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SAVIO
S.r.l.
1) PARAMETERS
The main parameters, characteristic to a fan, are four in number:
Capacity (V)
1.1) Capacity:
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
3
m
/min., m
/sec.
1.2) Pressure:
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).
1
2
pd =
у
v
2
V
v =
A
1.3) Efficiency:
The efficiency is the ratio between the energy yielded by the fan and the energy input to the fan driving motor.
V
pt
=
6120 P
1.4) Speed of rotation:
The speed of rotation
requirements.
As the number of revolutions varies (n), while the fluid specific gravity keeps steady (у), the following variations take place:
The capacity (V) is directly proportional to the speed of rotation, therefore :
n
1
V
= V
1
n
The total pressure (pt) varies as a function of the squared ratio of the speeds of rotation; therefore:
n
2
1
pt
= pt
1
n
The absorbed power (P) varies as a function of the cubed ratio of the speeds of rotation therefore:
n
3
1
P
= P
1
n
2) SIZING
The characteristics expressed in the following tables are referred to operation with fluid (air) at +15°C temperature and 760
mm Hg barometric pressure (specific gravity = 1.226 kg/m
The noise data are referred to a measurement taken in free field, at 1.5 m distance, with fan running at the maximum rate of efficiency.
The above-mentioned values undertake the following tolerance: ± 5% capacity
When the conveyed fluid conditions differ from the above-mentioned ones, the following should be considered, that the
temperature and the barometric pressure are directly affecting the specific gravity of the fluid .
As the specific gravity varies, the volume flowrate (V) keeps on constant, and the pressure (pt) and power (P) vary directly as
a function of the ratio of the specific gravities.
y
1
pt
=
pt
P
=
1
1
у
The specific gravity (y) may be calculated with the following formula:
Pb
13,59
y =
29,27
(273+t)
For ease of calculation, the air weight at various temperatures and heights a.s.l. have been included in the table below:
-40°C -20°C 0°C
0
1,514 1,395 1,293 1,247 1,226 1,204 1,165 1,127 1,092 1,060 1,029 1,000 0,972 0,946 0,898 0,834 0,746 0,675 0,616 0,566 0,524
500 1,435 1,321 1,225 1,181 1,161 1,141 1,103 1,068 1,035 1,004 0,975 0,947 0,921 0,896 0,851 0,790 0,707 0,639 0,583 0,537 0,497
1000 1,355 1,248 1,156 1,116 1,096 1,078 1,042 1,009 0,977 0,948 0,920 0,894 0,870 0,846 0,803 0,746 0,667 0,604 0,551 0,507 0,469
1500 1,275 1,175 1,088 1,050 1,032 1,014 0,981 0,949 0,920 0,892 0,866 0,842 0,819 0,797 0,756 0,702 0,628 0,568 0,519 0,477 0,442
2000 1,196 1,101 1,020 0,984 0,967 0,951 0,919 0,890 0,862 0,837 0,812 0,789 0,767 0,747 0,709 0,659 0,589 0,533 0,486 0,447 0,414
2500 1,116 1,028 0,952 0,919 0,903 0,887 0,858 0,831 0,805 0,781 0,758 0,737 0,716 0,697 0,662 0,615 0,550 0,497 0,454 0,417 0,386
GENERAL PRINCIPLES OF THE FAN DESIGN
Pressure (p)
pd
= dynamic pressure
Where:
у
= specific gravity of the fluid
v
= fluid speed at the fan opening worked by the system
V
= capacity
Where:
A
= gauge of the opening worked by the system
v
= fluid speed at the fan opening worked by the system
Where:
= efficiency
capacity
V
is the number of revolutions
Where:
n
= speed of rotation
V
= capacity
Where:
n
= speed of rotation
pt
= total pressure
Where:
n
= speed of rotation
P
= abs. power
y
Where:
1
P
pt = total pressure
y
P = absorbed power
y = fluid spec. gravity
Where:
273= absolute zero
t= fluid temp. (°C)
10°C 15°C 20°C 30°C 40°C 50°C 60°C 70°C 80°C 90°C 100°C 120°C 150°C 200°C 250°C 300°C 350°C 400°C
Efficiency (η)
P
= absorbed power
3
(m
/min)
pt
= total pressure
the fan impeller has to run in order to meet the performance
V
= new capacity obtained upon varying of the speed of rot.
1
n
= new speed of rotation
1
pt
= new total pressure obtained upon varying of the speed of rot.
1
n
= new speed of rotation
1
P
= new electrical input obtained upon varying of the speed of rot.
1
n
= new speed of rotation
1
3
) .
pt
= new total pressure obtained upon varying the specific gravity
1
P
= new abs. power obtained upon varying the specific gravity
1
y
= new specific gravity of the fluid
1
y
= air specific gravity at t °C
Pb
= barometric pressure
13,59
= mercury specific gravity at 0° C
Temperature
5
Speed of rotation (n° min.
(kW)
(daPa)
- +3 dB(A) noise.
(Kg/m
(mm Hg)
(kg/dm
-1
)
3
/h,
(Pa)
3
(Kg/m
)
(m/sec)
3
(m
/sec)
2
(m
)
(m/sec)
3
)
3
)
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