CEE 345 - Benjamin - Winter 2012 - Exam 1 Solutions(1)

CEE 345 - Benjamin - Winter 2012 - Exam 1 Solutions(1) -...

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1 CEE 345, Part 2; Win 2012, Exam #1 Solutions 1. From the Moody diagram, the friction factor for fully turbulent flow in pipe with relative roughness of 0.0008 is f = 0.019. The water therefore loses energy per unit weight equal to 1.9% of a velocity head for each diameter (2.4 m) traveled. Correspondingly, the loses 10 times its velocity head over a distance of (10)(2.4 m) / 0.019, or 1263 m. 2. If different values of ' Q were applied to different types of loop, continuity would be violated at the junctions between those pipes. 3. (a) Cavitation can occur because, even though the overall effect of the pump is to increase the head (and the pressure) of the water, the water first loses pressure as it accelerates inside the pump. As a result, the point of minimum pressure is not at the pump inlet, but rather between the eye and the outer edge of the impeller.Since the point of installing a pump in a pipeline is to increase the head of the water, it would seem that having a pressure at the pump inlet that is greater than the vapor pressure would assure that cavitation could not occur. Yet, cavitation can occur under those conditions. (b) The difference between the vapor pressure in the suction pressure is the net positive suction head required, NPSH R . (c) Cavitation is the formation of bubbles in the fluid. The damage caused by cavitation occurs when these bubbles collapse downstream of the point where they form. 4. (a) Shutoff head: The head developed by a pump when the discharge is zero. (b) Suction head: The total dynamic head (pressure head plus velocity head) at the inlet to a pump. (Alternatively, if you interpreted the question to be asking about the static suction head, an acceptable answer is the increase in static head [i.e., the decrease in elevation] between the surface of a reservoir and a pump that it feeds.) (c)
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This note was uploaded on 03/31/2012 for the course CEE 345 taught by Professor Batho,m during the Spring '08 term at University of Washington.

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CEE 345 - Benjamin - Winter 2012 - Exam 1 Solutions(1) -...

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