective heat transfer of a falling film for engineering applications.     

热管倾斜波纹翅片强化传热三维数值模拟与分析

利用CFD计算软件FLUENT,对均匀倾斜波纹翅片和倾角渐增倾斜波纹翅片的流体流动和传热过程进行了数值模拟,得到了翅片表面温度场、速度场和压力场的分布情况,并将其强化传热效果与平板翅片进行了对比,应用流体力学和场协同理论分析了模拟结果.模拟结果表明倾斜波纹翅片具有较好的传热效果,为热管翅片强化传热的研究提供了理论基础.     

稠油集输伴热管道轴向温度场数值模拟算法研究

分析了稠油集输伴热管道的传热特点,并在此基础之上建立伴热管道轴向温度场数值模拟的物理模型,给出求解的数学模型。求解方法与前人的方法有很大不同,其将欧拉坐标下伴热管道充分发展之后的稳态温度场看做是拉格朗日坐标下某一层流体从管道入口流动到管道出口温度场非稳态发展的结果。在求解过程中选取合适的极坐标奇点和边界条件的处理方法,确定最终的算法并进行算例分析,验证算法的良好性能。     

玻璃池窑的数值模拟

玻璃液在池窑内的流动状况与温度分布对玻璃生产起着决定性的作用。通过控制液流状况,可确保玻璃熔制的各个阶段(如配合料的熔化、玻璃液的澄清和降温)都能按正确的时序,在相应的窑池区域内进行。玻璃液流还承担着对配合料覆盖区域的热耗进行补偿的作     

Study of the influence of axial conduction in a boiling heated pipe

In this work a characterization of a horizontal heated pipe has been performed. This characterization consists in a steady state analysis of the thermohydraulic behavior of a boiling heated channel with subcooled liquid at the inlet. The temperature, velocities and pressure profiles along the heated section have been analyzed and the length of the single- and two-phase flow regions have been characterized. Without axial conduction and due to the big difference in the magnitude of the single- and two-phase heat transfer coefficient, steep temperature gradients were observed. By adding the effect of axial conduction, more heat is removed from the single phase region and added to the two-phase region through the wall. The net effect was a decrease in length of the two-phase flow region and consequent increase of the single-phase region. It was also observed that the axial conduction decreases the gradients in the wall temperature profile but it does not influence markedly its temperature differences with the fluid.     

熔窑玻璃液流数值模拟的新发展

熔窑玻璃液流数值模拟的新发展赵国昌（清华大学核能技术设计研究院，１０００８４）ＮｅｗＤｅｖｅｌｏｐｍｅｎｔｏｆｔｈｅＮｕｍｅｒｉｃａｌＳｉｍｕｌａｔｉｏｎｆｏｒＦｌｏｗａｎｄＨｅａｔＴｒａｎｓｆｅｒｏｆＧｌａｓｓＭｅｌｔｉｎＴａｎｋＦｕｒｎａｃｅ￥Ｚ...     

Numerical analysis of interphase heat and mass transfer of cluster in a circulating fluidized bed

Interphase heat and mass transfer characteristics of a naphthalene particle cluster in a circulating fluidized riser are numerically analyzed using a three-dimensional CFD model. Heat and mass transfer characteristics of gas over an in-line array of three naphthalene particles and an isolated naphthalene particle are analyzed. Distributions of gas concentration, temperature and velocity are obtained. The heat and mass transfer rates of gas-to-cluster increase with the increase of the cluster porosity and Reynolds number. Present simulations indicate that the small cluster gives higher heat and mass transfer coefficients than those of the large cluster. The heat and mass transfer rates of individual particles in the cluster are lower than that of an isolated particle and particles in an in-line array under a given cluster porosity.     

螺旋内槽管内的层流流动与传热的数值模拟

应用数值方法对一种螺旋内槽管管内的流体层流流动和传热进行了数值分析。采用数学变量置换把控制方程由原坐标系中的三维动量、能量及连续性方程转化为二维螺旋坐标系下的数值计算模型，并利用现有的二维数值模拟软件进行模拟计算。计算考察了恒壁温、轴向恒热流螺旋内层流充分发展流体的流动与传热随雷诺数的变化，并研究了螺距的影响。