Which term describes the transfer of heat through a fluid when heated fluid rises and cooler fluid sinks?

The term that describes the transfer of heat through a fluid, where the heated fluid rises and the cooler fluid sinks, is natural convection. In this process, the movement of the fluid is driven solely by temperature differences within the fluid itself, causing warmer, less dense regions to rise while cooler, denser regions sink. This type of heat transfer relies on the fluid's natural circulation due to gravitational effects and temperature variations.

In contrast, conduction involves heat transfer through direct contact between materials, where energy moves from a high-temperature area to a low-temperature area without the bulk movement of the material itself. Radiation refers to the transfer of heat in the form of electromagnetic waves, and does not require a medium. Forced convection, on the other hand, involves the movement of fluid being induced by external means, such as fans or pumps, rather than occurring naturally due to temperature differences. Hence, natural convection specifically captures the essence of heat transfer driven by density changes within the fluid itself.