Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

Assuming that the hydraulic efficiency is 70% and the mechanical efficiency is 90%,
determine
(i) the diameter of the inlet;
(ii) the net positive suction head;
(iii) the impeller slip factor using Wiesner’s formula;
(iv) the head developed by the pump;
(v) the power input.
Also calculate values for slip factor using the equations of Stodola and Busemann, comparing
the answers obtained with the result found from Wiesner’s equation.
9. (a) Write down the advantages and disadvantages of using free-vortex guide vanes upstream
of the impeller of a high pressure ratio centrifugal compressor. What other sorts of guide vanes
can be used and how do they compare with free-vortex vanes?
(b) The inlet of a centrifugal air compressor has a shroud diameter of 0.2m and a hub diameter
of 0.105m. Free-vortex guide vanes are fitted in the duct upstream of the impeller so that
the flow on the shroud at the impeller inlet has a relative Mach number, M r1 = 1.0, an absolute
flow angle of a 1 = 20° and a relative flow angle b1 = 55°. At inlet the stagnation conditions are
288 K and 10 5 Pa.
Assuming frictionless flow into the inlet, determine
(i) the rotational speed of the impeller;
(ii) the air mass flow.
(c) At exit from the radially-vaned impeller, the vanes have a radius of 0.16m and a design
point slip factor of 0.9. Assuming an impeller efficiency of 0.9, determine
(i) the shaft power input;
(ii) the impeller pressure ratio.
Centrifugal Pumps, Fans and Compressors 245