二元混合物降膜蒸发的数值模拟

提出了二元混合物在垂直圆管中降膜蒸发的传热传质耦合数学模型及其相应的数值解法 .模型考虑了液膜内传质对传热的影响 .计算表明传质对传热有明显影响 ,忽略传质的影响对预测膜平均传热系数会带来较大误差 .     

A multiscale mass transfer model for gas-solid riser flows: Part 1 — Sub-grid model and simple tests

The gas-solid mass transfer in circulating fluidized bed (CFB) riser flow is both structure-dependent and dynamic in nature. Recent progress in multiscale computational fluid dynamics (CFD) allows fresh insight into the dynamic flow structure, yet its influence on the mass transfer remains to be settled. To this end, a multiscale mass transfer model is established in this paper based on the extended framework of the energy-minimization multiscale (EMMS) model. The relevant algorithm named EMMS/mass is proposed for CFD-coupled mass transfer computation. Two testing cases accounting for sublimation of naphthalene and decomposition of ozone, respectively, are presented to demonstrate the characters of the model. It is shown that structural consideration can have significant effects on the model prediction. The normally used Reynolds number is not adequate to characterize these effects, while the combination of gas velocity and solids flux seems to capture the structural effects and allows to explain the variation of Sherwood number reported for CFB risers in the literature. Sub-grid coupling of this multiscale mass transfer model and CFD approach can be expected to provide a promising tool to probe the dynamic and structure-dependent nature of mass transfer in CFB risers.     

Polymerization of olefins through heterogeneous catalysis. III. Polymer particle modelling with an analysis of intraparticle heat and mass transfer effects

Propylene and ethylene polymerization in liquid and gas media are described by a multigrain particle model. Intraparticle heat and mass transfer effects are investigated for a range of catalyst activities. For slurry polymerization, intraparticle mass transfer effects may be significant at both the macroparticle and microparticle level; however, for normal gas phase polymerization, microparticle mass transfer effects appear more likely to be important. Intraparticle temperature gradients would appear to be negligible under most normal operating conditions.     

膜过程中热质耦合传递分析

研究了透过致密无孔膜的传热传质过程,考察了传热传质的相互作用,建立了膜过程中热质耦合传递的数学模型,并以湿空气透过薄膜分离过程为例,分析了温差及浓度差的变化对传热传质过程的影响,发现温差及浓度差的变化会引起热阻及湿阻的变化,从而进一步影响热流量和传质通量,所以对传热传质过程有加成作用。     

Interphase mass transfer in a gas fluidized bed

Mass transfer rates have been measured for bubbles containing ozone injected into an air-fluidized two-dimensional bed of particles. The overall mass transfer coefficient, corrected for unsteady bubble growth effects and with entrance effects eliminated, lies between predictions of models which assume that throughflow and diffusion are both additive and rate-controlling and those models which assume that mass transfer is governed by diffusion at the cloud boundary. The experimental value is consistent with a model which bases mass transfer purely on the throughflow predicted by Murray. Failure to account for bubble growth leads to drastic overestimation of the mass transfer coefficient.     

超重力旋转填充床氧解吸过程的数值模拟

基于旋转填充床流体流动的可视化结果,建立了超重力旋转填充床气液传质过程的数学模型,模拟氮气解吸水中溶解氧的传质过程。模拟结果表明,缩短液相停留时间、提高液相扩散系数都能增大液相传质分系数k_L;总体积传质系数K_La随超重力因子的增加而增大、随温度的上升而增大、随气相流率的增加略有下降、随液相流率的增加明显增大;空腔区传质贡献率随空腔区的增大而增大,随超重力因子的增大而减小;且短暂的停留时间是超重力旋转填充床对传质过程强化的本质原因。模型较好地符合文献的实验数据,误差在±16%以内。     

圆盘反应器中的PET缩聚过程

利用薄膜实验研究了PET缩聚过程反应和传质规律 ,建立了链增长、链降解反应动力学模型和泡沫脱挥时的传质速率方程 ;通过冷模实验研究了圆盘反应器中PET的混合、流动、成膜、膜表面更新以及传质规律 ;综合了反应和反应器研究结果 ,建立了圆盘反应器中的PET缩聚过程模型 ,对圆盘反应器中的PET缩聚过程进行了仿真分析 ,考察了温度、压力、停留时间、转速、催化剂浓度、负荷大小等各种因素的影响     

Modeling liquid-phase chemical reaction and interphase mass transfer in churn-turbulent bubble columns

The slug and cell model of liquid-phase mixing has been extended to consider the effects of interphase mass transfer and liquid-phase chemical reaction in isothermal churn-turbulent bubble columns. Inclusion of the effects of the gas phase is straightforward since the gas phase has previously been considered as it strongly affects the mixing of the liquid phase. The computational simplicity of the slug and cell model has been retained with the species conservation equations being reduced to a system of algebraic equations. The behavior of the model has been examined for two cases: (1) liquid-phase chemical reaction in the absence of interphase mass transfer and (2) in the presence of interphase mass transfer without liquid-phase chemical reaction. In the second case the model behavior has been compared to available literature data for the absorption of oxygen into water.     

