140

Eq. 44 is a combination of separate relationships described by Anderson for efficiency and speed as functions of flow rate6. Included is a correction for specific speed that is too conservative for N,. (us) > 2286 or Hs greater than about unity. With this qualification, Figure 10 is a useful representation for centrifugal pumps and is often as far as many users go in determining the performance of these machines.

Viscosity Effects Centrifugal pump geometries have not generally been optimized versus Reynolds number—often because the effect on hydraulic shape is not very great except for the highest viscosities of the pumpage, and a given application can sometimes experience a substantial range of viscosity. Studies of conventional centrifugal pumps over a range of Reynolds number have been combined in nomographic charts in the Hydraulic Institute Standards, which yield correction factors to the head, efficiency, and flow rate of the BEP of a low-viscosity pump in order to obtain the BEP of that pump when operating at higher viscosity7. Figure 11 is a presentation of these correction factors in terms of the head-flow Reynolds number. Strictly speaking, in view of Eq. 43, each pump geometry has a unique set of such correction factors, yet the data presented in Figure 11 have been widely utilized as reasonably representative of conventional centrifugal pumps.

NPSH Effects In many cases, the available NPSH is low enough, or the suction-specific speed ass at which the pump stage must operate is high enough for significant two-phase activity to exist within the impeller. This is to be expected in centrifugal impellers of water pumps if the available Hss is greater than about 3 to 4 (or Nss,(US) = 8,000 to 11,000). In such a case, Hss and the vaporization quantities |2-$) in Eq. 35 dictate a profound change in the impeller geometry into that of an inducer. The inducer has an entering or "eye" diameter that is significantly enlarged—together with tightly wrapped helical blading. Often the inducer is a separate stage that pressurizes the two-phase fluid as needed to provide a sufficiently low value of Hss at the entrance of the more typical impeller blading that is immediately downstream of the inducer. If the two-phase fluid is near its thermodynamic critical point, the |2-$) operate to greatly reduce the amount of two-phase

End of Days Apocalypse

End of Days Apocalypse

This work on 2012 will attempt to note them allfrom the concepts andinvolvement by the authors of the Bible and its interpreters and theprophecies depicted in both the Hopi petroglyphs and the Mayan calendarto the prophetic uttering of such psychics, mediums, and prophets asNostradamus, Madame Blavatsky, Edgar Cayce, and Jean Dixon.

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