Pumps theoretical capacity

A slurry of zinc powder in aqueous KOH was pumped through the cyclindrical cell whose outer surface comprised the air electrode and for which the negative current collector was an axial brass rod. The slurry was recirculated through the cell several times until an acceptable percentage of the theoretical capacity had been utilized (i.e. for zinc oxidation to soluble zincate). For recharge, the zincate ion was reduced to zinc powder either externally or in an electrolysis cell connected to the system. In this context... 

Figure 7 shows the rate of blow-by versus discharge pressure. As mentioned before, the curve is essentially constant for different pump speeds. At 10,000 psi and 225 rpm, blow-by amounts to 17 per cent of the theoretical capacity of the pump. 

Practically, the NPSH required for operation without cavitation and vibration in the pump is somewhat greater than the theoretical. The actual (NPSH)r depends on the characteristics of the liquid, the total head, the pump speed, the capacity, and impeller design. Any suction condition which reduces (NPSH ) below that required to prevent cavitation at the desired capacity will produce an unsatisfactoiy installation and can lead to mechanical dimculty. 

Tests conducted to operate centrifugal pumps as hydrauhc turbines throughout the head-capacity-speed range show that a good centrifugal pump generally makes an efficient hydraulic turbine. From theoretical considerations it is possible to state that at the same speed... 

The theoretical maximum suction lift at sea level for water (14.7 psi) (2.31 fi/psi) = 34 ft. However, due to flow resistance, this value is never attainable. For safety, 15 feet is considered the practical limit, although some pumps will lift somewhat higher columns of water. WTen sealing a vacuum condition above a pump, or the pump pumps from a vessel, a seal allowance to atmosphere is almost always taken as 34 feet of water. High suction lift causes a reduction in pump capacity, noisy operation due to release of air and vapor bubbles, vibration and erosion, or pitting (cavitation) of the impeller and some parts of the casing. (The extent of the damage depends on the materials of construction.)... 

The slip of a pump is fraction or percent loss of capacity relative to theoretical. Slip is (1 — Cvoi), w here e oi is the volumetric efficiency. Volumetric efficiency is the actual liquid pumped (usually considered water) relative to that which should theoretically be pumped based on piston displacement. 

Figure 32.29 (a) Effect of entrained gas on liquid displacement (b) solubility of air in oil. Example At 5 in Hg with 3% gas entrainment by volume, pump capacity is reduced to 84 per cent of theoretical displacement... 

Carefully apply the sample (see Notes 4 and 5) to the column. The sample may be applied using gravity flow or with a peristaltic pump, but use care not to disrupt the gel in the column. Theoretically, there is no limit to the volume of sample added, but the sample amount should not exceed the binding capacity of the column. 

Other physical characteristics of CNO (Table 6.10) such as viscosity, density, heat capacity (specific heat) and heat of fusion, are important, not only for theoretical considerations but also for plant design and engineering purposes in general. Viscosity is an important property, which determines, for example, the diameter of pipes and the power needed when oils are pumped or stirred. 

CHARACTERISTIC CURVES HEAD-CAPACITY RELATION. The plots of actual head, total power consumption, and efficiency vs. volumetric flow rate are called the characteristic curves of a pump. Such curves are illustrated schematically in Fig. 8.12. In Fig. 8,12a, the theoretical head-flow rate (often called head-capacity) relation is a straight line, in accordance with Eq. f8.21) the actual developed head is considerably less and drops precipitously to zero as the rate increases to a certain value in any given pump. This is known as the zero-head flow rate it is the maximum flow the pump can deliver under any conditions. The rated or optimum operating flow rate is, of course, less than this. 

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