Page 10 - FANS. Aerodynamic _Selection Meethod__Combine_part2

B. New theory

To apply the new theory for the selection of the c / b fan, you need to point
out a significant gap (or error, or inaccuracy of measurements) in previous
studies, most likely early studies, which have been transmitted for decades.

Namely: the lack of accurate testing (instrumental measurements) of the c /
b fan without a ventilation network (metal, stone), i.e. when it only works
with the atmosphere. The ambient atmosphere (static) when a stream of air
(i.e. air with kinetic energy) moves in it is a “duct” and also creates
resistance to moving air (deceleration and stop of flow occur in the
discharge direction) (see Fig.2a).

In the air velocity spectrum of the suction inlet of the fan, the surrounding

static atmosphere, as a “ventilation network,” also resists, since
atmosphere (air) - gaseous liquid, has a viscosity (viscous friction), inertia.
In the suction direction, the flow is accelerated, it is compressed with the
flow (term) into the suction inlet of the fan nozzle (the same happens for
the suction inlet of the duct) (see Fig.2в).

The noticeable (visible) boundary of the “ventilation network” of the
suction spectrum can be taken conventionally at a distance of about 1.5

dpatr [1.5 dсоn] from the suction nozzle of the fan with a diameter dpatr
[dcon (eng. - connection- short tube)], although theoretically in infinity.
Those. take the border where you can see the real movement of air. This
boundary of the 'ventilation network' can be represented as permeable
walls at the end of a muffled duct (or some volume).

Thus, a static atmosphere can be taken for the first ventilation

network.

The same pressures develop on the suction and discharge connections as in
the air duct: full, static and dynamic; and you can also calculate the total (∑)
total pressure of the fan, when it is working without a ventilation network.
At the suction side of the fan, all pressures will be “correct.” At the
discharge nozzle, the static pressure will be “negative” (below
atmospheric), and the dynamic pressure will be more than full. And the
total (∑) total pressure of the fan will be less than the dynamic pressure at
the discharge pipe (see Fig.3). And the static pressure of the fan (in the
existing terminology) will be “negative” (below atmospheric).

Fan performance will be maximum at a given speed of the impeller. And it
can be stated: at dynamic pressure (and corresponding to the exit rate -
very high) at the discharge pipe (value d-a, (see Fig.3)) - the total pressure
(i.e. resistance of the atmosphere) will have a smaller value (value d -в)

than the dynamic pressure itself.