What process characterizes heat transfer within a liquid or gas?

Heat transfer within a liquid or gas is characterized by convection. This process involves the movement of fluid where warmer, less dense areas of the liquid or gas rise while cooler, denser areas sink. This creates a circulation pattern that helps distribute heat throughout the fluid.

In convection, thermal energy is transferred by the movement of the fluid itself, as opposed to conduction, where heat is transferred through direct contact between materials. Additionally, insulation refers to materials or methods that reduce heat transfer and is not a mechanism of heat transfer, while evaporation is a process where a liquid changes to a vapor, which does not directly describe heat transfer within the body of the liquid or gas. Convection plays a vital role in various natural phenomena and engineering applications, such as weather patterns and heating systems, making it a critical concept in understanding thermal dynamics.