舰载燃气轮机间冷器内部流动的三维数值模拟

板翅式换热器是舰载燃气轮机首选换热器形式。针对平直型翅片的矩形通道的结构特点,建立了流动换热分析的耦合计算模型,采用计算流体动力学（CFD）方法对间冷器的通道流场进行了数值模拟。给出并分析了计算区域内多个截面的温度、压力、速度、局部传热系数等参数的分布图形和变化趋势,并考察了不同工况下间冷器的工作能力。     

A Multidomain Chebyshev Pseudo-Spectral Method for Fluid Flow and Heat Transfer from Square Cylinders

A simple multidomain Chebyshev pseudo-spectral method is developed for two-dimensional fluid flow and heat transfer over square cylinders. The incompressible Navier-Stokes equations with primitive variables are discretized in several subdomains of the computational domain. The velocities and pressure are discretized with the same order of Chebyshev polynomials, i.e., the P_N-P_N method. The Projection method is applied in coupling the pressure with the velocity. The present method is first validated by benchmark problems of natural convection in a square cavity. Then the method based on multidomains is applied to simulate fluid flow and heat transfer from square cylinders. The numerical results agree well with the existing results.     

Fluid Flow Distribution and Heat Transfer in Plate-Fin Heat Exchangers

Single-phase and two-phase flow distribution in plate-fin heat exchangers and the influence of nonuniform fluid flow distribution on the thermal performance of such heat exchangers were experimentally investigated. The experimental results show that flow maldistribution can be a serious problem in plate-fin heat exchangers because of nonoptimized header configurations. The uneven distribution of two-phase flow in plate-fin heat exchangers is more pronounced than that of single-phase flow. It is shown that the uneven distributions result in a significant deterioration of the heat transfer performance. The relationship between the flow maldistribution characteristics and the resulting loss in heat exchanger effectiveness has been studied in this work. Certain improved header configurations with perforated plates were proposed in order to solve the maldistribution problem. It was found that the new header configurations could effectively improve the thermal performance of plate-fin heat exchangers. By changing the header configuration, the degree of flow and temperature nonuniformity in the plate-fin heat exchanger was reduced to 16.8% and 74.8%, respectively, under the main test condition.     

CFD Analysis of Momentum and Heat Transfer Around a Pair of Square Cylinders in Side-by-Side Arrangement

A numerical investigation is conducted to analyze the steady and unsteady laminar flow and heat transfer in a channel with two square bars (of equal diameters) arranged side-by-side. The analysis is carried out for Reynolds number = 10–100, Prandtl number = 0.7–50, for transverse separation distance between the bars (i.e., gap ratio) of 1.5, 2, 2.5, 5, and 10 at the blockage ratio of 1/18. The results found here are in good agreement with previously published data. The effects of gap ratio, Reynolds number, and Prandtl number on the detailed kinematics of the flow and the heat transfer are presented. The engineering parameters such as total drag coefficient, average Nusselt number, and Strouhal number are calculated for the preceding range of conditions. It is observed that the overall drag coefficient decreases with increasing Reynolds number, whereas the average Nusselt number for the square cylinders increases with increasing Reynolds number and/or Prandtl number for all the values of gap ratios studied. The percentage enhancement in the value of the average Nusselt number is found to be more than 76% for the range of settings covered here.     

Fluid Flow and Heat Transfer in Plate-Fin and Tube Heat Exchangers in a Transitional Flow Regime

The unsteady behaviors of fluid flow and heat transfer in plain plate-fin and tube heat exchangers with a wide range of fin spacings from 2.06 mm to 16.48 mm and tube diameter 8.28 mm are studied by a large eddy simulation technique (LES). Velocity fluctuations and vortex sheddings induced by the tubes in the channel are modeled. The results found that the flow in passages of large spacings is quite different from that of small spacings. The flow is co-determined by two effects: the duct effect and the tube bank effect. The tube bank effect is more dominant with increasing fin spacings.     

