SHAPE OF TURBULENT LUMP IN A CIRCULAR PIPE FLOW DETERMINED BY SPATIAL-DEPENDENCE MATRIX

Contour line maps of velocity fluctuation of turbulent flow in a circular pipe are drawn based on the results of simultaneous measurements of axial velocity at sixteen radial positions. The regions where fluid elements are estimated to have the same behavior, i.e. turbulent lump, can be found out by using spatial-dependence matrices which are used in pattern analysis, and the shape of the eddy is made clear by drawing a contour line map of the index which shows the degree of mutual dependence of velocity fluctuations of the two points. The shape of the core part of the turbulent lump is different from that of outer part of the turbulent lump, and the scale of it and so on depend on the Reynolds number and the radial position. These tendencies predicted to have some effects on the diffusion of fluid elements.     

CONJUGATE HEAT TRANSFER WITH TURBULENT FLOW IN A CIRCULAR TUBE

A steady heat transfer problem has been analyzed as a conjugate problem with turbulent flow in a circular tube. The three kinds of thermal boundary conditions considered here are specified as constant temperature, constant heat flux and constant heat transfer coefficient at the outer surface of the wall.

From the results of numerical calculation for Prandtl numbers in the range 0.01 ≤ Pr ≤ 10 and for Reynolds numbers in the range 10⁴ ≤ Re ≤ 10⁵, it was confirmed that the dimensionless parameter R_c could have significant effects on the heat transfer and the temperature field in the fluid adjacent to the wall.     

A PROPOSAL FOR TREATMENT OF TURBULENT MIXING IN A TWO-PHASE SUBCHANNEL FLOW

We propose a practical method for the treatment of turbulent mixing rate in a two-phase subchannel flow in a hydrodynamic non-equilibrium state. Based on the assumption that the fundamental modes of the inter-subchannel fluid transfer in such a state are turbulent mixing, void drift, and diversion cross flow, the turbulent mixing rate is considered to be equal to that in the hydrodynamic equilibrium state that the flow will attain. The applicability of the method is examined by experiments concerning the axial variation in tracer concentration in a non-equilibrium flow without diversion cross flow. A good agreement is seen between the calculations and the measurements.     

拟稳态法测定气相扩散系数

根据拟稳态一维扩散原理,建立了气相扩散系数的测定装置。在该装置上,测定了8个体系的气相扩散系数,其中CH_2Cl_2-空气,CH_2Cl_2-H_2,CH_3CH_2Br-空气,CH_3Cl_2Br-H_2,CHCl_3-H_2等5个体系的气相扩散系数实验值,迄今尚未见文献报道。实验结果表明,本测试装置稳定性好,实验误差小,实验装置体积小,测试过程较为简便。     

THE CONVECTIVE VELOCITY OF HEAVY PARTICLES IN TURBULENT AIR FLOWS

This paper examines the influence of the “crossing trajectories” effect on the convective velocity for heavy particles suspended in a turbulent air flow. The fluid energy spectrum “experienced” by a falling particle is deduced from experimental data and is used to evaluate the turbulent component of the convective velocity. The results indicate a significant increase in the rms value of the turbulent component due to the “crossing trajectories” effect.     

A HEAT TRANSFER CORRELATION FOR VISCOELASTIC TURBULENT PIPE FLOWS

A modified version of Kale's heat transfer correlation for viscoelastic turbulent pipe flows in terms of drag reduction ratio and Weissenberg number is presented. The proposed correlation is validated with experimental data of Kwack and this study for Separan AP-273 and Polyox WSR-301 with concentrations ranging from 10 to 1000 ppm in thermally fully developed flow in pipes with diameters of 1·11 and 1·88 cm I.D. under constant wall heat flux. The agreement between the experimental data and the predictions is within a maximum deviation of 30%.     

A HEAT TRANSFER CORRELATION FOR VISCOELASTIC TURBULENT PIPE FLOWS

A modified version of Kale's heat transfer correlation for viscoelastic turbulent pipe flows in terms of drag reduction ratio and Weissenberg number is presented. The proposed correlation is validated with experimental data of Kwack and this study for Separan AP-273 and Polyox WSR-301 with concentrations ranging from 10 to 1000 ppm in thermally fully developed flow in pipes with diameters of 1·11 and 1·88 cm I.D. under constant wall heat flux. The agreement between the experimental data and the predictions is within a maximum deviation of 30%.     

