膜萃取过程的传质特性研究

膜萃取是一种新型的分离技术。本文在中空纤维膜器中研究了膜萃取过程的传质特性。通过四种不同体系的实验,求取了基于水相的总传质系数,提出了求算膜萃取过程中各分传质系数k_(?)、k_(?)、k_(?)的半经验关联式。研究表明,减小膜阻可以强化膜萃取过程,提高过程的总传质系数.比较和分析膜萃取过程中各部分传质阻力,可以看出,对于萃取相平衡常数m1的体系应选用疏水膜器,对于m1体系则应选用亲水膜器。     

螺旋状中空纤维膜萃取传质特性

在对中空纤维膜萃取以及螺旋管技术进行充分调研的基础上 ,选择水 -苯酚 - 30 %TBP煤油为实验体系 ,溶质由水相萃取到有机相 ,在不同结构的单束螺旋状中空纤维膜器中研究了螺旋管纤维膜管内外流速以及螺旋管结构等因素对传质系数的影响 .实验结果表明 ,螺旋管中空纤维膜可以有效地提高中空纤维膜的传质特性 .随着管内流速的增加 ,传质系数将有很大提高 ,而管外流速对于传质系数的影响则较小 .至于螺旋结构的影响为 :随着螺旋内径的减小或者是螺旋螺距的减小 ,总传质系数相应地有很大提高 .最后得到了在本实验条件下计算总传质系数K的关联式     

中空纤维膜萃取苯酚的传质及流动特性

以体积分数为30％的磷酸三丁酯＋煤油－水为实验体系，研究了中、高装填密度的中空纤维膜萃取处理苯酚衡溶液的传质效果和传质特性以及膜器壳程流动状况。实验结果表明，中空纤维膜萃取可以高效去除水中的苯酚，萃取率最高可达到99．9％。比较了总传质系数的实验值与多个传质系数关联式的预测值之间的偏差，发现从中、高装填密度膜器得到的传质关联式偏差较小，而从低装填密度膜器得到的传质关联式偏差较大。通过测量膜器壳程流动的停留时间分布曲线，证实了偏差是由于中、高装填密度的膜器壳程流动的复杂性造成的。     

2-乙基-1，3-己二醇萃取硼酸的传质系数

单液滴法因其测量结果精确与实验设备简单等优点广泛应用于萃取过程中的传质研究。应用此方法研究了硼酸在2-乙基-1,3-己二醇-甲苯/卤水体系中的传质系数。结果表明：传质系数随着有机相2-乙基-1,3-己二醇浓度、卤水相硼酸浓度及温度的增加而增大。通过双膜传质理论分析,并引入修正的传质系数关联式,将双膜传质模型应用到此萃取体系中,建立了新的针对此体系的传质系数模型。新模型的计算值与实验值的平均相对误差为7.59 %,两者吻合良好,因此,该模型可用于2-乙基-1,3-己二醇-甲苯体系萃取硼酸过程的设计与放大。     

螺旋管式膜强化传质过程的研究与进展

膜传质过程越来越为众多研究者关注,本文全面综述了近年来螺旋管式膜强化传质过程的机理以及研究进展,并结合膜萃取传质过程的特性,提出螺旋管式中空纤维膜强化膜萃取传质过程的机理,给出了螺旋管式中空纤维膜强化膜萃取的实验结果。结果表明,螺旋管式中空纤维膜比直管式中空纤维膜的传质系数可以大２～４倍。     

水萃取氯丙醇的传质性能

为满足水萃取氯丙醇萃取塔设计开发需要,采用单液滴法测定了水萃取氯丙醇的总传质系数,结果表明:总传质系数随着比表面积、温度的升高而增大。依据双膜理论,联合滴内、外分传质系数经验式,并引入修正的参数对传质系数方程进行了回归,建立了新的传质系数模型,将该模型应用到此萃取体系中,对比滴内、外分传质系数得出:影响传质的阻力主要集中在液滴内,可以通过提高通量来强化液滴内传质。最后,将该模型的计算值与实验值进行了比较,平均相对误差为9.626%,两者基本吻合,因此,该模型可用于水萃取氯丙醇工业设备的设计与放大。     

超临界流体填料萃取塔流体力学和传质性能(Ⅱ) 传质性能

根据双膜理论,建立了超临界流体填料萃取塔液相总体积传质系数关联式;依据柱塞流模型,应用超临界二氧化碳-异丙醇-水和超临界二氧化碳-乙醇-水2种实验体系在内径为25mm的塔内对金属板波和金属丝网θ环2种填料的传质性能进行了模拟计算。结果表明,本文提出的传质数学模型能较好地描述超临界流体填料萃取塔的传质性能。     

聚丙烯中空纤维膜萃取过程传质特性研究

在自制的中空纤维膜器中研究了膜萃取过程的传质特性.研究表明,自制的带折流板的膜器可以提供较高的传质效率.增大水相流速可以提高传质速率,而改变有机相流速对传质没有影响.通过对实验数据的回归分析得出了折流膜器的壳间传质关联式.该研究对折流膜萃取器的开发和设计具有参考价值.     

