Thermo-hydrodynamic analysis of drop impact calcium alginate gelation process

Abstract

The phenomenon of calcium alginate gel formation from sodium alginate drop impact on calcium chloride liquid pool generates enormous scientific interest. The present work features on the investigation of interfacial heat transfer during sodium alginate drop impact on a heated calcium chloride liquid pool. The liquid pool has been heated at different temperatures varying from 20 °C to 70 °C. The drop chemically reacts at the interface and calcium alginate gel starts to form which has been instantaneously captured in a high-speed camera. A mathematical model on crater dynamics has been presented to determine the heat transfer coefficient and amount of interfacial heat transfer during the chemical reaction. Now, drop levitation over the vapour layer generated from the evaporation of liquid pool is defined as Leidenfrost pool Effect. This is characterized from the heat transfer at the crater initiation stage and accumulated vapour layer thickness, vapour pressure developed. The release of drop liquid is aided by the surface tension difference between drop and pool at the interface and it is defined as thermal Marangoni Effect. It has been characterized from the variation of Marangoni pressure with temperature which tends to drain away accumulated vapour layer. A critical liquid pool temperature has been obtained when Leidenfrost vapour pressure dominates over Marangoni pressure and resists the drop release during the gel initial regime. The dynamics of calcium alginate gelation is governed by intricate interplay between thermal Marangoni effect and Leidenfrost pool effect with its effect on initial gelation time and total gelation time.