What is the term for the transfer of heat through a circulating medium of liquid or gas?

The term for the transfer of heat through a circulating medium of liquid or gas is convection. This process involves the movement of fluids (liquids or gases) and the transfer of heat as these fluids circulate. When a fluid is heated, it becomes less dense and rises, while cooler, denser fluid sinks. This creates a continuous motion that effectively transfers heat throughout the medium.

In contrast, conduction refers to heat transfer through direct contact between materials, where heat moves from the hotter object to the cooler one without any movement of the medium itself. Radiation involves the transfer of heat in the form of electromagnetic waves, such as sunlight warming the Earth, and does not require a medium to travel through. Diffusion is a process that describes the movement of particles from an area of higher concentration to an area of lower concentration and is not specifically related to heat transfer. Understanding these distinctions helps clarify why convection is the correct answer in the context of heat transfer in fluids.