Numerical investigation on flow instability of sessile ethanol droplets evaporating in its pure vapor at low pressure. (August 2020)

• Record Type: Journal Article
• Authors: Zhang, Yu; Zhang, Li; Mo, Dong-Ming; Wu, Chun-Mei; Li, You-Rong
• Is Part Of: International journal of heat and mass transfer. Volume 156(2020)
• Publication Date: 2020-08
• Subjects: Sessile droplet -- Evaporation -- Flow stability -- Thermal pattern -- Numerical simulation; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2020.119893
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Flow in evaporation sessile droplet in its pure vapor at low pressure is simulated. The transition Marangoni numbers of the thermal patterns are determined. Four types of the thermal patterns appear in sequence with substrate temperature. The relation between the evaporation rate and the contact angle is non-monotonic. The type of flow instability is independent on buoyancy convection. Abstract: In order to understand the flow instability in the evaporation sessile droplet, a series of numerical simulations are carried out on the ethanol droplet evaporating in its pure vapor at low pressure. The contact radius of sessile droplet on the substrate is 2.5mm. The temperature of the ethanol vapor is fixed at 298K, and the corresponding saturated vapor pressure is 7615Pa. Results show that with the increase of the substrate temperature, different types of the thermal patterns appear in sequence. They are the steady axisymmetric pattern or multi-cell pattern driven by tangential temperature gradient, Bénard-Marangoni cells mainly induced by vertical temperature gradient, and longitudinal rolls caused by inclined temperature gradient. The relation between the evaporation rate and the contact angle is non-monotonic, which depends on the combined effects of Marangoni flow intensity, evaporating surface area as well as the length of heat transfer path from substrate to evaporation surface. The type of flow instability is independent on gravity. However, buoyancy convection changes the transition Marangoni number of the thermal patterns.