Gustavo Nunez

Flow characteristics of concentrated emulsions of very viscous oil in water

This article 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. We believe that the results presented here unveil mechanisms that take place in the pumping and pipelining of oil‐in‐water emulsions and therefore contribute to the understanding of the dynamic stability of these systems.

Colloidal coal in water suspensions

We discuss the possible clean coal applications of colloidal suspensions of coal in water (CCW) manufactured with a proprietary wet-comminution device. These suspensions are a new material with new properties. First, the colloidal fraction plus water is a pseudo fluid good for transport, handling and suspension of large particles. Second, the surface area per unit volume of coal available for chemical reaction and burning is greatly increased and finally, CCW may be milled with a third fluid, seeding the mixture with submicron coal.The colloidal nature of the majority of particles provides for very good features such as outstanding long-term stability, in contrast to regular coal water slurries (CWS) which rapidly sediment under storage. Moreover, the very small particles create an increased reactivity to combustion because small particles with large surface area react faster than large particles with the same volume.

Rod climbing and normal stresses in heavy crude oils at low shears

This paper gives the results of a study of the nonlinear viscoelastic behavior of three heavy crude oils from California and Venezuela. A linear combination of normal stress coefficients at zero shear is expressed in terms of the quantity (the climbing constant) used to measure the height rise on a rotating rod. Measurements of the climbing constants are given for the crude oils. Values of both the first and second normal stress coefficients at zero shear are determined by the climbing constant when another combination of the two coefficients is known. In principle, the required information can be obtained by back extrapolation of the first normal stress difference, by back extrapolation of the dynamic modulus or by back extrapolation of the ratio of the second to first normal stress difference. Back extrapolation of data can be achieved when measurements are available at shear rates low enough to enter onto the second‐order plateau of the functions generated by different instruments. Examination of previously published data for well‐characterized solutions suggests that second‐order rheology is most readily obtained in rod climbing.