Feed rate characteristics of a blow tank solids conveyor in transport of granular material

Feed rate characteristics of a blow tank solids conveyor in which the conveying pipe exits at the upper part of the tank are experimentally examined by the use of polyethylene pellets having a large minimum fluidizing velocity. The flow pattern of solid particles in the tank resembles suction flow at the pipe inlet and bears a strong resemblance to that of gravity discharge of solids from an orifice, and there exists a dead solids region on the porous support through which compressed air is blown. Within this region pipe inlet height from the porous support and tank size have no effect on the feed rate. For a given tank, the feed rate increases with an increase in pipe diameter. An empirical equation is proposed to relate these variables.     

The calculation of particle deposition efficiency due to inertia,diffusion and interception in a plane stagnation flow

The particle deposition mechanism in a plane stagnation flow is investigated analytically and numerically. Particle deposition efficiency η_TID is obtained theoretically by taking into account particle inertia, diffusion and interception. It is compared with various calculated deposition efficiencies, i.e. η_T (due to inertia) + η_I (due to interception) + η_D (due to diffusion), η_TI, (due to inertia and interception) + η_D, etc. In the region where all of the three deposition mechanisms, i.e. inertia, interception and diffusion, act at the same time, real deposition efficiency η_TID is not accurately expressed by η_T + η_I + η_D. However, η_TID is nearly equal to η_TI + η_D unless the interception parameter is zero.The calculated results of particle concentration indicate that a high concentration region is formed near the deposition plate, and that the concentration becomes higher as particle inertia increases.     

Experimental analysis of static pressure in bins

A pressure transducer with a pressure-high sensitive semiconductor gauge was used to measure distribution of vertical pressure at the base and horizontal wall pressure in a bin packed with glass beads, which are typical cohesionless particles.Even when the glass beads were uniformly supplied to the bin, the vertical pressure at the base was distributed unevenly, with the maximum and minimum values. This seems to be attributable to the “arching” which results from its nonhomogeneous configuration. In addition, the results indicate that the larger the diameter of the bin, the more numerous the extreme values of vertical and horizontal pressure become.This implies that the distribution of particles is the principal mechanism affecting the distribution of pressure in a powder bed. Consequently, to analyze the mechanism of a powder bed, the transference of force among the particles should be evaluated considering the distribution of the particles and paying careful attention to each of the particles in the powder bed.     

Pressure drop in vertical pneumatic transport lines of powdery material at high solids loading

The compressibility of the air flow cannot be neglected in measuring the distribution of static pressure in vertical pipes. Measurements indicate that static pressure decreases almost linearly along the greater part of the pipe's length. This area, which has been termed a pseudo-established region by Fortier, shows the same decrease in pressure as a fully established region of incompressible flow. Then it is shown that the pressure drop in the pseudo-established region can be easily obtained in the same way as it is for an incompressible flow if the coefficient for the additional pressure drop due to solids and the Froude number are calculated in terms of atmospheric conditions.     

The reduction of pressure drop due to dust loading in a conventional cyclone

Experiments have been conducted to examine the effect of dust loading on pressure drop in a conventional cyclone. The presence of dust in the air stream reduced the cyclone pressure drop by as much as 30%, even at extremely low concentrations, such as 0.2 g/m³. In the range of 1.5–50 g/m³, the pressure drop ratio (the ratio of the pressure drop of dusty air to that of pure air with the same inlet velocity) was independent of dust concentration, and kept nearly constant; but it decreased as the concentration increased above 50g/m³. It was observed that the presence of dust reduced the tangential velocity. However the radii of a cross section of the cyclone, where the pressures are equal to those of the entrance and the exit, did not change noticeably. Calculating the pressure drop by integrating the term due to centrifugal force is also examined.     

Collection of submicron particles by H2 bubbles

A theoretical analysis is presented to describe the deposition of Brownian particles onto H₂ bubbles (flotation) by analogy with classical filtration theory.Experimentally, it is shown that submicron and smaller particles of MnO₂ are collected by H₂ bubbles without using the special collector or chemicals usually employed in flotation. The experimental technique for determining the total collection efficiency is described.A comparison between the theory and our experiment makes it clear that there are cases in which the simpler filtration theory is adaptable to a complicated flotation analysis. In addition, we find that the collection mechanisms of submicron particles of MnO₂ is predominantly characterized by interception and Brownian diffusion.     

Magnetic Sensorless Sensing of Plasma Position in the Superconducting Tokamak HT-7

Magnetic sensorless sensing experiments of the plasma horizontal position have been carried out in the superconducting tokamak HT-7. The horizontal position is calculated from the vertical field coil current and voltage without using signals of magnetic probes placed nearby a plasma. The calculations are focused on the ripple frequency component of the power supply.There is no drift problem with the time integration of magnetic probe signals. The error of the derived plasma position is lower than 2% of the plasma minor radius.