Effects of shear rate and time on deposit composition in the cold flow regime under laminar flow conditions

Abstract

The effects of shear rate and time on solid deposition and deposit composition, from wax–solvent mixtures in the cold flow regime under laminar flow conditions, were investigated experimentally using a cold finger apparatus. The deposition experiments were conducted with a 10 mass% multicomponent wax–solvent mixture at different agitation speeds, with a coolant temperature of WAT–12 °C, at a wax–solvent mixture temperature of WAT–6 °C, and for different deposition times. The experimental results indicated that the deposit mass increased with a decrease in the agitation speed (Re), or the shear rate, and an increase in the deposition time (t). The predictions from a transient model based on the moving boundary formulation agreed with these results. The wax content and carbon number distribution of deposit samples varied with Re and t. The deposit ‘aging’ behaviour was modeled successfully using a previously developed approach, based on the shear-induced deformation of a cubical cage, causing a partial squeezing out of the liquid phase from the deposit, in which the deformation angle (β) of the tilted cubical cage depends on Re and t. A correlation was developed for the effects of Re and t on deposit composition in the cold flow regime under laminar flow conditions. The results of this study further confirm that the deposition process is described very well by heat-transfer considerations and the ‘aging’ of deposit is modeled satisfactorily by considering the effect of shear stress during its formation and growth.