Microscopic Study of Wax Deposition: Mass Transfer Boundary Layer and Deposit Morphology

This study presents a pioneering effort to enable visualization of the in situ wax deposition process in a microscopic scale with an emphasis on mass transfer boundary layer and deposit morphology observations. The mass transfer boundary layer study validates the existence of partial wax supersaturation near the wax deposit and oil interface. The discrepancy between the actual mass transfer boundary layer thickness and the heat-mass transfer analogy prediction expands as the Reynolds number increases and the Delta T (temperature difference between the bulk and cold interface) decreases. This conclusion is in agreement with several flow loop data with the same oil and similar flowing conditions. The morphology study reveals that, under laminar conditions, the distribution of the deposit crystal aspect ratio resembles a log-normal pattern with a distribution mode between 2 and 3. This characteristic exhibits similarity with wax crystals observed under static cooling conditions. Deposits formed under laminar conditions have a relatively rough surface and random flake structure, while turbulent deposits have a smoother surface and more uniformly layered structure. The shear stripping phenomenon is not observed within the experimental range of this study.