IMPINGING STREAMS properties

Since there are significant differences of properties and performances between gas-and liquid-continuous impinging streams, the two kinds of impinging streams will be discussed separately in this book. 

Part I of this book focuses on problems relating to gas-continuous impinging streams, including basic regulations, properties, and some of its applications. 

It is clear that such significant deflection as that shown in Fig. 1.1 must be related to the properties of the liquid employed. In comparison with liquid, both the density and viscosity of a gas are much smaller, so that such a strong deflection could not be observed with gas jets. However, in principle, it is possible that such deflection phenomena could occur in gaseous single-phase impinging streams, but the degree of deflection may differ greatly from that of liquor ones. 

Since 1995, the author of the present book has organized a number of investigations, theoretical and experimental, on the properties and application of the submerged circulative impinging stream reactor (SCISR) [9, 13, 15-18, 31], The flow configuration inside the reactor is two impinging horizontal streams, as shown in Fig. 

As an example, let us now examine the specific case of particle motion at 25°C and atmosphere pressure. The related physical properties are dp = 0.001 m, pp = 1000 kg-nf p, = 1.145 kg-in. and pg = 1.798 Pa s. The calculated values for the terminal velocity and the operational condition ranges are given in Table 2.2. An important conclusion that can be drawn from the data listed in the fourth column of Table 2.2 is that the Stokes regime cannot exist in co-axial horizontal impinging streams while other regimes are applicable in this kind of impinging stream. 

The residence time distribution of particles is related to the properties of the particles and the gas flow, including the size distribution, and the velocity of gas flow and its profile. In practically applicable impinging stream devices, the particles being processed usually have relatively narrower size distribution the diameter of the tube to particles size ratio, d Jd,h is normally very large ( 15) while the gas velocity is high... 

Only solid particles residence time and its distribution are discussed in the present chapter although, because of the similarities of movements of the dispersed phases in impinging streams, the results described above are also of referential significance for gas-liquid impinging streams. The differences between the properties of liquids and solids and their influences will be discussed in detail in the relevant chapters. 

It should be noted that, generally, the properties of liquid should affect the mean diameter of spray droplets to some extent, both before and after the impingement. In the investigation on the dispersity of liquid in impinging streams described here, however, only water was tested as a process liquid while other liquids were not. This remains to be studied further. 

On the basis of a thorough understanding of the properties of gas-continuous impinging streams, including its advantages and disadvantages, the circulative impinging stream dryer (CISD) was developed and patented by the author of the present book [11, 103]. Primary tests on a quasi industrial scale have yielded satisfactory results, and it can be expected to be applied industrially in the near future. 

From the basic properties of gas-continuous impinging streams and the burning models derived in the last section, impinging streams intensify the combustion processes of atomized liquid and powdery solid fuels by the following mechanisms ... 

Because the properties of liquids are essentially different from those of gases, impinging streams with liquid and gas as the continuous phases exhibit totally different performances and it is therefore necessary to discuss them separately. Part II focuses on liquid-continuous impinging streams and related problems, including the features of LIS that efficiently promote micromixing, pressure fluctuation phenomena in LIS, promotion of kinetic processes by LIS, and the application of LIS in the preparation of ultrafine particles, etc. Finally, this we will introduce some important research and development on LIS devices and look forward to the future applications of LIS. 

DIFFERENCES BETWEEN PROPERTIES OF CONTINUOUS PHASES AND CLASSIFICATION OF IMPINGING STREAMS... 

Influences of property differences on the performance of impinging streams... 

The significant differences between the properties of liquids and gases result in totally different performances of impinging streams with liquid and gas as the continuous phase, as discussed below. 

From the discussions above we can see that, because of the significant differences between the properties of liquid and gas, the two kinds of impinging stream with liquid and gas as the continuous phase, respectively, give totally different performances. From the point of view of taxonomy, it is necessary to distinguish them. Therefore a supplementary classification should be made according to continuous phase, i.e., impinging streams should also be classified according to the continuous phase involved in ... 

Wu, Yuan (2001). Properties of application of impinging streams. Chem. Indus. Eng. Progress., 20(11) 8-13 (in Chinese). 

Tamir, A. and Luzzatto, K. (1985). Solid-solid and gas-gas mixing properties of a new two impinging stream mixer. AIChE J., 31 781-787. 

Impinging Streams Fundamentals, Properties, Applications By Yuan Wu... 

Rupe, J.H., A Correlation Between the Dynamic Properties of a Pair of Impinging Streams and the Uniformity of Mixture-Ratio Distribution in the Resulting Spray, Progress Repmt No. 20-209, Jet Propulsion Laboratory, Pasadena, CA, Mar. 28, 1956. 

For any impinging stream system, the heat transfer coefficient, both local and averaged over the total residence time of particles, increases as the gas velocity increases and decreases as the gas temperature increases. Such a temperature influence on heat transfer results not only from the variation in gas properties but also from an appreciable change in the hydrodynamic conditions with an increase in the gas temperature, the penetration depth into opposing gas stream increases, which extends the period of unsteady particle motion, thus enhancing the total heat transfer. 

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