Modified Verlet Method Involving Second-Order Mid-Point Rule Applied to Balls Falling in One-Dimensional Potentials

A modified Verlet method which involves a kind of mid-point rule is constructed and applied to the one-dimensional motion of elastic balls of finite size, falling under constant gravity in space and then under the chemical potential in the interface region of phase separation within a two-liquid film. When applied to the simulation of two balls falling under constant gravity in space, the new method is found to be computationally superior to the usual Verlet method and to Runge–Kutta methods, as it allows a larger time step for comparable accuracy. The main purpose of this paper is to develop an efficient numerical method to simulate balls in the interface region of phase separation within the two-liquid film, where the ball motion is coupled with two-phase flow. The two-phase flow in the film is described via shallow water equations, using an invariant finite difference scheme that accurately resolves the interface region. A larger time step in computing the ball motion, more comparable with the time step in computing the two-phase flow, is a significant advantage. The computational efficiency of the new method in the coupled problem is demonstrated for the case of four elastic balls in the two-liquid film.     

Experimental observations of flow boiling of liquid helium I in vertical channels

Results are reported of the flow structure and pressure drop of helium 1 flowing upwards in a vertical heated circular glass tube. The experiments covered heat fluxes from 4.5 to 600 Wm^?2, mass fluxes from 2 to 12 kg m^?2 s^?1 and pressures between 1 and 1.2 atm. The use of a glass tube made it possible to study with both high speed and ordinary photography the changing flow regimes in evaporating helium. For the bubble flow regime the shape, size and drag coefficient of the observed bubbles are reported.Slip velocity, void fraction and pressure drop measurements are compared with generally accepted two-phase flow theories. A void fraction correlation for two-phase helium flow is proposed.     

板式升膜蒸发器蒸发换热特性的实验研究

升膜蒸发利用被蒸发溶液在受热沸腾汽化产生的蒸气带动料液上升,形成一个稳定的液膜,从而加快蒸发,提高了传热系数.针对蒸发器液位、换热温差、加热蒸气的流量等因素对板式升膜蒸发传热系数的影响进行了实验研究,实验结果表明随着蒸发器内液位的降低升膜蒸发传热系数明显提高,此外,换热温差、加热蒸气的流量等因素对升膜蒸发换热性能也有明...     

长喉颈文丘里管气液两相流弹状流机理研究

为了实现气液两相流相含率测量并得到相关模型,结合气液两相流研究现状,采用近红外光谱技术与高速摄影技术结合的手段,利用近红外系统布置于长喉颈文丘里管喉管位置的新装置,将弹状流相间流动特征与近红外测量系统接收光强信号特征相结合,提出了把弹状流分成泰勒气泡与尾部气泡两部分的简化模型,在数据处理时对近红外接收光强高频信号进行有效分组,建立了新的气液两相流弹状流相含率测量模型。从一定程度上解决了弹状流不同部位的两相交界面对近红外接收探头接收光强信号影响差异较大的问题。新型模型的测量效果较好,所得结果测量误差较小。     

板式膜反转降膜吸收器设计与性能研究

板式膜反转降膜吸收器是一种将板式降膜吸收和膜反转技术相结合而开发的新型吸收器,合理设计与掌握其吸收性能对今后这种吸收器的工程应用十分重要.为此,通过建立、求解板式膜反转降膜吸收过程的数学模型,确立了设计条件下最佳吸收器结构;对于所设计的板式膜反转吸收器进行了不同吸收压力、溶液流量、进口浓度、进口温度及冷却条件下传热传质性能的计算,并与竖板降膜吸收器进行了比较.     

Calculation of the wave parameters of two-phase,ascending, film flow by the methods of statistics

The use of statistical methods to investigate two-phase film flow in the mode of concurrent ascending flow is demonstrated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 2, pp. 309–313, February, 1980.     

The heat transfer performance of horizontal tube bundles in large falling film evaporators

The performance of the horizontal heat transfer tube bundles in falling film evaporators in large compression refrigeration systems was investigated with numerical simulation in this paper. Four types of tubes, including plain tubes, and enhanced surface tubes of Turbo-B, Turbo-BII and Turbo-EHP, were employed in the simulation. Some factors, such as tube kind, tube pass arrangement, dry patch area on tube surface, liquid refrigerant flow rate, and number of flooded tubes, were analyzed based on simulated results. In the study, the maldistribution of liquid refrigerant flow caused by the distributor apparatus was discussed, which severely affects the performance of falling film evaporators according to the simulation. Some calculated results were verified by the experiment. These discussions and results can be used to guide the design of falling film evaporators under realistic flow conditions.     