Non-equilibrium thermodynamic analysis of coupled heat and moisture transfer across a membrane

Non-equilibrium thermodynamics theory is used to analyze the transmembrane heat and moisture transfer process, which can be observed in a membrane-type total heat exchanger (THX). A theoretical model is developed to simulate the coupled heat and mass transfer across a membrane, total coupling equations and the expressions for the four characteristic parameters including the heat transfer coefficient, molar-driven heat transfer coefficient, thermal-driven mass transfer coefficient, and mass transfer coefficient are derived and provided, with the Onsager’s reciprocal relation being confirmed to verify the rationality of the model. Calculations are conducted to investigate the effects of the membrane property and air state on the coupling transport process. The results show that the four characteristic parameters directly affect the transmembrane heat and mass fluxes: the heat and mass transfer coefficients are both positive, meaning that the temperature difference has a positive contribution to the heat transfer and the humidity ratio difference has a positive contribution to the mass transfer. The molar-driven heat transfer and thermal-driven mass transfer coefficients are both negative, implying that the humidity ratio difference acts to reduce the heat transfer and the temperature difference works to diminish the mass transfer. The mass transfer affects the heat transfer by 1%–2% while the heat transfer influences the mass transfer by 7%–14%. The entropy generation caused by the temperature difference-induced heat transfer is much larger than that by the humidity difference-induced mass transfer.     

Interfacial mass transfer in stripping of phenylalanine in a liquid-liquid extraction process

Stripping of L-phenylalanine from organic phase containing ALIQUAT 336 (tri-octyl-methyl-ammonium chloride) as complexing agent was studied using a stirred transfer cell. The study investigated the effects of concentration of the stripping agent, potassium chloride, in strip solution and temperature on mass transfer rates. A two-film model based on organic and aqueous phases mass transfer resistances was proposed to estimate mass transfer coefficients and it predicted adequately the experimental time-concentration data at different conditions studied. A comparison of mass transfer coefficients for stripping and previously published results on extraction for the same system was made.     

Gas—liauid mass transfer in three-phase stirred tank reagors: Newtonian and non-newtonian fluids

Gas—liquid mass transfer has been investigated in gas—liquid-solid three-phase stirred tank reactors with Newtonian and non-Newtonian liquids. Volumetric mass transfer coefficients and gas hold-ups were measured in a 0.2 m i.d. stirred tank reactor and the effects of low-density polymeric particles (ρ_s, =1030 and 1200 kg/m³; up to 15 vol%) on gas—liquid mass transfer were examined. The volumetric mass transfer coefficients in water were found to decrease due to the presence of solid particles at constant impeller speed and superficial gas velocity. On the other hand, solids loading led to higher mass transfer rates in non-Newtonian carboxymethyl cellulose aqueous solutions. Our previously proposed model for mass transfer in gas—liquid two-phase systems was extended to gas—liquid—solid three-phase systems. Reasonable agreement was found between the predictions of the proposed model and the experimental data.     

Mass transfer behavior of methane in porous carbon materials

The low mass transfer rate in porous materials hinders the use of adsorbed natural gas as vehicle fuel. Fundamentally, the mass transfer rate depends on the structures of the adsorbents and the operating conditions. Therefore, in this study, the effects of adsorbent (activated carbons) structure and operating conditions on the mass transfer rate of methane (main component of natural gas) were investigated quantitatively, providing a theoretical basis for the synthesis of efficient adsorbent materials. By performing Monte Carlo and molecular dynamics simulations and utilizing a nonequilibrium thermodynamic linearization transfer model, the mass transfer behavior of methane in porous carbon materials was quantitatively evaluated, specifically focusing on the material structure, operating conditions, and feasibility of using natural gas as vehicle fuel. The proposed linear nonequilibrium thermodynamic mass transfer model is applicable to interfacial gas species and provides a valuable tool for gas separation.     

Mass transfer coefficients in a pulsed packed extraction column

The volumetric overall mass transfer coefficients have been measured in a pulsed packed extraction column using diffusion model for the toluene/acetone/water system. The experiments were carried out for both mass transfer directions. The effects of operational variables such as pulsation intensity and dispersed and continuous phases flow rates on volumetric overall mass transfer coefficients have been investigated. The experimental findings indicate that pulsation intensity and mass transfer direction have great influence on volumetric overall mass transfer coefficient. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. The experimental results obtained in the present work are compared with some other types of extraction columns. Finally, two empirical correlations for prediction of the continuous phase overall mass transfer coefficient is derived in terms of Sherwood and Reynolds numbers. Good agreement between prediction and experiments was found for all operating conditions that were investigated.     

