Abstract
The decay of electrostatic charge within a conducting vessel partially filled with charged liquid is slowed by the temporary accumulation of a portion of the initial charge at the free surface of the liquid. This effect will prolong the period of exposure to vapor ignition hazards due to electrostatic discharge, especially when the fill level approaches 100%. However, if surface conduction is taken into account, surface charge accumulation tends to be offset by opposite sign charge flowing in from the conducting side walls. In this paper, the existing model for charge relaxation in partially filled conducting cylindrical vessels is modified to account for surface conduction. The principal result is that the extrinsic relaxation time constants associated with the modal solution are reduced. A dimensionless modulus is identified that compares the surface and volume conduction mechanisms and indicates that the effect of surface conduction is inversely proportional to the absolute vessel diameter. When the vessel diameter is small or when the surface conductivity is sufficiently high, the relaxation time for the electric field in the vapor space is reduced below the intrinsic charge relaxation time of the liquid. The practical implication of these results is that surface conduction can easily dominate in establishing the rate of decay of the electric field in the vapor space.
Published Version
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