Numerical Simulation of the Marangoni Effect with Interphase Mass Transfer Between Two Planar Liquid Layers

The Marangoni effect induced by mass transfer at the interface between two immiscible liquids displays important influence on laboratory and industrial operation of solvent extraction. A systematic numerical study of the two-dimensional Marangoni effect in a two liquid layer system was conducted. The linear relationship of the inter- facial tension versus the solute concentration was incorporated into a mathematical model accounting for liquid flow and mass transfer in both phases. The typical cases analyzed by Sternling ＆ Scriven （AIChE J., 1959） using the linear instability theory were simulated bv the finite difference method and good agreement between the theory and the numerical simulation was observed. The simulation suggests that the Marangoni convection needs certain time to develop sufficiently in strength and scale to enhance the interphase mass transfer, the Marangoni effect is dynamic and transient, and remains at some stabilized level as long as the mass transfer driving force is kept con- stant. When certain level of shear is imposed at the interface as in most cases of practical significance, the Maran- goni effect is suppressed slightly but progressively as the shear is increased gradually. The present two-dimensional simulation of the Marangoni effect provides some insight into the underlying mechanism and also the basis for further theoretical study of the three-dimensional Marangoni effect in the real world and in chemical engineering applications.

Comparison of heat transfer performances of helix baffled heat exchangers with different baffle configurations

Numerical simulations were performed on flow and heat transfer performances of heat exchangers having six helical baffles of different baffle shapes and assembly configurations, i.e., two trisection baffle schemes, two quadrant baffle schemes, and two continuous helical baffle schemes. The temperature contour or the pressure contour and velocity contour plots with superimposed velocity vectors on meridian, transverse and unfolded concentric hexagonal slices are presented to obtain a full angular view. For the six helix baffled heat exchangers,the different patterns of the single vortex secondary flow and the shortcut leakage flow were depicted as well as the heat transfer properties were compared. The results show that the optimum scheme among the six configurations is a circumferential overlap trisection helix baffled heat exchanger with a baffle incline angle of 20°(20°TCO) scheme with an anti-shortcut baffle structure, which exhibits the second highest pressure dropΔpo, the highest overall heat transfer coefficient K, shell-side heat transfer coefficient hoand shell-side average comprehensive index ho/Δpo.

Numerical Study on Heat Transfer Enhancement for Use of Corrugated, Nodal and Horizontal Grain Tubes

With isopentane as working fluid, the heat transfer performances for corrugated, nodal and horizontal grain tubes are simulated. The structural parameters of the three kinds of tubes are compared with those of the plain tube. The numerical results using computational fluid dynamics are validated with theoretical values. For the corrugated, nodal and horizontal grain tubes, the heat transfer enhancements(HTEs) are 2.31—2.53, 1.18—1.86 and 1.02—1.31 times of those of the plain tube, respectively. However, the improved HTEs are at the expense of pressure losses. The drag coefficients are 6.10—7.09, 2.06—11.03 and 0.53—1.83 higher, respectively. From the viewpoint of comprehensive heat transfer factor, the corrugated tube is recommended for engineering applications, followed by the horizontal grain tube.

Numerical Prediction for Subcooled Boiling Flow of Liquid Nitrogen in a Vertical Tube with MUSIG Model

Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.

基于传质数学模型研究丹参-枳实复方中成分存在状态与纳滤分离机制

目的基于传质数学模型,探索丹参-枳实复方中成分存在状态与纳滤分离机制。方法以原儿茶醛、迷迭香酸、丹酚酸B、辛弗林为指标,进行单体成分溶液及丹参-枳实复方溶液纳滤分离,收集膜通量与指标成分截留率,基于传质模型中传质系数与溶质浓度的幂值相关性,以单一成分为参照,拟合复方溶液中成分存在状态,探讨纳滤分离机制。结果分离压力与膜通量呈正性相关,指标成分在单体溶液和复方溶液中传质系数与浓度幂值相关性高,回归系数均大于0.98,纳滤传质模型成立。通过单一成分传质特征构建复方溶液中成分状态解析模式,丹参-枳实复方溶液中指标成分以复合态存在的比例为原儿茶醛26.17%、迷迭香酸79.87%、丹酚酸B89.15%,辛弗林96.92%。结论构建了复方溶液的成分存在状态解析模式,阐明了丹参-枳实复方提取液纳滤分离机制,为中药成分分离精制提供技术支撑。