中空纤维更新液膜传质性能的研究

研究了中空纤维更新液膜(HFRLM)技术的传质性能.以CuCl2水溶液-10%P204 煤油-盐酸为实验体系,研究结果表明,中空纤维更新液膜技术可以实现同级萃取-反萃,且总传质系数随料液相流速的增大而增大,在实验条件下,总传质系数受反萃相流速的影响较小.实验研究探讨了混合方式(料液与萃取剂混合和反萃剂与萃取剂混合)和体系分配系数对传质性能的影响.实验结果表明,由于相间分配系数的不同,总传质系数受混合方式的影响较大,以分配系数较大的一相与萃取相混合流经管程的方式对传质过程有利.     

硅橡胶复合膜用于渗透蒸发的膜传质动力学(Ⅰ)膜面上的对流传质

利用自制的硅橡胶平板复合膜对低浓度乙醇水溶液进行渗透蒸发分离乙醇实验 ,研究了过程的传质动力学。基于液 -膜的串联传质阻力模型 ,通过实验测定了膜的总传质系数 ,采用对比差值方法将总传质系数拆分为膜面上的液膜传质系数和膜内的扩散传质系数两部分 ,分析了液相边界层阻力和膜扩散阻力对总传质系数的影响。特别针对膜面上液体流动状况对膜传质的影响进行了探讨 ,得出了液膜传质系数与Reynolds数及温度的关联式。     

Mass transfer ambiguities in swirling pipe flows

A mathematical model of mass transfer in the boundary layer of swirl flow is developed. The equations obtained for Sherwood number and mass transfer coefficient generalize the equations obtained by Levich for the flat plate to the case of mass transfer in axisymmetrical swirl flow. For the first time it is shown that, in swirl flows, the mass transfer is not completely controlled by integral flow parameters (Reynolds number and the swirl number) but depends essentially on the type of vortex symmetry. The left-handed helical vortices generate wake-like swirl flows and increase mass transfer in comparison with axial flows. The right-handed helical vortices generate jet-like swirl flows, which can decrease mass transfer.     

Free convection heat transfer over a horizontal plate at low prandtl number

Boundary layer equations for free convection heat transfer along a semi-infinite horizontal plate are derived by giving more importance to the energy equation. The equations are obtained for low Prandtl number and two separate polynomials are used to approximate the temperature and velocity profiles in these regions. The rate of heat transfer is compared with the available analytical and numerical results based on conventional boundary layer equations.     

ON EXACT SOLUTIONS OF THE MAXWELL-STEFAN EQUATIONS FOR THE MULTICOMPONENT FILM MODEL

A general solution of the Maxwell-Stefan equations for mass transfer in multicomponent mixtures is obtained in terms of the characteristic roots (or eigenvalues) of these equations. The linear dependence among the composition gradients means that only n-1 of the eigenvalues are independent; the additional eigenvalue is always zero. A number of previously published exact solutions of the Maxwell-Stefan equations (obtained by a variety of mathematical methods) are shown to be essentially equivalent since they are special cases of the fundamental results described here. The general solution of Krishna and Standart may also be obtained using the same method. For the commonly encountered delerminacy conditions of transfer through a stagnant component and of equimolar counter transfer at least one of the independent eigenvalues may be evaluated explicitly in advance of calculating the molar rates of transfer thus reducing the computational eigenvalue problem from one of order n-1 to one of order n-1.     

