Impact of Deposit Aging and Surface Roughness on Thermal Fouling: Distributed Model

A kinetic model was recently proposed to describe the effect of aging on deposit thermal conductivity and the thermal performance of a shell-and-tube heat exchanger undergoing crude oil fouling. The model is adapted for implementation within a dynamic, distributed system with spatial and temporal distributions, relaxing several of the previous assumptions. The evolution of surface roughness is also considered, using conjectural linear and asymptotic functions. Simulations are performed for a single tube representative of a refinery exchanger. The results demonstrate the substantial effects over time of aging and roughness on heat transfer and pressure drop. Roughness effects yield apparently negative initial fouling resistances, as reported in some experimental tests. The importance of accounting for roughness dynamics in short time scale pilot plant scale tests and aging over longer time scales in industrial applications is highlighted. (C) 2010 American Institute of Chemical Engineers AIChE J, 56: 3257-3273, 2010