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Unformatted text preview: Lecture 31 pls-31.1 Energy Transfer (Heat) Media: 1. Convection demonstration 2. Excel sheet heat sim 3. Scene from A Christmas Story 3. Melting/nonmelting blocks 1. Convection Convection is energy transfer via macroscopic flow of material from one region to another. Important in fluids (gases and liquids), but not solids. Can be driven by gravity due to changes in density (in part of fluid) with temperature or can be forced (via a fan, e.g.) Demo: Convection demonstration 2. Conduction Conduction is energy transfer through a material that is due only to macroscopic motion inside the material. Important in solids; important in fluids if there is no (or very little) macroscopic flow. If flow is significant, then heat transfer via convection will typically dominate that by conduction. Conduction of energy is due to random , microscopic energy exchange among the constituents (atoms, usually) of a the solid. If a solid material does not initially have a well defined temperature, as illustrated on the left below, this random, microscopic energy exchange will bring the material into thermal equilibrium (such that it is described by one temperature). Lecture 31...
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