Impinging velocity

Type R. This mode corresponds to low impinging velocities at any surface temperatures considered (200-400 °C). A droplet spreads as a radial film after impinging on a hot surface. Then, it shrinks and rebounds from the surface without breaking up. Hence, the mode is called R type. 

Type H. Further increasing droplet diameter and/or impinging velocity from the level in type N, the number of spots where the vapor blows through the radial film increases as compared to that in type N. Small droplets blown by the vapor are distributed even over the radial film, but the blowing-through of the vapor is weaker than in the type N. The pieces of the broken radial film that remain on the substrate surface are similar to those in type N. 

Type F. As the droplet diameter and/or impinging velocity further increases from the level in type V, the small droplets resulted from the breakup disperse in the radial direction, leading to transition into type F. In this mode, the radial film leaves the substrate surface in whole because the vapor beneath the film blows through in the radial direction. Thereafter, as the diameter of the film further increases, it is tom and broken up by the vapor into small droplets while the vapor flows beneath it. The small droplets are dragged by the vapor and disperse in the radial direction at velocities faster than... 

L is the distance between the nozzles, n(l is the velocity of the jet just leaving the nozzles, i.e., impinging velocity, 8 is the transverse dimension of the nozzles, and Lis dynamic viscosity of the fluid. 

R is the radius of the conduits n the velocity at the outlet of the conduit, i.e., the impinging velocity. The velocity components in terms of stream function were given by Eq. (1.26) while the conditions of irrotational flow were determined by Eq. (1.21). 

The most important operating parameter for gas-continuous impinging streams is the velocity of the gas flow at the outlet of the accelerating tube, also called impinging velocity, u0. Therefore, the most convenient approach is to relate all the individual hydraulic resistances to u0. 

Some of the structural factors, such as the changes in cross section area of flow passage and flow direction etc., may also cause pressure losses. Obviously, these factors depend on the specific structure of the device under consideration and vary from device to device. For convenience, and for more generalization, the resistance resulting from all the structural factors is represented in terms of the combined local resistance coefficient, 1s, which is also related to the velocity of the gas flow in the accelerating tube, i.e., the impinging velocity, utl. i.e.. 

It is clear from Fig. 4.5 that the data for ,c>p are considerably concentrated over 85% of the values are in the range 4.3 to 6.2, and the average value is 5.34. This fact indicates that ,c>p can be considered to remain essentially constant and that, consequentially, Eq. (4.11) describes well the pressure drop behavior due to the acceleration and collisions of the particles. Therefore the combined consideration of the two kinds of collisions, i.e., the collisions of particles on the wall and between particles, is reasonable and feasible. It should be noted that, as described by Eqs. (4.5) and (4.6), for a given impinging velocity u0, the velocity of particles at the outlet of the accelerating tube depends on the length of the tube Lac, the particles to gas mass flow rate ratio and the mean diameter of particles dv. Therefore Eq. (4.11) actually... 

Two sets of typical data experimentally measured are illustrated in Figs. 5.3(a) and (b), in which the curves represent the results calculated by Eq. (5.2) with properly regressed parameters Q. It should be noted that u.d in the figures is the airflow velocity at the exits of the nozzles which is quite different from the impinging velocity, u , in both the nature and the order of magnitude. 

Run No Impingement distance S, mm Lower distance h, mm Impinging velocity o, nvs 1 Feed rate mv, kg-s Moisture content of product xf, kg-kg-1... 

The influences of the liquid and gas flow rates, the diameter of the absorption chamber, the distance between nozzles, and the flow configuration on absorption rate were studied by the researchers mentioned above. These will not be discussed in detail here because of the length limitation of the chapter for the details, the reader may refer to the original references as cited in the text above. It should be noted, however, that in all the investigations above, the data for mass transfer coefficients are always correlated with the gas and/or liquid flow rates, but not with the impinging velocity, m0, although the latter is the operation parameter extremely important in every impinging stream device. 

Using the model equations described above and from the experimental data yielding Fig. 7.13, the calculated data are given in Fig. 7.18 as the plot of kG versus nn. By regression, the experimental data are fitted to represent the relationship between gas-film mass transfer coefficient and impinging velocity by... 

It can be seen in Figs 7.18 and 7.19 that in range of the impinging velocity w0 from 5.53 TO 16.62 m s-1 the values for volumetric mass transfer coefficient and the gas-film one ranged from 0.577 to 1.037 s l and 0.00641 to 0.0416 m s1, respectively, showing clearly the effect of impinging streams enhancing transfer between phases. 

The following optimal or feasible conditions and structural parameters were determined liquid to gas flow rate ratio VJVG = 0.85-1.OxlO 3 m3m 3 impinging velocity u0 = 10-15 m-s 1 dimensionless impinging distance S/d0> 4 molar ratio Ca/S = 1.0 for pseudo flue gas without C02 the nozzles were mounted at the outlets of the gas conduits ... 

The data on the relationship between impinging velocity and gas-film mass transfer coefficient were fitted by kG = 2.9 xlO 4no75821, with the standard deviation SD = 2.45X10 4 m-s 1, implying u0 is a strong effecting variable, and thus a very important operation variable ... 

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