The main parameters, characteristic to a fan, are four in number:

Capacity (V) Pressure (p) Efficiency (n) Speed of rotation (n min.^{-1})

The main parameters, characteristic to a fan, are four in number:

Capacity (V) Pressure (p) Efficiency (n) Speed of rotation (n min.^{-1})

The capacity is the quantity of fluid moved by the fan, in volume, within a unit of time, and it is usually expressed in m^{3}/h, m^{3}/min., m^{3}/sec.

The total pressure (pt) is the sum of the static pressure (pst), i.e. the energy required to withstand opposite frictions from the system, and the dynamic pressure (pd) or kinetic energy imparted to the moving fluid (pt = pst + pd). The dynamic pressure depends on both fluid speed (v) and specific gravity (y).

Where:

pd= dynamic pressure (Pa)

y=specific gravity of the fluid(Kg/m3)

v= fluid speed at the fan opening worked by the system (m/sec)

Where:

V= capacity(m3/sec)

A= gauge of the opening worked by the system (m2)

v= fluid speed at the fan opening worked by the system(m/sec)

The efficiency is the ratio between the energy yielded by the fan and the energy input to the fan driving motor

Where:

n= efficiency (%)

V= capacity (m3/sec)

pt= absorbed power (KW)

P= total pressure (daPa)

The speed of rotation is the number of revolutions the fan impeller has to run in order to meet the performance requirements.

As the number of revolutions varies (n), while the fluid specific gravity keeps steady (?), the following variations take place:

The capacity (V) is directly proportional to the speed of rotation, therefore :

Where:

n= speed of rotation

V= capacity

V1= new capacity obtained upon varying of the speed of rotation

n1= new speed of rotation

Where:

n= speed of rotation

pt= total pressure

pt1= new total pressure obtained upon varying of the speed of rotation

n1= new speed of rotation

The absorbed power (P) varies with cube of rotation ratio, therefore:

Where:

n= speed of rotation

P= abs. power

P1= new electrical input obtained upon varying of the speed of rotation

n1= new speed of rotation

The specific gravity (y) may be calculated with the following formula

Where:

273= absolute zero(°C)

t= fluid temp(°C)

y= air specific gravity at t C(Kg/m3)

Pb= barometric pressure(mm Hg)

13.59= mercury specific gravity at 0 C(kg/dm3)

For ease of calculation, the air weight at various temperatures and heights a.s.l. have been included in the table below:

Temperature | ||||||||||||

-40°C | -20°C | 0°C | 10°C | 15°C | 20°C | 30°C | 40°C | 50°C | 60°C | 70°C | ||

Height above sea level in meters | 0 | 1,514 | 1,395 | 1,293 | 1,247 | 1,226 | 1,204 | 1,165 | 1,127 | 1,092 | 1,060 | 1,029 |

500 | 1,435 | 1,321 | 1,225 | 1,181 | 1,161 | 1,141 | 1,103 | 1,068 | 1,035 | 1,004 | 0,975 | |

1000 | 1,355 | 1,248 | 1,156 | 1,116 | 1,096 | 1,078 | 1,042 | 1,009 | 0,977 | 0,948 | 0,920 | |

1500 | 1,275 | 1,175 | 1,088 | 1,050 | 1,032 | 1,014 | 0,981 | 0,949 | 0,920 | 0,892 | 0,866 | |

2000 | 1,196 | 1,101 | 1,020 | 0,984 | 0,967 | 0,951 | 0,919 | 0,890 | 0,862 | 0,837 | 0,812 | |

2500 | 1,116 | 1,028 | 0,952 | 0,919 | 0,903 | 0,887 | 0,858 | 0,831 | 0,805 | 0,781 | 0,758 |

Temperature | ||||||||||||

80°C | 90°C | 100°C | 120°C | 150°C | 200°C | 250°C | 300°C | 350°C | 400°C | 70C | ||

Height above sea level in meters | 0 | 1,000 | 0,972 | 0,946 | 0,898 | 0,834 | 0,746 | 0,675 | 0,616 | 0,566 | 0,524 | 1,029 |

500 | 0,947 | 0,921 | 0,896 | 0,851 | 0,790 | 0,707 | 0,639 | 0,583 | 0,537 | 0,497 | 0,975 | |

1000 | 0,894 | 0,870 | 0,846 | 0,803 | 0,746 | 0,667 | 0,604 | 0,551 | 0,507 | 0,469 | 0,920 | |

1500 | 0,842 | 0,819 | 0,797 | 0,756 | 0,702 | 0,628 | 0,568 | 0,519 | 0,477 | 0,442 | 0,866 | |

2000 | 0,789 | 0,767 | 0,747 | 0,709 | 0,659 | 0,589 | 0,533 | 0,486 | 0,447 | 0,414 | 0,812 | |

2500 | 0,737 | 0,716 | 0,697 | 0,662 | 0,615 | 0,550 | 0,497 | 0,454 | 0,417 | 0,386 | 0,758 |