High flux,single solute mass transfer in spherical rigid drops

High flux (i.e. high solute concentrations) mass transfer in spherical, rigid drops has been studied for the case of a single transferring solute. Model equations have been solved for the cases of (a) infinite and (b) finite continuous phase mass-transfer coefficients—or constant, and variable, interface compositions.The partial differential equations were solved to illustrate the influences of high solute concentrations and the continuous phase mass-transfer coefficients. In fact, the model diffusion equation resulting from a differential solute balance remains unchanged from the well-known low flux equation. It is only at the boundary, where the convective flux contribution must be taken into account, as it increases the total flux into (or out of) the drop as solute concentrations increase. Extraction efficiencies were also calculated. These proved relatively insensitive to the concentration level because the solute convective flux contribution simply increases the drop size. The diffusive flux into the drop interior changes little with the concentration level, so resulting in the small differences in the extraction efficiencies.     

Mass transfer from single gas bubble — a comparative study on experimental methods

A comparative study on the experimental techniques which have been used for the study of mass transfer from single gas bubble was made. The instantaneous mass transfer rates from a single carbon dioxide bubble rising through quiescent liquid medium (water) were measured using two different methods. For the first method, two movie cameras were placed on a moving platform along perpendicular directions and were used to record the position and size change of the bubble. The second method measured the mass transfer rates by recording the pressure changes in the free space at top of the bubble column, which was caused by the change of bubble size. The instantaneous mass transfer coefficients determined by either method exhibited wide scattering which is typical of work of this kind. Discussions are given on the relative merits of these two methods.     

Local enhancement of liquid-to-wall mass transfer by a single gas bubble

Local liquid-to-wall mass transfer enhancement by a single bubble was studied. Both photographic and local current measurements were taken. The effects of the bubble form, wake and trajectory were analysed for vertical and down-facing inclined electrodes. For angles lower than 40°, bubbles rise over the surface with small hops of regular amplitude. High current increases were observed where the bubble hits the electrode. For higher angles, the bubble glides, producing high constant currents. This paper was presented at the International Workshop on Electrodiffusion Diagnostics of Flows held in Dourdan, France, May 1993.     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities—Numerical investigations

Full 3D-simulations of transient interfacial mass transfer accompanied by Marangoni convection at a single spherical droplet in a quiescent liquid were performed in a moving reference coordinate system. The flow and concentration field are solved simultaneously, coupled via the additional Marangoni stress generated by concentration gradients at the interface. Fluid dynamics and mass transfer are investigated in the Marangoni convection dominated toluene/acetone/water system. The numerical results are qualitatively and quantitatively compared with own experimental results. The simulation results reveal that mass transfer is always enhanced—compared to calculations where no Marangoni convection appears—independently from the initial solute concentration. The enhancement factor of mass transfer ranges between 2 and 3.     

Heat and mass transfer from cylinders to a turbulent fluid stream — A critical review

A review is made of recent experimental and theoretical work on the transfer of heat and mass between a circular cylinder and a turbulent fluid stream in cross flow. Special attention has been given to the transport mechanism over the wake region and the different approaches used to model it. The overall and boundary layer transport characteristics are briefly discussed. The review is limited to investigations under subcritical flow conditions over the Reynolds number range from 10³ to 10⁵.     

Mass transfer in a reciprocating plate extraction column — effects of mass transfer direction and plate material

The mass transfer performance of 5 cm diameter reciprocating plate column has been measured with the system n-butyric acid/kerosene (dispersed)/water (continuous). In most of the tests, the reciprocating plate stack was made of stainless steel which was preferentially wet by the continuous phase. During the mass transfer process the holdup and in some cases the Sauter mean droplet diameter were measured. The mass transfer effectiveness, expressed as the height of a transfer unit (H_ax) corrected for axial mixing, depended on the phase flow rates, the agitation rate and the direction of mass transfer. For continuous to dispersed phase mass transfer (c → d), the mass transfer was more effective, i.e. H_ax was lower than for d → c mass transfer under the same external conditions. Qualitative and quantitative observations indicated much larger drop sizes in the d → c case due to enhanced coalescence. Although mass transfer was less effective under d → c conditions, the column capacity was increased. The same effects were also observed when the plate stack was modified by inserting some Teflon plates which were partly wet by the dispersed phase.     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities - experimental investigations

