Thermal patterns from an evaporating flat surface under nonuniform heating

Abstract

Previous research on thermocapillary flows during evaporation has often neglected key factors,

including evaporation’s role in surface instability, precise heat source positioning at the liquid- vapor interface, and the influence of low-pressure environments on thermocapillary

instabilities. Experiments with droplets have also struggled with nonuniform surfaces, complicating control over surface tension variations. This study addresses these gaps by examining controlled temperature gradients on thermal pattern formation during ethanol evaporation. Nonuniform heating using resistive wires at 35°C, 45°C, and 55°C was applied under open (atmospheric) and closed (reduced pressure) conditions to observe thermal pattern evolution under single heating wire and dual heating wire configurations. Temperature measurements were taken at four points—Wire Top, Wire Edge, Mid Field, and Far Field— along the tank centerline, and thermal patterns were captured at 1 ms intervals. Results show that reduced pressure stabilized and enhanced thermal patterns, with minimal flow under low heating and increased instability and turbulence under higher heating conditions. Dual heating setups demonstrated stable thermal boundaries and minimized movement under reduced pressure. These findings highlight the critical role of temperature gradients and environmental control in pattern formation for applications in microelectronics cooling and aerospace. Future work should explore broader pressure ranges, diverse liquids, and surface properties to deepen understanding of thermocapillary dynamics and integrate numerical simulations for enhanced insights.