ENCH 403 Chapter 7: ENCH 403 Chapter 7 Summary Notes
9 Nov 2016
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Compute heat transfer for surface in external flow. Confine to problems of low-speed, forced convection with no phase change: forced convection is motion maintained external force, e. g. fan, pump. Primary objective: determine convection coefficients for different geometrics. Subscript x indicates a particular location on surface. Overbar indicates an average from =(cid:882) (where boundary layer develops) to location of. There are two approaches to obtaining the function for h: interest. By measuring convection at different test conditions, data can be represented algebraically by: Since fluid properties vary along x direction, the film temperature is used mean boundary layer: experimental/empirical approach, theoretical approach. Local nusselt number found to be: = (cid:1863) =(cid:882). (cid:885)(cid:885)(cid:884)(cid:1857)(cid:2869)(cid:2870)(cid:2869)(cid:2871) If flow is laminar over entire surface, subscript x may be replaced by l, and equation. = =(cid:882). (cid:888)(cid:888)(cid:886)(cid:1857)(cid:3117)(cid:3118)(cid:3117)(cid:3119) (cid:1829)(cid:3033),= ,(cid:3048) (cid:3118)/(cid:2870)=(cid:882). (cid:888)(cid:888)(cid:886)(cid:1857) (cid:3117)(cid:3118) (cid:1829) (cid:3033),=(cid:883). (cid:885)(cid:884)(cid:890)(cid:1857) (cid:3117)(cid:3118) In comparison with the laminar boundary layer, one can see that turbulent boundary layer grow is much more rapid.
