Peter W. Dietz

Electrical Charge Measurements on Fine Airborne Particles

A small parallel-plate precipitator and a theoretical collection model have been used to determine the distribution of charges acquired by monodisperse airborne polystyrene latex particles in a corona charger. The mean charge based on the total number of particles was found to be slightly higher than half the predicted saturation charge, and it agreed well with independent measurements made in a Faraday cage particle separator. The importance of careful measurements of particle charge in fine particle transport studies is highlighted by a discussion of the effect of charge (particle mobility) distribution width on observed transport characteristics.

Heat transfer in bubbling electrofluidized beds

Abstract When an electric field is applied to a fluidized bed, the resulting bed dynamics can be appreciably altered from those of a conventional bed. In the bubbling-flow regime, which is studied here, the bubbles elongate in the direction of the applied electric field, and particle mixing is reduced. Since bubble motion and particle mixing are important to the transfer of heat in a fluidized bed, measurements of the heat transfer rates in an electrofluidized bed may provide insight into the electromechanics of the bed. In addition, variations in the heat transfer rate with the applied electric field may provide a valuable control mechanism for thermal processes in fluidized beds. Heat transfer coefficients are measured for horizontal tubes immersed in a 6.35 cm square fluidized bed. An electric field is applied by supplying a voltage to the electrodes which form two of the walls of the bed. The data indicate three regimes: a low field regime in which the field has little effect on the heat transfer; an electromechanical regime in which the heat transfer coefficient decreases; and a frozen regime in which particle motion ceases and the heat transfer coefficient depends on the configuration into which the bed has frozen. A model is developed for the onset of electromechanical effects based on a calculation of the interparticle forces. This model is compared with experiment.

The Electrospouted Bed

Strong localized dc electric fields affect the solids recirculation of semi-insulating particles in a draft-tube-equipped spouted bed. Experimental evidence i

Cohesive force and resistivity between electrostatically-precipitated particles

provided in the form of pressure/flow and solids recirculation rate data versus voltage. The electrode structure is placed near the inlet spout, where strong electric fields tend to freeze the particles in the lower part of the annulus, reducing their rate of entrainment into the central gas stream. The electrospouted bed (ESB) increases the flexibility of spouting as a process applicable in chemical reacting, drying, and coating technologies.

Electrostatically augmented cyclone apparatus

Abstract In electrostatic precipitators, the precipitated particles experience a cogesive force due to the corona current which flows through the dust layer. Because this current must pass from particle to particle at, or near, the interparticle contacts, the electric field strength in these regions can become sufficiently high to initiate electrical breakdown. In the present article, a model is developed for the cohesive force between particles which analytically includes the limiting electric field. The resultant expression for the cohesive stress varies nearly linearly with the electric field in the layer and provides reasonable agreement with the data of McLean. Also, the resistivity of the layer is computed.