CEE 454SSSWS: Prelim 1Oct.5, 2006 - 8:40 AM -9:55AMOpen book
May the time you spent preparing for this exam pay off. Read each problem carefully before beginning to work on the answer!
Make sure you answer each part of each question (6 points each).
1)Explain the hypothesized role of indoor plumbing in reducing the incidence of typhoid between 1900 and 1940.
2)Describe 2 public health concerns related to intermittent water supplies but not related to water storage in the home.
3)Describe how a home water storage tank such as used in Honduras could be part ofafecal-oral route.
4)Why might homes with an intermittent water supply use more water than homes with a continuous supply?
5)What are the two essential components of a constant flow control device that relies on gravity to power the flow?
6)From an operator’s perspective which is preferable, a flow control device with flow adjustment by turning a valve or with flow adjustment by changing the elevation of the effluent tube? Explain why.
7)Why do the hypochlorinators used in Honduras not provide a constant flow (what is wrong with the hydraulic design)?
8)Explain the concept of open source engineering.
Design Challenge
You realize that turbulent pipe flow causes mixing and so you would like to know if there is enough mixing in the pipe between the grit chamber and the flocculation tank to eliminate the need for a rapid mixer. The plant is designed to work in the range of 200 to 400 liters per minute. The distance between the rapid mix unit and the hydraulic flocculator is 5 m. You have already determined that the pipe must be at least 4” (10 cm) in diameter to avoid excessive head loss, and you recall from that analysis that the friction factor was 0.024 over the range of plant flows. There are 2 90° elbows in the pipe on the way to the flocculation tank. The elbow minor loss coefficient is approximately 0.3 (for each elbow).
1)(15 points) What is the head loss in this pipe at the maximum flow rate (in centimeters)?
2)(15 points) What is the average velocity gradient in the pipe at maximum flow?
3)(15 points) Perform a calculation to determine if there is adequate mixing to blend the aluminum sulfate with the raw water.
4)(5 points) Comment on the need for an inline static rapid mixer.
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