Characteristics from a hydrodynamic model of a trapezoidal artificial reef

Flume experiments and numerical simulation were conducted to characterize the hydrodynamics of a trapezoid artificial reef.Measurements in particle image velocimetry were conducted to observe the formation of upwelling and vortices;and forces for the reef model were measured by load cell.The results of flume experiments agree well with the numerical data.In addition,the flow structure around a reef combining trapezoidal and cubic blocks was simulated numerically under two deployment schemes,showing a more complicated flow structure than that of a stand-alone reef.Relationship between drag coefficient and Reynolds number suggest that the degree of turbulence can be assessed from the value of drag coefficient downstream from the reef.The role of the reef in water flow is to reduce flow velocity and generate turbulence.

Numerical study on freezing-thawing phase change heat transfer in biological tissue embedded with two cryoprobes

A two-dimensional model for freezing and thawing phase change heat transfer in biological tissue embedded with two cryoprobes was established.In this model,the blood vessels were considered as tree-like branched fractal network,and the effective flow rate and effective thermal conductivity of blood were obtained by fractal method.The temperature distribution and ice crystal growth process in biological tissue embedded with two cryoprobes during freezing-thawing process were numerically simulated.The results show that the growth velocity of ice crystal in freezing process from 200 to 400 s is more rapid than that from 400 to 600 s. Thawing process of frozen tissue occurs in the regions around cryoprobes tips and tissue boundary simultaneously,and the phase interfaces are close to each other until ice crystal melts completely.The distance of two cryoprobes has a more profound effect on the temperature distribution in freezing process at 400 s than at 800 s.

Multi-sensor Hybrid Fusion Algorithm Based on Adaptive Square-root Cubature Kalman Filter

In the normal operation condition, a conventional square-root cubature Kalman filter （SRCKF） gives sufficiently good estimation results. However, if the measurements are not reliable, the SRCKF may give inaccurate results and diverges by time. This study introduces an adaptive SRCKF algorithm with the filter gain correction for the case of measurement malfunctions. By proposing a switching criterion, an optimal filter is selected from the adaptive and conventional SRCKF according to the measurement quality. A subsystem soft fault detection algorithm is built with the filter residual. Utilizing a clear subsystem fault coefficient, the faulty subsystem is isolated as a result of the system reconstruction. In order to improve the performance of the multi-sensor system, a hybrid fusion algorithm is presented based on the adaptive SRCKF. The state and error covariance matrix are also predicted by the priori fusion estimates, and are updated by the predicted and estimated information of subsystems. The proposed algorithms were applied to the vessel dynamic positioning system simulation. They were compared with normal SRCKF and local estimation weighted fusion algorithm. The simulation results show that the presented adaptive SRCKF improves the robustness of subsystem filtering, and the hybrid fusion algorithm has the better performance. The simulation verifies the effectiveness of the proposed algorithms.

Numerical Investigation of Heat Transfer Coefficient in a Low Speed 1.5-Stage Turbine

The paper numerically investigated the heat transfer coefficients over the rotating blades in a 1.5-stage turbine. The hexahedral structured grids and k-ε turbulence model were applied in the simulation. A film hole with diameter of 0.004 m, angled 36°and 28° tangentially to the suction side and pressure side in streamwise respectively, was set in the middle span of the rotor blade. Simulations are done at three different rotating numbers of 0.0239, 0.0265 and 0.0280 with the blowing ratio varying from 0.5 to 2.0. The effects of mainstream Reynolds number and density ratio are also compared. Results show that increasing blowing ratio can increase the heat transfer coefficient ratio on the pressure side, but the rule is parabola on the suction side. Besides, increasing rotating number and Reynolds number is positive while increasing density ratio is negative to the heat transfer on both the pressure side and the suction side.

A Simulation for the Piston Effect in Supercritical Carbon Dioxide with the Non-flow Model

A simulation for piston effect in supercritical carbon dioxide by employing a simple model is conducted. In the first place, the thermal properties of carbon dioxide near its liquid-vapor critical point are discussed. It is calcu- lated that the heat capacity ratio and isobaric expansion coefficient of supercritical fluids are extremely high. Furthermore, the simulation for piston effect in supereritical carbon dioxide between two infinite vertical walls is presented. The numerical results prove that piston effect has a much faster speed of heat transfer than thermal conduction under mierogravity conditions. Moreover, the piston effect turns out to be stronger when closer to the critical point.