practice_problems_ii

practice_problems_ii - Practice problems for convection...

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Practice problems for convection heat transfer 1) Air is flowing over a flat plate of length 2 m. Transition to turbulence occurs at x c = 0.75 m. (a) Assuming that the film temperature is 400 K and the critical Reynolds number is 5e5, determine the air velocity. (b) The local heat transfer coefficient is measured. One finds that in the laminar region h ( x )= C 1 x -0.5 and in the turbulent region, h ( x )= C 2 x -0.2 . Where, C 1 = 9.25 W/(m 1.5 K) and C 2 =52.3 W/(m 1.8 K). Determine an expression for the mean heat transfer coefficient as a function of x . 2) A blower in a wind tunnel can provide air velocities up to 60 m/s at 28 ° C. What is the minimum length of a plate if one wants to study boundary layer behavior up to Re x =1e8? At what distance from the leading edge does transition occur. 3) Transition occurs at Re x =5e5 for flat plate boundary layers. For a fluid velocity of u=2 m/s, determine the distance from the leading edge at which transition occurs for a) air, b) water, and c) engine oil at 50 ° C 4) For a triangular duct with a characteristic length of L =0.75 m in cross flow the mean heat transfer coefficients are determined at two different flow velocities: h 1 = 60 W/(m 2 K) @ 25 m/s and h 2 = 50 W/(m 2 K) @ 18 m/s. Assume that the Nusselt correlation has the form : Nu = C Re m Pr n What is the heat transfer coefficient at 20 m/s if the characteristic length is 0.5 m? 5) Determine the velocity boundary layer thickness at a distance of 25 mm from the leading edge of a flat plate in parallel flow with a velocity of 1.5 m/s for a film temperature for different fluids a) water, b) air, c) engine oil, and d) mercury. 6) A flat plate is subjected to parallel flow on both sides. The free stream velocity is 10 m/s and the free stream temperature is 15 ° C. Determine the average convective heat transfer coefficient and the convective heat transfer rate for a flow of air if the plate is 3 m long and 2 m wide. The

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This note was uploaded on 11/30/2011 for the course EML 4140 taught by Professor Any during the Fall '08 term at University of Florida.

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practice_problems_ii - Practice problems for convection...

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