25.3.1. Efficiency of Systems

Try these first

1. 1.

   What does the hydraulic gradient line correspond to in an open channel flow?

   Hint

   Consider what represents the water's surface.

2. 2.

   Define pump efficiency.

   Hint

   What does a pump do to energy?

3. 3.

   What does the hydraulic gradient line indicate in a pipe?

   • Pressure head
   • Velocity head
   • Energy head

   Hint

   Think about what forces the water up.

4. 4.

   True or False: Pumps extract energy from the fluid.

   • True
   • False

   Hint

   What role does a pump play in increasing pressure?

5. 5.

   A system uses a pump to supply water through a 50 mm diameter pipe at a flow rate of 25 L/s. Given a roughness of 0.1 mm, calculate the head loss due to friction over a 100 m length of pipe.

   Hint

   You will need to calculate the Reynolds number for determining flow regime first.

6. 6.

   Determine the efficiency of a turbine if it extracts 120 kW of mechanical energy from fluid flowing at a mass flow rate of 15 kg/s with an inlet pressure of 300 kPa and outlet pressure of 100 kPa.

   Hint

   Make sure to consider the power generated at both pressures.