Pneumatic mixing

The negative exponent on the Reynolds number of -0.32 indicates that Re has a medium effect on the mean diameter. This result is about in accordance with those obtained by Gretzinger and Marshall [801 in their investigation on the external mixing pneumatic spray nozzles. 

Bioreactors come in many different designs and shapes. The stirred tank reactors are common. They comprise a cylindrical tank, a mechanical stirrer, and a guidance system for the liquid to reduce stress and enhance mixing. Pneumatic reactors use air or oxygen to mix the fermentation broth. The gas is introduced near the bottom of the reactor and induces circulation of the liquid. 

The various types of plug flow bioreactors were recently surveyed by Moser (1985a). They utilize surface aeration by means of a variety of rotating brushes, rotors, cone aerators, or gas or fluid jets such as are found in biological waste water treatment plants. Beyond all mechanically driven systems, reactors can also be both aerated and mixed pneumatically, or one pump can serve for both mixing and hydrodynamic stirring. 

For the comparison of effervescent atomization with conventional pressure swirl and external mixing pneumatic atomization, maltodextrin solutions were chosen. In Fig. 21.34, the results for the pressure swirl nozzles are displayed. The two pressure... 

As with a plasma-arc furnace, various gases and pneumatically conveyed soHds have been added to the various types of a-c open-arc furnaces to decrease alloy loss, to stabilize the arc, and to decrease the noise level, but with mixed commercial success. 

Dried coal is pneumatically conveyed to feed bins, pressurized through lockhoppers, and fed to the refractory-lined fluidized-bed gasifier vessel by variable-speed screws. The gasifying agent, mixed oxygen and steam, is fed near the bottom of the gasifier. The bed operates at 2.5 MPa (25 bar) and... 

Fig. 16. Single-stage pneumatic conveyor dryer using a venturi for material acceleration and gas—soflds mixing.

In a process loop with a pneumatic controller and a large process time constant. Here the process time constant is dominant, and the positioner will improve the linearitv of the final control element, Some common processes with large time constants that benefit from positioner application are liquid level, temperature, large volume gas pressure, and mixing,... 

I Although these steps, when carefully selected, can aid mixing, caution must he exercised with pneumatic conveying and vibrating, as they may tend to separate materials. 

The process steps listed in Table I9-I can sometimes be used to promote mixing. However, they are primarily for funcI ions other than solids mixing. (Note precautions for pneumatic conveying and vibrating in Table I9-I.)... 

A 3-1. round-bottomed three-necked flask is equipped with a mechanical stirrer, a 500-ml. dropping funnel, and a 250-ml. dropping funnel. The flask is contained in a pneumatic trough through which water at room temperature is circulated. A mix-... 

Solid-gas Mixing of immiscible liquids Pneumatic conveying of solids Fluidized beds... 

Aeration of ferric sulfate should be held to a minimum because of the hygroscopic nature of the material, particularly in damp atmospheres. Mixing of ferric sulfate and quicklime in conveying and dust vent systems should be avoided as caking and excessive heating can result. The presence of ferric sulfate and lime in combination has been known to destroy cloth bags in pneumatic unloading devices. Because ferric sulfate in the presence of moisture will stain, precautions similar to those discussed for ferric chloride should be observed. 

Dust explosion possible if in powder or granular form, mixed with air. If dry, it can be charged electrostatically by swirling, pneumatic transport, pouring, etc. 

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