Validating Heat-Transfer-Based Modeling Approach for Wax Deposition from Paraffinic Mixtures: An Analogy with Ice Deposition

摘要

The process of solid deposition from wax solvent mixtures was compared with that of ice deposition from liquid water by means of experiments using a cold-finger apparatus and a transient mathematical model based on the Stefan "moving boundary problem" formulation. Two agitation speeds of 250 rev min(-1) (Reynolds number of 4100) and 500 rev min(-1) (Reynolds number of 8200), with two coolant temperatures of T-f - 4 degrees C and T-f - 7 degrees C, at four water temperatures (from Tf + 3 degrees C to T-f + 0.7 degrees C), and for 11 deposition times between 30 s and 8 h, were used in the ice-deposition experiments. The wax deposition experiments were undertaken using a 10 mass % wax-solvent multicomponent mixture, at an agitation speed of 250 rev min-1 (Reynolds number of 1400), with a constant coolant temperature of wax appearance temperature (WAT) - 12 degrees C, at four mixture temperatures (from WAT + 6 degrees C to WAT), and for 17 deposition times ranging from 2 s to 48 h. Both the ice deposition and the wax-deposition processes were remarkably similar. Both of these phase-change systems were extremely rapid during the first few minutes. A higher deposit mass was achieved by lowering the liquid water temperature, the coolant temperature, and the agitation speed. The experimental results from this investigation, supported by those from previous studies, indicated that a higher deposit mass is achieved with lowering of the liquid mixture temperature, the coolant temperature, and the agitation speed. The results of both sets of experiments were consistent with predictions from the Stefan moving boundary problem framework, which considers both of these phase-change processes to be governed only by the heat transfer steps involved in the freezing of a liquid. This study confirms that the solid deposition from wax-solvent mixtures is described adequately based entirely on heat-transfer considerations.