A highly elevated mass transfer rate process for three-phase,liquid-continuous fluidized beds

Average gas holdup and gas-to-liquid mass transfer in three-phase fluidized beds with non-Newtonian fluids were studied. The effects of liquid property, gas distributor type and magnetic field intensity on mass transfer coefficient and overall gas holdup were examined. The volumetric gas-to-liquid mass transfer coefficient was determined by fitting the oxygen concentration profile data across the bed to the axial dispersion model. The average gas holdup and mass transfer coefficient were all correlated with operating parameters including gas velocity and effective viscosity.Experimental results showed that a three-fold increase in mass transfer coefficient and a two-fold increase in average gas holdup were observed with properly designed liquid property and gas distributor. A modified process was developed to highly elevate the volumetric gas-to-liquid mass transfer rate. The bubble coalescing property of three-phase fluidized beds with small particles is eliminated, and its application to biotechnology and enzyme-catalyzed processes with high gas-to-liquid mass transfer rate could be achieved.     

活性炭纤维填充床内多组分竞争吸附

建立了活性炭纤维填充床内多组分竞争吸附传质动力学模型 ,采用正交配置方法求解数学模型以预测突破曲线 ,从理论上探讨了竞争吸附平衡及吸附质在填充床内的轴向弥散、纤维内扩散和纤维外对流传质等因素对强、弱吸附组分突破曲线的影响。在间歇和填充床吸附器内进行了脱除水溶液中酚类化合物的实验 ,测定了活性炭纤维吸附水溶液中苯酚和氯代苯酚的吸附等温线 (间歇吸附 )以及苯酚和氯代苯酚在活性炭纤维填充床内竞争吸附时的突破曲线 ,并与模型计算值进行了比较。结果表明 ,吸附质在活性炭纤维内扩散和纤维外对流传质阻力不是填充床内吸附过程的控制步骤 ,而轴向弥散影响显著 ,不可忽略     

鼓泡床中基于气泡结构的多相反应模型

气固鼓泡床是一个流动、传热/传质和反应多尺度时空耦合的复杂系统。其中介尺度流动结构（如气泡）对于气固相间传递起着关键性的作用。为了准确描述气固流态化系统中的“三传一反”行为,需要在合理物理简化的基础上建立介尺度模型。提出了基于气泡结构的多流体反应模型,考虑了介尺度非均匀结构对于鼓泡床内气固相间反应的影响;定义了基于气泡的反应非均匀因子修正双流体（TFM）传质反应模型,从而使模型更加易用。通过鼓泡床内的臭氧催化分解反应模拟,对模型进行了初步验证,模拟结果与文献结果相符。     

Mathematical Model for Batch Drying in an Inert Medium Fluidized Bed

A modified three-phase model is proposed for batch drying of fine powders in an inert medium fluidized bed. The overall heat and mass transfer coefficients between the interstitial gas and solid phases have been determined by the proposed surface-stripping model in which the Biot number is a governing parameter. The effects of gas velocity, inlet gas temperature and mass ratio of starch to inert particles on the drying characteristics of starch in a 0.083 m ID × 0.80 m high medium fluidized bed have been determined. Based on the proposed model, the internal resistance of mass transfer at the powder is equal to the external resistance. The model predicts well the bed temperature, humidity of outlet gas, moisture content of solid particles, heat and mass transfer in an inert medium fluidized bed.     

湿工况下泡沫金属内换热和压降的数值模拟和实验验证

泡沫金属应用到换热器空气侧有望提高析湿工况下的换热性能。为了了解湿空气在泡沫金属内的热质传递和压降特性,建立了泡沫金属内液滴形成、生长和运动特性的数值模型。基于液滴成核数目和成核临界半径得出液滴形成过程的传质率模型;通过建立液滴与湿空气相界面附近湿空气中水蒸气的组分守恒方程,得出液滴生长过程的传质率模型;通过对不同孔棱柱表面液滴的受力分析,建立在重力和风力的共同作用下的液滴接触角模型。将液滴形成及生长的传质率模型和接触角模型分别作为质量源项和表面张力源项,加入连续性方程、动量方程和能量方程组中,实现对泡沫金属内液滴生长、形成和运动过程模拟。模型的实验验证结果表明,换热量预测值与实验结果的最大偏差为11.9%,压降预测值与实验结果的最大偏差为17.7%。     

血液透析过滤传质动力学的简化模型

血液透析（HD）、血液过滤（HF）和血液透析过滤（HDF）是目前临床上治疗慢性 肾功能衰竭最常用的 3种疗法。以往人们对 HD的传质动力学作了较多的研究l’，‘］，而对 HF、HDF的研究则较少。虽然PopoviCh等门、Jaffrln等M相继提出了描述HF、HDF 传质动力学的一、二维模型，但文献囚的模型仅适用J” HD和 HDF；而巳，其解的形式     

喷雾塔内雾粒粒径对传质行为的影响

本文研究了喷雾塔内的两相混合及雾粒粒径对传质行为的影响.建立了描述粒子群在塔内运动和传质规律的数学模型,这一模型既考虑了两相的返混,也考虑了粒径的影响,即所谓粒子群的向前混合.通过稳态浓度剖面法求解模型方程,得到了两相的返混准数Pe_x、Pe_y及粒子的真空传质系数K_(oco)用线性最小二乘法关联得到计算这些参数的经验方程.这些关联式可用于计算塔内的真实浓度剖面,并能适用于不同结构和尺寸的喷嘴.