液体温度对空泡生长和溃灭过程的影响

采用光偏转测试系统研究了不同温度纯净水中激光空泡脉动过程,通过实验获得了激光空泡在靶表面膨胀和收缩全过程,确定了空泡的最大、最小泡半径、脉动周期和泡壁运动速度。实验采用0℃到70℃的纯净水,测量了空泡的泡半径和脉动周期等特征参量变化情况。实验结果表明,液体温度是影响空泡脉动的一个非常重要的因素,随着液体温度的增加空泡的最大泡半径和溃灭周期均呈增加趋势。给出了相应的理论解释。     

基于行为金融理论的非理性投机泡沫模型

为了从投资者非理性的角度揭示资产泡沫的生成机理,为股市泡沫监管提供更有效的工具,本文在基于行为金融理论的价值函数基础上,对噪音投资者模型进行改进,从利空和利多两个方面考查投资者行为因素的影响,从而构造出新的非理性投资泡沫模型,并利用我国股市数据对模型进行实证研究.结果证明,该模型更切合事实的非理性投机泡沫的发展过程.     

Cavitation characteristics of pit structure in ultrasonic field

Bubble collecting, bubble holding and micro-bubble ejecting characteristics of pit structure and the influence of cavitation bubble on the development of erosion pit are investigated by means of high-speed photography experiments. Pits tend to collect and hold wandering cavitation bubbles. The air holding phenomenon of pits can be a destination of the incubation period in the process of cavitation erosion. The holding bubble tends to eject micro-bubbles from the top of holding cavitation bubble, making the pit a source of nuclei. With bubbles being held in pits, the diameters of pits increase rapidly. But in the given experiment condition, there is a specific stable value beyond which the diameter of pits will not increase. This characteristic will be helpful in understanding and predicting the cavitation erosion process. Supported by the National Basic Research Program of China (“973” Program) (Grant No. 2007CB714105) and the National Natural Science Foundation of China (Grant No. 50539060)     

沸腾两相流动压力波动信号的特性

研究了竖直管内沸腾两相流动时压力波动信号的特性,对压力波动时间序列进行了标准偏差分析、功率谱密度函数分析、分维数分析、相关维分析及Kolmogorov熵分析,考察了热流密度对压力波动的影响规律.结果表明沸腾两相流动具有非线性混沌特性,且热流密度对各特征参数有不同影响.     

HYDRODYNAMIC STUDIES IN FISCHER-TROPSCH DERIVED WAXES IN A BUBBLE COLUMN

Gas hold-up and Sauter mean bubble diameter measurements were made in a 0.051 m diameter by 3 m long glass bubble column in the system, nitrogen-molten wax, with three different waxes (paraffin wax FT-300, Sasol's Arge wax and Mobil's reactor wax). Paraffin wax has a tendency to foam and gas hold-up is a strong function of gas distributor type, temperature and start-up procedure, whereas the reactor waxes do not foam and are much less affected by these variables, In experiments at 265°C with a 1.85 mm single hole orifice plate distributor the gas hold-ups were nearly the same for all three waxes. However, significant differences in Sauter mean bubble diameters were obtained in experiments with different waxes; FT-300 wax produced the smallest Sauter mean bubble diameters whereas Mobil's reactor wax produced the largest bubbles. Addition of 1-octadecanol and octadecanoic acid (up to 10wt%) to the FT-300 paraffin wax caused an increase in gas hold-up and a delay in the foam break-up in runs at 265°C with the 1.85 mm orifice plate distributor.     

Prediction of dispersed phase holdup in a modified multi‐stage bubble column scrubber

This paper reports on the experimental investigation carried out to evaluate fractional dispersed phase holdup for a gas‐liquid mixture in a modified multi‐stage bubble column (with contraction and expansion disks), which has been conceived, designed and fabricated as a wet scrubber for control of air pollution; in addition it has versatile use as a gas‐liquid contactor in chemical process industries. A correlation developed for predicting fractional dispersed phase holdup has been found to be encouraging and highly significant from statistical analysis.     

