Separation of water from oil has been a significant subject for a crude-oil purification in the petroleum industry and chemical processing. This dissertation reports theoretical and experimental studies on separation of water from water-in-oil emulsions under combined treatment of a radial electric field and elevated temperature. Compared to macroemulsion, there are fundamental differences when considering microemulsion. It is difficult to separate microemulsion by an electric field due to its tiny droplet size. Microemulsion can be transformed to macroemulsion state over the cloud point. Therefore, heating is applied to the microemulsion to change its phase, then an electric field is applied to the system to expedite the separation speed.

The enhanced separation performance using the combined method can be mainly attributed to the reduced viscosity and dissociated surfactants at elevated temperature and the accelerated droplet coalescence under the radial electric field. Theoretical analysis shows that temperature and electric strength can strongly affect the movement of the water droplets, and these effects are also experimentally validated by water/oil separation tests. In our experiments, a cylindrical cone-shaped separation tube equipped with coaxial cylindrical electrodes was built to improve the separation using a non-uniform radial electric field. From the result of the numerical calculations, the precipitation and collision times of water droplets are rapidly reduced as the operating temperature increases. This theoretically expected values accurately predict the experimental results of the water-in-oil emulsion separation tests. It is experimentally observed that increasing the applied voltage and/or temperature can significantly reduce the separation time and the residual water concentration in the emulsion. Lastly, the dynamic water/oil separation system was designed using the combined method of heating and electric field. The effects of operating temperature and flow rate on the quality of the separated oil are investigated by executing several tests at different temperatures and flow rates. From the results of the dynamic separation tests, the residual water concentration in the separated oil reduces as the operating temperature increases under the boiling point. Also, the water concentration of the separated oil increases as the flow rate increases due to the reduced residence time.