基于MUSIG模型的竖直圆管内液氮过冷沸腾数值模拟研究(英文)

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.     

黏性液体中单个上升气泡的流体动力学行为(英文)

The rising behavior of single bubbles has been investigated in six systems with different viscosity and Morton number(Mo) from 3.21×10-11 to 163. Bubbles with maximum equivalent diameter of up to 16 mm were investigated. The bubble Reynolds number(Re) ranged from 0.02 to 1200 covering 3 regimes in which two func-tions are obtained relating the drag coefficient,CD,with Re and Mo. It has been found that in the high Reynolds number regime the drag coefficient increases until the Reynolds number of about 1200. The classic expression of Jamialahmadi(1994) is improved and extended to high viscosity liquids. A new relationship for the aspect ratio of deformed bubbles in terms of Re,the Etvs number and Mo,applicable to a wide range of system properties,espe-cially in high viscosity liquids,is also suggested.     

稳定性条件驱动的结构演化:探索气固和气液系统的内在相似性(英文)

As the core of the Energy-Minimization Multi-Scale(EMMS) approach,the so-called stability condi-tion has been proposed to reflect the compromise between different dominant mechanisms and believed to be in-dispensable for understanding the complex nature of gas-solid fluidization systems.This approach was recently ex-tended to the study of gas-liquid bubble columns.In this article,we try to analyze the intrinsic similarity between gas-solid and gas-liquid systems by using the EMMS approach.First,the model solution spaces for the two systems are depicted through a unified numerical solution strategy,so that we are able to find three structural hierarchies in the EMMS model for gas-solid systems.This may help to understand the roles of cluster diameter correlation and stability condition.Second,a common characteristic of gas-solid and gas-liquid systems can be found by comparing the model solutions for the two systems,albeit structural parameters and stability criteria are specific in each system:two local minima of the micro-scale energy dissipation emerges simultaneously in the solution space of structure parameters,reflecting the compromise of two different dominant mechanisms.They may share an equal value at a critical condition of operating conditions,and the global minimum may shift from one to the other when the oper-ating condition changes.As a result,structure parameters such as voidage or gas hold-up exhibit a jump change due to this shift,leading to dramatic structure variation and hence regime transition of these systems.This demonstrates that it is the stability condition that drives the structure variation and system evolution,which may be the intrinsic similarity of gas-solid and gas-liquid systems.     

柴油液滴内空化气泡的破碎研究(英文)

A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of fluids stabilize the cavitation bubble, while inertial force destabilizes the cavitation bubble. The droplet viscosity plays a dominant role on the stability of cavitation bubbles compared with that of air and bubble. Bubble–droplet radius ratio is a key factor to control the bubble stability, especially in the high radius ratio range. Internal hydrodynamic and surface tension forces are found to stabilize the cavitation bubble, while bubble stability has little relationship with the external hydrodynamic force. Inertia makes bubble breakup easily, however, the breakup time is only slightly changed when bubble growth speed reaches a certain value (50 m·s?1). In contrast, viscous force makes bubble hard to break. With the increasing initial bubble–droplet radius ratio, the bubble growth rate increases, the bubble breakup radius decreases, and the bubble breakup time becomes shorter.     

基于模型预测控制的部分分散控制系统设计(英文)

An expansion procedure to design partially decentralized controllers via model predictive control is proposed in this paper. Partially decentralized control is a control structure that lies between a fully decentralized structure and a fully centralized one, and has the advantage of achieving comparable performance as a fully centralized controller but with simpler structure. The proposed method follows the expansion method proposed in a previous paper where internal model control (IMC) was used to design controllers for non-square subsystems. The method requires computing the pseudo-inverse of a non-square matrix via pseudo-inverse factors. Instead, the proposed method uses dynamic matrix control (DMC) to design PID controllers for non-square subsystems without using additional factors. The effectiveness of the proposed method is demonstrated on several chemical examples. Simulation results show that the proposed method is simple and can achieve better performance.     

高气液化下分布器设计对结构化床层气液分布的影响(英文)

Experiments were carried out to investigate the liquid flow distribution at high gas/liquid ratios in a cold model monolith bed of a 0.048 m diameter with 62 cells per cm2.Three types of distributor for the liquid distribu-tion were used to evaluate their distribution performance.Local liquid saturation in individual channels was meas-ured using 16 single-point optical fiber probes mounted inside the channels.The results indicate that 1) The optical fiber probe technique can measure phase distribution in the monolith bed;2) Liquid saturation distribution along the radial direction of the monolith bed is not uniform and the extent of non-uniformity depends on the distributor de-sign and phase velocities;and 3) The tube array distributor provides superior liquid distribution performance over the showerhead and nozzle distributors.     

