课程名称︰流体力学 课程性质︰大二必修 课程教师︰陈瑶明 开课学院：工学院 开课系所︰机械系 考试日期（年月日）︰2008.Apr.25 考试时限（分钟）：110 min 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1. (a) Express the Bernoulli equation in the way using "Heads" and discuss the major assumptions of this equation. (b) What's Kinetic energy correction factor? When is it significant? (c) Explain the importance of the Reynold transprot theorem and describe how the linear momentum equation is obtain from it. 2. Air is flowing through a venture meter whose diameter is 4.2 in at the enterance part (location 1) and 2.8 in at the throat (location 2). The gage pressure is measured to be 16.8 psia at the enterance and 15.2 psia at the throat. Neglecting frictional effects, show that the volume flow rate can be expressed as ╭ ╮(1/2) . │ 2(P1-P2) │ V = │────────────── │ │ ρ(1-((A2)^2/(A1)^2)) │ ╰ ╯ and determine the flow rate of air. Take the air density to be 0.078 lbm/ft^3. 3. A ruducing elbow is used to deflect water flow at a rate of 38 kg/s in a horizontal pipe upward by angle θ=40° from the flow direction while accelerating it. The elbow discharge water into the atmosphere. The cross-section area of the elbow is 160 cm^2 at the inlet and 40 cm^2 at the exit. The elevation difference between the center of exit and the inlet is 45 cm. The mass of the elbow and water in it is 55 kg. Determine the anchoring force needed to hold the elbow in place. Take the momentum-flux correction factor to be 1.04. 4. Consider a centrifugal blower that has a radius of 22 cm and a blade width of 8.4 cm at impeller inlet, and a radius of 48 cm and a blade width of 5.8 cm at the outlet. The blower delivers air at a rate of 0.79 m^3/s at a rotational speed 900 rpm. Assuming the air to enter the empeller in radial direction and to exit at an angle of 50 °from the radial direction, determine minimum power consumption of the blower. Take the density of the air to be 1.22 kg/m^3. --

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