最小?损优化方法在椭圆换热管内的应用

在流体对流换热分析的基础上得到局部?损率的表达式,以局部?损率为优化目标,满足能量与质量守恒条件,在流动功耗为定值条件下,根据拉格朗日泛函极值原理得到?损为极值时的控制方程组,发展了最小?损优化方法。将该方法应用到椭圆换热单管中,得到优化后的速度场与温度场。优化结果表明,优化流动结构为纵向旋流,具有较好的传热及流动性能,相比未优化椭圆管综合换热性能（Nu/Nu_s）/（f/f_s）可达3.21,同时得到了纵向涡在流场中的分布情况,这对椭圆管内强化换热发展具有指导意义。     

THE DRYING OF SOYBEAN SEEDS IN COUNTERCURRENT AND CONCURRENT MOVING BED DRYERS

The aim of this work was to analyze the simultaneous heat and mass transfer between air and soybean seeds in countercurrent and concurrent moving bed dryers by simulation. The technique chosen was based on modeling from mass and energy conservation equations for the fluid and particulate phases. The equilibrium, heat transfer and mass transfer equations were taken from specific studies. The equation representing drying kinetics was obtained by means of a thin-layer study, whereas the equilibrium equations was chosen from rival model discrimination, based on nonlinearity measures. Hence, the model parameters were defined by the respectives studies. The profiles for temperature and humidity of the fluid and the temperature and moisture of the seeds were obtained by numerical solution of the model. This model consisted of ordinary differential equations and the solution was obtained by a specific code. The simulated results indicated a significant.     

THE DRYING OF SOYBEAN SEEDS IN COUNTERCURRENT AND CONCURRENT MOVING BED DRYERS

ABSTRACT

The aim of this work was to analyze the simultaneous heat and mass transfer between air and soybean seeds in countercurrent and concurrent moving bed dryers by simulation. The technique chosen was based on modeling from mass and energy conservation equations for the fluid and particulate phases. The equilibrium, heat transfer and mass transfer equations were taken from specific studies. The equation representing drying kinetics was obtained by means of a thin-layer study, whereas the equilibrium equations was chosen from rival model discrimination, based on nonlinearity measures. Hence, the model parameters were defined by the respectives studies. The profiles for temperature and humidity of the fluid and the temperature and moisture of the seeds were obtained by numerical solution of the model. This model consisted of ordinary differential equations and the solution was obtained by a specific code. The simulated results indicated a significant.     

Analysis of the integro-differential equation of constant-rate particle transfer

Some conclusions from the integro-differential equation of constant-rate particle transfer were considered. In a sense, this equation is a microscopic kinetic equation for the phenomenological macroscopic equations of heat transfer, diffusion, and other transfer processes. It was shown that, in the limiting case, the above integro-differential equation can be reduced to these macroscopic equations. Formulas were derived for calculating the thermal conductivity and the diffusion coefficient as tensor quantities. With the use of the concepts of Galerkin’s method, the hyperbolic differential equations of heat and mass transfer were obtained.     

Calculation of limiting current density of metal electrodeposition on vertical plane electrode under conditions of natural convection

An approximate analytical solution of problem of ion transfer near a vertical plane electrode surface is obtained for the metal electrodeposition proceeding at the limiting current from electrolyte containing ions of three types under the conditions of natural convection. In contrast to previous studies, no transport numbers are used here, and the migration transfer of electroactive electrolyte component is taken into account. The equations obtained take into consideration the effect of supporting electrolyte concentration and its migration on the limiting current. The limiting current densities (mass-transfer coefficients), which are calculated by equations proposed here and by the finite-difference method, are compared.     

RETARDATION OF DROPLET MOTION BY SURFACTANT. PART 1. THEORETICAL DEVELOPMENT AND ASYMPTOTIC SOLUTIONS

The equations describing the retardation by surfactant of an essentially spherical droplet in creeping flow through an unbounded Newtonian liquid are developed in a general way. The concentration distribution is determined by convection and the coupled mass transfer processes of liquid-phase diffusion, adsorption kinetics, and surface diffusion. Assuming that mass transfer occurs rapidly, an asymptotic solution is obtained showing uniform retardation, treating both phases and all mass transfer mechanisms simultaneously. For slow mass transfer, an asymptotic solution is obtained for stagnant cap behavior.     

RETARDATION OF DROPLET MOTION BY SURFACTANT. PART 1. THEORETICAL DEVELOPMENT AND ASYMPTOTIC SOLUTIONS

The equations describing the retardation by surfactant of an essentially spherical droplet in creeping flow through an unbounded Newtonian liquid are developed in a general way. The concentration distribution is determined by convection and the coupled mass transfer processes of liquid-phase diffusion, adsorption kinetics, and surface diffusion. Assuming that mass transfer occurs rapidly, an asymptotic solution is obtained showing uniform retardation, treating both phases and all mass transfer mechanisms simultaneously. For slow mass transfer, an asymptotic solution is obtained for stagnant cap behavior.