采用 UNIFAC 模型预测吸收式循环氨-离子液体工质对的气液相平衡简

On the basis of reported experimental vapor-liquid equilibrium （VLE） data of NH3-1-ethyl-3-methylimidazolium acetate （NH3-[Emim]Ac）, NH3-1-butyl-3-methylimidazolium tetrafluoroborate （NH3-[Bmim][BF4]）, NH3-1,3-dimethylimidazolium dimethyl phosphate （NH3-[Mmim]DMP） and NH3-1-ethyl-3-methylimidazolium ethylsulfate （NH3-[Emim]EtOSO3） binary systems, the interaction parameters of 14 new groups have been regressed by means of the UNIFAC model. To validate the reliability of the method, these parameters have been used to calculate the VLE data with the average relative deviation of pressures of less than 9.35%. The infinite dilution activity coefficient （ γ1∞ ） and the absorption potential （ φ1 ） are important evaluation criterions of the affinity between working pair species of the absorption cycle. The UNIFAC model is implemented to predict the values of and φ1 of t6 sets of NH3-ionic liquid （1L） systems. The work found that the φ1 gradually increases following the impact order： φ1（[Cnmim][BF4]）〈φ1（[Cnmim]EtOSO3）〈φ1（[Cnmim]DMP）〈φ1（[Cnmim]Ac） （n= 1, 2, 3, … ） at a given cation of IL species and constant temperature, and φ1（[Mmim]X）〈φ1（[Emim]X）〈φ1（[Pmim]X）〈 φ1（[Bmim]X）（X= Ac, [BF4], DMP or EtOSO3） at a given anion of IL species and constant temperature. Furthermore, the φ1 gradually increases with increasing temperature. Then, it could be concluded that the working pair NH3-[BmimlAc has the best potential research value relatively.     

单乙醇胺和二乙醇胺甲酸盐离子液体对水、甲醇和乙醇挥发度的影响(英文)

Vapor pressures were measured for six binary systems containing water, ethanol, or methanol with one of the two ionic liquids （ILs） at different component concentrations and temperatures using a quasi-static ebulliometer, with the ILs mono-ethanolammonium formate （[HMEA][HCOO]） and di-ethanolammonium formate （[HDEA][HCOO]）. The vapor pressures of the IL-containing binary systems are well correlated using the NRTL model with an overall average absolute relative deviation （AARD） of 0.0062. The effect of ILs on the vapor pressure depression of sol-vents at 0.050 mole fraction of IL is that [HDEA][HCOO]〉[HMEA][HCOO], and the vapor pressure lowering de-gree follows the order of water〉methanol〉ethanol. Further, the activity coefficients of three solvents （viz. water, ethanol, and methanol） for the binary systems{solvent （1）＋IL （2）}predicted based on the fitted NRTL parameters at T=333.15 K indicate that the two ILs generate a negative deviation from Raoult’s law for water and methanol and a positive deviation for ethanol to a varying degree, change the relative volatility of a solvent. [HMEA][HCOO] may be a promising entrainer to efficiently separate ethanol aqueous solutions by special rectification.     

基于ARX-PLS解耦框架下的多回路约束迭代模型预测控制方法(英文)

A multi-loop constrained model predictive control scheme based on autoregressive exogenous-partial least squares （ARX-PLS） framework is proposed to tackle the high dimension, coupled and constraints problems in industry processes due to safety limitation, environmental regulations, consumer specifications and physical restric-tion. ARX-PLS decoupling character enables to turn the multivariable model predictive control （MPC） controller design in original space into the multi-loop single input single output （SISO） MPC controllers design in latent space. An idea of iterative method is applied to decouple the constraints latent variables in PLS framework and recursive least square is introduced to identify ARX-PLS model. This algorithm is applied to a non-square simulation system and a stirred reactor for ethylene polymerizations comparing with adaptive internal model control （IMC） method based on ARX-PLS framework. Its application has shown that this method outperforms adaptive IMC method based on ARX-PLS framework to some extent.     

离子液体[BMIM][DBP]+水+甲醇/乙醇三元工质溶液蒸汽压的测量和预测(英文)

The ionic liquid, 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) was prepared and the vapor pressures of three set of binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM][DBP](2) were measured at different temperature and in the ILs mole fraction range from 0.1 to 0.6 with a static equilibrium apparatus. The measured vapor pressures were correlated with Non-Random Two Liquid (NRTL) activity coefficient model and the average relative deviations (ARD) between experimental and correlated vapor pressures for these binary solutions were 3.19%, 2.42% and 2.95%, respectively. Then, the vapor pressures of two set of ternary solutions H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3) were measured with an inclined boiling apparatus and further predicted with NRTL activity coefficient model based on the binary interaction parameters coming from fitting the vapor pressures of the binary solutions. The results indicated that the ternary solutions containing [BMIM][DBP] were shown a strong negative deviation from Raoult’s Law when the mole fraction of [BMIM][DBP] was larger than 0.2, which meant that ternary solutions could absorb the refrigerant vapors at the same or below solution temperature. Meanwhile, the average relative deviations between experimental and predicted vapor pressures for ternary solutions were 2.92% and 3.06%, respectively. Consequently, the NRTL active coefficient model used for non-electrolyte solutions was still valid for predicting vapor-liquid equilibrium of binary or ternary solutions containing ILs.     

