THE INFLUENCE OF ELECTROSTATIC CHARGE ON THE FILTRATION OF HYDRAULIC FLUIDS BY FIBROUS FILTERS

Scope and Method of Study. The problem examined in this thesis is concerned with the effects of electrostatic charge upon the performance of hydraulic fibrous filters. Specific objectives were the investigation, both theoretically and experimentally, of the charge generation and accumulation characteristics of a recirculating filtered hydraulic system. In addition, the effects of this charge upon filtration performance parameters was to be examined.;The experimental analysis included the verification of the generalized charge accumulation model by conducting tests at various fluid equilibrium conductivities and flow rates while taking measurements of the fluid charge density both upstream and downstream of the filter. The relationships between conductivity, particulate impurities, relative humidity and fluid additives were also experimentally determined. Finally, the influence of electrostatic charge upon measurable filtration performance parameters was determined by conducting thirty-nine multi-pass tests on six different filter element models at various charge levels.;Empirical equations were then developed, based upon the experiments and theoretical considerations, to describe the influence of electrostatic charge upon filter separation performance and parameters of the log-normal filter model.;Findings and Conclusions. From the results of this study, it can be concluded that the electrostatic charge dissipation in a hydraulic system can not be described by the exponential or hyperbolic relaxation laws but by a generalized model which includes the characteristics of both laws.;The theoretical considerations include a development of a generalized charge relaxation and accumulation model for predicting charge transfer and accumulation in a multi-pass hydraulic filter test facility. A filter performance model based upon the log-normal distribution function was proposed to allow the determination of electrostatic charge influences upon filter design parameters.;The log-normal filter separation efficiency models contain parameters representing the geometric mean "effective pore size" and geometric standard deviation; and from the data collected in this investigation, it appears that the model is suitable for hydraulic fibrous bilter description for efficiencies above ten percent.;The experimental evaluations of the influence of electrostatic charge on filter performance resulted in definite relationships. Increasing charge levels and increasing particle sizes both resulted in an increase in the filter particle retention capabilities. The geometric mean diameter from the log-normal efficiency model decreased exponentially with increasing charge density and the geometric standard deviation showed a slight exponential increase.