Flow characteristics of concentrated emulsions of very viscous oil in water

This paper advances ideas and presents experiments on the flow characteristics of concentrated emulsions of Venezuelan bitumen in water plus surfactant. These emulsions are studied under a variety of flow conditions, namely between rotating cylinders, in a colloid mill and in pipes. The ideas advanced here concern the modeling of the highly viscous bitumen drops as solid spheres and their fracture under contact forces between neighboring drops, as in comminution, rather than break up by hydrodynamic forces. Further, we observe and discuss the local inversion of an emulsion due to local increases of the bitumen fraction induced by flow and the conditions that lead to slip flow, in which the drag is reduced by the formation of a lubricating layer of water at the wall. The identification of flow characteristics of highly concentrated dispersions of bitumen droplets in water plus surfactant is complicated beyond the complexities inherent to composite media because of lubrication effects at bounding walls, drop refinement by contact forces, as well as by hydrodynamic forces, and by local inversion instabilities. In this paper we shall identify flow characteristics of concentrated emulsions of heavy Venezuelan bitumen in water, emphasizing novel features which are associated with the high viscosity of the disperse phase. Such emulsions are currently being marketed worldwide as coal-substitute fuels, under the name of Orimulsion. The paper is divided in two parts: Part I deals with the conceptual framework of this research and part II outlines the experiments carried out to support our conclusions. The review of relevant literature is carried out in Part I.