一个用于计算鼓泡塔平均循环速度的模型

A new model without any fitting parameter for estimating the mean liquid recirculating velocity has been derived from previous work direct]y. The prediction agrees with experimental data reasonably well. Accurency of prediction from the new model is comparable with the models reported in the literature. However, the new model has a potential capability to predict the average liquid recirculation velocity at elevated pressure bubble columns since n and c is developed under pressure. However this needs to be further tested experimentally.     

A General Correlation for the Rise Velocity of Single Gas Bubbles

A correlation for the terminal rising velocity of a single gas bubble in an infinite Newtonian fluid is proposed. The model is an extension to high Reynolds numbers of a model developed recently by the author (Rodrigue, 2001a). This new equation, which is explicit in velocity, is able to predict the velocity for any bubble volume in any Newtonian fluid.     

Evolution of the Population of Bubbles in 2D Fluidized Beds

The size of the bubbles in a solid‐gas 2D fluidized bed was estimated by image capture and digitalization using a CCD camera. It was confirmed that the size distribution for the bubbles in a slice of the bed was skewed, varying with the location of the slice. The results were analyzed using the Agarwal (1985) model, which is based on a population balance. For this model, four adjustable parameters are required, as well as the knowledge of bubble size just above the distributor. Experimental data were compared with values predicted by the model. The parameters that the model needs were obtained by three procedures: i) the constants supplied by Agarwal (1985) and Rowe and Everett (1972); ii) the parameters obtained from experimental data for a 1 cm wide slice bed; and iii) the parameters obtained by fitting the bubble diameter to all the bubbles in the bed. The second and third methods provided the best results.     

三元体系液体混合物粘度的工程应用预测模型

从普遍适用的热力学关系出发，对Eyring模型进行修正，得到一个新的修正Eyring粘度模型。对三元体系液体混合物粘度的预测结果表明，与McAllister二维三体模型相比，修正的Eyring粘度模型预测结果较优，因此其修正更为合理，更具工程应用的前景。     

竖直环形通道内液氮流动沸腾的数值模拟

在多尺寸组模型的基础上,从加热壁面上脱离汽泡的受力分析人手,对液氮过冷流动沸腾模型进行了修正.将新模型应用于环形通道内液氮过冷流动沸腾的数值模拟,同时为了比较,采用基于Kirichenko,Fritz汽泡脱离直径公式的多尺寸组模型对同一管道内液氮过冷流动进行了数值模拟.结果表明:结合脱离汽泡受力分析模型的多尺寸组模型可...     

A Mathematical Model for Prediction of Pore Size Distribution Development during Activated Carbon Preparation

A new modeling approach was introduced for the prediction of pore size distribution development during activated carbon preparation. The mathematical model is based on the modification of a single-pore model for pore growth rate estimation using a population balance and applying a variable structural parameter random-pore model. The model predictions were compared with experimental pore size distributions and conversions at various times for pistachio shell char activation by steam between 800° and 950°C, and the kinetic parameters were estimated.     

Discrete Bubble Model for Prediction of Bubble Behavior in 3D Fluidized Beds

A discrete bubble model has been developed taking into account multiple bubble‐bubble interactions and a delayed coalescence method. The obtained simulation results were compared with experimental data reported in literature. The simulation results predicted by the developed model indicate clearly that the multiple interactions of bubbles lead to more reasonable results than those predicted by a binary interaction model. In addition, two types of interaction models were applied and predicted results were compared. The frequency of gas bubbles passing through the bed cross section versus bed height follows the same trend as the experimental data.     

A CFD-PBM coupled model under entire turbulent spectrum for simulating a bubble column with highly viscous media

To account for the effect of liquid viscosity, the bubble breakup model considering turbulent eddy collision based on the inertial subrange turbulent spectrum was extended to the entire turbulent spectrum that included the energy-containing, inertial, and energy-dissipation subranges. The computational fluid dynamics-population balance model coupled model was modified to include this extended bubble breakup model for simulations of a bubble column. The effect of turbulent energy spectrum on the bubble breakup and hydrodynamic behaviors was studied in a bubble column under different liquid viscosities. The results showed that when the liquid viscosity was <80 mPa s, the bubble breakup and hydrodynamics were almost independent on the turbulent spectrum. At liquid viscosity >80 mPa s, the bubble breakup rate and gas holdup were significantly under-predicted when the inertial turbulent spectrum was used, and when using the entire turbulent spectrum the predictions were more consistent with experimental data.     

A Population Balance Model for Disperse Systems： Particle Size Distribution in Suspension Polymerization

On the basis of population balance a mathematical model is developed to describe the formation of polymer partlcle in styrene suspension polymerization. The characteristics of coalescence and breakage of droplets and the gel effect are analyzed in particular. Parameters of the models are esthnztted by experimental. on reaction conversion and particle size distributlon. The results show that the model is suitable for predicting polymerization processes.