Power requirement, pumping liquids

This investigation is limited to an estimation of the differences in power requirements between liquid pumping and gas compression systems. An evaluation of capital and maintenance costs is beyond the scope of this paper. 

It should be noted that the difference in power requirements of liquid pumping and gas compression is smaller at high heat leak (small plants). This fact is not obvious until the calculation has been made. Heat leak may be looked upon... 

Figure 3.10 Reduction of the maximum power requirement for liquid ring vacuum pumps with variable outlet slots in open systems depending on the altitude.

In the case of a liquid recycle, the cost of this pressure increase is usually small. Pumps usually have low capital and operating costs relative to other plant items. On the other hand, to increase the pressure of material in the vapor phase for recycle requires a compressor. Compressors tend to have a high capital cost and large power requirements giving higher operating costs. 

Viscosity (See Sec. 5 for further information.) In flowing liquids the existence of internal friction or the internal resistance to relative motion of the fluid particles must be considered. This resistance is caUed viscosity. The viscosity of liquids usuaUv decreases with rising temperature. Viscous liquids tend to increase tlie power required by a pump, to reduce pump efficiency, head, and capacity, and to increase Friction in pipe lines. 

This is provided to prevent reverse rotation of the pump in the event of a power failure or a deliberate shutdown due to backflow of liquid from the rising mains (pipelines). This is located immediately after the last pump stage casing/discharge outlet to prevent the shaft from rotating in the reverse direction. The provision of a non-return valve also ensures that the pump always starts in a shut-off condition, when the power requirement is at a minimum. 

For proper selection and corresponding operation, a pump capacity must be identified with the actual pumping temperature of the liquid in order to determine the proper power requirements as well as the effects of viscosity. 

The difference between the brake horsepower and the water or liquid horsepower is the pump efficiency. The requirement in either case is the horsepower input to the shaft of the pump. For that reason, the brake horsepower represents the power required by the pump, which must be transmitted from the driver through the drive shaft through any coupling, gear-box, and/or belt drive mechanism to ultimately reach the driven shaft of the pump. Therefore, the losses in transmission from the driver to the pump itself must be added to the input requirement of the driven pump and are not included in the pump s brake horsepower requirement. 

The horsepower is established by the manufacturer by testing the various types and models. In general, the horsepower requirements will be a combination of the power to pump the liquid inside the compressor casing plus the power to compress the gas or vapor. If a recirculating seal liquid system is used, the recirculating pump horsepower is not reported as a part of the compressor requirements. 

The nature of the liquid to be pumped. For a given throughput, the viscosity largely determines the friction losses and hence the power required. The corrosive nature will determine the material of construction both for the pump and the packing. With suspensions, the clearances in the pump must be large compared with the size of the particles. 

You must install a centrifugal pump to transfer a volatile liquid from a remote tank to a point in the plant 500 ft from the tank. To minimize the distance that the power line to the pump must be strung, it is desirable to locate the pump as close to the plant as possible. If the liquid has a vapor pressure of 20 psia, the pressure in the tank is 30 psia, the level in the tank is 30 ft above the pump inlet, and the required pump NPSH is 15 ft, what is the closest that the pump can be located to the plant without the possibility of cavitation The line is 2 in. sch 40, the flow rate is 100 gpm and the fluid properties are p = 45 lbm/ft3 and (j, = 5 cP. 

Along with electronic transport improvements must come attention to substrate transport in such porous structures. As discussed above, introduction of gas-phase diffusion or liquid-phase convection of reactants is a feasible approach to enabling high-current-density operation in electrodes of thicknesses exceeding 100 jxm. Such a solution is application specific, in the sense that neither gas-phase reactants nor convection can be introduced in a subclass of applications, such as devices implanted in human, animal, or plant tissue. In the context of physiologically implanted devices, the choice becomes either milliwatt to watt scale devices implanted in a blood vessel, where velocities of up to 10 cm/s can be present, or microwatt-scale devices implanted in tissue. Ex vivo applications are more flexible, partially because gas-phase oxygen from ambient air will almost always be utilized on the cathode side, but also because pumps can be used to provide convective flow of any substrate. However, power requirements for pump operation must be minimized to prevent substantial lowering of net power output. 