An experimental study of transient drop rise velocities and mass transfer rates was carried out in the system toluene/acetone/water which is known to show interfacial instabilities. The rise velocity of toluene drops was studied without added solute (acetone) in the diameter range 1-3 mm and with added solute for 2 mm drops. The initial concentration of the transferred solute was varied from 0 to 30 g/L. The transient drop rise velocities were used to quantify the Marangoni effect since the drag coefficient depends on the strength of the Marangoni convection patterns caused by interfacial tension gradients. In addition, mass transfer measurements were carried out in order to determine the modification of the mass transfer rate due to Marangoni convection. Velocity and mass transfer measurements were then correlated via the contact time. Results reveal the existence of a range in which a critical value for the solute concentration can be defined for Marangoni convection.     

Interphase mass transfer in binary liquid systems — Laminar liquid jets

Interphase mass transfer was investigated in binary liquid systems using the laminar jet technique. A mathematical model of the mass transfer process was developed and appropriate experimental measurements were made in the cyclohexanol-water, isobutanol-water and ethyl acetate-water systems. Good correspondence was obtained between predicted and measured mass transfer rates, which was taken to validate the use of the model. In particular the results indicated that, within the limits of experimental accuracy, interfacial equilibrium prevails in these systems for contact times on the order of one-half second.     

Creeping flow mass transfer to a single active sphere in a random spherical inactive particle cloud at high schmidt numbers

Using the solution by Tam of Navier-Stokes equations for creeping flow around an active sphere surrounded by a random cloud of inactive spheres, an asymptotic solution of the convective diffusion equation is obtained for high Schmidt numbers. The Sherwood number for the overall mass transfer coefficient to the active sphere has been analytically related to the Peclet number as

It agrees very well with the experimental mass transfer data on single active spheres for σ = 0476, Re < 10 and large Sc. This analytical result becomes invalid as σ decreases to 0.33. Pfeffer's model for the same problem has excellent agreement with the mass transfer data on single active spheres for σ = 026, Re < 10 and Sc = 1600. Pfeffer's model seems to be quite satisfactory for the usual range of void volume fractions in packed beds. The present model seems to be more accurate at higher values of void volume fractions in packed and distended beds.     

Treatment of landfill gas by gas permeation — pilot plant results and comparison to alternatives

Landfill gas is an interesting source of prime energy since it contains about 50–55% volume methane. Utilization, however, must take into account the traces of halogenated hydrocarbons and H₂S, which are present in the gas. The paper reports of two years experience with a pilot plant for the production of a gas with natural gas quality. Essentially the process consists of two stages, an adsorption for the separation of the trace components and a membrane unit for the separation of CO₂. The process is discussed in detail and compared with alternatives for the utilization of landfill gas such as power generation by gas engines/generator, eventually in combination with a waste heat boiler.     

Salt dissolution in drilling muds — a generalized correlation for mass transfer in non-newtonian fluids

The rate of dissolution of rock salt in drilling mud was measured as a function of flow rate and temperature under conditions simulating those in a well. A water based drilling mud, containing about 10% solids and additives was used, as well as a polymer “mud” composed of a Xanthan gum polymer solution and 5% salt, but no solids. The non-Newtonian muds were pumped through a “slit” flow cell, with a slab of rock salt flush with one side of the cell wall. The data (including water over the same range of conditions) were described by a mass transfer coefficient, and were correlated in dimensionless form based on the theoretical solution of the analogous heat transfer problem, adapted to non-Newtonian fluids. The non-Newtonian properties were described by an effective viscosity, which is consistent with either the power law or Bingham plastic viscosity model.     

The internal circulations on internal mass transfer rate of a single drop in nonlinear uniaxial extensional flow

The internal flow of a droplet in the nonlinear extensional flow field will exhibit more than two internal circulations with the variation of nonlinear intensity(E). In this paper, the effect of positions and sizes of internal circulations on internal mass transfer rate of a single spherical droplet in a nonlinear extensional flow field is studied and compared with that in a linear extensional flow field. The simulation results show that when E ≥ 0, there are two symmetrical internal circulation...     

