Use of CFD to Determine Effect of Wire Matrix Inserts on Crude Oil Fouling Conditions

Abstract

Crude oil fouling rates are strongly affected by both local surface temperature and local surface shear stress. The use of in-tube inserts (such as hiTRAN) in heat exchangers has been shown to be effective in mitigating crude oil fouling while at the same time enhancing heat transfer. However, the introduction of inserts means that there will be axial and radial distributions of both local shear stress and local heat transfer coefficient between the repeating insert–wall contact points, which could mean that there will be local variations in fouling rate. While estimation of local shear stresses and film heat transfer coefficients is facile for bare round tubes, this is no longer the case for tubes fitted with inserts. Accordingly, this article describes a possible solution to the design challenge using computational fluid dynamics (CFD) simulation, the output of which is the temperature and velocity distributions in a three-dimensional geometry of the fluid flow in a tube fitted, for example, with a hiTRAN insert. A simple algorithm is then described for calculating the overall heat transfer coefficient based on the resulting temperature distribution along the wall of the tube. Simulated values of the overall heat transfer coefficient are then compared with those obtained by experiment, showing that there is good agreement, thereby indicating that predicted local values are accurate. Use of CFD in fouling applications now allows the prediction of local conditions when inserts are used and hence can be used to predict whether, and where, fouling might occur.