课程名称︰流体力学及操作 课程性质︰化工系大二必修 课程教师︰葛焕彰教授 开课学院：工学院 开课系所︰化工系 考试日期（年月日）︰ 2019/06/18 考试时限（分钟）： 100分钟 试题 : Closed Book(70%) 1.(15%) At the entrance region of a laminar flow in a straight pipe, the transition length for the fluid flow (uniform at the entrance) to be fully developed is roughly proportional to the product of the diameter of the pipe and the Reynolds number. Pleaase give an explanation (mathematical derivation) based on the boundary layer theory for flow over a flat plate. 2.(25%) A packed bed is composed of identical cylinders having a diameter D = 0.030m and a length l=D. The bulk density of the overall packed bed is 960 kg/m3 and the density of the solid cylinder is 1600 kg/m3 (a) Calculate the sphericity (shape factor) of the cylindrical particles. (b) Calculate the void fraction of the bed. (c) Calcualte the specific surface area of the bed. 3.(30%) Conider the scale-up from a small-scale agitation tank 1 to a full-scale tank 2 in geometric similarity for the same fluid. A scale-up rule n_2 = n_1*R^(-a) must be selected to determine the rotation speen n_2 to duplicate the small- scale results using n_1, where R is the scale-up ratio (=D_2 / D_1 , and D is the impeller diameter). Determine α, respectively, when each of the following quantities is constant in the scale-up: (a) the Froude number; (7%) (b) the impeller tip speed (v_θ at r = D/2) (7%) (c) the power per unit volume (for the turbulent case, where the power number N_p = P/(n^3 D^5ρ) = constant); (7%) (d) the power per unit volume (for the laminar case, where N_p*Re = constant) Open Books(30%) 4. For the fully developed flow of water at room temperature in a 10 cm ID smooth pipe at a rate of 6.4x10^-3 m^3/s, determine using the universal velocity distribution: (a) thickness of the laminar sublayer, (b) thickness of the buffer layer, (c) thickness of the turbulent layer, (d) the velocity of fluid at the outer rage of the laminar sublayer, (e) the maximum velocity, (f) the shear stress at wall, and (g) the local shear stress at the hypothetical junction of the turbulent core and the buffer layer. --

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