Vacuum assisted flow initiation in arching powders

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The discharge of powders from hoppers usually takes place in open atmosphere. However, in powder pressing industries (e.g. manufacturing of pharmaceutical tablets, detergents, ceramics, powder metallurgy etc.) there are handling operations where powders are filled into closed cavities such as dies. During this process the air pressure is increased as powder is delivered into the die. At the same time typical tablet production equipment creates a suction effect. A critical orifice measurement apparatus was developed to study powder flow initiation from an arching state into an enclosure where the air pressure is reduced. It was shown that a very small reduction of pressure changed the critical orifice diameter significantly. Dimensional analysis was carried out to relate powder properties (particle size and density) and processing parameters (geometry of the system and differential pressure necessary to break the arch). A relationship was developed to calculate the pressure difference necessary to initiate powder flow. The relationship has two empirical parameters which are calibrated by performing simple experiments using the testing rig developed

Mathematical and Experimental Modelling of Adsorption in Fixed Bed. II. Experimental Investigation of Nonisothermal Single Solute Adsorption and Adsorber Simulation

The adsorption separation process of n -heptane on a molecular sieve in a fixed bed adsorber is investigated. Experimental concentration and temperature breakthrough curves are obtained using different gas inlet concentration and temperature, different bed length and gas mixture flow rate. The mentioned experimental data are simulated a priori by means of a two-phase mathematical model. The model parameter values used in the simulations are estimated either through available semiempirical correlations or by independent experimental runs. An example of predicted and experimental concentration and temperature breakthrough curves comparison is presented

Mathematical and Experimental Modelling of Adsorption in Fixed Bed. I. Mathematical Model Development and Numerical Investigation of Nonisothermal Single Solute Adsorption

Mass and heat balances describing the process of a nonisothermal one-component adsorption in a fixed bed adsorber are formulated. The mathematical model permits simulation of bed performance under isothermal, adiabatic or nonisothermal-nonadiabatic conditions and incorporates heat and mass transport resistances within and around the adsorbent particle. Both heat and mass axial dispersion in the bed and moderate heat losses to the surroundings are considered. The adsorption equilibrium is described by a temperature-dependent Langmuir isotherm. The mathematical model is solved for different values of the physicochemical parameters. Numerical investigation results for different values of axial heat dispersion coefficient, effective pore diffusivity and overall heat transfer coefficient are compared with real adsorption data available from the literature