Analytical investigation of two different absorption modes: falling film and bubble types

The objectives of this paper are to analyze a combined heat and mass transfer for an ammonia–water absorption process, and to carry out the parametric analysis to evaluate the effects of important variables such as heat and mass transfer areas on the absorption rate for two different absorption modes — falling film and bubble modes. A plate heat exchanger with an offset strip fin (OSF) in the coolant side was used to design the falling film and the bubble absorber. It was found that the local absorption rate of the bubble mode was always higher than that of the falling film model leading to about 48.7% smaller size of the heat exchanger than the falling film mode. For the falling film absorption mode, mass transfer resistance was dominant in the liquid flow while both heat and mass transfer resistances were considerable in the vapor flow. For the bubble absorption mode, mass transfer resistance was dominant in the liquid flow while heat transfer resistance was dominant in the vapor region. Heat transfer coefficients had a more significant effect on the heat exchanger size (absorption rate) in the falling film mode than in the bubble mode, while mass transfer coefficients had a more significant effect in the bubble mode than in the falling film mode.     

Features of two-phase flow in a rectangular microchannel

A two-phase (liquid-gas) flow in a short horizontal slit channel of rectangular cross section with a height (thickness) of 200 μm has been experimentally studied using laser-induced fluorescence and schlieren photography methods, which allowed the pattern of flow in the channel to be monitored and its quantitative characteristics to be measured. It is established that a separate (stratified) flow regime can exist in the system. The two-phase flow in the given channel can exhibit features in the form of liquid drops and rivulets. A change in the height of the horizontal slit channel significantly influences the boundaries between different regimes.     

The safety of rock climbing protection devices under falling loads

Safe participation in the sport of rock climbing is dependent on using a range of equipment and using appropriate techniques. However, the level of safety achieved will depend on the specific equipment used, in terms of design, type, adequate load rating and condition, and also upon the climbing technique as this can significantly help to minimise any impact loads in the advent of a fall. In addressing these issues, this paper describes some mechanical tests which have been carried using a specially designed drop load rig in which falling weights have been applied to samples of climbing rope to establish impact loads. The load-time histories have been recorded and peak loads have been compared with those determined theoretically. In addition, some new and also used anchor nuts have been test loaded to failure and the different failure modes which resulted are described. Finally, the general design of climbing equipment is discussed.     

水平管降膜式蒸发器管间流动模式的研究

对应用于空气调节和制冷方面的水平管降膜式蒸发器原理进行简述，在分析设计水平管降膜式蒸发器时，需要考虑制冷剂在水平光管上流动模式。给出影响制冷剂在水平光管上流动模式的关键参数。     

制冷空调系统水平管降膜蒸发研究

在制冷剂面临严峻的环境保护控制要求的背景下,研究表明,降膜蒸发由于其较低的制冷剂充注量在制冷空调行业具有重大的应用潜力。本文主要从降膜蒸发管外液膜的流动模式和强化传热2个方面,对水平管降膜蒸发的国内外研究现状进行研究分析。分析表明,管外液膜存在滴状流、射（柱状）流和片状流等模式,而且强化传热须区分高低热流密度情况。为了进一步探究降膜蒸发的机制,从换热和可视化的角度开展强化管外降膜蒸发的特性实验研究。     

Effects of nonuniform heating and thermocapillarity in evaporating films falling down an inclined plate

Summary. The dynamics of a thin evaporating liquid film falling down an inclined plate is studied in the cases of both uniformly and nonuniformly heated plates. The film flow is influenced by gravity, mean surface tension, thermocapillary force and mass loss. The dynamics of the two-dimensional evaporating film is studied by the use of long-wavelength theory. Numerical solution of the evolution equation indicates that the evaporation has a strong stabilizing effect on the film instability and that a sequence of instability, stability and then instability of the falling film during its evaporation exists. The effect of nonuniform heating is dominant prior to film disappearance and it enforces film rupture. Due to the joint action of thermocapillarity and evaporating mass loss, the film evolution exhibits the formation of multi-hump structures, the downstream propagation of which is suppressed. When the nonuniformities in the imposed temperature differences are increased, large deformations of the liquid-vapor interface occur that lead to an enhancement of the heat transfer processes.     

