SOLID-LIQUID MASS TRANSFER AT THE BASE OF A RECTANGULAR AGITATED VESSEL

Rates of mass transfer between the bottom of a rectangular agitated vessel and a solution were studied by measuring the limiting current of the cathodic deposition of copper from acidified CuSO₄. Variables studied were rotation speed of a 45° pitched blade turbine impeller, physical properties of the solution, equivalent diameter of the vessel base area (de), distance between the impeller and the bottom of the vessel (L), and the presence of the drag-reducing polymer in the solution (Polyox WSR-301). The data were correlated for polymer-free solution by the equation

Polyox addition was found to reduce the mass transfer coefficient by an amount ranging from 24.2 to 56.6% depending on Re and polymer concentration. Practical implications of the present work for the design and operation of dialyzers and electrochemical and heterogeneous catalytic and biochemical reactors are highlighted. Also, the importance of the present work in predicting the rate of diffusion-controlled processes that may take place inside the agitated vessel such as corrosion, electroless plating (chemical plating), and electroplating is discussed.     

SOLID-LIQUID MASS TRANSFER STUDY OF THE OZONATION OF PHENANTHRENE

Phenanthrene, a priority, hazardous pollutant, is found in the vapor and paniculate phase in the atmosphere as well as in aquatic ecosystems. Water droplets can form around the particulates and dissolve the phenanthrene. Subsequent oxidation of the phenanthrene by ozone can result in the formation of secondary pollutants. Thus the mass transfer of solid phenanthrene with and without ozonation reactions in water is investigated and a simple mathematical model based on film theory is formulated to predict the changes in bulk ozone concentrations and enhancement factors. Physical mass transfer coefficients for phenanthrene in water measured at room temperature in an agitated vessel increased from 1·174 ×10^-5 to 2·932 × 10^-5 m/s as the agitation speed increased from 65 to 315 RPM. The ozonation of phenanthrene significantly increases the mass transfer rates of phenanthrene into water as indicated by enhancement factors which range from 2 to 7·8. At low agitation speeds, the film model agreed well with the experimental data regarding the rates of disappearance and concentrations of the bulk ozone. However, the calculated and measured concentrations of ozone deviated as much as 55% at high speeds of agitation probably due to turbulent effects. Nevertheless, the model is useful for estimating the enhancement factor; the theoretical and experimental values are in good agreement with the maximum deviation of 25%.     

ON THE METHODS FOR THE DETERMINATION OF THE OXYGEN TRANSFER COEFFICIENT IN MECHANICALLY AGITATED VESSELS

This paper reports on the determination of the overall oxygen transfer coefficient in mechanically agitated vessels. Many variants of the sulfite oxidation method are compared with the dynamic method. A new variant of the sulfite oxidation method, called the reaction time method, is proposed. Overall oxygen mass transfer coefficients were obtained with two probes having significantly different time constants and for various agitation levels. The advantages and disadvantages of the main methods used for the determination of the oxygen transfer coefficient are reviewed and discussed.     

固液非均相反应器RTD研究

建立并检验了固液非均相反应系统停留时间分布（ＲＴＤ）的流动模型，研究了固液两相ＲＴＤ的变化规律，及该特定系统的放大规律，并给出了相应的放大经验模型，初步确立了固液非均相反应器的最佳中试规模。为固液非均相反应器的中试放大提供了理论和实验依据。     

通气式搅拌槽的传热特性

研究了通式搅拌槽槽壁给热系数（ｈｗ）随通气速率和搅拌转速变化的规律和机理，在搅拌过程中存在一个临界转速，它决定了通气是增大还是减小ｈｗ。通过引入综合反映操作条件对ｈｗ影响的无因次数Ｈｚ，获得了一个偏差较小并且简单实用的ｈｗ半经验关联式。     

PARTICLE-LIQUID MASS TRANSFER IN MULTIIMPELLER MECHANICALLY AGITATED CONTACTORS

The mass transfer coefficients between solid particles and liquids in high aspect ratio contactors agitated by multiple impellers have been reported. Two vessel sizes i.e., 0.15 m and 0.30m I.D. each with a length of 1.0 m were used. The effects of particle size, liquid viscosity and agitation speed were studied using two types of impellers, i.e., disc turbine (DT) and pitched turbine downflow (PTD). The spacings between two impellers were maintained at tank diameter. A simple mass transfer correlation based on critical suspension speed is proposed.     