FCC细颗粒湍流流化床流体力学性能研究

ＦＣＣ细颗粒湍流流化床流体力学性能研究李俊，张蕴璧，闫遂宁（西安石油学院，西安７１００６１）（西北大学）（洛阳石化公司）关键词：流化床，湍流，气泡，空隙率１前言湍流流化床有着广泛的工业背景。湍流流化床反应器存在着物质空间分布的不均匀现象，这种分布对湍...     

EXPERIMENTAL STUDIES ON HEAT TRANSFER AND FRICTION FACTOR CHARACTERISTICS OF TURBULENT FLOW THROUGH A CIRCULAR TUBE FITTED WITH RIGHT AND LEFT HELICAL SCREW-TAPE INSERTS

Experimental investigation on heat transfer and friction factor characteristics of a circular tube fitted with right-left helical screw inserts of equal and unequal length of different twist ratios is presented. The experimental data obtained were compared with those obtained from plain tube published data. The heat transfer enhancement for right-left helical screw inserts is higher than that for straight helical twist for a given twist ratio. The effect of right-left twist length on heat transfer augmentation is presented. The empirical relations for Nusselt number, friction factor relating Reynolds number, twist ratio, and right-left twist distance were formed and found to fit the experimental data within 10% and 20% for Nusselt number and friction factor respectively. Performance evaluation analysis was made, and the performance ratio of more than one was obtained, indicating that the proposed twist inserts can be used effectively for heat transfer augmentation without any loss in pumping power.     

STOCHASTIC MODELING AND ANALYSIS OF A TURBULENT FLOW SYSTEM

A stochastic model is developed to describe the axial movement of an element or particle in a turbulent flow system, where diffusion or local transition is not the major mechanism dictating particle motion. The model is a generalization of the diffusion equation for particle movement and includes both diffusion and random displacements. From this model, one can determine the residence time distribution and estimate the parameters characterizing the flow system.     

EVALUATION OF LAGRANGIAN PARTICLE DISPERSION MODELS IN TURBULENT FLOWS

This work evaluates the performance of Lagrangian turbulent particle dispersion models based on the Langevin equation. A family of Langevin models, extensively reported in the open literature, decompose the fluctuating fluid velocity seen by the particle in two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, i.e., the closure is at the level of the fluid velocity seen by the particle. We will call those models generically the “standard model.” On the other hand, the model proposed by Minier and Peirano (2001) is considered; this approach is based on the probability density function (PDF) and performs the closure at the level of the acceleration of the fluid seen by the particle. The formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping simple the mathematical manipulation of the stochastic model, avoiding some pitfalls, and simplifying the derivation of macroscopic relations. The performance of the previous dispersion models is evaluated in the configurations of grid-generated turbulence (Snyder and Lumley, 1971; Wells and Stock, 1983), simple shear flow (Hyland et al., 1999), and confined axisymmetric jet flow laden with solids (Hishida and Maeda, 1987).     

TURBULENT FLOW IN A PIPE WITH INTERMITTENT ROUGH PATCHES: AN ANALOGUE OF ANNULAR TWO-PHASE FLOW

The response of turbulent pipe flow to sudden changes in wall roughness and flow cross-sectional area has been studied experimentally and numerically. Changes typical of those encountered by the gas phase in annular gas-liquid flow have been considered. The results show that the flow field and the pressure field can be significantly distorted at these transitions. Good agreement has been obtained between the measured results and those calculated using the Harwell-FLOW3D computational fluid dynamics (CFD) code.     

从系统工程视角试论基于基团贡献法的树脂基体的分子设计

从系统工程的观点,提出了基于基团贡献法的树脂基体的计算机辅助分子设计的框架轮廓,以图促进潜在地作为传统树脂基体研发方法的有效替代或者至少是有益的补充的树脂基体的计算机辅助分子设计方法的发展。     

MASS TRANSFER IN AC ELECTROLYSIS: EXTENSION OF A FILM MODEL TO TURBULENT FLOW ON A ROTATING HEMISPHERE

Turbulent mass transfer to a rotating hemisphere during AC electrolysis was examined with a film model. The analytical results for the limiting AC current density were compared to the experimental data obtained with sinusoidal, square and triangular wave AC. The limiting AC current density in turbulent flow was found to depend on both the Reynolds number as a dimensionless AC frequency K = (ω/Ω)Sc^1/3 The prediction by the film model agreed with the experimental data to within ±15%. For a given root-mean-square of applied AC, the periodic concentration overpotential decreased in the order of quare, sinusoidal, and triangular AC. The phase shift between the applied AC and the concentration overpotential wave decreased with increasing Reynolds number in turbulent flow.     

