8.3 Temp and Heat

# 8.3 Temp and Heat - Heat Transfer The temperature of an...

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1 8.3 Temperature and Heat Heat Transfer Conduction Convection Radiation Thermal Energy Balance Heat Transfer Q in Q ou t T The temperature of an object depends on the input and output of thermal energy The rate of heat flow depends on the pathways for heat transfer. Heat Flow T H T L dQ H dt = Heat flows from High temperature to low temperature The rate of heat flow depends on the thermal connection between the two systems. Mechanisms of heat transfer • Conduction- important for short distances, depends on the material through which heat flow occurs. • Convection – involves the movement of heated mass, more efficient than conduction for long distances. • Radiation – occurs even through a vacuum, depends on the properties of the radiating surface. Conduction T Hk A x =− k = thermal conductivity W/m•K The minus sign means that flow is opposite to the direction of increasing T Heat flow is negative out of the region of high temperature Thermal conductivities 0.30 0.046 Goose down 5-6 0.7-0.9 Glass 1644 237 Aluminum 0.78 0.11 Wood (pine) 0.18 0.026 Air British Units BTU•in/h•ft 2 o F SI Unit W/m•K Material

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2 Question Find the heat flow through a 1.0 m 2 styrofoam slab 2.0 cm thick
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## This note was uploaded on 06/01/2009 for the course PHYS phys2c taught by Professor Okamura during the Spring '09 term at UCSD.

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8.3 Temp and Heat - Heat Transfer The temperature of an...

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