Tests on a centrifugal pump showed that at the design discha

Tests on a centrifugal pump showed that at the design discharge of 0.03m^3/s of water at 15degree C a net positive suction head of 3m was required to prevent cavitation. Determine the maximum elevation of this pump above the water level in a sump from which it is required to pump 0.03m^3/s of water at 15degree C if cavitation is to be avoided at this discharge. Length of 100mm ID galvanised steel suction line=20m (regardless of the elevation of the pump). Atmospheric pressure = 101kPa. Neglect minor losses in the suction line. Assume a pipe friction factor f = 0.02. (b) Explain briefly why the potential for cavitation is affected by (i) The height of the pump above the water surface from which it is pumping. (ii) the elevation above sea level of the pump. (iii) the temperature of the water being pumped. (c) The H-Q of a centrifugal pump is as shown below. The pump supplies water to a header tank 10m above the pump outlet. The supply pipe has a diameter (D) of 250mm, a length of 137m, and a friction factor f = 0.02. You may assume minor losses are negligible. By considering a single pump (P), two of the pumps in series (P+P) and two of the pumps in parallel (P//P), determine, (i) The H-Q (head vs flow rate) curve of each of the three pump configurations in the form of a neat table and/or plot. (ii) Which combination will be capable of discharging at least 0.23 m^3/s. (iii) Given a pump efficiency of 60% and a motor/transmission efficiency of 90%, what is the power required for each of the three pump configurations.

Solution

The loaded four wheel trailer shown in Figure P8.10 has a total mass of 5t and is pulled along a level road. Average resistance to motion (friction and windage) is 2 per cent of the total weight and acts at the same horizontal level as the applied force P. Determine the normal reaction at each of the front and rear wheels when the trailer moves:

a) at constant velocity

b) with forward acceleration 1.5m/s².

(Average resistance to motion is 2% of total weight is not required.)