This is the process of transferring heat through the movement of liquids or gases. Heat causes liquid or gas to expand, decrease density, thus creates movement via mixing cold and hot pockets, rather than on a microscopic process as which happens with diffusion. Convection occurs with gases and moving fluids such as when wind/fan blows, a fire burns due to hot air rising. The greater the fluid velocity and mixing (turbulence), the increased rate of convective heat transfer. There are two categories of convection: Free/ Natural Convection and Forced Convection. Natural convection occurs when a heated fluid rises and a cooler fluid lowers due to cold liquid being denser, i.e., buoyancy. Forced convection occurs when an external force, like a fan or pump is used to move fluid to transfer heat. (ISTA)
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