Divider, pneumatic

Nebulizers can be divided into several main types. The pneumatic forms work on the principle of breaking up a stream of liquid into droplets by mechanical means the liquid stream is forced through a fine nozzle and breaks up into droplets. There may be a concentric stream of gas to aid the formation of small droplets. The liquid stream can be directed from a fine nozzle at a solid target so that, on impact, the narrow diameter stream of liquid is broken into many tiny droplets. There are variants on this approach, described in the chapter devoted to nebulizers (Chapter 19). 

The pneumatic classification system should be designed to handle ha2ardous dust (28). A ha2ardous dust is one which, when finely divided and suspended in air in the proper concentration, bums, produces violent explosions, or is sufficiently toxic to be injurious to personnel health (see Air pollution control methods Powders, handling). At the least, almost any dust can be irritating to personnel because of inhalation or skin or eye contact. Fully oxidi2ed and hydrated materials are generally considered safe. 

Conveying systems normally use air as the transport medium to convey granular, crushed, or pulverized materials. Modelling the flow of pneumatic conveying and calculating its pressure loss is a problematic task. The greatest problem arises from the fact that different mass flow ratios, solid flow rate divided by the gas flow rate, imply different flow types in pneumatic conveying. Each of these flow types, which can be classified in many different ways, requires its own specific model in order to provide a concrete calculation method. 

Attrition of particulate materials occurs wherever solids are handled and processed. In contrast to the term comminution, which describes the intentional particle degradation, the term attrition condenses all phenomena of unwanted particle degradation which may lead to a lot of different problems. The present chapter focuses on two particular process types where attrition is of special relevance, namely fluidized beds and pneumatic conveying lines. The problems caused by attrition can be divided into two broad categories. On the one hand, there is the generation of fines. In the case of fluidized bed catalytic reactors, this will lead to a loss of valuable catalyst material. Moreover, attrition may cause dust problems like explosion hazards or additional burden on the filtration systems. On the other hand, attrition causes changes in physical properties of the material such as particle size distribution or surface area. This can result in a reduction of product quality or in difficulties with operation of the plant. 

Materials-handling equipment is logically divided into continuous and batch types, and into classes for the handling of liquids, solids, and gases. Liquids and gases are handled by means of pumps and blowers in pipes, flumes, and ducts and in containers such as drums, cylinders, and tank cars. Solids may be handled by conveyors, bucket elevators, chutes, lift trucks, and pneumatic systems. The selection of materials-handling equipment depends upon the cost and the work to be done. Factors that must be considered in selecting such equipment include ... 

Nebulizers can be divided into several main types. The pneumatic forms work on the principle of breaking up a stream of liquid into droplets by mechanical means the liquid stream is forced through a fine nozzle and breaks up into droplets. There may be a concentric stream of gas to aid... 

The cutters in use in mechanical sampling are divided into diverter types and bucket types. Both types are used to cut a stream falling due to gravity off the end of a conveyor belt or from the discharge end of a pneumatic conveying pipe or a chute. 

Fig. 5.66 is the view into a pipe after pneumatically conveying a slightly moist, finely divided quartz powder showing the heavy build-up in crust and massy deposit as well as the remainder of a dune. Massy deposits can be also formed by the action of other influences, such as centrifugal and inertial forces at elbows. 

Fig. 5.66 View into the pipe of a horizontal pneumatic conveyor after conveying a slightly moist, finely divided quartz powder at low velocity.

A fluid bed is a relatively stable mixture of a fluid, generally a gas, and finely divided solids which is intermediate between a fixed bed and the pneumatic transport condition. It resembles a boiling liquid in behavior. Fluid velocities are in the range which will lift and stir the suitably sized particles without carrying the particles completely out of the containing vessel. Solid particle sizes in the range from % in. to 10 microns (/i)... 

Transfer Lines, Pneumatic conveying of solids is an important factor in successful fluid-bed operation just as pumping of liquids is vital in other process operations. Lines are divided into two types standpipes in which solids flow downward concurrently with the gas and risers in... 

The splitting tool has specific levers and joints that divide the entry strength or impulse (e.g., by a hammer or pneumatic hammer) into two orthogonal forces or impulses. 

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