This paper summarizes measurements in which both external electric field, applied by electrodes at the fabric surface, and flyash electrical charge, controlled by an upstream corona precharger, are independent variables in a factorial performance experiment carried out in a laboratory pulse-jet baghouse. In agreement with previous publications, increasing either the electric field strength or the magnitude of the flyash chargelmass reduced the rate at which the pressure drop across the bags built up. And although increasing both field and dust charge together produced still further reduction in the pressure drop buildup rate, bag weighings showed that adding charge to the flyash reduced the quantity of flyash deposited on the bag during one filtration cycle, whereas increasing the electric field had no detectable effect on this quantity. These observations suggest that the mechanism by which the external field enhances the performance of the fabric filter is increasing the permeability of the collected flyash layer, while the precharger enhancement mechanism is primarily that of a prefilter. Since the magnitude of the electrical charge/mass of the test flyash does not affect the magnitude of the enhancement induced by the external electric field, the enhancement mechanism by which the external field increases the dust cake permeability is concluded not to be a coulomb capture force.

As attention has focused on indoor air quality, it has become important to obtain basic information on the effects of heating, ventilating, and air-conditioning system operating parameters on office aerosols. In addition, it is important to know the particle size distributions (PSDs) in a typical office environment in order to address mitigation strategies. Therefore, this study was undertaken to evaluate the effect of percent outdoor air supplied and occupation level on the PSDs and mass concentrations for a typical office building. The outdoor, return, and supply air streams, as well as hallway air, were sampled using measuring equipment covering particle diameters from below 0.1 to above 3.5 pm. The mass concentrations, when the building was occupied, increased by a factor of approximately 2 when return air was recycled over ventilating with maximum outdoor air. The concentrations when unoccupied were at least as low using minimum outdoor air as those when occupied using maximum outdoor air. As expected, the outdoor air was cleaner than the other streams. The next lowest concentrations were obtained for supply air, then return air, with hallway air showing the highest concentrations. The normalized number distributions were found to have a single mode consistently near 0.13 pm; the volumetric distributions show a peak at 0.3 pm. The influence of the damper setting and occupancy level shows up only in the magnitude of the peaks. The distributions found in the hall and for the air streams showed the same general shapes, but the differences in instrumentation preclude other conclusions.

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