多孔介质中高温气体非稳态渗流传热数值计算

针对水平导管中填充颗粒物料层内的高温气体参流传热现象，考虑渗流与传热的相互作用并采用局部非平衡假设建立多孔介质中的瞬态渗流传热物理数学模型。研究不同情况下填充物料中的渗流速度和气固温度分布。计算结果表明，高温热气体对水平导管中移动颗粒料层的热渗透主要发生在渗流入口端区域，随着渗流时间延长，热渗透深度沿导管推进。增大入口渗流速度以及减小出料速度，将导致物料温度沿导管慢速下降，热渗透深度扩大，热渗透作用区域内的物料温度水平提高。在热渗透作用区域，孔隙率对流场和温度场有很大的影响。研究对于高温反应器的颗粒输运和给料器的设计与运行有一定的参考作用。     

Generalized Prediction of Maximum Heat Transfer to Single Cylinders and Spheres in Gas-Fluidized Bed

A simple dimensionless correlation is presented and compared with data from 35 experimental studies. Data include spheres, horizontal and vertical cylinders, cylinder diameters from 0.13 to 220 mm, particle diameters from 104 to 15,000 μm, bed temperatures up to 900° C, and bed pressures up to 9.25 bars. Fluidizing gases include air, helium, CO₂, H₂, and R-12. Particle densities range from 1986 to 11,340 kg/m³ and p_sC_s from 1474 to 4173 kJ/m² °C. A total of 142 data points are correlated with a mean deviation of 17%. Complete tabulations are provided for all data analyzed. Application to tube bundles is discussed briefly.     

基于CFD的活塞振荡冷却的流动与传热仿真研究

由于柴油机热负荷不断提高,必须要对活塞进行有效冷却。应用计算流体动力学(CFD)方法对活塞的振荡冷却瞬态传热进行了仿真分析,得到了不同转速下冷却油腔的机油填充率以及壁面换热系数等随曲轴转角的变化规律。研究结果表明,随着发动机转速的提高,冷却油腔内的机油填充率下降,但是壁面换热系数却有所提高;机油的振荡冲击对冷却油腔顶部和底部的强化换热明显高于侧壁。此结果可为活塞有限元分析提供热边界条件,在活塞概念设计阶段为活塞的优化设计提供依据。     

海水脱硫散堆填料塔流体流动及传热研究

在大型可移动式海水脱硫试验台上进行了中试规模的试验,在体积平均法的基础上,结合试验数据获得的压损拟合公式建立了描述散堆填料塔内气、液两相的流动及传热模型;通过计算,获取了在不同液气比下塔内流体速度、孔隙率分布、压力分布及海水温度分布,并就压力损失和海水出口温度与试验值进行了对比,预测值与试验值吻合较好。分析计算结果发现,靠近壁面处存在着显著的壁流现象,其形成原因是近壁面处的孔隙率明显高于中间区域。海水温度在顶部分布较不均匀,靠近壁面处海水温度波动较大,向塔中心处逐渐趋于均匀,沿塔高度从上到下,温度逐渐下降均匀,到塔高一半处基本不再变化(△T<0.1 K),说明在塔高一半处气液间的热交换已基本完成。     

Heat Transfer and Fluid Flow on Dimpled Surface With Bleed Flow

This study investigates the effects of bleed flow on heat transfer and fluid flow on a dimpled surface in a rectangular channel. The heat transfer on a dimpled surface with bleed flow is compared with that on a dimpled surface without bleed flow. The height of the channel is 15.0 mm. The dimples are arrayed in staggered on the bottom surface of the channel with a pitch of 15.0 mm. The dimple depth is 3.75 mm and the dimple footprint diameter is 13.0 mm. The bleed hole is installed on the inner surface of the dimple and the diameter of the hole is 1.3 mm. The tests were conducted with varying Reynolds numbers from 1000 to 10,000 and 0.5% of total mass flow is flowing out through a bleed hole. A numerical method was employed to determine the detailed heat transfer coefficients. Commercial computational fluid dynamics software, ANSYS CFX 13.0, is adopted and the Shear Stress Transport model is set to turbulent model. As a result, the overall heat transfer rate on dimpled surface with bleed flow is 10–20% higher than that without bleed flow.     

