Using the expression of e from Eq. (29.3), we have

	(29.4)

The inlet blade angle of a Francis runner varies and the guide vane angle angle from . The ratio of blade width to the diameter of runner B/D, at blade inlet, depends upon the required specific speed and varies from 1/20 to 2/3.

Expression for specific speed. The dimensional specific speed of a turbine, can be written as

Power generated P for a turbine can be expressed in terms of available head H and hydraulic efficiency as

Hence, it becomes

	(29.5)

Again, ,

Substituting from Eq. (29.2b)

	(29.6)

Available head H equals the head delivered by the turbine plus the head lost at the exit. Thus,

since

with the help of Eq. (29.3), it becomes

or,		(29.7)

Substituting the values of H and N from Eqs (29.7) and (29.6) respectively into the expression given by Eq. (29.5), we get,

Flow velocity at inlet can be substituted from the equation of continuity as

where B is the width of the runner at its inlet

Finally, the expression for becomes,

	(29.8)

For a Francis turbine, the variations of geometrical parameters like have been described earlier. These variations cover a range of specific speed between 50 and 400. Figure 29.2 shows an overview of a Francis Turbine. The figure is specifically shown in order to convey the size and relative dimensions of a typical Francis Turbine to the readers.