Coalescence Dynamics in Oil-In-Water Emulsions at Elevated Temperatures

Abstract

Emulsion stability in a flow field is an extremely important issue relevant for many daily-life applications such as separation processes, food manufacturing, oil recovery etc. Microfluidic studies can provide micro-scale insight of the emulsion behavior but have primarily focussed on droplet breakup rather than on droplet coalescence. The crucial impact of certain conditions such as increased pressure or elevated temperature frequently used in industrial processes is completely overlooked in such micro-scale studies. In this work, we investigate droplet coalescence in flowing oil-in-water emulsions subjected to higher than room temperatures namely between 20oC to 70oC. We use a specifically designed lab-on-a-chip application for this purpose. Coalescence frequency is observed to increase with increasing temperature. We associate with this observation the change in viscosity at higher temperatures trigerring a stronger perturbation in the thin aqueous film separating the droplets. Using the scaling law for rupture time of such a thin film, we establish a mechanism leading to a higher coalescence frequency at elevated temperatures.

Microbubble and nanobubble-based gas flotation for oily wastewater treatment: a review

“…Radzi (2016) noted that the viscosity of both the oil and water phase and surface tensions were reduced at higher temperatures. Hasan et al (2010) studied the effect of temperature on the viscosity of heavy crude oil, and they observed a reduction in viscosity from 10 to 6.3 Pa•s when the temperature was increased from 25 to 75 • C. Furthermore, Bera et al (2021) investigated the coalescence between oil droplets and observed higher coalescence frequencies at elevated temperatures (from 20 to 70 • C). Sadeghi and Vissers (2020) used a laboratory scale flotation unit to investigate the effect of temperature on bubble size, and they found that the increase in temperature slightly reduced the size of large bubbles from 96 to 81 μm; however, it did not have significant effect on small bubbles (20 μm).…”

Investigation of microbubbles and nanobubbles gas flotation for oil separation from marine oily wastewater using response surface methodology

“…Hasan et al (2020) studied the effect of temperature on the viscosity of heavy crude oil, and they observed a reduction in viscosity from 10 Pa•s to 6.3 Pa•s when the temperature was increased from 25 °C to 75 °C. Furthermore, Bera et al (2021) investigated the coalescence between oil droplets and observed higher coalescence frequencies at elevated temperatures (from 20 °C to 70°C). Sadeghi and Vissers (2020) used a laboratory scale flotation unit to investigate the effect of temperature on bubble size, and they found that the increase in temperature slightly reduced the size of large bubbles from 96 μm to 81 μm; however, it did not have significant effect on small bubbles (20 μm).…”