Noun
English Wikipedia has an article on:natural convectionWikipedia
natural convection (plural natural convections)
free convection
Natural convection will be more likely and/or more rapid with a greater variation in density between the two fluids, a larger acceleration due to gravity that drives the convection, and/or a larger distance through the convecting medium. Source: Internet
Natural convection, or free convection, occurs due to temperature differences which affect the density, and thus relative buoyancy, of the fluid. Source: Internet