Floodable flow

When powders flow, they do so either in a steady controlled fashion (as in the case of dry sand), or in a uncontrolled gushing manner (as would damp sand, for which the entire bulk tries to move in a solid mass). This latter condition is termed floodable flow it is most characteristic of the flow of cohesive, sticky... 

When powders flow, they do so either in a steady controlled fashion (as in the case of dry sand), or in an uncontrolled gushing manner (as would damp sand, for which the entire bulk tries to move in a solid mass). This latter condition is termed floodable flow, and is most characteristic of the flow of cohesive, sticky powders. The floodability of a powder is determined by its overall flowability (the determination of which has just been described), the angle of fall (obtained as the new repose angle when the powder cone is mechanically shocked), the dispersibility (ability of a given powder to become fluidized), and the angle of difference (obtained as the numerical difference between the angle of fall and angle of repose). 

The classification system introduced by Carr [29,30] was used to evaluate the flow properties of the sorbitol powders. In Carr s system, a flowable powder is defined as free flowing and will tend to flow steadily and consistently. This is to be contrasted with a floodable powder, which will exhibit an unstable, discontinuous, and gushing type of flow. The parameters in Carr s system include the angle of repose, angle of spatula, compressibility, cohesion, and dispersibility. Based on these parameters, flowability and floodability indices are calculated to determine the handling properties of bulk solids. 

The floodability index was calculated from the dispersibility, cohesion, angle of fall, and flowability index parameters. The values for this property ranged from 55 to 76. The most floodable material was lot 4405K5, and the least floodable material lot was the instant sorbitol, which is in agreement with the flow index and the particle size data. The... 

Other classification systems are used less frequently. Carr " also devised a system to classify materials as to their floodability. He defines the floodability of a material as its tendency to flow like a liquid because of the natural fluidization of a mass of particles by air. In order to so classify a material, the flowability is determined utilizing the method just described. This value is equivalent to a measurement Carr calls the angle of fall, angle of difference, and dispersibility. Though referred to in any of the papers mentioned here, this system is much less utilized then the flowability measurements. Geldart reported on a characterization system of powders according to their ability to aerate and later Molerus modified this system. In a more recent symposium this method of powder classification was examined. ... 

Floodability is the propensity of powders for flooding, i.e. an uncontrolled liquid-like flow out of a hopper. Flooding is attributable to the self-fluidization of a mass of particles caused by the sudden breakage of an arch or by the flow of material into or through a hopper which is wholly or partly empty. 

Floodability of a material is its tendency to have a liquid-like flow characteristic, which is caused by aeration within the powder. Powders can, when discharged from a hopper, behave in an unstable, liquid-like manner, which may be discontinuous, gushing and uncontrollable. The reasons for flooding are generally due to excessive aeration within the powder bed, which leads to easy powder fluidisation and ultimately to flooding. 

The flowability of a powder can be predicted from a series of laboratory tests using four different bulk powder flow parameters in a similar manner to Carr s floodability index. Howa-bility can thus be ranked from 0 to 100 using the four different bulk properties listed below ... 

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