A steady-state heat-transfer model for solids deposition from waxy mixtures in a pipeline

A steady-state heat-transfer model is presented for the formation of a deposit-layer from wax-solvent 'waxy' mixtures in a pipeline under turbulent flow. The waxy mixture is taken to enter the pipeline under the single-phase hot flow regime (where the average mixture temperature is higher than its wax appearance temperature, WAT) and, upon gradual cooling, the mixture transitions into the cold flow regime (where its average temperature is lower than its WAT). The cold flow regime is characterized by two-phase flow, in which solid particles are suspended in the liquid phase. The effect of deposit aging is incorporated via a shear-induced deformation approach proposed in the literature. The model predictions are reported for the deposit thickness, waxy mixture temperature, pressure drop and the rate of heat loss in the hot flow and cold flow regimes for a range of inlet mixture temperature, surrounding temperature, and the Reynolds number. The predicted deposit thickness is shown to increase axially in the hot flow regime, to reach a maximum as the liquid temperature approaches the WAT of the wax-solvent mixture, and to decrease gradually to zero in the cold flow regime. The trends in the model predictions compare satisfactorily with those reported from bench-scale experimental studies as well as the predictions from an unsteady state moving boundary problem formulation. (C) 2014 Elsevier Ltd. All rights reserved.