Impinging streams, heat transfer

As mentioned earlier, in gas-continuous impinging streams heat and mass transfer between phases are enhanced efficiently mainly by the following factors (1) Very high relative velocity between phases round the impingement plane, even higher than in common devices by several tens of times (2) Oscillation movement of particles or... 

As mentioned before, the concept of impinging streams (IS) was originally suggested for enhancing heat and mass transfer between a solid and a gas, and the development of the application of impinging streams were long focused mostly on multiphase systems. However, the problems involved in multiphase impinging streams are considerably complex so that it is necessary to study the behaviors of the individual phases separately. 

A theoretical analysis is helpful for understanding the basic characteristics of impinging stream processes and the performances of the related devices. In an impinging stream device, where the residence time distribution of particles is most important is in the impingement zone, because this zone is the major active region for heat and mass transfer between phases in such a device. Unfortunately, it is basically... 

In most cases, the major part of the particles movement in this stage is in the turbulent regime because of the high relative velocity between particles and gas flow, and so this space is also an active region for heat and mass transfer in the impinging stream device. 

Gas-continuous impinging streams with a liquid as the dispersed phase has wide application, such as in the combustion of liquid fuel droplets, absorption, water-spray cooling of air, etc. [9]. In such systems the dispersity of liquids plays a very important role affecting heat and mass transfer rates, because it influences both the interface area and the mean transfer coefficient. Wu et al. [68] investigated the influence of impinging streams on the dispersity of liquid. 

As mentioned, like any other technical method, the method of impinging streams (IS) cannot be a universal tool. On one hand, IS has the outstanding advantage of significantly enhancing heat and mass transfer between phases while on the other, it also has its intrinsic faults. From the discussions in the previous chapters, the essential characteristics of gas-continuous impinging streams can be summarized briefly as follows ... 

For drying, the typical parallel heat and mass transfer process, the feature of impinging streams that significantly enhances transfer, should of course be fully utilized. 

In principle, gas-continuous impinging streams (GIS) can be applied for the combustion of gases, powdery solids and sprayed liquids. Since gas-combustion is relatively simple and the process is essentially independent of the major feature of GIS, i.e., that it significantly enhances heat and mass transfer between phases, the discussions in this chapter will focus on the combustion of the latter two kinds of fuels. 

Elperin, I., Enyakin, Yu, P. and Meltzer, V. (1968). Experimental investigation of the hydrodynamics of impinging gas-solid particles streams. Heat and Mass Transfer in Dispersed Systems, (5) 454-496. 

Meltser, V. L. and Elperin, 1. T. (1968). Motion of single particle in apparatus with impinging streams, in Investigation of Convective Heat and Mass Transfer. Smolsky, Minsk, (p. 334-343). 

Kitron, Y. and Tamir, A. (1988). Performance of a coaxial gas-solid two impinging streams (TIS) reactor Hydrodynamics, residence time distribution and drying heat transfer. I EC Research, 27 1760-1767. 

Impinging streams [73] is a unique and multipurpose configuration of a two-phase suspension for intensifying heat and mass transfer processes in the following heterogeneous systems gas-solid, gas-liquid, liquid-liquid and solid-liquid. 

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