气态膜吸收法脱除水中氨的传质效果

利用聚丙烯中空纤维气态膜对氨/水分离过程及影响因素进行研究,考察膜两侧液体流速、浓度、温度等工艺条件对传质系数和氨脱除率的影响。研究结果表明：气态膜-化学吸收法对氨/水有很好分离效果;原料液温度和流速的影响较为显著,传质系数随温度升高而升高,而提高原料液的流速,膜通量增加,氨的脱除率却下降,压力降升高;氨的初始浓度对膜通量影响较大,膜通量随初始浓度升高而增大;吸收液中反应物浓度相对于透过氨浓度过量时,吸收液的浓度、流速对传质过程影响较小。     

水力喷射空气旋流器中射流流型及其对传质面积和气相压降的影响

为了进一步提高水力喷射空气旋流器（WSA）的传质效率以及认识射旋流体系的气液传质机理,对WSA中的射流流型进行了系统的观察研究,绘制出了不同进口气速下射流流型图。以CO₂-NaOH化学吸收体系测定了相应射流流型下的有效比相界面积a。结果表明,在低射流流速（≤4.42 m·s^-1）下,液相射流随着进口气速增大,主要存在稳态射流、变形旋线射流、破碎旋线射流、雾化旋线射流、贴壁雾化旋线射流5种流型;在高射流流速（≥6.19 m·s^-1）下,射流主要出现稳态射流、破碎旋线射流以及雾化旋线射流3种流型。a值与流型有关,雾化旋线射流下的a值大于其他流型下的对应值。低流速下的贴壁雾化,不利于气液两相充分接触,对应a值较小。a值与射流流速有一定关系,随着射流速度的增大而略有增大,且随着射流流速增大至8.84 m·s^-1以上,增大的幅度变大。     

Kinetic analysis of benzyl alcohol oxidation by alcohol oxidase in aqueous—organic two-phase systems

Alcohol oxidase-catalyzed oxidation of benzyl alcohol to benzaldehyde was studied in three two-liquid phase systems involving butyl acetate, xylene and n-decane. A more highly hydrophobic solvent resulted in more favorable partitioning of the substrate into the aqueous phase and less deleterious effect on the enzyme activity. As a result, the overall production of aldehyde was highest with the n-decane system and lowest with the butyl acetate system. In addition, the organic solvent served as an extractant for the product, which acted both as a competitive inhibitor and as a denaturant of the enzyme. The time courses of benzaldehyde production were simulated by a simple mathematical model assuming Michaelis–Menten kinetics in the aqueous phase, enzyme deactivation by organic solvents and the equilibrium partitioning of the reagents between the two phases.     

Experimental studies of interphase mass transfer with chemical reaction — Saponification of esters

This study concerns the transfer of ethyl acetate from a supernatant still liquid into a lower layer of caustic solution in which a saponification reaction occurs. Apparatus and techniques for measuring the concentration profiles which develop in the turbulent reaction layer in the aqueous phase at the liquid-liquid interface are described. In particular, the effects of turbulence on the reaction layer propagation, the reaction zone in the turbulent layer, and the concentration distribution of various components of the system were observed and measured. From these data, mass transfer rates and enhancement factors were deduced. The effects of turbulence in the aqueous phase were presented in terms of an eddy diffusivity model.     

三种填料结构旋转床传质及压降性能对比

为了考察自主设计的新型板式旋转填料床传质及压降性能,分别以NaOH-H_2O和空气-水为实验体系,采用对比实验的研究方法,考察了转速、液量和气量对新型板式填料床、传统丝网填料床和鲍尔环填料床的传质与压降性能的影响。传质性能研究表明:在相同操作条件下,丝网填料床传质性能最优,但新型板式填料床传质性能与丝网填料床相差不大(<1.0 s~(-1));压降性能研究发现,气量是影响填料床压降的重要因素,且在相同操作条件下,压降值始终有丝网填料床>鲍尔环填料床>新型板式填料床,丝网填料床压降值与新型板式填料床相差33%以上。新型板式填料床在传质效率损失不大的情况下,损失了较低能耗,表现出优良的综合性能。     

Solid—liquid mass transfer in a shaking vessel for a bioreactor with “current pole”

A shaking vessel with “current pole”, which is a center pole installed at the bottom, had shorter mixing time than a shaking vessel with a cone at the bottom. The mass transfer rate on the suspended particles was also measured in the shaking vessel where ion-exchange resin beads were used as the suspended particles. The dependence of the solid-liquid mass transfer coefficient on the circulating frequency changed at the critical circulating frequency for complete suspension N_JS. For a circulating frequency higher than N_JS, the mass transfer coefficient was correlated with the power consumption per unit volume, regardless of presence or not of the current pole.