Analysis of Core Annular Flows by Height Functions -A basic study on spilled heavy oil on the sea (2nd Report)-

Abstract

Spilled heavy fuel oil on the sea increases its viscosity up to about several hundred times from the original value in the process of mixing with water. In the case of the spilled heavy fuel oil from the Russian tanker in 1997, almost all of recovering machines were useless, because the pipes and pumps in the machines were choked with highly viscous oil. The purpose of the present paper is to investigate an applicability of a core annular flow (CAF) to recover a highly viscous fuel oil on the sea. The CAF consists of a thin water film introduced between the oil and the pipe wall. This film gives a reduction of pressure-gradient. In this paper, two-dimensional simulations using k-ε turbulent model and height functions were conduced with 176～4, 000 mPa・s oils keeping constant interfacial tension. Some of main results are as follows: 1) Pressure drop of the core annular flow with highly viscous oil in the core is slightly higher than that of single-phase water flow. 2) The core annular flows with different oil viscosity showed little difference in pressure drop. This result indicated a high potential of the core annular flow to the recovery of highly viscous spilled oil. 3) In the case of lifting or sinking core, tha pressure difference between the upper surface and the lower surface was counter-balanced with the lifting or sinking force. 4) Simulation of a core annular flow with a height function did not work well when the surface of the core became steep and multiple-valued function of the position.