Heat Transfer in a Turbulent Flow of Gas in a Tube under Conditions of Resonance Oscillation of the Flow Rate

A prediction study is made into the heat transfer in a turbulent flow of gas (air) in a narrow tube with superimposed resonance oscillation. The model of turbulent transfer includes the effect of nonstationarity on the turbulent stress and heat flux. The finite difference method is used to solve the equations of motion and energy. The distribution of the flow rate and pressure along the tube is found by way of numerical solution of a set of cross section-averaged nonstationary equations of motion, continuity, and energy. The effect of the process parameters (Reynolds number, dimensionless oscillation frequency, thermal boundary conditions on the wall) on the period-average heat transfer and heat flux to the wall is analyzed.     

Numerical Simulation of Heat Transfer under Conditions of Turbulent Separated Flow in Tube Banks

The separated flow and heat transfer in an in-line bank of round tubes are calculated using a multiblock computational algorithm and the semi-empirical Menter and Spalart-Allmaras models of turbulence. An ingenious procedure is suggested for the correction of the mass-average temperature. Analysis is made of the effect of viscosity on the vortex structure and heat transfer from a remote cylinder within the bank.     

Symmetry-Preserving Discretization of Heat Transfer in a Complex Turbulent Flow

Convective and diffusive operators are discretized such that their symmetries are preserved. The resulting discretization inherits all symmetry-related properties of the continuous formulation. It is shown that a symmetry-preserving discretization is unconditionally stable and conservative. A fourth-order, symmetry-preserving discretization method is developed and tested for the numerical simulation of turbulent (flow and) heat transfer in a channel with surface-mounted cubes, where the temperature is treated as a passive scalar. The Reynolds number (based on the channel width and the mean bulk velocity) is Re=13,000. The results of the numerical simulation agree well with available experimental data.     

Investigation of Heat Transfer in the Case of Upward and Downward Turbulent Flow of a Mixture of Gas and Solid Particles in a Pipe

The continual model developed by us is used to investigate the effect of the force of gravity on a nonisothermal turbulent flow of a gas suspension in a vertical pipe for upward and downward motion. The reasons behind the intensification of heat transfer in the case of a downward locally nonequilibrium motion of gas suspension are found.     

Heat Transfer in Plug Flow of a Fibrous Suspension in a Tube

The problem of heat transfer in plug flow of a fibrous suspension in a straight round tube with a constant wall temperature is solved.     

Hydrodynamics and Heat Transfer in Pulsating Turbulent Pipe Flow of a Liquid of Variable Properties

The effect of the variability of properties on the characteristic features of heat transfer and of pulsating turbulent pipe flow of incompressible liquid is investigated. The results are obtained by using the method of finite differences to solve numerically a set of equations of motion, continuity, and energy written in a narrow channel approximation. The set is closed by relaxation equations for turbulent stress and turbulent heat flux. A stable difference scheme is used, which is valid for high relative amplitudes of oscillation. The calculations are performed for a dropping liquid in view of the temperature dependence of viscosity. The results of calculation of heat transfer and friction resistance for two limiting cases of steady-state flow of a liquid of variable properties and of pulsating weakly nonisothermal flow fit well the available experimental data.     

R134a臣卧式螺旋管内流动沸腾换热特性实验研究

对R134a在水平直管和螺旋管内的沸腾换热特性进行了实验研究.在三个不同的蒸发温度(5℃、10℃和20℃),工质R134a的质量流量范围为100～400kg/(m~2·s)和干度范围为0.1～0.8的条件下,实验得到了R134a在水平直管和螺旋管内的沸腾换热系数随其质量流量和干度的变化关系,将水平直管和螺旋管内的沸腾换热特性数据进行了比较,结果显示,在实验条件下,卧式螺旋管的传热系数比直管的平均增加13.7%.     

机载蒸发循环系统两相流换热特性实验研究

相变传热凭借其良好的传热能力和较低的能耗的特点在航空航天领域的电子设备冷却尤其是蒸发制冷循环系统中得到应用。飞行器在机动飞行或进出大气层都会遇到超重状态。超重状态下的两相流的流动及传热特性相对于静止状态时候发生了很大的变化。以流动水为介质,通过搭建旋转平台对超重状态下两相流系统进行了实验研究,得到流体在过载时流动特性和传热特性的初步变化规律。结果显示超重对流动和换热都会产生显著影响。试验结果对于飞行器上相变换热器的理论分析和设计积累了有价值参考资料。     

Two-Phase Flow and Heat Transfer During Chilldown of a Simulated Flexible Metal Hose Using Liquid Nitrogen

For many industrial, medical and space technologies, cryogenic fluids play irreplaceable roles. When any cryogenic system is initially started, it must go through a transient chill down period prior to normal operation. Chilldown is the process of introducing the cryogenic liquid into the system, and allowing the system components to cool down to several hundred degrees below the ambient temperature. The chilldown process is an important initial stage before a system begins functioning. The objective of this paper is to investigate the chilldown process associated with a flexible hose that was simulated by a channel with saw-teeth inner wall surface structure in the current study. We have investigated the fundamental physics of the two-phase flow and quenching heat transfer during cryogenic chilldown inside the simulated flexible hose through flow visualization, data measurement and analysis. The flow pattern developed inside the channel was recorded by a high speed camera for flow pattern investigation. The experimental results indicate that the chilldown process that is composed of unsteady vapor-liquid two-phase flow and phase-change heat transfer is modified by the inner wall surface wavy structure. Based on the measurement of the channel wall temperature, the teeth structure and the associated cavities generally reduce the heat transfer efficiency compared to the straight hose. Furthermore, based on the measured data, a complete series of correlations on the heat transfer coefficient for each heat transfer regime was developed and reported.     

