CURRENTS MOVING IN fluids are convection. More specifically, fluids—liquids, gases, andrheids—undergo movements as convection currents. Convection plays a major role in heat transfers. In fluids, both movement of mass in the fluid, and the heat it contains, occurs in a random way, if Brownian motion occurs. However, in the process of advection, large motions develop in the fluid, which move not only its mass, but also the energy it contains. Convection means the transfer of mass and heat by diffusive and advective movements. Heat is the [Page 283]transfer of energy from one body to another. Heat is a cause of convection currents in fluids, because the fluid motion is initiated and continued by the energy transfers occurring in the fluid.

As a fluid is heated, it ...