【摘要】 作者采用四个体系,测定有机溶剂液滴在水相中自由下降时溶质的传递速率。所选择的溶质,其分配系数均极有利于有机相,故滴内阻力可以略而不计。 实验中竭力防止系统的沾染,获得了重现性好的实验数据。作者比较了计算滴外系数的各种关系式的适用性,发现各式仅在一定的范围内适合。并提出了纯物系和实际萃取过程中沾染物系的滴外传质系数的一般关联方法。 在所选择的体系的浓度范围内,以光纹技术进行观察,当液滴悬垂于静止的水溶液中,未发现可察觉的介面骚动现象,故作者提出的一般关联方法仅能适用于无介面骚动现象的传质过程。更多还原

【Abstract】 Four ternary systems have been used for the determination of mass transfer rates between single organic drops and aqueous solutions. The solutes chosen are highly in favor of organic dispersed phase so that the resistance can be considered solely in the continuous aqueous phase.In the experiments for pure systems, special attention has been paid to the purification of all substances employed and to the avoidance of possible contaminations of apparatus and both liquids, and reproducible mass transfer results can thus be obtained over the range of drop Reynolds number between 4 and 1000. These data have been used to test various correlations proposed by different authors, and it has been found that each correlation can fit only a limited range of drop Reynolds number, i.e. at Re≤50, the measured continuous phase coefficients essentially follow those of solid spheres during dissolution, at Re≥1000, nearly agree with those predicted from the equation proposed by Handles and Baron[26], and at 100<Re<700, can fit the empirical correlation of Thorsen and Terjesen[32].Since in all practical extractions the conditions of pure systems can hardly be attained, and since the rate of mass transfer between drops and their surrounding liquid is sometimes very sensitive to the presence of impurities and may be reduced ultimately to that of rigid spheres, the present authors propose to include both the coefficients for pure systems and those for systems of varying degrees of contamination in a single and general scheme of correlation, based on that of Thorsen and Terjesen for pure systems only. In Fig. 7 where Sh is plotted against Re1/2 Sc1/3, the relationship for pure systems is represented by the upper curve which determines the highest possible coefficients attainable. This curve may be considered as composed of three portions with a lower turning point referring probably to the transition of mechanisms of mass transfer from rigid spheres to circulating drops and an upper turning point to the transition from circulating to oscillating drops respectively. The lower line GS represents the correlation for solid spheres proposed by Garner and Suckling[24], and alsothe lowest limit for liquid drops when contaminated with sufficient impurities or surface active agents. The region between the upper and the lower curves should therefore represent all situations of partly contaminated drops probably frequently found in practical extractions.Other than the four pure systems, tap water as well as distilled water containing small amounts of different surface active agents has been used as continuous phase in a series of runs, and within the experimental conditions the results can be correlated on the same diagram aswhere A and B depend on the nature and concentration of the impurities present.It is known that in certain cases interfacial turbulence[8-14] occurs during mass transfer between liquid phases, and that the rate of transfer may thus be greatly enhanced. However, all systems used in the present investigation have been examined by means of Schlieren-optical technique and no perceptible inter-facial turbulence has been observed. Therefore, the proposed correlation might be considered only applicable to the cases where no such turbulence is present.更多还原