Conveying of particles

Konrad, K., Harrison, D., Nedderman, R. M. and Davidson, J. F. (1980). Prediction of the Pressure Drop for Horizontal Dense-Phase Pneumatic Conveying of Particles. Pneumotransport, 5,225. 

K. Konrad, D. Harrison, R.M. Nedderman and J.F. Davidson, Prediction of the pressure drop for horizontal dense phase pneumatic conveying of particles, Proc. 5th Int. Conf. on Pneumatic Transport of Solids in Pipes, Pneumotransport 5, pp.225-244 (1980). 

According to the chemical theory of olfaction, the mechanism by which olfaction occurs is the emittance of particles by the odorous substances. These particles are conveyed to the olfactory epithelium by convection, diffusion, or both, and dkecdy or indkectly induce chemical changes in the olfactory receptors. 

Spouted beds are used for coarse particles that do not fluidize well. A single, high velocity gas jet is introduced under the center of a static particulate bed. This jet entrains and conveys a stream of particles up through the bed into the vessel freeboard where the jet expands, loses velocity, and allows the particles to be disentrained. The particles fall back into the bed and gradually move downward with the peripheral mass until reentrained. Particle-gas mixing is less uniform than in a fluid bed. 

As a simple and efficient particle separation device, cyclone collectors can be used for anything from dust removal in a fluid stream to material collection in the fluid conveying system. However, the cyclone is not suitable or economical for the separation of extremely small particles (say, less than 1 /xm), which frequently occur in industrial processes. It is recommended that the size of particles to be separated in an industrial ventilation cyclone be in the region of around 10 to 100 p.m. However, for the purpose of aerosol sampling, the size of particles to be separated may be much less than 10 jxm. 

Durand<62) has also studied vertical transport of sand and gravel of particle size ranging between 0.18 mm and 4.57 mm in a 150 mm diameter pipe, and Worster and Denny 63 conveyed coal and gravel in vertical pipes of diameters 75, 100, and 150 mm. They concluded that the pressure drop for the slurry was the same as for the water alone, if due allowance was made for the static head attributable to the solids in the pipe. 

As the particles enter the conveying line, they tend to settle out before they are fully accelerated. They form dunes which are then swept bodily downstream giving an uneven longitudinal distribution of particles along the pipeline. 

The conveying of fine particles in vertical pipes of diameters 25 mm, 50 mm, and 75 mm has been studied by BoOTHROYD(75 . He measured the pressure gradient in the pipeline, and found that the frictional pressure drop was less than that for air alone in the 25 mm pipe, but was greater in the larger pipes. This effect was attributed to the fact that the extent to which the fluid turbulence was affected by the presence of the particles was markedly influenced by pipe size. 

James, J. G. and Broad, B. A. Transport and Road Research Laboratory, TRRL Supplementary Report 635 (1980) Conveyance of coarse particle solids by hydraulic pipeline Trials with limestone aggregates in 102, 156 and 207 mm diameter pipes. 

In order to evaluate the extent of attrition and its impact on the particle size distribution, there is a need of a qualitative and quantitative characterization. This, however, is not as simple as it may seem at first. There are many different properties, parameters and effects that manifest themselves and could be measured. In addition, as will be shown, the choice of the assessment procedure is strongly connected with the definition of attrition which, on its part, depends on the degradation mechanism that is considered to be relevant to the process. Hence there are a lot of procedures and indices to characterize the process of particle attrition. Section 3 deals with those which are relevant to fluidized beds and pneumatic conveying lines. 

Wall-Hardness. One can assume that the particle degradation increases with the hardness of the vessel wall. This effect will increase with increasing ratio of particle-to-tube diameter and will thus in practice be relevant in pneumatic conveying lines only. 

Most studies of hydrocyclone performance for particle classification have been carried out at particle concentrations of about 1 per cent by volume. The simplest theory for the classification of particles is based on the concept that particles will tend to orbit at the radius at which the centrifugal force is exactly balanced by the fluid friction force on the particles. Thus, the orbits will be of increasing radius as the particle size increases. Unfortunately, there is scant information on how the radial velocity component varies with location. In general, a particle will be conveyed in the secondary vortex to the overflow, if its orbital radius is less than the radius of that vortex. Alternatively, if the orbital radius would have been greater than the diameter of the shell at a particular height, the particle will be deposited on the walls and will be drawn downwards to the bottom outlet. 

The pumps of the DRYVAC family are the classic dry compressing claw vacuum pumps that are preferably used in the semiconductor industry, whereby the pumps need to meet a variety of special requirements. In semiconductor processes, as in many other vacuum applications, the formation of particles and dusts during the process and/or in the course of compressing the pumped substances to atmospheric pressure within the pump, is unavoidable. In the case of vacuum pumps operating on the claw principle it is possible to convey particles through the pump by means of so called pneumatic conveying". This prevents the deposition of particles and... 

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