Homework of Chapter (5)

Transcription

1 Dead Line: Wednesday (18/04/2018) The Islamic University of Gaza, Instructors: Dr. Khalil M. Al Astal Civil Engineering Department, Hydraulics -Discussion, Second semester, T.A: Eng. Mohammed AbuRahma T.A: Eng. Reem Sbaih Homework of Chapter (5) A pump delivers 30 C water from a supply reservoir to an elevated tank at a rate of 120 liters per second. The elevation difference between the reservoirs is 45 m, and the supply line is 150 m long (ductile-iron pipe) and 35 cm in diameter. The suction line is 10 m of the 150m length. Minor loss coefficients in the suction line total 3.7, If the pump is installed l m to 3 m above the supply reservoir (depending on fluctuations in the water level), will the installation be susceptible to cavitation? The net positive suction head of the pump is rated at 6 m. 1

2 A pump delivers water at 10 C between a reservoir and a water tank 20 m higher. The suction side consists of a strainer (ks = 2.5), three 90 bends (R/ D = 2), and 10m of ductileiron pipe, 25 cm in diameter. The discharge side includes a 160-m-long, ductile-iron pipe, 20 cm in diameter, and a gate valve. The friction factor for the pipeline is 0.02, the net positive suction head is 7.5 m, and the design discharge is 170 liters/sec. Determine the allowable elevation difference between the pump and the reservoir water surface to avoid cavitation. 2

3 The efficiency of a pump will drop suddenly if cavitation takes place in the pump. This phenomenon is observed in a particular pump (with σ = 0.08) operating at sea level, and the pump delivers 0.42 m 3 /sec of water at 40 C. Determine the sum of the gauge pressure head and the velocity head at the inlet (i.e., the sum, not the individual components). The total head delivered by the pump is 85 m, and the suction pipe diameter is 30 cm. 3

4 5.5.3 Consider a pump-pipeline system that delivers water from reservoir A to B with EA = 45.5 m and EB = 52.9 m. The pipe has a length of L = 3,050 m, diameter of D = 0.50 m, and a Darcy-Weisbach friction factor of f = Minor losses incl11de an inlet, exit, and swing-type check valve. The pump characteristics are shown in the following table. Determine the flow rate and velocity in the pipeline. 4

5 Water is being pumped from a supply reservoir to an elevated holding lank. The elevation gain is 14.9 m, and the length of the ductile iron supply pipe (f = 0.019) connecting the reservoirs is 22.4 m. The pipe is 5.0 cm in diameter, and the performance curve of the pump is given by HP = Q 2, where HP is in meters and Q is in liters per second. (The equation is valid for flows less than or equal to l.5liters per second.) Using this pump, what flow do you expect in the pipeline if minor losses are ignored? What pump head is required for this flow? 5

6 A pump is required to deliver rn 3 /sec of water (20 C) from reservoir A to reservoir B (water surface elevations of m and m, respectively). The pipeline (concrete) is 300m long with a diameter of m and contains five bends (R/ D = 6) and two gate valves. Determine the appropriate pump from Figure 5.24 along with the working conditions. 6

7 A pump station is required to deliver 20 C water from a reservoir to an elevated storage tank at a minimum required discharge of 300 L/sec. The difference in elevations is 15m, and a 1,500-m-long, wrought-iron pipe that is 40 em in diameter is used. Select the pump(s) from the set given in Figure Determine the number of pumps, the configuration (series or parallel), discharge, total head, and efficiency at which the pumps operate. Ignore minor losses. 7

8 Two identical pumps have the characteristic curves shown in Figure 5.13, which are shown in the following table. The pumps are connected in series and deliver water through a 40-cm-diameter, 1,000-m-long commercial steel pipe into a reservoir where ~he water level is 25 m above the pump. Neglecting minor losses, determine (a) the discharge in the system if only one pump is used, and (b) the discharge when the system contains two pumps connected in series. [Hint: Use a spreadsheet with the Swamee-Jain equation (3.24a) applied to determine the friction factor.] 8

9 Consider a pump-pipeline system that delivers water from reservoir A to B with EA = 45.5 m and EB = 52.9 m. The pipe has a length of L = 3,050 m, diameter of D = 0.50 m, and a Darcy-Weisbach friction factor of f = Minor losses include an inlet, exit, and swing-type check valve. The pump characteristics are shown in the following table. When a single pump is used in the pipeline, the flow rate is m3/sec with a pump head of about 66.3 m. Determine the flow rate in the pipeline if two identical pumps are used in a series combination. Also, determine the flow rate in the pipeline if two identical pumps are used in a parallel combination. 9

10 The design of a centrifugal water pump is studied by a 1/10 scale model in a hydraulic laboratory. At the optimum efficiency of 89 percent the model delivers 75.3 L/sec of water against a 10-m head at 4,500 rpm. If the prototype pump has a rotational speed of 2,250 rpm, what is the discharge and efficiency required to operate the pump under this condition? 10