Thermal insights of the temperature gradient-induced convections in an evaporating meniscus

Abstract

The present study investigates thermal patterns and convection mechanisms in evaporating ethanol menisci using infrared thermography. High-resolution spatiotemporal temperature distributions were captured at the menisci formed within quartz cuvettes with inner diameters of 25.7 mm and 36.5 mm and inner base temperatures ranging from 47.4 °C ± 0.2 °C to 75.4 °C ± 0.2 °C. Four distinct convection stages were identified, including Thermally-driven Chaotic Initiation (TCI), Large-scale Fractal Division (LFD), Radial Migration-dominated Generation (RMG), and Ending & Dryout (ED). Analysis reveals that liquid layer thickness regulates transitions between Rayleigh-Bénard, Marangoni, and thermocapillary convection regimes. Larger cuvettes with thinner films suppress large-scale fractal “croissant-shaped” thermal cells while enhancing the Marangoni stress-driven radial migration of small-scale cells. The Marangoni-to-Rayleigh number ratio (Ma/Ra) exhibits weak temperature dependence but can be used to calculate the critical liquid layer thickness threshold (δ_c range of 3.00 ∼3.21 mm for ethanol) below which Marangoni effects govern interfacial transport. Outcomes of the present study provide insights into the complex interactions between thermal gradients, fluid properties, and convection regimes in curved evaporating liquid films, which are critical for predicting regime transitions in liquid film-based thermal management systems.