MASS TRANSFER CHARACTERISTICS IN A SLURRY REACTOR

The gas-liquid and solids-liquid mass transfer characteristics of a slurry reactor with vibratory agitation have been studied in gas-liquid-solids three phase systems. It has been found that the rates of mass transfer between both the gas-liquid and the solids-liquid phases are influenced by the solids concentration and the gas flow rate if the solids concentration and the gas flow rate exceed 5 to 10% by volume and about 0.2 cm/s, respectively.     

EXPERIMENTAL DETERMINATION AND MODELLING OF LIQUID-SOLID MASS TRANSFER COEFFICIENTS IN A THREE-PHASE REACTOR

Apparent mass transfer coefficients for solid dissolution in a liquid with and without a chemical reaction were experimentally determined in a fixed bed three phases reactor with downward cocurrent gas and liquid flows. The chemical system selected was benzoic acid, sodium hydroxide in aqueous solution, and atmospheric air. Continuous gas, pulse and dispersed bubble regimes were studied and the results were correlated obtaining apparent mass transfer coefficient as a function of liquid and fluid volumetric flow. It was found that gas flow effect on mass transfer coefficient was small over continuous gas and dispersed bubble regimes, but appreciable over pulse regime. Additionally, it was found that the mathematical model that best described the mass transfer process under pulse regime, by using the increment factor due to the instantaneous chemical reaction, is the film theory     

CONTINUOUS MONITORING OF MASS TRANSFER RATES IN BATCH AGITATED LIQUID-LIQUID SYSTEMS BY ELECTRICAL CONDUCTIVITY

In continuous monitoring of mass transfer rates by electrical conductivity in batch agitated liquid-liquid systems, it is helpful to identify those conditions under which the conductance is predominantly due to solute concentration in the continuous phase only. In such cases there is no need for correction to accomodate dispersed phase conductivity effects. This problem is addressed here, with extension to include transient and dispersed phase conductivities; mass transfer between the two phases; repeated breakup, rebounding, and coalescence of the droplets due to agitation; and deformation of the dispersed phase particles in turbulent flow.     

FREE CONVECTION MASS TRANSFER AT HORIZONTAL CYLINDERS

Natural convection mass transfer at horizontal cylinders was studied using an electrochemical technique involving the deposition of copper from acidified copper sulphate solution. Cylinder diameter and copper sulphate concentrations were varied to provide a range of Sc. Gr from 1.55 × 10¹⁰ to 2 × 10¹². Under these conditions, the data were correlated by the equation:

Measurement of mass transfer distribution revealed the fact that mass is transferred at the lower hemicylinder by a laminar flow mechanism and at the upper hemicylinder by a turbulent flow mechanism.     

LIQUID-SOLID MASS TRANSFER AT HORIZONTAL WOVEN SCREENS WITH UPWARD COCURRENT GAS-LIQUID FLOW

Rates of liquid-solid mass transfer at horizontal single screens and an array of horizontal parallel separated screens were studied under upward cocurrent gas (N₂)-liquid bubbly flow using the electrochemical technique. Variables studied were gas and liquid flow rates, and screen characteristics (e.g., mesh number and wire diameter)

Under the present conditions where relatively low solution flow rates were used the rate of mass transfer was found to be mainly determined by the gas flow rate. For a given gas flow rate, the mass transfer coefficient decreased with increasing solution flow rate. The data for single screen were correlated with a dimensionless equation. Rates of mass transfer at an array of separated horizontal screens were lower than those at the single screen by an amount ranging from 3 to 45% depending on screen mesh number and flow conditions. The importance of the present study for building continuous high space time yield catalytic, and electrochemical reactors suitable for electrochemical air pollution control is highlighted.     

