Homogenization with liquid jets

In homogenization with jets the mixing time can be relatively accurately calculated on the assumption 3 ac V/q [555]. The total liquid throughput q is composed of the propulsion jet and the quantity of entrained liquid. For calculating the propulsion jet see [140, 180] and for the quantity of entrained liquid see [14, 127]. 

The nozzle can be positioned centrally in the tank just under the liquid surface and operated by the liquid contents of the tank, so that the jet streams perpendicularly downwards and sets the liquid contents of the tank in circulation. Experiments [174] were carried out, in which 3% of the vessel contents was utilised and the mixing time, which is necessary for attaining 99% homogeneity, determined. 

The following mixing time characteristic (ti - jet velocity in the nozzle, d - nozzle diameter) was found  

The homogenization of relative thin liquids (p 100 mPa s) in storage tanks can be particularly effectively realized by rising gas bubbles from a sparger (sintered 

0(g/D) / = 4.75fr- / (dHVD ) / with Fr = After transformation it becomes  

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In fact, the concept of the quasi-homogeneous gas/liquid mixture, on which also the formulation of the target pi-number Y = (kLa/v) with intensity quantities is based, and which was fully verified in bubble columns with perforated plates as gas distributors, proves to be totally inappropriate when injectors are used as gas dispersers. The explanation for this fact is that in the case of injectors the coalescence takes place both in the free jet of the G/L dispersion and at its disintegration into a bubble swarm, while in the case of gas distribution with perforated plates this process has already been completed just above the perforated plate. 

The various dynamic methods give the surface tension of more or less recently formed surfaces, and may yield results different from the static methods, if adsorption occurs, and is incomplete at the moment when the tension is actually measured. One factor in dynamic measurements, which cannot be satisfactorily measured at present, is the time which has elapsed between the formation of the surface from the homogeneous interior liquid, and the actual measurement of the surface tension. If this could be varied, and measured with an accuracy of say 10 4 second, a valuable new weapon would be available for investigating the progress of adsorption. Bohr s work on oscillating jets is probably the best on any dynamic method. 

Based on these results, an new homogenizer was devised without the end-section with the edges and with improved geometry for the inlets of both phases. The calculations for this new design (Figure 3) show that the ftee liquid jet is not broken any longer due to a wider second nozzle. Therefore the pressure in the inlet region is much lower so self-suction of the dispersed phase could be expected. 

In appliances with only one degree of freedom (e.g. high-pressure homogenizers) power is being introduced by the liquid throughput itself. Here, the relevant intensively formulated quantity is therefore jet power per liquid throughput, P/q. Due to the fact that in nozzles P Ap q, this results in... 

Duineveld PC. (2003) The stability of ink-jet printed lines of liquid with zero receding contact angle on a homogeneous substrate. / Fluid Mech 477 175-200. 

Pearson s theoretical treatment was based on a linear stability analysis of the type described in Section 10.4 in connection with jet stability to small disturbances and paralleled Rayleigh s analysis for buoyancy driven instability. He assumed an infinite homogeneous liquid film of uniform thickness h whose lower surface is in contact with a rigid heat conductor at a fixed temperature and whose upper surface is free. Gravity is neglected (Ra = 0) and a linear temperature distribution across the film is assumed, with the high temperature at the lower surface. The surface tension is a function of temperature alone, and the rate of heat loss from the free surface is also a function of temperature only. 

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