| This study presents a novel mathematical model, based on the moving boundary problem formulation, for solids deposition from 'waxy' crude oils. An experimental study was undertaken to measure the phase transformation temperature and the liquid phase composition of prepared wax--solvent mixtures. It was established that the wax disappearance temperature (WDT) rather than the wax appearance temperature (WAT) is closer to the liquidus or saturation temperature of 'waxy' mixtures. The mathematical model, utilizing the moving boundary problem framework, was used for predicting the growth of deposit layer from 'waxy' mixtures, both radially and axially, under static and laminar flow conditions in a circular pipe. The model predictions indicated that a higher value of mixture temperature, pipe-wall temperature and/or heat transfer coefficient would yield a thinner deposit layer with a faster approach to thermal steady-state.;A novel formulation, based on the one-dimensional deformation of a cubical-cage, was proposed for incorporating the effect of shear stress on the deposition process. It was postulated that the application of shear stress causes tilting of the cubical-cage, which leads to the release of a portion of the liquid phase. Whereas an increase in the deformation angle was predicted to cause wax-enrichment in the deposit, the deposit-layer thickness was dependent primarily on the heat-transfer and phase equilibrium considerations. An increase in the deformation angle was predicted to delay the deposition process, due to an increase in the average solid-phase fraction in the deposit, and it caused the deposit to become enriched in heavier n-alkanes and depleted in lighter n-alkanes. The agreement between the predicted trends and published experimental results confirmed the deposition process to be primarily thermally-driven. |
