DE-Lecture11-Perfomance-of-Pumps

DE-Lecture11-Perfomance-of-Pumps - Dredging Engineering...

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Unformatted text preview: Dredging Engineering Dredging Engineering Lecture 11 Lecture 11 Performance of Pumps Performance of Pumps Luis Prieto-Portar 2010 The Pumps Output. The dredge pumps output is a function of several variables, such as,- The desired velocity of the flow, - The size of the discharge pipe,- The required length of the shoreline pipe,- The required lift to reach the discharge point,- The horsepower ,- The pumps efficiency ,- The type of soil dredged, he uantity f the soil to be dredged, and- The quantity of the soil to be dredged, and- The maximum depth to be dredged. These 9 variables are all mutually inter-dependent and optimizing a pump is a difficult job. Rather, the Engineer needs to determine a range of operations, and optimize the pump that will fit within that range at a reasonable cost. The dredge output is measured in bank cubic yards (bcy) per hour . That is, the material in-situ. Obviously, the material will expand upon being dredged, and that must be taken into account in the volume calculations. The dredge output is thus a function of the diameter of the discharge pipe, the velocity of the flow and the slurry concentration of solids. The output in gallons per minute (gpm) Q is, where d is the discharge pipe diameter in feet, and v is the velocity in fps. Most dredgers use an output Q in cubic yards per hour (cyph), Notice that the conversion factor from gpm to cyph is 0.2971. The next two slides show tables to find the output in both system of units. ( 29 2 352.5 Q d v = ( 29 2 104.7 Q d v = The Required Horsepower for the Pump. The power needed to move the slurry out the discharge is called the water horsepower HP w , where HP w is in horsepower, Q is in gpm and H total is the total dynamic head on the pump, in feet . However, that is not the power actually expended. Pump losses must be taken into ccount through the pumps efficiency Therefore, the power expended is called 3960 s slurry total w G QH HP- = account through the pumps efficiency E . Therefore, the power expended is called the brake horsepower HP b , The efficiency of a pump is called its hydraulic efficiency, and is affected by (1) hydraulic losses due to eddies, turbulence, shock and friction in the fluid between solids and water, etc; (2) leakage losses from high pressure areas to suction area, also called flow-back losses, etc; (3) mechanical and frictional losses from bearings, the stuffing box and disk friction of the runner in the slurry, etc. The next slide shows where all these losses are occurring in the pump. w b HP HP E = Characteristic Curves of a Punp. Pump curves are the plot of output Q versus head h as shown below. When a specific pipe is considered, it is called a system curve, and when horsepower is added, then the characteristic curves give an overall picture of the hydraulic-system operation. The system curves shown above indicate the head against which a pump has to work for...
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DE-Lecture11-Perfomance-of-Pumps - Dredging Engineering...

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