Effective Conductivity

The charging process in liquids of low conductivity alters the concentration of charge carriers. In the charged state, such as downstream of microfilters, petroleum products with measured (rest) conductivities above about 2 pS/m often display a relaxation time a factor of 3–4 times longer than predicted. However, for rest conductivities less than about 2 pS/m, relaxation times become much shorter than predicted. For example, the relaxation time of jet fuel having a conductivity of 0.01 pS/m is about 30 min based on Ohmic relaxation. In practice it is found that highly charged, nonviscous liquids of such low conductivity relax charge hyperbolically rather than Ohmically. The provision of 100 s of residence time downstream of filters is found to reduce the charge to about 5% of its initial value, whereas via Ohmic relaxation this would require three relaxation times (>1 hour) of residence time. In Appendix B, nonviscous liquids whose rest conductivities are usually measured at about 2 pS/m or less are not assigned a relaxation time but instead a 100 s “dissipation time.”