Question 1: Open Channel Flow

a) Consider, there is a trapezoidal open channel and the depth of flow on the channel centerline is 3.3 m. The bottom and top widths of the channel are 4.0 m and 17.2 m, respectively.

(i) Compute the value of the wetted perimeter, the hydraulic radius, and the hydraulic mean depth (i.e. Area/Top width).
(ii) If the optimum hydraulic section for a trapezoidal channel is half of a hexagon prove that the top width of the channel is 2.309 D, where D is the centerline depth.
(iii) If D is 3.3 m then what should be the dimensions and side slopes of the channel to obtain the maximum discharge?

b) The expected discharge from an urban subdivision is (2.5 m3/s + F/10) and the allowable gradient to the outfall is 1 in 850. Two design possibilities are to either construct a concrete-lined open channel, or to carry the flow through a concrete pipe. Manning's (n) in each case is 0.012.
(i) Calculate the dimensions of a trapezoidal channel with side slopes at 450 and a bottom width twice the depth.
(ii) For the concrete pipe design, calculate the pipe diameter if it is to be designed running just about full.

c) Explain why it is essential for an engineer to know whether the flow is subcritical or supercritical when designing an open channel and a bridge that will have its abutments in the channel.

Question 2: Flow Measuring Devices and Pumps & Turbines

a) Briefly discuss the operation and application of venturi meter, pitot tubes, electromagnetic and acoustic meters in fluid measurements.

b) Give a brief overview (with figures) of the types of pumps available to convert electrical/mechanical power to work including reciprocating, positive displacement and centrifugal pumps.

c) Briefly explain the difference between parallel and series pump arrangements. When is each arrangement most suitable? (4 marks)

d) Briefly discuss the energy conversion system of turbines in general, and describe the principles of operation and application of different types of turbines including Francis, Kaplan, and Pelton Wheel.