Pumps flow characteristics

The melting pot is heated either electrically or by gas to 427—524°C. The pot capacity is typically over 100 kg of lead alloy, and periodically the top of the molten metal must be skimmed to remove the dross. The pot fumes must be removed by adequate ventilation (forced suction). When the molten metal has reached the proper temperature and flow characteristics, it is transported by pump to the grid mold. 

FIG. 8-82 Installed flow characteristic as a function of percent of total system head allocated to the control valve (assuming constant head pump, no elevation head loss, and an R equal 30 equal-percentage inherent characteristic). 

To use Eq. (18--50) one must know the pattern of the filtration process, i.e., the variation of the flow rate and pressure with time. Generally the pumping mechanism determines the filtration flow characteristics and serves as a basis for the following three categories [Tiller and Crump, Chem. Eng. Prog., 73(10), 65 (1977)] ... 

The viscosity of a cement affects the pumping properties. The viscosity must be kept low enough to ensure pumpability of the slurry during the entire operation period. In deep wells, because of the increased temperature, the viscosity becomes increasingly lower, which leads to undesirable flow characteristics of the slurry. This effect can be serious, because the viscosity follows the Arrhenius law. Some of the additives used for viscosity control also... 

The static pressure difference will be independent of the fluid flow-rate. The dynamic loss will increase as the flow-rate is increased. It will be roughly proportional to the flow-rate squared, see equation 5.3. The system curve, or operating line, is a plot of the total pressure head versus the liquid flow-rate. The operating point of a centrifugal pump can be found by plotting the system curve on the pump s characteristic curve, see Example 5.3. 

Syringe pumps driven by screw mechanisms were popular in the 1960s because of their inherent precision and pulseless flow characteristics. Their disadvantages are higher manufacturing costs and the problems associated with syringe refill cycles. Syringe pumps are currently used in specialized systems for microbore and capillary HPLC. 

Batch operation in a larger scale - in laboratory or even industrial applications - frequently is reahzed using a flowthrough cell with optimized flow characteristics, which is coupled by circulating pumps with reservoirs that contain the reaction solutions. 

The pumping speed characteristic of a pump is easily derived from the measured pumping speed (volume flow rate) characteristic of the pump as shown for a 6000 l/s diffusion pump (see curve S in Fig. 2.76). To arrive at the throughput characteristic (curve Q in Fig. 2.76), one must multiply each ordinate value of S by its corresponding pA value and plotted against this value. If it is assumed that the inlet pressure of the diffusion pump does not exceed 10 mbar, the maximum throughput is 9.5 mbar l/s... 

Mixes in both low- and high-cement-content classes are more prone to problems than the medium range. In low-cement-content mixes, poor cohesion results in segregation and in high-cement-content mixes thixotropy causes pipeline friction. Admixtures will modify the flow characteristics of the paste, helping to achieve and maintain optimum flow characteristics. Because pumped concrete must not only meet specified job performance criteria (e. g. strength, freeze-thaw resistance) but should also remain stable under a variety of job conditions, particularly in hot and cold weather, it is common to find that concrete to be pumped often contains two or more types of admixtures. 

Binder, R. C., and Knapp, R. T., Experimental Determinations of the Flow Characteristics in the Volutes of Centrifugal Pumps, Trans. ASME 58, 1936. 

In this process, water crosses the outer semi-permeable membrane of the pump. The characteristics of the semipermeable membrane including permeability, pore size, and thickness are key factors determining the rate at which water molecules enter the osmotic sleeve. The water that is drawn across the semipermeable membrane causes the osmotic chamber to expand. This force compresses the flexible drug reservoir, discharging the drag solution through the flow moderator. 

Most hazardous waste streams contain contaminants (Pb, Cd, Ni, and Zn) that can be treated by contacting with a phosphate solution. This treatment entails simply washing the waste stream with a phosphate solution. The amount of phosphate stabilizer is small (5 wt%). At the end of the treatment, the waste stream retains its free-flowing characteristics and hence is easy to load on a truck, or to pump at a disposal site. Because the waste volume does not increase due to this treatment, disposal cost is low. Furthermore, the binder cost is also kept to a minimum. 

In this situation, if the pressure filtration stays unchanged, the filtrate rate will decrease with time. When unacceptable values of the filtrate rate are reached, the process must be stopped and the membrane cleaned or replaced. This mode of operation is uneconomical. One solution to this problem is to increase the transmembrane pressure in order to maintain the flow rate but, in this case, the pumping flow rate has to be reduced because pumps generally present a pre-established and characteristic flow rate-pressure relation which is, a priori, unchangeable. Consequently, when the pressure is continuously increased, the clogging rate will increase faster than when a high tangential velocity is used in the unit. 

When a glow discharge is initiated with a steady-state flow of monomer (without system pressure control), the system pressure changes to a new steady-state value as a steady-state luminous gas flow is established. This change of the system pressure from that of a pure monomer flow to that of a flow under LCVD conditions is caused by the following two major factors (1) the gas phase changes because of the creation of the luminous gas phase, and (2) the pumping-out characteristics... 

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