Diffusion of 'dissolved wax', particle transport of 'precipitated wax' and sloughing of deposited mass are the main mechanisms involved in wax deposition in crude oil carrying pipelines operating below the Wax Appearance Point (WAP). It is known that diffusion of dissolved wax plays a key role in the deposition process. The involvement of particle transport has long been uncertain since most attempted experimental studies at 'zero heat flux' have shown no significant deposition. This study investigated the phenomenon of particle migration in the complex non-Newtonian rheology of a crude oil in pipe flow. Transparent model oil was constituted that mimicked the low temperature viscosity of a crude oil. Solubility studies were done based on a novel Fourier Transform Infrared Spectroscopy (FTIR) method. High Temperature Gas Chromatography - Simulated Distillation (HTGC-SimDis) carbon number characterization and density measurements were also performed. Laser Light Scattering (LLS) by wax particles was used to view a diametrical plane along the test-section axis. Particle Image Velocimetry (PIV) was used to obtain radial velocity profiles. Particles showed an annular aggregation close to the pipe center. They were also seen diffused out on either side of this annular location. In a very interesting result, deposition was observed under all conditions of heat flux (positive, negative or zero) as long as the wall temperature was below the WAR Sloughing was seen to play a dominant role in the overall deposition process. A new theory of particle transport is proposed based on the experimental observations. This theory is also incorporated into a new deposition model and the results compared with a popular model.
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