The answer to Prob. 11.40 is that the dimensionless specific diameter takes the form Ds = D

The answer to Prob. 11.40 is that the dimensionless €œspecific diameter€ takes the form Ds = D (gH*)1/4/Q*1/2, evaluated at the BEP. Data collected by the writer for 30 different pumps indicates, in Fig. P11.46, that Ds correlates well with specific speed Ns. Use this figure to estimate the appropriate impeller diameter for a pump which delivers 20,000 gal/min of water and a head of 400 ft running at 1200 rev/min. Suggest a curve-fit formula to the data (Hint: a hyperbola).

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20 18 16 14 12 s 10 Data from 30 different pump designs 6 4 2 500 1000 1500 2000 2500 3000 3500