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

•The temperature and flow characteristics of the capillary meniscus are analyzed from the point of view of force.•Both temperature and flow are symmetrically distributed in the horizontal section of the meniscus.•The flow instability in the vertical section of the meniscus decreases with the increase of the capillary diameter.•Evaporation at the bottom of the capillary is more intense due to gravity.