Start-up flows of Dullaert-Mewis viscoplastic-thixoelastic fluids: A two-dimensional analysis

The restart problem of pipelines filled with gelled waxy crude oils is investigated numerically using the finite volume method (FVM). Based on the rheological data obtained using the MCR-301 rheometer for a typical Iranian waxy crude oil, the Dullaert-Mewis (DM) rheological model was adopted to represent the viscoplastic/thixoelastic nature of such oils. A full two-dimensional analysis was used with the only assumption being that the flow is axisymmetric. Based on the numerical results obtained in the present work, it is concluded that the gel's elasticity has a negative effect on the restart operation. That is to say that, for highly-elastic gels the restart operation is predicted to fail completely. For weakly-elastic gels, the restart operation is predicted to be successful but the gel's elasticity still lowers the flow throughput. A complete parametric study was undertaken in order to investigate the effect of different parameters in the DM fluid model on the start-up flow.