32 thermal[1] - Thermal Analysis Thermal Analysis Overview...

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Thermal Analysis Thermal Analysis Overview Modes of Heat Transfer There are three basic modes of heat transfer: Conduction - internal energy exchange between one body in perfect contact with another or from one part of a body to another part due to a temperature gradient. Convection - energy exchange between a body and a surrounding fluid. Radiation - energy transfer from a body or between two bodies by electromagnetic waves. In most cases, we are analyzing heat conduction problems with convection and/or radiation boundary conditions.
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Thermal Analysis Overview Conduction Heat flux due to conduction is given by Fourier’s Law of Conduction: Negative sign indicates that heat flows in the opposite direction of the gradient (i.e., heat flows from hot to cold). qK T n K T T n nn nn * =− = = heat flow rate per unit area in direction n Where, = thermal conductivity in direction n = temperature thermal gradient in direction n T n q* dT dn Thermal Analysis Overview Convection Heat flux due to convection is given by Newton’s Law of Cooling: Convection is typically applied as a surface boundary condition qh T T h T T fS B f S B * () = heat flow rate per unit area between surface and fluid Where, = convective film coefficient = surface temperature = bulk fluid temperature T B T s
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Thermal Analysis Overview Radiation The radiant heat flow rate from surface i to surface j is derived from the Stefan-Boltzmann Law: QA F T T A F T T ii j i j i ij i j =− = σε σ ε () 44 heat flow rate from surface i to surface j Where, = Stefan - Boltzmann Constant = emissivity = area of surface i = form factor from surface i to surface j = absolute temperature of surface i = absolute temperature of surface j i j Geometry Can either be created within ANSYS or imported . Include details to improve results: Goal is to sufficiently model the thermal mass of the structure. Convection loads requires areas be correctly modeled. Heat generation loads requires the volumes be correctly modeled. A. Preprocessing Geometry
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Element type The table below shows commonly used thermal element types. The nodal DOF is: TEMP. Commonly used thermal element types A. Preprocessing Meshing Material properties Minimum requirement is Kx, thermal conductivity for steady state analysis. Setting preferences to “thermal” limits the Material Model GUI to display only Thermal properties. Real constants / Section properties Primarily needed for shell and line elements. 2-D Solid 3-D Solid 3-D Shell Line Elements Linear PLANE55 SOLID70 SHELL57 SHELL131 LINK31,32,33,34 Quadratic PLANE77 PLANE35 SOLID90 SOLID87 SHELL132 Thermal loading conditions can be: Temperatures Regions of the model where temperatures are known.
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This note was uploaded on 01/20/2010 for the course ME master taught by Professor Mon during the Spring '09 term at Hanyang University.

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32 thermal[1] - Thermal Analysis Thermal Analysis Overview...

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