A theoretical model for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe

A theoretical model was developed for core-annular flow of a very viscous oil core and a water annulus through a horizontal pipe. Special attention was paid to understanding how the buoyancy force on the core, resulting from any density difference between oil and water is counter-balanced. This problem was simplified by assuming the oil viscosity to be so high that any flow in the core may be neglected and hence any variation with time of the oil-water interfaced form. So in the model the core is assumed to be solid and the interface to be a solid-liquid interface.