| Because of high mass transfer, short residence time, little back-mixing and easy to continuous production, impinging stream-rotating packed bed(IS-RPB) is widely used in rapid liquid-liquid mixing, reactions, emulsification, extraction and so on. Its significant characteristic is to intensify the edge effect of free impinging jets reactor(FIJRs) through the end effect of the inner diameter of rotating packed bed(RPB). Two times mixing is proceeded with reagents. The key to eliminating the edge effect and enhance mixing quality is coupling the size of FIJRs with the size of the inner diameter of RPB. However, to our knowledge, flow characteristics such as turbulent kinetic energy(TKE) distribution in FIJRs have rarely been investigated. It is of great significance to seek suitable means or methods to study the collision process, flow characteristic and mixing mechanism in FIJRs. It can provide theoretical guidance for the design of IS-RPB.In order to understand the mixing mechanism in FIJRs, the breakup mode, the impingement plane diameter, instantaneous velocity, mean velocity, the position of the stagnation point and TKE distribution at different Reynolds number(Re), jet spacing and jet diameter(w/d) ratio were analyzed by using PIV. The streamlines which characterize the tracer of liquids indicate that the flow-back does not occur in a FIJR. It seems like a plug flow reactor which can increase mass transfer and reaction rate. Different breakup modes show that the coalescence-dispersion model is fit for mixing mechanism in FIJRs. The instability and sensitivity of the stagnation point at unequal volumetric rate ratio illuminate that it is a feature of this kind of impinging jet reactors with two nozzles. As a consequence, it is not appropriate for the rapid liquid-liquid mixing, reaction which involves unequal volumetric rate ratio or more than three streams mixing.Flow imbalance commonly occurs in liquid-liquid mixing and reaction in industrial production, the impingement plane deviates from the center between the opposed jets and shifts towards to the lower momentum jet when two streams collide with each other at unequal flow/volumetric rate, resulting in poor mixing quality, affecting the progress of chemical reaction and the quality of the products. Motivated by the needs described above, free tripleimpinging jets(FTIJs) were designed to improve mixing for rapid liquid-liquid mixing and reactions with unequal volumetric flow rate ratio. An integrated flow characteristic method was proposed which included three steps: the qualitative study of liquid structures by using a high speed camera, the liquid motion law and turbulent degree with PIV, the micromixing investigation by chemical reactions. The liquid structures and breakup mode were analyzed at different impingement angles, Re, w/d, basic angles and volumetric flow rate ratio. Expansion angle and the homogeneity of liquid sheet dispersion were used to assess the dispersion degree and turbulent degree of liquids. The reasonability for the design of FTIJs was verified.According to the optimized operational parameters in above experiments using a high speed camera, the effect of Re and jet spacing on instantaneous velocity, mean velocity, the position of the stagnation point and TKE distributions of FTIJs were investigated by adopting PIV at unequal volumetric flow rate ratios. With TKE as an evaluation index, the results show that Re significantly influences the liquid motion directions, TKE distributions and peak values of TKE. Similar velocity distributions and TKE distributions of a large jet spacing can be obtained by increasing the jet velocity as a small jet spacing performed. The present work provides the theoretical supporting for prediction the mixing quality in FTIJs.2,2- dimethoxypropane(DMP) acid catalyzed hydrolysis was used to test the micromixing efficiency, and to verify the accuracy of the flow behavior in FTIJs. Adopting the conversion of DMP to characterize micromixing in FTIJs,the results show a satisfactory agreement with above visualization investigations. When compared micromixing efficiency between FIJRs and FTIJs, micromixing quality of FTIJs is much better than that of FIJRs at unequal volumetric flow rate ratio, indicating that the superiority of micromixing efficiency of FTIJs is performed in rapid liquid-liquid mixing and reactions at at unequal volumetric flow rate ratio. The present work can provide the foundation and guidance for the design of IS-RPB, as well expanding its industrial applications. |
PDF Full Text Request