HW 3 13-16) a), b) F1-2 = 0.07 c) F1-2 = 0.08 13-33) Q3 = 781 W

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General Equation

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Chapter 8- Forced Convection-Heat Transfer Correlations for Internal Flow Correlations exist for various problems involving internal flow, including laminar and turbulent flow in circular and non-circular tubes and in annular flow. For laminar flow we can derive h dependence theoretically For turbulent flow we use empirical correlations .

Ludwig Prandtl (1875-1953) Wilhelm Nusselt (1882-1957)

Turbulent Flow in Circular Tubes For a smooth surface and fully turbulent conditions the Dittus – Boelter equation may be used for small to moderate temperature differences Ts-Tm: n=0.4 for heating (Ts>Tm) and 0.3 for cooling (Ts<Tm) For large property variations, Sieder and Tate equation: All properties, except ms evaluated at average value of mean temperature Internal Flow 25

Turbulent Flow in Circular Tubes The effects of wall roughness may be considered by using the Petukhov correlation: For smaller Reynolds numbers, Gnielinski correlation: Friction factors may be obtained from Moody diagram etc. Internal Flow Chee 318 26

Example (1) :

Example (2) :