Hydrodynamic model of pneumatic classification of powder materials

Abstract

In our days in such fields of manufacturing as precision engineering, electronics, pharmaceutics there is a great interest in creating new materials, obtaining mainly in a powder form. The intensive researches in this area are carried out all over the world. Among the methods of production and processing of powders the pneumatic ones are most perspectives. On the basis of these methods a lot of various construction units are designed and applied in industry. The pneumatic circulating unit (PCU), designed in RIAMM (TSU) [l] is enough perspective for further developments. This unit allows carrying out the combined processes of powder production e.g. mixing, drying, grinding, and classification.The unit consists of (fig. 1) cylindrical-conical chamber 1 with coaxial pipe 2. The circulating motion of powder material is realized by the injection of the last by the compressed air feeding through the noz--zle block 3 in the bottom of the unit, the conveying of powder through the pipe and the precipitation of particles into the packed bed after the separation stage. For the classification of particles by their sizes the build-in vane rotating classifier 4 is applied. The main element of the classifier is the rotor, which generates a powerful centrifugal field around itself by its rotation and allows to achieve a high performance and sharp classification.It should be noticed that the gas flow in the separation zone has a turbulent nature and the turbulent difhsion of particles takes place. The concentration of particles in the flow in the separation zone is about 10 kg/kg and more, thus there are frequent particle-particle collisions and so-called secondary capture of small particles by large ones. All above factors significantly complicate a quantitative examination 2 -0 0 7 air of physical processes proceeding in the unit. The investigation of the classification process is reduced to construction of simplified stochastic models of a "black box" which impossible to be generalized to a wide class of materials. Although in view of considerable progress in the development of the computer technology it becomes more possible to solve the similar problems applying the numerical approaches.In terms of aforesaid in this paper the "interpenetrating and interacting continua" concept is implemented [2] in which base there is a suggestion that more then one phase can exist at the same location at the same time. This suggestion depends on the ideas of time and space averaging. The phases "share" this space; and they may, as they move within it, interpenetrate. In the given activity 2 phases are considered: the carrying -gas and the discrete -particles. Any small volume of the space in question, at any particular time, can be regarded as containing a volume fraction a, of the i-th phase, so that the sum of all a, must be equivalent 1. The interaction between the phases is taken into account by the determination of the drag force of particles. 0-7803-5729-9/99/$10.00 0 1999 IEEE

Modeling Identification and Control of an Air Preheating Furnace of a Pneumatic Conveying and Drying Process

“…The drying operation in these units is characterized by a coherent flow of a preheated gas–grain mix, in which grains are dehydrated or dried by the preheated air during transportation through the air duct, and thereafter the grains are separated according to size by some cyclone systems. There has been enormous research work in the broad area of pneumatic conveying and powder technology. − In convective drying, air temperature, relative humidity, and velocity have a significant effect on the drying kinetics and quality of food products. − Since the preheating of air before mixing with wet material improves the overall performance, reducing energy consumption and drying time, most pneumatic convective dryers use an air preheater. In a majority of the applications, the outlet air temperature of the air preheater is dynamically controlled according to the airflow rate, as required for the sustained conveyance of materials and moisture content of the input raw material, so that the moisture content of the final product remains within the desired limits; however, the airflow rate is mainly governed by the inlet wet material flow rate and moisture content.…”