单滴内的传质Ⅰ

本文应用Colburn-Welsh方法研究了正丁醇和异丁醇向下降的环流水滴的传质速率。实验结果经校正端效应后,曾与Kronig-Brink理论值以及Johnson和Heertjes等的数据作了比较。 实验结果表明,Kronig-Brink模型仅可适用于Re<50或60的情况,而在Re>80完全不能适用。实验结果和Johnson的单滴数据甚为符合,但较Heertjes的喷洒塔数据为高。异丁醇-水系的数据一般较正丁醇-水系的略高,但从光纹技术观察,两个系统都无可察见的介面骚动现象。

MASS TRANSFER RATES TO SINGLE CIRCULATING DROPS

Mass transfer rates of n- and i-butanol into single water drops falling through continuous phases of these liquids have been measured using Colburn and Welch technique. The results, after having been corrected for end effects and expressed as dispersed-phase mass transfer coefficients as well as a correlation factor R, have been compared with the Kronig and Brink model and with some selected data published in literature. From the results obtained it seems reasonable to conclude that the Kronig and Brink model will apply to circulating drops up to a drop Reynolds number of 50 or 60, which is similar to the conclusion reached recently by Treybal after careful examination of Johnsons paper, and will fail to remain valid above 80. The data are generally in agreement with those given by Johnson et. al. on single drops but somewhat higher than those of Heertjis et. al. in spray towers. The i-butanol-H2O system is found to show larger deviations all the way from the theoretical values than the n-butanol-H2O system. In as much as no interfacial turbulence has been observed by Schlieren technique in both cases, the difference in mass transfer rates between two systems can only be attributed to the difference in drop behaviour caused by the difference in such properties as viscosity and interfacial tension, and shape of drops. The variation of drop terminal velocities with drop sizes has also been examined. The results are found to be lower than those predicted by the correlation of Hu and Kintner for drops without mass transfer, but they are similar in trends in that the terminal velocities show also a maximum value at a certain transition drop diameter of about 3.5mm (this is in fair agreement with the calculated values of 3.5 and 3.8 mm for n- and i-butanol, respectively). It is thus likely that the Kronig and Brink model could apply to these systems up to such a drop size, above which the results would appear to approach a model descri bing the behaviour of oscillating drops such as that of Handles and Baron.