十二排圆形翅片管换热器的传热与流动特性研究

采用数值计算方法研究12排大管圆形翅片表面空气侧流体的流动特性,获得不同雷诺数下圆形翅片的速度分布云图、温度分布云图和流线分布图,并将模拟的结果与实验和实验关联式分别进行验证。研究结果表明：翅片间距为9.6mm第一排管壁侧和翅片表面的传热系数分别是翅片间距为2.4mm的1.67和0.97倍;前面六排翅片表面和管壁表面的传热系数具有很强的波动,而在第六排后翅片表面和管壁表面的传热系数趋向于稳定。     

Turbulent Fluid Flow and Heat Transfer Calculation in Mold Filling and Solidification Processes of Castings

Based on the time-averaging equations and a modified engineering turbulence model, the mold filling and solidification processes of castings are approximately described. The algorithm for the control equations is briefly introduced, and some problems and improvement methods for the traditional method are also presented. Both calculation and tests proved that. comparing with the laminar fluid flow and heat transfer, the simulation results by using the turbulence model are closer to the real mold filling and solidification processes of castings.     

Numerical Calculation of the Turbulent Flow of a Gas Suspension in a Tube

A mathematical model for describing the turbulent flow of a gas suspension in a tube has been formulated within the framework of the combined Euler–Lagrange approach. Results of calculations by this model are in good agreement with theoretical data obtained using the continuous model developed by the authors [Teplofizika Aéromekhanika, No. 1, 5?–71 (1999)]. The importance of detailed modeling of the turbulent structure of the carrying medium in the near‐wall zone has been shown based on a comparative analysis of computational and experimental data.     

Modeling of the Influence of Viscosity on the Tornado Heat Exchange in Turbulent Flow around a Small Hole on the Plane

The influence of viscosity on turbulent flow around a small spherical hole on the plane and on vortex heat exchange is analyzed numerically.     

水平细通道内CO_2流动沸腾换热流态特性实验研究

本文对水平细通道内CO_2流动沸腾换热过程中流态及其转变特性进行理论分析和可视化实验研究。根据可视化实验结果,更新了CO_2在低蒸发温度下的理论流动状态预测模型。实验工况为:热流密度(7. 5～30 k W/m2)、质量流率(50～600kg/(m2·s))、饱和温度(-40～0℃)、干度(0～1)、内径(1. 5 mm)。理论分析表明:质量流率对换热过程中经历的流态形式有决定性作用,热流密度对环状流-干涸区域、干涸区域-雾状流边界转变曲线影响较大,饱和温度对流态转变具有重要影响。可视化研究表明:基于理论流态图对于CO_2在细通道内流动沸腾换热的流态能够较好的预测,也能反映不同工况下流态的变化趋势,但理论流态图对干涸区域和雾状流区域预测偏差较大;在实验数据的基础上,增加了液气黏度比的无量纲因子,并提出一种新的临界热流密度预测模型。在考虑质量流率和热流密度影响的情况下,根据更新后临界热流密度预测模型和实验数据,引入沸腾数Bo对理论流态图中环状流-干涸区域、干涸区域-雾状流及间歇流/弹状流-环状流边界转变曲线进行了更新,可视化研究获得的流态数据中89. 4%符合更新后的CO_2理论流态预测模型。     

The Effect of Hydrodynamic Unsteadiness on the Flow Structure and on the Coefficients of Heat Transfer and Skin Friction under Conditions of Turbulent Pipe Flow of Heat-Transfer Agent

Critical analysis is made of the current status of investigations of heat transfer and skin friction under conditions of unsteady-state turbulent pipe flow. This analysis is based on the experimental data on the structure of turbulent flows and heat transfer. Comparison is made of experimental and theoretical results.     

空调替代工质R404A在水平内螺纹管中的沸腾换热研究

比较了CAVALLINI的纯质和混合工质水平内螺纹管中流动沸腾换热系数的关联式,结果显示在内螺纹管中,对近共沸混合工质R404A的沸腾换热系数进行工程计算时,R404A被看作纯质和混合工质计算所得的沸腾换热系数值差别最大不到10%,因此可将其以纯质对待;对CAVALLINI的纯质和混合工质、KOYAMA及THOME等四个水平内螺纹管流动沸腾换热系数的影响因素进行对比分析,结果表明R404A的沸腾换热中对流沸腾换热占主导地位,且随干度增加而增加.对关联式的理论预测和实验结果进行对比,表明CAVALLINI和THOME关联式的预测误差小于21%,因此它们对R404A适用性较好,这对R404A蒸发器的工程设计及优化具有一定参考意义.     

空冷凝汽器蛇形翅片扁平管空气侧流动与换热特性研究

针对应用于电站直接空冷凝汽器的蛇形翅片扁平单排管,对其空气侧的流动及换热特性进行了数值模拟。给出了该管件基本结构的雷诺数和欧拉数随迎面风速的变化关联式;结果显示,同一迎面风速下,随着翅片间距、高度的增大,换热变差,流动变好。但当间距增加到一定程度时,风速与间距对换热流动性能的影响都变得很小。风速越大,换热性能对翅片间距、高度越敏感,而流动则相反,需根据实际工况来选择合适的翅片间距及高度。