hw13 - S09 - Chemical Engineering 150A Spring Semester,...

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Chemical Engineering 150A Spring Semester, 2009 Homework 13: Convection Problem 1 Forced air at T = 25 ºC and V = 10 m/s is used to cool electronic elements on a circuit board. One such element is a chip, 4 mm by 4mm, located 120 mm from the leading edge of the board. Experiments have revealed that flow over the board is disturbed by the elements and that convection heat transfer is correlated by an expression of the form 1 3 0.85 0.04Re Pr x x Nu = Estimate the surface temperature of the chip if it is dissipating 30 mW. Problem 2 A viscous fluid with physical properties ( μ , k , ρ , C p ) assumed constant is in laminar flow in a circular tube of radius R . For z < 0 the fluid temperature is uniform at the inlet temperature T 1 . For z > 0 there is a constant radial heat flux q r = - q o at the wall. (Such a situation exists, for example, when a pipe is wrapped uniformly with an electrical heating coil, in which case q o is positive. If the pipe is being chilled, then q o is taken as negative.) a)
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hw13 - S09 - Chemical Engineering 150A Spring Semester,...

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