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 0.2 m and a hub diameter of 0.105 m. 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, M1,rel = 1.0, an absolute flow angle of α1 = 20°, and a relative flow angle β1= 55°. At inlet the stagnation conditions are 288 K and 105 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 0.16 m 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