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The Affinity Laws – Pump Laws

The centrifugal pump is a very capable and flexible machine. It is not necessary to design a specific pump for each specific system. The performance of the centrifugal pump can be changed by the change in impeller diameter or its rotational speed. The affinity laws, or the pump laws, state how such changes influence the pump’s performance. These laws are summarized in the following points.

• The flow rate or capacity is directly proportional to the pump speed: double the speed / double the flow.

Q ∝ n

• The pump head is directly proportional to the square of the pump speed: double the speed/multiply the pressure by four.

Hp ∝ n2

• The power required by the pump motor is directly proportional to the cube of the pump speed: double the speed/multiply the power by eight.

P ∝ n3

These principles apply regardless of the direction of the change in speed or impeller diameter. It must be noted the Affinity laws give approximate results. There is a discrepancy between the real hydraulic values and the calculated. This discrepancy is due to hydraulic efficiency changes.

 
References:
Reactor Physics and Thermal Hydraulics:
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  3. W. M. Stacey, Nuclear Reactor Physics, John Wiley & Sons, 2001, ISBN: 0- 471-39127-1.
  4. Glasstone, Sesonske. Nuclear Reactor Engineering: Reactor Systems Engineering, Springer; 4th edition, 1994, ISBN: 978-0412985317
  5. Todreas Neil E., Kazimi Mujid S. Nuclear Systems Volume I: Thermal Hydraulic Fundamentals, Second Edition. CRC Press; 2 edition, 2012, ISBN: 978-0415802871
  6. Zohuri B., McDaniel P. Thermodynamics in Nuclear Power Plant Systems. Springer; 2015, ISBN: 978-3-319-13419-2
  7. Moran Michal J., Shapiro Howard N. Fundamentals of Engineering Thermodynamics, Fifth Edition, John Wiley & Sons, 2006, ISBN: 978-0-470-03037-0
  8. Kleinstreuer C. Modern Fluid Dynamics. Springer, 2010, ISBN 978-1-4020-8670-0.
  9. U.S. Department of Energy, THERMODYNAMICS, HEAT TRANSFER, AND FLUID FLOW. DOE Fundamentals Handbook, Volume 1, 2 and 3. June 1992.
  10. White Frank M., Fluid Mechanics, McGraw-Hill Education, 7th edition, February, 2010, ISBN: 978-0077422417

See above:

Centrifugal Pumps