纯工质池内核沸腾关联式的评价

对池核沸腾换热关联式的研究是一个重要方领域。由于影响沸腾换热的因素比较多,在总结关联式时不能将所有影响因素全部包括。因此现有的关联式的适用范围和精度都还有待于进一步提高。收集了国内外公开发表或现场经常应用的池内沸腾换热系数计算公式。通过对其分析与比较,阐明了公式的适用范围,为准确估算不同工质的池内沸腾换热系数提供了依据。     

高压过冷池沸腾换热机理的研究

目前还没有一种被广泛承认的理论能够解释高压过冷池沸腾换热,其机理尚不明确。为了揭示高压池内过冷核沸腾的物理传热机理,并获得气泡脱离频率与活化穴半径的函数关系,根据池内过冷核沸腾加热表面活化穴的分布,在统计方法的基础上,提出了高压池内过冷核沸腾的一个数学模型。从该模型中发现,池内过冷核沸腾热流密度是壁面过热度、液体过冷度、活化穴尺寸、流体的接触角以及流体物理特性的函数。对不同的过冷度,将模型预测的结果与实验数据进行了比较,两者吻合得极好,从而证明了数学模型的可靠性。该解析模型更深刻地揭示了过冷池沸腾换热的物理机理,且没有增加新的经验常数。     

毛细微槽内的相变传热的实验研究

本文对矩形毛细微槽竖直板的相变传热特性进行了实验研究。结果表明毛细微槽对相变换热具有很大的促进作用。当壁面过热度较小时,相变换热形式主要是三相接触线附近的蒸发换热机制。而当过热度较大时,微槽内发生剧烈的沸腾。微槽内相变换热的临界热负荷有两种产生机理:其一是当微槽长度较大时微槽内由于流动阻力而产生的液体输运临界;另一机理是当微槽长度较小时的池内沸腾临界现象,亦即由动态微液层模型决定的临界机理。实验还得到了微槽强化传热的最佳优化尺寸。     

自然循环型气液固三相流载气蒸发传热的实验研究

符号表Cs固体颗粒在液体中的含量vol．％dp固体颗粒直径mmde实验段当量直径mmh表面传热系数kw／m2Kk液体导热率W／mKq热通量kw／m2r液体汽化潜热kJ／kgTw加热壁面温度℃ug载气表现速度mm／sul循环液速m／sρg载气的密度kg／m3ρl液体的密度kg／m3ρs固体颗粒的密度kg／m3μg气相粘度mPa·sμl液相粘度mPa·sBo沸腾准数Nu努塞尔准数Reg载气雷诺数Rel液体雷诺数沸腾与蒸发装置内换热壁面上的结垢与结疤是降低换热效率的重要因素之一。换热装置的防垢抗垢一直受到重视。近年来，一些研究者将固体颗粒引入换热器的加热管内，形成流化床换热…     

微槽内二元混合液体的流动沸腾

1引言微型结构由于其巨大的应用潜力，作为热控制和冷却的有效手段已被引入电子集成电路、生物医学、航天、高效紧凑式与微型换热器、材料加工等现代高新技术领域。由于相交换热能传递更多的热量，微结构中的流动沸腾受到了日益重视。但微通道中流体流动和换热的特性当然与所用工质有关。微通道内液体混合物的流动沸腾至今极少见到公开报道［‘］。彭和王等人l‘－‘］报道了对微通道和微槽结构内单组元液体流动沸腾的研究，发现起始沸腾点所需壁面过热度比常规尺度槽道内的低得多，没有明显的部分核沸腾现象，同时发现微槽尺寸对流动沸腾的…     

10－6—10－4m2/s黏度液体中靶受力学作用的测试与分析

通过自行研制的光纤传感器对不同黏度液体中材料靶后的力学作用进行研究，获得了液体黏度变化对等离子体烧蚀力、射流冲击力及空泡生存周期的影响. 实验结果表明：液体黏度相同时，靶材所受冲击力幅值随作用激光能量的增加单调上升；液体黏度增加时，靶材所受的冲击力减小，靶材的空化空蚀程度亦减小；受液体黏度增大的影响，空泡膨胀或收缩过程减缓，相应的生存周期也增大. 此外，对空泡溃灭周期公式进行修正, 结果表明修正后的理论估算值与实验值的一致性较好.     

