Behavior of electrostatic charge and velocity distribution of petroleum flowing in relaxation pipe

Electrostatic charge in petroleum, generated by flow electrification in a filter and a transportation pipe, is very hazardous and has to be reduced before the petroleum is put into a storage tank. It is shown that a relaxation pipe (RP) is effective for this purpose. In order to get more effective RP, the velocity distribution of kerosene in RP was measured by laser Doppler velocity (LDV), and compared with values calculated from the finite difference method. This method was used to obtain the numerical values of the Navier-Stokes equation and the stream function. It was found that a layer of back flow existed in the neighborhood of the RP wall. The existence of a back-flow layer was supported by the measured LDV data. Furthermore, the charge-carrier velocity toward the RP wall was calculated by Poisson´s equation of a two-dimensional cylindrical function. From these results, it is suggested that a strong electrostatic field must exist toward the RP wall, and that a large area of laminar sublayer in the back flow layer must also be present in an effective RP.