CFD Methodology to Determine the Hydrodynamic Roughness of a Surface with Application to Viscous Oil Coatings

Abstract

Water-lubricated pipe flow technology is an economic alternative for the long-distance transportation of viscous oils, such as heavy oil and bitumen. In the industrial-scale application of this technology, a thin oil film is always observed to coat the pipe wall. The natural process of wall coating during the lubrication is often referred to as wall fouling. A wall-fouling layer produces ultrahigh values of hydrodynamic roughness (∼1 mm), which have not been studied sufficiently to date. In this work, the hydrodynamic effects of a viscous wall-coating layer were experimentally investigated. A customized flow cell was used for the purpose. The equivalent sand grain (hydrodynamic) roughness was determined using a methodology involving computational fluid dynamics (CFD) simulations. The hydrodynamic roughness was also determined from the measured topology (physical roughness) of the surface. Additional verification of the method was obtained by applying it to analyze the hydrodynamic roughness produced by sandpapers and biofouling layers. The primary outcome of the present study is the validation and application of a CFD-based methodology to quantify the hydrodynamic roughness produced by any surface, including viscous oil coatings and biofouled surfaces. Additionally, it has been shown that the hydrodynamic roughness of a viscous oil coating, for the range of conditions tested here, is much more dependent on the coating thickness than on the Reynolds number. This has significant implications for the modeling of lubricated pipeline flows involving heavy oil and water.