The flow rate through a cross-section, A, of the circumferential angle, φ, is generally calculated as:

 

Using results in an equation to calculate the circumferential angle, φ, dependent on the outer radius ra:

 

 

b(r) is a geometrical function which is defined according to the shape of the cross-section. The velocity cu is chosen in accordance with the design instructions. Under Design rule, two alternatives can be selected.

 

ΠPfleiderer

Experience has shown that the losses can be greatly minimised if the volute housing is dimensioned such that the fluid flows in accordance with the principal of conservation of angular momentum. The cross-section areas are therefore designed in accordance with the principal of conservation of angular momentum, i.e. angular momentum exiting the impeller is constant. In addition, an exponent of angular momentum, x, can be chosen so that the principle curx = const. is obeyed. When x=1, the angular momentum is constant. For the extreme of x=0, the circular component of the absolute velocity cu remains constant at the impeller outlet.

 

The integral can be explicitly solved for simple cross-section shapes (rectangles, trapezoids, circles). For other, arbitrary, shapes, it can be solved numerically.

 

 Stepanoff

Alternatively, it can be beneficial to design the volute with a constant velocity in all cross-sections of the circumference. According to Stepanoff, this constant velocity can be determined empirically: . The constant ks can be determined dependent on the specific speed nq (see Approximation function).

Ž Self

Contrary to Œ and  the geometry progression is defined directly. The end cross section is defined by radius or cross section area, the distribution by Radius- or Area progression.

 

 

By clicking on Default, you can return to the standard values for each design instruction.

 

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