This paper presents the numerical simulation and experimental study of an immiscible liquid-liquid flow dispersion in conical spiral pipes for oil-water separation. Flow patterns of oil-water flow in the pipe are identified. The flow characteristics such as pressure drop, cross sectional phase distribution, and outlet flow rate are obtained. In addition to flow behavior, separation performance of the conical spiral pipes is examined under different operating conditions. The effects of geometric parameters such as conical angle, pipe diameter, pitch height, and outlet split ratio, on oil-water separation are revealed. Moreover, the effects of inlet velocity, inlet oil concentration, and operating temperature on the separation are obtained. In addition, it has shown that surface treatment for the conical spiral pipes has an impact on the oil-water separation. In particular, the V-shaped sawtooth surface microstructure can enhance the oil-water separation, and Graphene-coated surface exhibits good separation capacity under high flow velocity. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.