Heat Transfer 11-1a1 Conduction R = L Fouriers Law of Conduction - PowerPoint PPT Presentation

Heat Transfer 11-1a1 Conduction R = L Fourier’s Law of Conduction Thermal Resistance: kA Rate of Heat Transfer: • Through a composite wall: • Through a wall: R total = R 1 + R 2 = L 1 k 1 A + L 2 k 2 A Q = Qt Professional Publications, Inc. FERC

Heat Transfer 11-1a2 Conduction • Through a cylindrical wall of length L : ln r 2 r 1 R = 2 � kL Professional Publications, Inc. FERC

Heat Transfer 11-2 Convection Convection Heat Transfer For a straight fin: P = exposed perimeter k = thermal conductivity A c = cross-sectional area T b = temperature of fin base T � = fluid temperature Professional Publications, Inc. FERC

Heat Transfer 11-3 Radiation � = emissivity 2 � K � = 5.67 � 10 � 8 W/m 4 (Stefan-Boltzmann constant) Black Body vs. Gray Body Black Body: emissivity( � ) = absorptivity ( � ) = 1 Gray Body: � = � , and both are between 0 and 1 Professional Publications, Inc. FERC

Heat Transfer 11-4 Radiant Heat Transfer For any body, radiation must be absorbed, reflected, or transmitted through: Professional Publications, Inc. FERC