PREDICTION OF DROP SIZE IN PULSED PERFORATED-PLATE EXTRACTION COLUMNS

A single expression for the prediction of drop size in the mixer-settler, transition and emulsion regimes of operation in pulsed perforated-plate liquid/liquid extraction columns is presented. Analysis of 326 published drop size measurements both with and without mass transfer for 16 liquid/liquid systems from 12 different data sources show that the Sauter mean drop diameter, d ₃₂, in the dispersion is given in terms of column geometry, operating conditions and physical properties of the phases by:

in which ρ_* and σ _* are the density and surface tension of water at 20°C and α and 1 are the fractional plate free area and compartment height respectively. This equation predicts the drop diameter with an average deviation of 11·3% which is much better than the average errors obtained using other available correlations.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose-NaCl-water, 20-5-75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

MODELING WATER LOSS DURING FRYING OF POTATO STRIPS: EFFECT OF SOLUTE IMPREGNATION

ABSTRACT

The effect of solute impregnation on water loss and oil uptake during potato strip frying was studied. Blanched potato strips were impregnated at 25°C by soaking in a solution of sucrose–NaCl–water, 20–5–75% by weight. After rinsing and air drying, strips were deep fried in sunflower oil at 160, 170 and 180°C. A control treatment, consisting of potato strips blanched but not soaked and later air dried was also conducted. Solute impregnation provided a decrease of the oil uptake. Two models, based on Fick's law were used to describe water loss during frying. The first one is the classic model with an effective moisture diffusion coefficient assumed a constant value. The second model considers that diffusion coefficient varies during the frying process. For a given frying temperature, constant diffusion coefficient for control potatoes resulted in lower values than the impregnated ones. The variable diffusivity model showed a two-stage behavior: during the first stage of frying, diffusion coefficient increased with frying temperatures, but from a given time on an inverse behavior began. This last fact was found to be related to an increase of the measured peak force needed to penetrate the potato crust.     

THE DYNAMICS OF PULSED PLATE EXTRACTION COLUMNS PART 2 DROPLET SIZE STUDIES IN THE ABSENCE OF MASS TRANSFER

Published droplet size data for the system 30X TBP/OK - 2M aqueous nitric acid have been re-evaluated and compared with new measurements for the system 2 OX TBP/OK - 3M aqueous nitric acid.

Correlations are presented for the Sauter mean and the dispersed phase holdup. At frequencies in excess of 1.5 Hz, pulsed plate columns tend to operate in the continuous dispersion regime and dvs increases linearly with holduo provided that the column internals ara not wetted by the dispersed phase, so that

dvs = d^ovs + mx

In this expression, m is a constant for a given system and is a measure of the rate of increase of droplet size with holdup. The term d^o _vs+ mx is the characteristic droplet size, i.e. the limiting value of d_vsat substantially zero holdup and is a function of the system properties and the pulse frequency and amplitude. In the case of the 20% TBP/OK system, it was found that equation (2) only described the variation of droplet size with holdup provided that the additional requirement (2fA) >4 × 10^?2ms^?1was met.This is thought to reflect the tendency for the sieve plates to promote droplet coalescence when (2fA) < 4 × 10^?2ms^?1.

At pulse frequencies less than 1.5 Hz, mixer- settler type operation is apparent and is accompanied by considerable droplet coalescence during each pulse cycle. In this situation, the mean droplet size becomes larger and independent of holdup so that dvs becomes synonymous with d^o _vsand, for a given system, depends only upon the pulse frequency and amplitude.

These results are discussed in the context of the wetting characteristics of the column internals.There is evidence that the latter plays a major part in droplet recombination processes, and gross coalescence induced by wetting can be more significant than simple interdroplet coalescence. Until the wetting characteristics of column internals can be taken into account quantitatively, the present results should be considered specific to the equipment and extraction systems employed.     

用动态响应曲线法研究脉冲筛板萃取柱的传质特性

用动态响应曲线法研究了内径150mm脉冲筛板萃取柱的传质特性,并考虑了轴向混合。实验体系采用30％TBP(煤油)-硝酸-水,操作条件:脉冲频率:1.0～2.5s~(-1),脉冲振幅=0.0067～0.030m,有机相/水相=1/1～3.3/1.实验结果表明,本法与稳态浓度剖面法同样可靠,且省时、省料,可在更宽流比范围内用于大柱径萃取设备的研究。     

THEORETICAL PREDICTION OF GAS HOLDUP IN BUBBLE COLUMNS WITH NEWTONIAN AND NON-NEWTONIAN LIQUIDS

A simple model based on an energy balance which takes into account the friction losses at the gas-liquid interface and the slip velocity of single bubble is used to simulate the gas holdup in bubble columns containing Newtonian and non-Newtonian liquids which circulate in both laminar and turbulent flows. Experimental data available from the literature for bubble columns up to 7 m height and 1 m diameter with water and glycerol as Newtonian liquids and different solutions of CMC in a wide range of concentrations as non-Newtonian liquids are simulated with good agreement despite the simplifications made to describe the gas liquid flow regimes. Most of the differences between experimental and calculated gas holdup are justified on the basis of the simplifying assumptions.     

液膜法提取浓缩氨基酸

本文研究了用液膜法提取浓缩谷氨酸。用ＴＯＭＡＣ为载体，ＥＣＡ４３６０Ｊ为表面活性剂，在适当的酸度下，以氯离子的浓度差作推动力，提取率可达６０％，浓缩倍数可达５倍。谷氨酸可以克服１１－１２倍的浓度梯度进行能动的膜输送而进入内相，这比文献报导的数值高出近一倍。     

臭氧吸收中液相臭氧浓度和增强因子理论预测

研究了臭氧在鼓泡塔中吸收时,水中溶解臭氧浓度随时间的变化规律以及pH值对它的影响。建立了臭氧吸收数学模型,可较准确地预测水中溶解臭氧浓度;同时基于稳态膜理论,提出了带有一个一级臭氧自分解反应和多个一级或二级臭氧氧化反应臭氧吸收过程的增强因子理论预测模型,与文献值比较,结果合理。