MASS TRANSFER IN AC ELECTROLYSIS: EXTENSION OF A FILM MODEL TO TURBULENT FLOW ON A ROTATING HEMISPHERE

Turbulent mass transfer to a rotating hemisphere during AC electrolysis was examined with a film model. The analytical results for the limiting AC current density were compared to the experimental data obtained with sinusoidal, square and triangular wave AC. The limiting AC current density in turbulent flow was found to depend on both the Reynolds number as a dimensionless AC frequency K = (ω/Ω)Sc^1/3. The prediction by the film model agreed with the experimental data to within ±15%. For a given root-mean-square of applied AC, the periodic concentration overpotential decreased in the order of quare, sinusoidal, and triangular AC. The phase shift between the applied AC and the concentration overpotential wave decreased with increasing Reynolds number in turbulent flow.     

MASS TRANSFER IN AC ELECTROLYSIS: EXTENSION OF A FILM MODEL TO TURBULENT FLOW ON A ROTATING HEMISPHERE

Turbulent mass transfer to a rotating hemisphere during AC electrolysis was examined with a film model. The analytical results for the limiting AC current density were compared to the experimental data obtained with sinusoidal, square and triangular wave AC. The limiting AC current density in turbulent flow was found to depend on both the Reynolds number as a dimensionless AC frequency K = (ω/Ω)Sc^1/3 The prediction by the film model agreed with the experimental data to within ±15%. For a given root-mean-square of applied AC, the periodic concentration overpotential decreased in the order of quare, sinusoidal, and triangular AC. The phase shift between the applied AC and the concentration overpotential wave decreased with increasing Reynolds number in turbulent flow.     

离子交换膜扩散系数的测定方法评述

本文叙述了电解质通过离子交换的扩散系数，离子的相互扩散系数及自扩散系数的测定方法，原理，推导了有关公式，并对有些方法作了评述和实验上的比较。     

A METHOD OF SKIN FRICTION DETERMINATION OF A CIRCULAR CYLINDER IN A WATER FLOW FIELD

Using a partially-heated cylinder with a thin heat transfer sensor, it is clarified that the skin friction coefficient of a cylinder in water can be calculated by the Brown's equation, when the profile of its pressure coefficient has been measured. It is also revealed that the separation angles of the boundary layer on the cylinder surface can be determined by the skin friction profiles. These results are ascertained to be reliable by a flow visualization method.     

FULLY DEVELOPED TURBULENT FLOW AND HEAT TRANSFER IN A SQUARE DUCT WITH TWO ROUGHENED FACING WALLS

An experimental and analytical study was conducted on a fully developed turbulent flow in a square duct, two opposite walls of which had been roughened. The flow was measured by means of a hot-wire anemometer. The calculation was performed with the k model and with the k and e model coupled to the algebraic stress model developed by Launder and Ying. The results of the calculation are compared with the measurements. In this duct, a result hitherto unobserved became apparent: namely, there were four relatively large longitudinal vortices. A prediction of heat transfer was also performed under conditions of a constant wall-temperature and a calculated flow field.     

混凝土中氯离子二维扩散分析的边界元法

混凝土二维扩散分析的有限元法等常用数值法通常需要在空间域和时间域中同时采取细密的离散网格,计算量大.针对混凝土中氯离子二维扩散问题,提出了计算长度的概念及其计算表达式,首次建立了相应的边界元计算方法,确定了时间域离散的步长.通过该计算模型研究了混凝土结构的拐角等几何形状复杂位置的氯离子分布规律.由于边界元法可以将二维问题简化为一维离散问题,而且该计算模型在时间域内的离散网格非常稀疏,因此,相对于其他数值方法,该方法计算量很小,算例分析验证了该方法具有很高的计算精度和计算效率.同时,对角点等位置的氯离子浓度的计算结果表明,二维方法能够更准确地反映氯离子在混凝土结构中的扩散和积聚规律.