Turbulent impinging streams

The theoretical method describing turbulent impinging streams was presented first by Champion and Libby [37] although it may not be the best, there is nothing better to date. 

Champion and Libby analyzed both the planar two-dimensional impinging streams and the impingement of two co-axial-cylindrical jets in which the flow is axis symmetrical. Actually, the results they obtained are applicable for both the two cases, provided the two-dimensional coordinates in planar impinging streams are replaced by the cylindrical coordinates. 

The second parameter is the measure of the turbulence intensity and is defined as k0/iiQ. It was found in laboratory experiments that turbulence intensities resulting from a grid or a baffle are such that ku/uq is of the order of 0.01 and LJiJJl) is of the order of 0.1. The fact that the two parameters are very small forms the basis of an asymptotic analysis of the model. As the quantity k0 /Uq approaches zero, the ratio 

The two-dimensional flow equations employed by Champion and Libby [37] are just the well known Reynolds stress equations [38], 

Of principal interest are the dimensionless axial and radial intensities, respectively, defined as 

---

Kostiuk et al. [40] measured experimentally the flow field of the vertical co-axial turbulent impinging streams with a two-component Laser Doppler velocity meter. The opposing gas streams were ejected from two burner nozzles, which were designed to produce a uniform axial velocity profile at their exits. The turbulence in the flow was generated by a perforated plate located at the end of the contraction section in each nozzle. The air velocity at the exit of the nozzle was varied from 4.1 to 11.4 m s and... 

In both stages, turbulent flow of the impinging streams is very desirable. The spent acid of the second stage, upon separation of the TNT, is fortified with aq nitric acid and is reused as the nitrating acid for the first stage... 

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. 

Bar and Tamir [63] studied the two-impinging stream dryer with two pairs of airfeeding tubes, as briefly shown in Fig. 6.7. The purpose of adding the lower two air streams is to increase the hold-up and the mean residence time of the particles in the dryer, and also aims to enhance the turbulence between phases in order to increase the drying intensity. However, the experiments did not show that the secondary air streams increased either the hold-up or the transfer coefficient. On the other hand, the induction of the two secondary air streams results in the greatly increased hydraulic resistance of the system. The pressure drop across the dryer, with two pairs of air-feeding tubes and with a volume treble that of the dryer shown in Fig. 6.6, is as high as 3800 Pa. 

Two streams of PUR chemicals collide with each other violently and under high pressure generally at 1,500 to 3000 psi (10.3 to 24.1 MPa) inside the mixer. When these impinging streams collide, the flow is very turbulent and the reaction begins. The stream exits the mixhead and is directed into the mold. After the pour a piston inside the mixhead scrapes the walls of the chambers completely clean so that no reacted foam is left inside the mixhead. 

Besides the high intensity of turbulence in the impingement zone, a common feature of any impinging stream is the unsteady particle motion, acceleration, deceleration, and movement of the particles against the gas stream for... 

---