Exsolving two-phase pipeflow*

Exsolving two-phase flows occur in systems such as oil wells and volcanoes, where the exsolution of dissolved gas is due to depressurisation of the flow along the vertical conduit. We consider such a system with a liquid inflow containing a saturated concentration of dissolved gas at high pressures. Along the pipe, as the pressure decreases, dissolved gases exsolve and a two-phase bubbly flow is initiated. We will present a two-fluid model that explicitly accounts for the exsolution of the dissolved gas. Assuming thermodynamic equilibrium through Henry’s law for the dissolved gas concentration results in the unexpected prediction that a foam is rapidly formed. A possible reason for this is that non-equilibrium nucleation and bubble growth occur.  We therefore generalise the two-phase flow model to include non-equilibrium dynamics. A critical parameter controlling the rate at which exsolution occurs is found. We discuss solutions of the new model to illustrate the effect of this parameter on the flow.