The Numerical Comparison of Heat Transfer in a Coated and Fixed Bed of an Adsorption Chiller

Ecological adsorption technology is becoming a focus of attention by industry due to the utilization of low grade thermal energy sources for cooling production. It can be a promising part of sustainable development concept of the global economy. Therefore, research aiming at improving their performance i.e. Coefficient of Performance (COP) by optimizing the construction of sorption beds with a built in heat exchanger system is crucial. The heat transfer characteristics between the bed of porous media (sorbent) and surface of the heat exchanger system determine the heating power of an adsorption chiller. The HP increase can be obtained by heat transfer intensification due to the increase in the thermal conductivity of the sorbent layer in the vicinity of the heat exchanger’s surface. The novel modification of the sorbent layer structure is proposed in the paper in order to improve the heat transfer processes in the heat exchanger boundary layer. The analysis of desorption process conditions in the parametric model of a coated and fixed adsorption bed design is presented in the paper. The computational fluid dynamics (CFD) with conjugate heat transfer analysis is used to determine the crucial input parameters (temperature distribution in the sorbent bed) for further analytical calculations. The commercial code Ansys Fluent was used to perform numerical simulations. The developed computational model consisted of three subdomains representing heating water, heat exchanger material (copper) and sorbent (silica gel). The comparison of a novel coated design and a conventional fixed bed is discussed in the paper. The numerical analysis is based on experimental thermal conductivity measurements of the sorbent layer in different configurations, which were performed using Laser Flash Method.     

缸内对流换热与气体流动的计算分析

摘要本文将内燃机燃烧室简化成轴对称的二维空间,将计算缸内流动的二维模型与边界层模型相结合,分析了缸内气体的迁移特性与对流换热.文中介绍了在内燃机工作过程中缸内气体边界层的分布与变化、边界层对对流换热的影响,给出了对流挟热系数沿燃烧室表面的分布与变化.与实测结果的比较表明,本文的模型具有较高的精度.     

膜片管通道流动与换热过程的数值模拟

采用SIMPLE算法模拟膜片管通道中的流动与换热,分析流场中出现的非线性现象以及不同管束排列方式对换热的影响。物理模型长度为185. 6 mm,高度为92. 8 mm,圆管直径为32 mm。烟气入口温度为400 K,上下两侧固体壁面温度为300 K。假设流动与换热进入充分发展阶段,雷诺数(Re)的取值范围是3 000～25 000,通入不同流速的烟气与两侧的壁面进行换热。结果表明:采用雷诺应力模型(RSM)所得的努塞尔数(Nu)与实验关联式结果最吻合,而且相对误差在5%～17%间;采用直接模拟(DNS)模拟时,稳态到非稳态的临界Re是100;在同一Re时,随着管间距减小,Nu是逐渐增加的,当Re取为25 000,管束水平间距和竖直间距均取为43. 2 mm时,通道换热能力达到最大且相应的Nu是195. 23。     

热镀锌锌锅中的流动与传热数值研究

在带钢连续热镀锌生产中,锌液在锌锅内的流动及温度分布情况对于镀层质量有着重要的意义。以某热镀锌锌锅为研究对象,通过实验获得的锌锅边界传热情况,推算得到锌锅计算的边界条件。使用CFX商业软件对锌锅内的流场及温度场进行模拟,并比较研究了带钢的宽度与运行速度对锌液流动的影响。结果表明,模拟与实验测量数据良好吻合,证明了计算方法的正确性。不同带宽的锌锅流场具有相似性,而带钢速度的不同将对锌锅流场产生较大的影响。带速的上升一方面使得锌锅温度的不均匀程度降低,另一方面则增加了底渣卷起而附着在带钢上的可能性。     

