Themal Patterns Of An Evaporative Sessile Droplet With The Interfacial Temperature Variation

Abstract

The use of volatile fluids have produced interesting thermal patterns from which the internal fluid dynamics and heat transfer can be understood using a non–intrusive infra-red camera. Various studies have been conducted on a droplet that evaporates to dryness. However, the changing droplet geometry becomes a variable should we want to analyse the underlying cause of the thermal patterns. Therefore, this study focuses on a stable droplet under the influence of different stage geometry and temperature and would discuss the behaviour, thermal motion and evolution of hydrothermal waves in ethanol, novec–7100 and deionized water. Two sets of experiments, droplet evaporation on a flat stage and on a stage with a raised edge were conducted to achieve the experimental objective. Prior to that, the flow-rate and contact angle were the parameters investigated for a stable, sessile droplet. HW1 waves were characterized by spirals at low temperatures and became linear and thinner convective rolls at higher temperatures. HW2 waves were found to be petal-like in shape and behaved differently in ethanol and novec. A greater number of hydrothermal waves and maximum interfacial temperature difference were produced by the stage with a raised edge. The relationship between the two were discussed. Also, Rayleigh convection and Marangoni flow were found to have complemented each other in the droplet on a stage with a raised edge. Finally, a finding on a prolonged effect (due to new fluid being pumped) of Phase 1 as proposed by Sefiane and Bennacer [7] was made.