Floodability

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. 

Although flooding is clearly associated with aeration and deaeration, de-aeration or fluidization tests alone are not sufficient to establish floodability. A long de-aeration time and large bed expansion observed in a simple de-aeration test usually, but not always76, coincide with a high likelihood of flooding. 

Bruff76 used another, more reliable, test as an indicator of flooding. A glass tube containing 200 g of the powder is aerated manually by shaking and then raised up from a table thus allowing 

Recent work by Geldart suggests that the ratio of the minimum bubbling and fluidization velocities, as obtained from fluidization tests (section 7.1), can be a measure of those properties which influence flooding, with the largest values corresponding to the powders which behave worst. 

There might be a way of assessing floodability indirectly from other powder tests, as Carr and Geldart suggest, but there is still a need for a standard, direct floodability test which could be used as a common yardstick further development in this area is needed. 

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. 

Powder Density (kg/m ) Mean particle size dp (mm) Hausner ratio (—) HowabrUty 

Carr categorised the potential for powders to flood by using four parameters, each parameter being given a weighting of 25 points. Thus 25 points were allotted to each of the following factors  

Summation of the above four factors contributes to a range of performance on a scale 0-100. 

The more dispersible a powder is the dustier (see Seetion 1.4.8) it becomes and therefore the more floodable. 

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Some drawbacks to the weigh belt are that it is a zero-reference device and thus needs frequent caHbration (re-zeroing). Buildup on the belt and roUers affects accuracy and operation, as does belt tension and dusty or floodable materials. Flexible connections are required to isolate the feeder from upstream and downstream equipment, unless the belt feeder/weigh idler concept is used. 

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... 

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... 

The buoyancy and floodability systems of retired NSs pending complex decommissioning require continuous servicing and maintenance of technical preparedness to prevent unauthorized sinking. 

To ensure safe shipment and observe the requirements of both the Russian Register and the International Supervisory Bodies to MVs, the new vessel should be equipped with double bottom, double sides, necessary number of cofferdams, biological shielding and physical protection devices, radiation control systems and equipment to ensure the above-water floodability. 

To exclude hypothetical incidents during temporary waterborne storage of damaged NS 175 and NS 610, appropriate measures were taken on ensuring their buoyancy and floodability. 

Considering that standard NS buoyancy equipment is presently in poor condition due to lack of servicing, scheduled repairs and corrosion processes, the Pacific Fleet s personnel uses basic buoyancy devices to ensure floodability of these NSs (installation of pontoons, filling of driving ballast tanks with polystyrene). 

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. ... 

The above-defined angle of fall is a rather poor measure of floodability, however, and is very rarely used in this country the definition of the measurement conditions is also poor, particularly of the jarring, and the tested values are certain to depend on the mass and the kind of support of the base plate of the instrument. 

Nelson, L. S., Buxton, L. D., and Planner, H. N., "Steam Explosion Triggering Phenomena. Part 2 Corlum-A and Corium-E Simulants and Oxides of Iron and Cobalt Studied with a Floodable Arc Melting Apparatus," Sandia National Laboratories, Albuquerque, NM, NUREG/CR-0633, SAND79-0260, May 1980. 

Descriptions and operating procedures are provided for each experiment, and will be found in the Console Information Book and/or posted at the beam ports. For example, the "Fast neutron/low gamma" biological experiment has the innermost aluminum can lined with thin lead, thicker lead liners in most of the remainder of the 6-inch section except for one section which as a 6-inch thick lead shield, a floodable aluminum outer plug, a 1-inch thick lead disk, and, finally, a large water-filled aluminum tank to serve as a beam stop. Irradiations are done inside the large concrete block between the shield wall and the beam stop. Samples are lowered through the door on the top of the concrete block while the shutter is closed and the outer collimator is flooded. 

The largest category of bulk powder behaviour, expressed in the terms of the three-dimensional parameters, is either a mass-time or a volume-time relationship. This category measures the rate of discharge from orifices, as opposed to the bulk powder properties of flowability and/or floodability of powders (Table 1.1). 

The degree of particle tensile strength was found by Yokoyama et al. (1982) to affect the floodability of a powder. The floodability index, using the various test methods for characterising bulk solids by the Carr s indices (ASTM D 6393-99 1999) was used to evaluate an intermediate condition between an aerated powder and a packed dense powder (see Section 1.8.1). 

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