Numerical Simulation of Fluid Flow and Heat Transfer in U-Shaped Microchannels

The numerical simulation of transport in complex microchannel systems for thermal management is considered, focusing on U-shaped microchannels. The simulation is carried out in conjunction with an experimental study. A physical system for fluid flow in U-shaped microchannels with heat generation at the bottom has been set up. This system approximates the use of microchannel flow for heat removal from electronic devices. Different numerical models are considered for system modeling and simulation. By comparing the results from these models and the obtained experimental data, it is found that the two channel model, which employs two channels with periodic boundary conditions, is the optimal model to simulate the overall heat transfer performance. Thus, the focus of the study is on the use of combined experimentation and numerical simulation for an accurate and realistic modeling of such complex microchannel systems, without excessive computations needed for simulating each microchannel of the system.     

圆管螺旋流的流动与传热数值模拟

针对工程中常见的圆管流,采用切向引入装置使流体产生旋转流动,通过建立圆管螺旋流的三维模型,采用RNG-模型对管内流场进行了数值模拟,获得螺旋流的速度场以及强化传热特性。研究入口不同速度对强化传热性能的影响,为旋流强化传热装置的应用提供了必要的依据。     

Recent Studies on Fluid Flow and Heat Transfer in Thermal Microdevices

Control and measurement of fluid flow and heat transfer in microdevices is of great importance to the development and application of MEMS and Bio-MEMS such as thermal inkjet printer heads, microchemical reactors, and PCR. Thus, the detailed flow behavior, in particular the two-phase flow in microdevices, has attracted much attention in recent years. Several types of thermal micropumps have been developed, although there is still room for further development. Various techniques for measuring the temperature, which are applicable to microscale devices, have also been proposed. As the cooling problem in microdevices becomes increasingly significant, a prospective view on integrated heat and mass transfer is quite necessary. Thus, in this work, some issues and future prospects for fluid dynamics and heat transfer of thermal microdevices are presented and discussed, in terms of thermocapillary pump, temperature measurement in microdevices, and flow near an evaporating meniscus.     

脉动流化床传热特性

在讨论脉动燃烧对传热特性影响的基础上,基于脉动流化燃烧概念,试验研究了脉动流化床中的传热特性,得到不同空截面风速、静止床层高度和声波扰动下的传热系数,并与同一运行参数条件下非脉动流化床及纯气流脉动燃烧器中的传热特性进行对比．总结影响脉动流化床传热特性的各种因素,分析不同运行参数对传热的影响作用．     

无反向流脉动条件下波纹管内流体传热及阻力特性研究

利用数值模拟与实验相结合的方法,在无反向流脉动条件下,分析脉动参数雷诺数Re、斯特劳哈尔数St及振动分率P对波纹管中流体的传热和阻力特性的影响。入口速度为脉动速度,入口温度设为300 K,出口设为自由出口,壁面采用恒温壁面,温度为350 K。研究表明：波纹管内流体处于层流状态时,随着Re的增大,传热强化幅度不断增大;流体处于湍流状态时,传热强化幅度随Re的增大而降低;随着St的增加,传热强化幅度增大;振动分率P对传热强化幅度的影响不明显;平均摩擦系数随着Re的增大而减小,随着振动分率P的增加而小幅度增大,在一个脉动周期内摩擦系数呈正弦规律变化,且随着St的增大发生明显变化,但平均值几乎不变。     

二维串列双圆柱层流对流传热的数值分析

基于流场分析软件,结合UDF编程技术和动态网格技术,分别对二维串列放置的静止和振动的双圆柱在不同间距比时的对流传热特性进行了仿真分析.结果表明:二维串列双圆柱对流传热时,静止和振动条件下的间距比均存在一个临界值3.5,小于该临界值时,传热较弱,大于该临界值时,传热增强且随间距比的变化波动较小.在相同间距比下,振动时圆柱面平均Nu明显增大,对流传热能力显著提高.在不同间距比下,二维串列双圆柱绕流时,速度场和温度梯度场之间的协同程度不同,双圆柱的振动使场协同进一步得到改善,从而提高了双圆柱的对流传热能力.