The specific speed Ns, as defined by Eq. (11.30), does not contain the impeller diameter. How then should we size the pump for a given Ns? Logan [7] suggests a parameter called the specific diameter DS, which is a dimensionless combination of Q, (gH), and D.
(a) If DS is proportional to D, determine its form.
(b) What is the relationship, if any, of DS to CQ*, CH*, and CP*?
(c) Estimate DS for the two pumps of Figs. 11.8 and 11.13.