Impinging velocity coefficient

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.. 

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 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 ... 

Here, Ap is the pressure drop across a microchannel heat sink subject to an impinging jet and p, Vq, e, K, Ce, H, Re, Wc, and Ar are density, impinging velocity at the inlet of the microchannel heat sink, fluid dynamic viscosity, porosity, permeability, Ergun coefficient, channel height, Reynolds number, channel width, and aspect ratio, respectively. The correlations for the pressure drop and the thermal resistance were compared with experimental results, and both match with experimental results within 10 %. 

In the impinging streams of gas-liquid systems, high relative velocity between phases and collision between droplets favor surface renewing of droplets, resulting in reduced liquid film resistance and thus increased overall mass transfer coefficient. 

On one hand, solid materials to be processed with an impinging stream device have various sizes, while, on the other hand, the relative velocity between gas and particles varies from time to time in acceleration and deceleration stages of particle motion. Both factors make the value for Rep vary continuously with considerably large amplitude, which may be across various flow regimes. So, the variation of the drag coefficient, Cd, in various flow regimes has to be taken into account in the solution of the motion equations for the particle in various stages. 

When an uitrasonic compressionai wave impinges normaiiy on a boundary between two materiais of different acoustic impedances, it is partly reflected and partly transmitted. The ratio of the ampiitude of the refiected wave A ) to that of the incident wave A is called the reflection coefficient (R), and the ratio of the amplitude of the transmitted wave At) to that of the incident wave the transmission coefficient (T). The appropriate coefficients when particie velocity amplitudes are used are [41]... 

The heat-transfer coefficient as a function of jet velocity, the pressure drop at the nozzle, and the power requirement are the key parameters in the design of impingement dryers. These parameters are inflnenced by various geometric parameters (e.g., arrangements of nozzles and exhaust... 

Continuous metal hand (heated by forced convection air, IR, direct steam or direct hot water) Heat transfer coefficient from impinging hot air. U = 0.06-0.09 kW/m K air velocity 15-25 m/s 5-50 kg water evaporated/m drying surface 1.5-2 kg steam/kg water evaporated power required is 20-30 kW with values relatively independent of the size. 

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