The Fan: Including the Theory and Practice of Centrifugal and Axial Fans (Classic Reprint)

Excerpt from The Fan: Including the Theory and Practice of Centrifugal and Axial Fans

In the following pages I give a theory of the fan which differs considerably from anything that I have seen in print, and which may therefore meet with some criticism.

That this equation cannot be that of all fans is obvious when we remember that in many fans the manometric efficiency increases at first as the orifice increases from zero, while this equation states that it decreases; nor can it be maintained that the equation applies to fans whose manometric efficiency is greatest at zero orifice, for if the curve of manometric efficiency be drawn with this as ordinate and orifices as abscissic, it will be found that the tangent at the point where the curve cuts the vertical axis is horizontal; and that this is not the case may be seen from fig. 44, which gives curves for eleven fans differing widely in construction. Having already studied the centrifugal pump, it occurred to me about ten years ago that its theory might be applied to that of the fan; and except that the fan does not actually lift air, as the pump lifts water, but acts like a centrifugal pump that pumps against the resistance of horizontal piping only, I consider that the same theory may be applied to both.

In Chapter XII. I have endeavoured to show that my theory agrees with the results of experiment, as far as these may be trusted. The following pages commence with the theory of the centrifugal fan following which are experiments with and descriptions of this type; and in Chapter XIV. is given a description of Prof. Rateau's high-pressure fans, in whose design it may be mentioned the variation of the density of the air must be taken into account.

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