TMC Fluid Systems Products

Fan Affinity Laws

Affinity laws can be used to calculate volume capacity, head or power consumption - when speed or rpm, and wheel diameters are changed.

Volume Capacity

The volume capacity of a centrifugal fan can be expressed as:

q1/q2 = (n1/n2)x(d1/d2)3

where,

q = volume flow capacity (m3/s, gpm, cfm, etc.)

n = wheel velocity - revolution per minute - (rpm)

d = wheel diameter

Head or Pressure

The head or pressure of a centrifugal fan can be expressed like

dp1/dp2 = (n1/n2)2x(d1/d2)2 

where,

dp = head or pressure (m, ft, Pa, psi, etc.)

n = wheel velocity - revolution per minute - (rpm)

d = wheel diameter

Power

The power consumption of a centrifugal fan can be expressed as

P1/P2 = (n1/n2)3x(d1/d2)5

where,

P = power (W, bhp, etc.)

n = wheel velocity - revolution per minute - (rpm)

d = wheel diameter