Pumping efficiency speed

In the case of speed changes, the pump efficiency is not affected except for a minor change owing to Reynolds number change, but the diameter cut may reduce the efficiency appreciably on account of increased gap and losses between the impeller OD and a collector (casing or diffusor). 

This shows that the pump head is determined primarily by the size and speed of the impeller and the pump efficiency, independent of the flow rate of the fluid. This is approximately correct for most centrifugal pumps over a wide range of flow rates. However, there is a limitation to the flow that a given pump can handle, and as the flow rate approaches this limit the developed head will start to drop off. The maximum efficiency for most pumps occurs near the flow rate where the head starts to drop significantly. 

You need a pump that will develop at least 40psi at a flow rate of 300 gpm of water. What combination of pump size, motor speed, and impeller diameter from the pump characteristics in Appendix H would be the best for this application State your reasons for the choice you make. What are the pump efficiency, motor horsepower and torque requirement, and NPSH for the pump you choose at these operating conditions ... 

You must chose a centrifugal pump to pump a coal slurry. You have determined that the pump must deliver 200 gpm at a pressure of at least 35 psi. Given the pump characteristic curves in Appendix H, tell which pump you would specify (give pump size, speed, and impeller diameter) and why What is the efficiency of this pump at its operating point, what horsepower motor would be required to drive the pump, and what is the required NPSH of the pump The specific gravity of the slurry is 1.35. 

In example 1, a volume throughput of 300 1/h is pumped at a rotational speed of 300 rpm. Eqs. 7.2 to 7.10 and the typical physical properties of density p=1000 kg/m3 and specific heat capacity c=2000 J/kg-K are used to calculate the back-pressure length, pumping efficiency, energy input and temperature rise in the polymer for the two available screw elements. 

When changing a mechanical pump s oil, first run the pump for a short time to warm the oil. Warm oil will drain more efficiently from the pump. Open the side valve and let the oil pour directly into a container (use a funnel if necessary). If it is physically possible, tipping the pump may speed oil draining, but it should not be required. The pump may retain small pockets of pump oil within small sections of the pump. These pockets can be emptied out by partially closing the exhaust... 

The speed ranges indicated here are based on different pumps, not ranges of efficiency of one pump. That is, a small, small pump s speed is about 1.5 liters/m, but a big, small pump s speed is about 20 liters/m. 

Determine the pump efficiency and impeller shape. Figure 6.12 shows the general relation between impeller shape, specific speed, pump capacity, efficiency, and characteristic curves. At Ns — 2000, efficiency = 87 percent. The impeller, as shown in Fig. 6.12, is moderately short and has a relatively large discharge area. A cross section of the impeller appears directly under the Ns = 2000 ordinate. 

Pumping is a unit operation that is used to move fluid from one point to another. This chapter discusses various topics of this important unit operation relevant to the physical treatment of water and wastewater. These topics include pumping stations and various types of pumps total developed head pump scaling laws pump characteristics best operating efficiency pump specific speed pumping station heads net positive suction head and deep-well pumps and pumping station head analysis. 

In the initial development of LC-MS, the gas load to the vacuum system was a serious concern. A mobile-phase flow of 1 ml/min corresponds to a gas flow between 0.3 and 2.1 Pa mVs, depending primarily on the molecular mass of the solvent used. The effective pumping speed at the El ion-source housing of a differentially pumped MS system is between 0.3 and 0.7 mVs, which allows the introduction of ca. 2 pl/min of water, which is oidy ca. 0.2% of the typical flow-rate of a conventional 4.6-mm-ID LC column. In order to introduce the complete effluent of a 4.6-mm-ID LC column into the ion-source housing, a substantial increase of the effective pumping efficiency at the ion-source housing is required. This can be done in various ways ... 

The flow rate, head, and impeller speed at the best efficiency point (BEP) of the pump characteristic are used to dehne the pump specific speed ... 

The pump efficiency function, fpj(U), is frequently available as a low-order polynomial in U, in which case the differentiation d fpj/dU is a simple matter. Alternatively, the differentiation may be carried out graphically by finding the tangent to the fpjfU) vs. U curve. However, before we can solve equation (23.35), we still need to find the total derivative of pump speed to pump volume flow, dN/dQ, when the power supplied is kept constant. To do this we proceed as follows. 

The efficiency is set by the pump manufacturer when the final pump selection is made. It is usually based on their shop tests for the same model and size pumps. The pump efficiency can vary between 10% and 80%. Pump electric motor specifications require mechanical and electrical requirements. Motors can vary in size depending upon power, speed (RPM), frame size, area classification, orientation, service factor and type of enclosure (e.g. totally enclosed fan closure). 

In most pumps, the speed is generally not varied. Characteristic curves for a typical single-stage centrifugal pump operating at a constant speed are given in Fig. 3.3-2. Most pumps are usually rated on the basis of head and capacity at the point of peak efficiency. The efficiency reaches a peak at about 50 gal/min flow rate. As the discharge rate in gal/min increases, the developed head drops. The brake hp increases, as expected, with flow rate. 

Figure 18.11 shows the performance curve for a centrifugal conpressor. It is immediately observed that the y-axis is the ratio of the outlet pressure to inlet pressure. This is in contrast to punp curves, which have the difference between these two values. Curves for two different rotation speeds are shown. As with punp curves, curves for power and efficiency are often included but are not shown here. Unlike most pumps, the speed is often varied continuously to control the flowrate. This is because the higher power required in a conpressor makes it economical to avoid throttling the outlet as in a centrifugal punp. 

Figure 11 Centrifugal pump efficiency as a function of pump specific speed and pumping rate. [15J liU.7 Pump speed...

There is one pump modeled per loop. The pump component is modeled after a generic compact single stage centrifugal pump, prototypic of what would be used in this water system. The pump head is 300 m /s with a torque of 0.3 Pa m and speed of 356 rad/s (3400 RPM). At steady state conditions, the resulting pressure drop for the loop is 293 kPa with a flow rate of 0.52 kg/s. The electric power needed to run the pump is 0.530 kWe assuming the pump efficiency is 30%. 

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