Deposition from waxy mixtures in a flow-loop apparatus under turbulent conditions: Investigating the effect of suspended wax crystals in cold flow regime

The effect of suspended wax crystals in wax-solvent mixtures on the solid deposition process in the cold flow regime was investigated experimentally and analyzed with a steady-state heat transfer model. A bench-scale flow-loop apparatus, incorporating a concentric-cylinder heat exchanger, was used to measure solid deposition, in the cold flow and hot flow regimes, from wax-solvent mixtures under turbulent flow conditions. The deposition experiments were performed with two wax-solvent mixtures, at two flow rates, with two coolant temperatures, at 8 wax-solvent mixture temperatures, and for several deposition times. The role of wax crystals on the deposition process was investigated by repeating some of the deposition experiments with a pre-filtered wax-solvent mixture. In all experiments, the deposit was formed rapidly such that a thermal steady-state was attained within 30 min. The deposit mass increased with decreasing the mixture temperature in the hot flow regime, reached a maximum as the mixture temperature became equal to the WAT, and then decreased linearly to zero in the cold flow regime as the mixture temperature approached the coolant temperature. Also, the deposit mass decreased with an increase in the Reynolds number and the coolant temperature. The data and predictions confirmed the solid deposition to be a thermally-driven process. The experimental deposit mass results in the cold flow regime, supported by model predictions, were identical for the unfiltered and filtered mixtures, which showed that the suspended wax crystals do not affect the deposit mass or thickness.