Experimental Investigation of Time-Dependent Thickness and Composition of Multicomponent Wax Deposits on Cold Surfaces

The time-dependent rates of growth of thickness of wax deposits, as well as the spatial distributions of wax components within the deposits, formed on a cold finger from stirred baths of n-dodecane (n-C12) and mineral oils containing multiple, high-carbon-number, n-alkane wax components, were measured for multiple stirring rates of the bath and multiple oil viscosities. While the deposit thickness was found to stop growing at long time, its composition continued to become more enriched in higher molecular weight compounds. The growth of the deposit thickness was explained largely by heat transfer, but the slower enrichment of the deposit required consideration of convective and diffusive mass transfer. Both the heat and mass transfer coefficients for transport through a boundary layer at the interface between the bath and the deposit were measured as functions of stirring speed and were found to follow expected heat and mass transport correlations involving Reynolds, Prandtl, and Schmidt numbers. The findings provide a set of data that should help in the development of refined models for wax deposition on cold surfaces, including the interior surfaces of oil pipelines.