Multi-Layer Visco-Plastic Flows
Multi-layer viscoplastic flow with application in lubricated pipe flow
Multi-layer flow has several applications in industry, such as lubricated pipeline flow, coextrusion, and coating. I am interested in its application in lubricated pipe flow. As an example, heavy oil or waxy crude oil has a very high viscosity and its transportation is very challenging. one method is to use lubricated pipeline flow which is proposed 50 years ago. In this method, a low viscous fluid is used to lubricate the pipeline via core-annular flow. But this method introduces several problems. First, core-annular flow is only stable and achievable for extremely limited operational conditions. Second, the interface is highly unstable due to density and viscosity mismatch. Third, there is a density mismatch between different layers. However, if this method successfully applies, the pressure drop reduces significantly. As a result, using the viscoplastic fluid as the lubricant is proposed. Viscoplastic fluid’s characteristic is yield stress and if the applied stress to this fluid is less than its yield stress, it does not flow and act like a solid otherwise it flows. The idea is placing the viscoplastic fluid in a way which is unyielded at the interface to freeze the interface and stabilize the flow. However, this method alone is not applicable as when the viscoplastic fluid is unyielded or slightly yielded, its effective viscosity is really high and comparable to heavy oil and the method is not applicable. Therefore, we proposed adding another layer. The core is heavy oil which is encircled with unyielded viscoplastic fluid to stabilize the flow and a low viscous fluid like water lubricate these two layers.