Keeping your feet dry
A pump is used to drain a flooded excavation ditch in a construction site, as shown in the figure. Commercial steel pipes are used, with two different nominal sizes, d1 = 2 in and d2 = 4 in. The pipe lengths are as follows: z1 = 3 m, z2 = 3 m, l = 10 m.
a) Explain whether the flow rate through the pipes can be increased indefinitely by decreasing the pump suction pressure, or whether there is a minimum suction pump pressure at which the flow will stop. If this is the case, explain what will make the flow stop.
b) Determine the maximum water flow rate through the pipes if all frictional losses are neglected.
c) Determine the maximum water flow rate through the pipes if all losses are taken into account as accurately as possible. Compare this value with the result you found in (b).
Contributed by Stavros Tavoularis,
Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada.