Page 11 - FANS. Aerodynamic _Selection Meethod__Combine_part2

The point “в” gives a solution to the whole problem of selecting a c / b fan -
“according to full” and not “according to static” pressure, and
fundamentally and significantly improves the accuracy of selection.

The point “b” is the first reference point for building a curve of the

characteristics of the “first ventilation network” - the atmospheric
resistance network, which we assign for the first time (!) Designation
(by ventilation) - Рatv, where at - atmosphere (English), v – ventilation (
English)

The curve of the characteristics of the 'first ventilation network' can be
built:

1. according to the formula Рatv = K × L²
2. or, more precisely, according to actual measurements, with a stepped
decrease in engine speed.

Note 2: Dynamic pressure curve (Fig. 1) for aerodynamic the
characteristic is generally not required to be applied, as carrying no
meaning

For the “operating point” “e”, having the total pressure “g-e”, the value of
“g-f” will show a part of the total pressure value, which is spent on
overcoming the resistance of the static atmosphere and it is designated as
Рatv. The remaining part of the total pressure “f-e” is denoted by Рnw (nw -
network (eng.) - network). And this part is spent on overcoming the
resistances of the ventilation network (metal, stone), where the pressure
drop occurs due to friction and local resistances, resistance of the built-in

equipment, but without taking into account the dynamic pressure at the
outlet of the ventilation network.

And this will objectively reflect the distribution of parts of the full pressure
of the fan and not depend on the configuration of the discharge duct, when
a negative relative static pressure can occur at the blower nozzle and,
therefore, high dynamic pressure,

which can pass from the full pressure “g-e” from “h” to “i”, and for real
measurements of network resistance, the value of Psi = “i-e” (according to
the existing terminology) is not confirmed.

When applying the atmospheric resistance curve Рatv, the confusion with
the redistribution (distribution) of Ps and Pv (according to the old
terminology) will not need to be assessed at all (see also Note 2).