LIQUID-SOLID MASS TRANSFER AT HORIZONTAL WOVEN SCREENS WITH UPWARD COCURRENT GAS-LIQUID FLOW

Rates of liquid-solid mass transfer at horizontal single screens and an array of horizontal parallel separated screens were studied under upward cocurrent gas (N₂)-liquid bubbly flow using the electrochemical technique. Variables studied were gas and liquid flow rates, and screen characteristics (e.g., mesh number and wire diameter)

Under the present conditions where relatively low solution flow rates were used the rate of mass transfer was found to be mainly determined by the gas flow rate. For a given gas flow rate, the mass transfer coefficient decreased with increasing solution flow rate. The data for single screen were correlated with a dimensionless equation. Rates of mass transfer at an array of separated horizontal screens were lower than those at the single screen by an amount ranging from 3 to 45% depending on screen mesh number and flow conditions. The importance of the present study for building continuous high space time yield catalytic, and electrochemical reactors suitable for electrochemical air pollution control is highlighted.     

SOLID-LIQUID MASS TRANSFER IN PACKED BEDS: ENHANCEMENT DUE TO ULTRASOUND

Enhancement in the solid-liquid mass transfer coefficient in packed beds due to sonic vibrations (ultrasound) has been studied. The results show considerable enhancement at relatively high power inputs. A correlation for the Sherwood number in such systems has been proposed.     

THE MEASUREMENT OF BUBBLE DIAMETER DISTRIBUTIONS AND LIQUID SIDE MASS TRANSFER COEFFICIENTS IN A GAS-LIQUID AGITATED VESSEL USING A REAL-TIME,HIGH-SPEED IMAGE PROCESSING SYSTEM

In this study, we report the measurement results of various spatial distributions, such as Sauter diameter, gas holdup ratio, and interface area per unit liquid volume, in a vessel using a real-time, high-speed image processing system developed by ourselves. We attempted to separate liquid side mass transfer coefficients, k L , from overall volumetric mass transfer coefficients, k L a, based on the results mentioned above. And we examined the relations between power consumption per unit volume, P v , and both k L and k L a in order to establish correlation equations of k L and k L a with P v , gas holdup ratio, gas superficial velocity, v s , and surface tension.     

MASS TRANSFER CHARACTERISTICS OF THE MEMBRANEOUS GAS DISTRIBUTOR

1 INTRODUCTIONIt is well known that the throughput of many gas-liquid reactors is limited by the rate atwhich a gaseous component can be transferred from the gas to the liquid.For example,it isthe oxygen transfer capacity of a fermentor that set the upper limit to the productivity ofmost aerobic fermentation.Therefore,studies have been in progress to increase the masstransfer rate between the gas bubble and the broth by acting on classical parameters of bubblesize and the turbulence of flow.However,the intensive turbulence of flow usually means     

析气界面上气泡滑移促进的传质模型探索

本文在充分研究析气界面上气泡行为的基础上，根据界面上析出气泡的动力学行为，结合界面附近流体及相间传质理论。导出了气泡滑移促进的传质模型     

挡板进气多级搅拌槽内的气－液分散特性

研究了挡板进气多级搅拌槽内的气－液分散流型、临界分散转速、搅拌功率、气含率和气泡停留时间。试验证明，这种结构的搅拌槽，比标准通气式搅拌槽具有更优良的气－液分散特性，并回归得到了搅拌功率、气含率和气泡停留时间的关联式。     

SOLID-LIQUID MASS TRANSFER AND WETTING FACTORS IN TRICKLE BED REACTORS: EFFECT OF THE TYPE OF SOLID PHASE AND THE PRESENCE OF CHEMICAL REACTION

The solid-liquid wetting factor, f, for solid dissolution in a liquid with and without chemical reaction was experimentally determined in a fixed bed three-phase reactor with downward concurrent gas and liquid flows (Trickle Bed Reactor). The method employed consisted of comparing the volumetric solid-liquid mass transfer coefficient obtained when two phases (liquid and gas) circulated through the bed, with those coefficients obtained at liquid full bed conditions, maintaining the intrinsic liquid velocity constant. The chemical system selected was benzoic acid and acetylsalicylic acid as solid phases, water and sodium hydroxide in aqueous solution, and atmospheric air. Experiments were carried out in which the flow of both phases was modified, obtaining a direct dependency of f with the flow and holdup of liquid. The gas flow effect over f was not important in the flow regime studied, defined as the low interaction regime. Furthermore, the wetting factor is not affected by the nature of the solute and by the presence of a chemical reaction.