Use of CFD to correlate crude oil fouling against surface temperature and surface shear stress in a stirred fouling apparatus

Experimental data on the fouling of various crude oils is being obtained in a small (1 litre) batch stirred cell which is operated at temperatures up to 400 o C and pressures up to 30 bar. The cell is based on the Eaton and Lux patented design. The fouling resistance is found to increase more-or-less linearly with time after an induction period. Distributions of shear stress, surface temperature and heat flux over the cell’s heated test finger are modelled using the Comsol CFD package. The CFD simulation results are validated against the measured temperature data at various axial positions on the heated test probe. At the end of a fouling run, the cell is dismantled and the fouling layer thickness is measured using the Proscan technique. The profile of fouling layer thickness along the heated surface is found to be in an almost parabolic form, with its maximum thickness near to the middle of the surface. The CFD-predicted surface temperature profiles are strikingly similar whilst the predicted shear stress profiles are found to be virtually flat. Hence, it becomes possible to correlate, for a fixed surface shear stress, the local fouling rate against the local surface temperature, and hence to obtain an Arrhenius plot from one experimental run. The local experimental shear stress can be varied by changing the speed of rotation of the cell’s cylindrical stirrer and so the effect of shear stress on fouling behaviour can be studied as well