An analysis of flow characteristics during ethanol natural evaporation in capillary tubes with varying diameters

Abstract

For the design of the heat transfer system, heat transfer characteristics and flow state near the evaporation interface are crucial. This paper aims to experimentally investigate Marangoni convection and temperature distribution in thin films during natural ethanol evaporation in capillary tubes of varying diameters. In both horizontal and vertical views, the infrared camera and PIV are used to measure the flow pattern and interfacial temperature distribution of Marangoni convection. The quartz glass capillary has inner diameters of 0.3 mm, 0.5 mm, 0.7 mm, and 1 mm. As a result, the fluid in the capillary is less affected by gravity in the horizontal cross-section. Consequently, the temperature and the flow state exhibit a symmetrical phenomenon, and the lowest temperature value can be found near the capillary wall's angle. The interface from the center to the edges of the Marangoni macroscopic flow is characterized by two symmetrical, counter-rotating vortices. Due to the conflicting effects of gravity and surface tension, the vertical section exhibits both single and double vortices. Small inner diameters of capillaries are also less affected by gravity. As a result, as the capillary diameter decreases, the double vortex phenomenon gradually emerges, which is already apparent in tubes with an inner diameter of 0.3 mm.