Theoretical and real slip factor in centrifugal pumps

The slip factor is connected to the flow behaviour in the blade passages. Considering such a flow, we have defined two slip factors - the theoretical slip factor uTh (FGT) - the real slip factor uX (FGR) The theoretical slip factor will depend of the unavoidable slip of the non viscous flow in the impeller channels~ We will make the distinction between two theoretical slip factors FGT : the two dimensional one (FGT2) and the three dimensional one (FGT3) following the type of calculation process used to determine the factor. Varying systematically the main geometrical parameters of the impeller, we have established a general table for FGT2 which can be very useful for the pumps designer. A detailed experiment al study, covering five different impellers and having involved the development of special instrumentation, has provided the local and global values of FGR; this latter is strongly influenced by the working conditions. A correlation between the real and theoretical slip factors has been derived for any working conditions; this allows a more accurate prediction of performance at off-design conditions.