Wave Structure of Liquid Films during the Transition to the Turbulent Flow Mode

Technical Physics Letters - The results of an experimental study of the waves on the surface of a vertically falling liquid film in the range of the Reynolds numbers of film flow 80 < Re...     

Flow regimes during condensation in superheated zone

Heat transfer experiments with flow visualization were performed with R134a in a smooth horizontal tube in order to verify that condensation occurs outside the two-phase region. The visualization performed for this work is unusual in that a diabatic visualization section was used, more closely approximating the behavior of the fluid in an actual condenser than typical adiabatic visualization experiments. In addition to the flow visualization, liquid film thickness measurements were taken and used to determine the cumulative latent heat transferred from the refrigerant. The measured film thicknesses and recorded videos confirm the presence of liquid in the bulk superheated region. Condensate appeared first as droplets and rivulets on the tube wall and then formed a thin film. The flow later passed through misty annular and wavy flow regimes as the refrigerant transitioned to the two-phase region.     

制冷用水平降膜式蒸发器研究进展

降膜式蒸发器目前在牛奶、制药、化工、海水淡化等行业取得了较为广泛的商业应用,它从上世纪90年代以后开始应用于制冷空调系统。目前针对制冷用水平降膜式蒸发器的研究目的主要是明确各个参数对蒸发器传热性能的影响以及他们之间的联系,由于降膜式蒸发器的独特结构和内部传热传质的复杂性,这些研究尚处于初步阶段。在介绍其工作原理的基础上,针对水平降膜式蒸发器,着重讨论了布液器的结构与高度、管束(包括管径、管排数、管道表面形状)、制冷剂(流型、流量)等参数对其性能的影响。由于经验关联式在实际应用中的巨大优势,还总结了前人提出的关联式及其适用的范围,文章将为制冷用降膜式蒸发器的进一步研究和应用提供参考。     

Liquid-phase mass transfer in high-pressure systems with a supercritical and a liquid phase

Liquid-phase diffusion coefficients and mass-transfer coefficients were measured in binary two-phase systems at high pressures. Both were determined from the rates of absorption of the gaseous component into the liquid. Diffusion coefficients were measured by observing unsteady-state diffusion into a sell) i infinite liquid phase and fitting transient counterdiffusion mass-flow rates to the visually determined change of the position of the interface between the liquid and the supercritical phase. Mass-transfer coefficients in the liquid phase were determined from the absorption rate of the gaseous component into a falling liquid film of known flow and physical properties. Experiments were performed with the binary systems carbon dioxide-oleic acid, carbon dioxide -methyl myristate, and carbon dioxide-methyl palmitate. Liquid-phase diffusion coefficients rise significantly with concentration as viscosity decreases. Temperature also has a strong effect on diffusivities. Experimental mass-transfer coefficients in nearly saturated liquids agree well with calculations for falling films with known properties, whereas far from equilibrium, Marangoni convection greatly enhances mass-transfer rates. Close to the critical point of the binary system at a given temperature, a sharp decline of the mass-transfer coefficient is observed.     

水平管式降膜蒸发器布液器的方案比较

介绍降膜蒸发器原理及其核心部件一一布液器,并通过流场模拟与理论分析,总结3种布液器方案的优缺点,为研发及生产提供参考。     

水平管外R404A降膜蒸发传热的实验研究

搭建了降膜蒸发实验台,研究了水平单管外的降膜蒸发传热特性。测试管为外径19mm、有效实验长度为2500mm的光滑管和强化管。实验采用R404A作为管外降膜蒸发工质,与管内热水进行换热。布液采用喷嘴喷淋的方式,通过21个喷口当量直径为2mm的喷嘴完成。分别在变饱和温度(0、5、10、15℃)、变热流密度(从8到30kW/m2)和变喷淋量(从0.07到0.11kg/(m·s)时进行实验,研究了降膜蒸发换热性能相应的变化情况,得到R404A的管外降膜蒸发换热的一些规律,这对降膜蒸发器的设计及应用具有一定的参考作用。     

微通道换热器两相流分布研究现状与展望

两相流进入微通道换热器容易出现分布不均匀的现象,显著降低微通道换热器的性能.本文对微通道换热器两相流分布的研究动态进行了归纳与分析,主要介绍了微通道换热器中两相流分布特性的影响因素、提升微通道换热器中两相流分布均匀性的技术方案、微通道换热器两相流分布特性的仿真研究及相分离技术在微通道换热器中的应用;论述了两相流在微通道...