机械加工多孔层在大气压和高于大气压时的沸腾换热

1引言在过去的二十年中，已研制出诸如HighFI。、Thermoexcel－E、Ge、－T、CIT等多种高性能强化沸腾换热结构［‘－’］，其中ThermoexcelE型结构是机械加工多孔层中有代表性的一种，并进行了较多研究＊‘］。但迄今为止，研究工作多限于一个大气压时的沸腾工况［‘，’］，而较少涉及非大气压时的情形。本文对一种ThermoexcelE型机械加工多孔层在大气压和高于大气压时的沸腾传热进行了实验，提出了简化物理模型，进行了流动与传热分析，综合实验数据，建立了相应的传热关联式。2实验研究实验装置参见文献＊。多孔层基体为厚壁紫铜管…     

过冷液体沿水平板受迫湍流时的膜沸腾传热

本文在前文分析的基础上,提出过冷液体沿水平板受迫湍流时膜沸腾传热的物理模型,建立起相应的数学模拟方法,对轸高流速和过冷度的平板湍流膜沸腾传热作了理论分析,并根据实验数据得到了可供实际工程应用的半经验传热计算式。     

圆形液体浸没射流冲击核沸腾传热的实验研究

本文严格按照实验程序，系统地研究了核沸腾传热受射流速度大小、液体流动方向、喷嘴直径和液体过冷度等因素的影响。实验结果表明：核沸腾传热曲线随过冷度增加而向左移动，与其它因素无关。池核沸腾和冲击核沸腾曲线可用同一关联式表达。对高速射流冲击驻点的核沸腾曲线及其过冷度进行了修正，使前者向左移动，而后者增加。     

纳米颗粒悬浮液池内泡状沸腾的实验研究

本文对纳米颗粒悬浮液在平壁面上池内沸腾进行了实验研究。实验用的纳米粒子为26 nm的铁粉和13 nm的三氧化二铝纳米粉末,基液为去离子水。分别配成体积浓度为0．1％, 1％和2％的悬浮液。实验结果表明,纳米悬浮颗粒对液体沸腾换热过程的影响会随着纳米颗粒性质,颗粒浓度及热流密度大小的不同而出现不同的效果;加入纳米颗粒后, 对基液沸腾换热的影响存在着两个相反的作用机制,它们分别为:纳米颗粒增强了液体内部的热量迁移能力(热物性的影响)和改变了加热面的表面结构特性(加热面特性的影响)。     

滞止区内过冷液体喷流沸腾的临界热流密度

本文对高温平板滞止区内三种过冷液体的圆形喷流冲击沸腾的临界热流密度进行了系统的稳态实验研究。考察了过冷度、流速、喷流直径等流动条件对喷流沸腾临界热流密度的影响。建立了预示液体临界热流密度的半经验型方程。     

大空间和毛细管内液氮池沸腾传热的实验研究

文中以直径50μm,长20mm的磷青铜丝作为加热丝和测温元件,采用控制热流密度的方式测量了0°,30°,60°和90°倾角下大空间和玻璃毛细管内液氮的沸腾曲线,分析了毛细管对核态沸腾传热的影响以及管径和倾角对临界热流密度的综合影响。结果表明,在实验管径内,毛细管对于核态沸腾传热有明显的强化作用;并存在一最佳管径,可在30°~90°倾角范围内获得最大的CHF值,并且其值高于大空间时的CHF。     

NUCLEATE POOL BOILING UNDER DC ELECTRIC FIELD

This article deals with an experimental study of the influence of a DC uniform electric field on the nucleate boiling heat transfer. Electrohydrodynamic (EHD) effects on heat transfer coefficients for dielectric liquids are quantitatively investigated by performing experiments on various liquids with different properties. In these experiments, n-pentane, R-113, and R-123 are used as working fluids and the boiling phenomenon takes place on a horizontal plane copper surface. The experimental results have shown: (1) a threefold increase of nucleate pool boiling heat transfer coefficients, (2) a threefold increase of the critical heat flux (CHF), and (3) the disappearance of the hysteresis phenomenon. For nucleate pool boiling and CHF regimes, heat transfer laws based on dimensionless numbers are proposed. The results obtained by the proposed EHD model are in good agreement with the experimental results.     

FC-72在浸泡于液池中的微小圆管内的沸腾传热

本文对浸泡于FC-72液池中的两个微小圆管进行了沸腾实验研究,得到了沸腾曲线和传热系数,并用DV摄像机拍摄到了圆管出口处的沸腾状况,研究了管道尺寸对沸腾传热特性的影响。实验结果显示,管道尺寸对沸腾传热特性有显著的影响。传热系数和CHF随着管道尺寸的缩小而减小.直径为1.10mm的圆管出口处在低热负荷加热时发生了汽泡阻塞,并导致了剧烈的沸腾滞后现象。     

AN EXPERIMENTAL INVESTIGATION OF POOL BOILING ON NARROW HORIZONTAL TUBES

Pool boiling characteristics on horizontal tubes with diameter lying between wires and industrial tubes have been investigated experimentally. Boiling experiments are carried out at near atmospheric pressures with water and R-123 as boiling liquids. The experimental results show quite a different boiling behavior compared to larger tubes or plates. The commonly used correlations are found to be ineffective over this range of diameters. A developing sliding bubble mechanism can be attributed to such behavior which shows a strong diameter effect. The heat transfer is found to increase with diameter which is contrary to that on industrial size tubes. Useful boiling data are presented in this range of diameters in which experimental data are scarce. The need for more investigations is stressed in view of emerging applications in this area.     

