Pump Design Basics-Affinity Law in Fluid Mechanics and Hydrodynamics-Mechwix Technology.

What is the affinity law? Basics characteristics of hydro dynamics for design of pumps and allied machineries.

AFFINITY LAWS-Characteristics Curve as follows:

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The performance of the pump at different diameters for the same speed or different speed for the same diameter. Since in practice impellers of different diameters are not geometrically identical, the author's of the section called Performance Parameters in the Pump Handbook recommend limiting the use of this technique to a change of impeller diameter no greater than 10 to 20%. In order to avoid over cutting the impeller, it is recommended that the trimming be done in steps with careful measurement of the results. At each step compare your predicted performance with the measured one and adjust as necessary. The affinity laws were developed using the law of similitude which provide three basic relationships.

 Relation Between Flow vs diameter & Speed as follows:

Figure-1

Relation Between Head vs diameter & Speed as follows:

Figure-2

Relation Between Power vs diameter & Speed as follows:

Figure-3

        The process of arriving at the affinity laws assumes that the two operating points that are being compared are at the same efficiency. The relationship between two operating points, say 1 and 2, depends on the shape of the system curve. The points that lie on system curve A will all be approximately at the same efficiency whereas the points that lie on system curve B are not. The affinity laws do not apply to points that belong to system curve B. System curve B describes a system with a relatively high static head vs. system curve A which has a low static head.

Author & Engineer: Md Kamaluddin

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