COMMENTS The Carnot vapor cycle as illustrated by Example 2.1 is not practical. Difficulties arise in the isentropic processes of the cycle. One difficulty is that the isentropic turbine will have to handle steam of low quality. The impingement of liquid droplets on the turbine blade causes erosion and wear. Another difficulty is the isentropic compression of a liquid-vapor mixture. The two-phase mixture of the steam causes serious cavitation problems during the compression process. Also, since the specific volume of the saturated mixture is high, the pump power required is also very high. Thus, the Carnot vapor cycle is not a realistic model for vapor power cycles. 

A Carnot engine with a steady flow rate of 1 kg/sec uses water as the working fluid. Water changes phase from saturated liquid to saturated vapor as heat is added from a heat source at 300° C. Heat rejection takes place at a pressure of lOkPa. Determine (1) the quality at the exit of the turbine, (2) the quality at the inlet of the pump, (3) the heat transfer added in the boiler, (4) the power required for the pump, (5) the power produced by the turbine, (6) the heat transfer rejected in the condenser, and (7) the cycle efficiency. 

Water circulates at a rate of 80kg/sec in an ideal Rankine power plant. The boiler pressure is 6 MPa and the condenser pressure is lOkPa. The steam enters the turbine at 600°C and water leaves the condenser as a saturated liquid. Find (1) the power required to operate the pump, (2) the heat transfer added to the boiler, (3) the power developed by the turbine, (4) the thermal efficiency of the cycle. 

Consider a steam power plant operating on the ideal regenerating Rankine cycle 1 kg/sec of steam flow enters the turbine at 15 MPa and 600°C and is condensed in the condenser at lOkPa. Some steam leaves the high-pressure turbine at 1.2 MPa and enters the open feed-water heater. If the steam at the exit of the open feed-water heater is saturated liquid, determine (1) the fraction of steam not extracted from the high-pressure turbine, (2) the rate of heat added to the boiler, (3) the rate of heat removed from the condenser, (4) the turbine power produced by the high-pressure turbine, (5) the turbine power produced by the low-pressure turbine, (6) the power required by the low-pressure pump, (7) the power required by the high-pressure pump, and (8) the thermal cycle efficiency. 

The power-generating potential of a water-dominated resource depends on the geothermal fluid temperature and production flow rate (Fig. 2). The figure gives the net power output, which accounts for parasitic loads caused by the condenser and feed pump power requirements. The output power from two-phase water-steam or steam alone is much greater than the curves shown for liquid in Fig. 2. 

Future developments that may facilitate ocean measurements from vessels or buoys include miniaturization of chromatographic equipment (so less solvent is needed per analysis), new solvent transport systems, such as electrokinetic transport, to reduce power requirements on the pumps, and more sensitive detectors for liquid chromatography. Certain combinations of very short columns and flow injection analysis are also promising for real-time studies. 

Refrigeration cycles "absorb" heat leaked in at a temperature level below that of the environment and "pump" it back to that environment. The minimum amount of work per Joule of heat absorbed, W, is given by the equation in the footnote of this chapter. Calculate W for the following temperatures 6°C, -18°C (freezer), -111°C (liquefied natural gas), and -253°C (liquid hydrogen). Assume that the temperature of the environment, To, is 20°C. What are the qualitative implications for the flow rate of heat leaked in and the power required to pump it back to the environment ... 

A pump operates adiabatically with liquid water entering at T, and P] with a mass flow ra rh. The discharge pressure is P2, and the pump efficiency is 17. For one of the following sets operating conditions, determine the power requirement of the pump and the temperature of the wa stream discharged from the pump. 

The liquid is put into the absorption tower by means of a nozzle at the top of the tower. The pressure just before the nozzle is 35 psig. Assume the pump for the liquid must supply power to lift the liquid to the top of the tower and compress the liquid to 35 psig. Use a 10 percent safety factor on the above pumping-power requirements to take care of the friction in the lines and other minor losses. 

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