Impinging streams (IS) are classified into gas-continuous and liquid-continuous ones (GIS and LIS). Large number of experimental data has shown GIS promotes transfer very efficiently; while it has the intrinsic faultiness of very short residence time, and its flow configuration is relatively complex, resulting in difficulty in arranging multistage process. Essentially, GIS is applicable only for rapid processes controlled by gas film diffusion. The effect of LIS enhancing transfer is negligible; while it has the features of efficient micromixing and strong pressure fluctuation both which are resulted from the intensive interaction between the opposing streams and can promote process kinetics. All the features of IS, including GIS and LIS, have great potential of application. Reviewing the results of number investigations, mostly worked by the authors, a somewhat detailed introduction to the features of IS and several cases of its successful applications, such as wet FGD, preparation of ultrafine or nano powders, successful industrial application of large scale LIS reactors and crystallizers, etc, are described. 1. Introduction Impinging streams (IS), as a novel technical method in chemical engineering, first presented by Elperin [1] was aimed at enhancement of transfer between solid and gas phases, as shown in Figure 1. Because of its well properties and application potential, wide investigations on IS were made in the former Soviet Union, Israel [2], China, and some other countries since 1960s; the concept of IS was also extended, including the extension of phase conditions, that is, the continuous phase in IS can also be a liquid. Results of number investigations have illustrated that the properties and performances of IS with a liquid as the continuous phases are quite different from those with a gas as the continuous phase [3]. In order to favor understanding, Wu [4, 5] proposed the supplemental classification, classifying IS into two categories: gas-continuous impinging streams (GIS) and liquid-continuous impinging streams (LIS). The features of both GIS and LIS have important values for application. Figure 1: Original idea of impinging streams [ 2]. In addition, to make the concept clear, the definition of IS was proposed as follows [6]. Impinging Streams are the flow configuration in which two continuous steams with certain momentum fluxes, containing dispersed phase(s) or not, flowing along the opposing directions, respectively, vertical to the bisection across the impinging point, impinge against each other. Reviewing the results from a number
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