Page 18 - FANS. Aerodynamic _Selection Meethod__Combine_part2

ventilation network (only the metal part!) Was obtained at air flow L
= 1800 m³ / h developed by the fan, the total pressure in the
ventilation system P = 600Pa (value 13-11).

6. Adjust the original design point (v. 9) - by reducing the resistance of
the projected ventilation network by 9 * –9 (for example, by 50Pa at
a flow L = 2000 m³ / h). Then the new calculated point will be v.9 *,
which will move to the curve of the aerodynamic characteristics of the
fan in t.10 *, and then in t.11 * - the real 'operating point of the fan',
i.e. the desired operating point of the ventilation system.
7. With the new calculated total pressure drop in the ventilation
network (value 14-9 *) and air consumption L = 2000 m³ / h, we get

the actual value of the total pressure drop in the ventilation network
(12 * -11 *), which are equal to each other. With the full pressure
developed by the fan, for example, Рt = 580 Pa and productivity L =
2000 m³ / h.

Results and conclusions

1. This method can be assigned the name: 'Two-grid method of selection
of a centrifugal fan.'
2. The method shows that the dynamic pressure Pv, reflected in the
aerodynamic characteristics of centrifugal fans, is absolutely
unnecessary, it has nowhere to apply.
3. Curve Patv is a constant for this type and fan number (the dynamic

pressure curve Pv is not constant), does not depend on the dynamic
pressure at the exhaust nozzle of the fan, does not depend on the
configuration of the discharge duct, and thus provides:
 accurate selection of a centrifugal fan (definition of the
'operating point of the fan')
 accurate adjustment of the designed (constructed) ventilation

network
 the possibility of accurate aerodynamic assessment of the
mounted ventilation unit; and comparison with the project
 possibility of exact replacement of the fan with another fan, on
the same ventilation network for obtaining other parameters of
the ventilation unit

4. The aerodynamic characteristics of the fan should show the

aerodynamic resistance curve of the atmosphere Patv for a given type
and fan number, and not the dynamic pressure curve of the fan Pv.