Chaotic forecasting of time series of heat-transfer coefficient for an evaporator with a two-phase flow

The time series of heat-transfer film coefficient for an evaporator with a vapor-liquid two-phase boiling flow were forecasted by the chaotic prediction or the local nonlinear short-term prediction. The forecasting method was based on the phase space reconstruction theory and a mathematic model in the form of datum driving had been developed to carry out the prediction. The signals of heat-transfer film coefficients predicted by this method were compared with those obtained from the experimental measurements. Different from the previous work, the comparisons in this work were done both from the point of view of the time trajectory and from the point of view of macroscopic or general characters. Besides the time-averaged statistics characteristics, such as the average value, average deviation and standard deviation, the power spectrum, phase plane map and chaotic invariants including the correlation dimension and Kolmogorov entropy had been calculated and been compared for the time series obtained both from the experimental measurement and from the forecast. The comparison for each parameter between the value calculated from the time series measured and that estimated from the time series forecasted by the chaotic forecast method shows satisfactory agreement. The limited length in time with an accuracy prediction indicates that the system is chaotic. The agreement of the comparison of the general parameter indicates that the chaotic prediction is effective for the estimations of the heat transfer characteristics of the two-phase flow boiling system and that the chaotic prediction method may be a potential tool for the effective thermo-fluid control for such evaporators.     

液相中气泡上升行为与界面传质:实验研究与数值计算

在工业生产过程中，气泡在液相中的上升行为及气液界面的传质行为极为常见。本文针对不同条件下气泡上升过程的实验研究方法以及数值计算方法进行了总结。从实验与数值计算的角度，综述了单气泡上升过程的影响因素、多气泡上升过程聚并与破裂的现象和机理以及工业装置中气液两相流型和气泡特性，并对传质模型进行了归纳，主要关注了气侧-界面传质模型的研究现状。综述结果表明：当前对于单气泡上升行为的研究较为充分，而对于多气泡的行为机理的研究尚需深入。此外，受到研究手段的限制，进行气侧-界面传质模型研究具有一定挑战性。针对当前的相关研究进展和存在的问题，对今后气泡上升行为和传质行为的研究提出以下建议，即开展气泡聚并与破裂可控性研究，强化对气侧-界面传质过程的研究，包括泡内流体行为可视化研究和相关传质模型的建立。     

Trajectory Simulation for Underwater Vehicle with Power-Lunched

The motion of combustion gas bubble produced by underwater ignition was developed based on Rayleigh-Plesset equation. Combining the bubble motion equation with the underwater launched vehicle motion equation in the longitudinal plane, a trajectory simulation model with power-launched was established. The hydrodynamic characteristics of underwater ignition at different depths and the trajectory analysis of the underwater vehicle with power-launched were given by simulation. The simulation results have a good agreement with experimental results, and show that the thrust peak caused by underwater ignition and the stable thrust both decrease slightly with the increase of the water depth, and the thrust peak will decline obviously by enlarging the initial radius of gas bubble; the thrust peak generated at the instant of ignition and the low-frequency oscillation of the stable thrust have no significant influence on the trajectory of underwater vehicle.     

Numerical simulation and optimization of the cylinder head water jacket based on the two-phase flow boiling heat transfer

Boiling heat transfer and the controllability of the thermal load of the cylinder head were studied. The thermodynamic phase change characteristics of the cylinder head coolant were considered and the mass, momentum and energy transfers between two phases were calculated with the interface transfer sub-models by using the computational fluid dynamics software CFX. Results showed that compared with the single-phase flow without considering the boiling heat transfer, the sub-cooled boiling heat transfer of the cylinder head was greatly increased. According to the results of the numerical simulation, an optimized structure of the water jacket was proposed. Finally, temperature and velocity of coolant, diameter of flow passage and mean bubble diameter that influences sub-cooled boiling were studied using the orthogonal experiment method.