Design of tunable surface mode waveguide based on photonic crystal composite structure using organic liquid

With the method of replacing the surface layer of photonic crystal with tubes, a novel photonic crystal composite structure used as a tunable surface mode waveguide is designed. The tubes support tunable surface states. The tunable propagation capabilities of the structure are investigated by using the finite-difference time-domain. Simulation results show that the beam transmission distributions of the composite structure are sensitive to the frequency range of incident light and the surface morphology which can be modified by filling the tubes with different organic liquids. By adjusting the filler in tubes, the T-shaped, Y-shaped, and L-shaped propagations can be realized. The property can be applied to the tunable surface mode waveguide. Compared with a traditional single function photonic crystal waveguide, our designed structure not only has a small size, but also is a tunable device.     

Heat Transfer of Dilute Polyacrylamide Solutions in Flattened Tube Exchangers

Heat transfer studies of dilute viscoelastic liquids in four flattened tubes with 0.635 cm original diameter, about 173 cm long, and with aspect ratios ranging from 1.4 to 5.7 were conducted. Hot water was used as the heating medium, and dilute solutions of polyacrylamide in water and in water mixtures were used as the viscoelastic solutions. Flattening the tubes could increase heat transfer by 101%, while secondary flow could further increase heat transfer coefficient by 75% at an aspect ratio of 1.6. Greater polyacrylamide concentrations increased heat transfer performance marginally. Viscosity does not influence the formation of secondary flow.     

Application of Autoradiography for the Study of Penetration of Aggressive Liquids into Plastics under the Stress

Aggressive liquids are often stored and transported in plastic vessel, tanks or tubes in chemical industry. Such plastic material is exposed to both mechanical and chemical stress. This stress causes penetration of liquids into plastics. Penetration of some liquids was studied by means of autoradiography. A special device was developed for the study of penetration of aggressive liquids into plastics under stress. This device and results of measurements of such penetration are described. It is shown that penetration occurs through microsplits in the studied system.

Aggressive Flüssigkeiten werden häufig in Behältern, Tanks oder Röhren aus plasten gelagert oder transportiert. Solche Plastwerkstoffe unterliegen dabei sowohl mechanischen als auch chemischen Angriffen, die ein Durchdringen der Flüssigkeiten verursachen können. Die Durchdringung einiger solcher Flüssigkeiten wurde mittels Autoradiographie untersucht. Dazu wurde eine besondere Anordnung entwickelt, um solche Eindringvorgänge von aggressiven Flüssigkeiten unlersuchen zu können. Sowohl die Versuchsanordnung als auch einige Meβergebnisse werden beschrieben. So wurde festgestellt, daβ die Durchdringung in den untersuchten Systemen in Mikrospalten vor sich geht.     

Measurement of viscosity and shear wave velocity of a liquid or slurry for on-line process control

An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid-fluid interface, has been developed by the staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear wave reflection at the solid-fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were conducted for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick-similar to pipe wall thickness) we increased the sensitivity of the measurement. At the sixth echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silicone oils). The results show that, for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silicone oils are very small and range from 315 to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated. These results show that, depending on the fluid characteristics, either the viscosity or the shear wave velocity can be used for process control. There are several novel features of this sensor: (1) The sensor can be mounted as part of the wall of a pipeline or tank or submerged in a tank. (2) The sensor is very compact and can be located within the process stream. (3) The sensor can interrogate and characterize very attenuative liquids or slurries because the sensor operation depends upon reflection at the interface between the solid and the fluid, rather than on transmission through a liquid. (4) The sensor performance is not affected by fluid flow rate, entrained air, or vibration.     

Real-Time Laser Ultrasound Tomography for Profilometry of Solids

We studied the possibility of applying laser ultrasound tomography for profilometry of solids. The proposed approach provides high spatial resolution and efficiency, as well as profilometry of contaminated objects or objects submerged in liquids. The algorithms for the construction of tomograms and recognition of the profiles of studied objects using the parallel programming technology NDIVIA CUDA are proposed. A prototype of the real-time laser ultrasound profilometer was used to obtain the profiles of solid surfaces of revolution. The proposed method allows the real-time determination of the surface position for cylindrical objects with an approximation accuracy of up to 16 μm.