HomeworkSolutions_C7

# HomeworkSolutions_C7 - Homework Set 7 Problem#1 What...

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Homework Set # 7 Problem #1 What pressure drop is needed for pumping water at 20 C, through a pipe of 25 cm diameter and 1234 m length at the rate of 1.97 m 3 /s? The pipe is at the same elevation through out and contains four standard radius 90 0 elbows and two 45 0 elbows. The resistance of s standard radius 90 0 elbow is roughly equivalent to that offered by a pipe whose length is 32 diameters; a 45 0 elbow, 15 diameters. Answer: The average velocity at the given conditions is ( ) 2 4/ 40.1 / w vm D ρ π == s and the Reynolds Number is 6 9.99 10 Dv v Thus the flow is turbulent and fig 6.2-1 (see textbook or lecture note) gives f = 0.0020 for hydraulically smooth pipe. The total equivalent length of the pipe and fittings is; () ( ) o o 1234 mof pipe 4 32 0.25 m equivalent for four 90 -elbows 2 15 0.25 m equivalent for two 90 -elbows 1274.5 m e L = + + = From the definition of friction factor for circular straight tubes, the required pressure drop is then 2 7 2 3.3 10 Pa e oL L pp v f D −= = Problem #2: A hollow sphere, 5 mm in diameter, with a mass of 0.05 g, is released in a column of liquid and attains a terminal velocity of 0.5 cm/s. The liquid density is 0.9 g/cm 3 . The local gravitational acceleration is 980.7 cm/s 2 . The sphere is far enough from the containing wall so that their effect can be neglected.

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HomeworkSolutions_C7 - Homework Set 7 Problem#1 What...

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