resists the current. Unfortunately, scientific research in
the field of hydromechanics
has not found a practical solution. The theoretical results obtained differ from the
experimental conclusions by a small number of deviations, and the theory has not yet
been fully resolved.
The easiest option for research in this field is to find, model, and apply the x-
local resistance coefficient in the laboratory under high-precision to high efficiency in
manufacturing and industrial plants. Under laboratory conditions, the high x-local
resistance coefficient is determined as follows.
The manifestations of local
resistance are many and varied, but there is a
common guideline for all of them. In hydraulic calculations, if the pipe is short and
the local resistances are large, then the pressure lost for local resistances will be much
greater than the pressure lost along the length of the channel.
In this case, local resistance will be important. Of course in hydraulic
calculations we must take into account these local resistances. If in any section of
pipe there are several local resistances, of course, local
resistances at the point of
entry, exit of the vessel, exit of the vessel, bend of the pipe at an angle, sudden
expansion and contraction, the local resistance coefficients
of that place are
determined, the local resistance coefficient of each local equal to the sum of the
resistance coefficients, viz
𝜉 = 𝜉
𝑖𝑛𝑡𝑟𝑜𝑑𝑢𝑐𝑡𝑖𝑜𝑛
+ 𝜉
𝑓𝑎𝑢𝑐𝑒𝑡
+ 𝜉
𝑡𝑢𝑟𝑛
+ ξ
exit
In that case the local lost pressure is equal to H
мах
=
Σ𝜉
𝑉
2
2𝑔
Finding the lost pressure at the expense of local resistances requires theoretical
knowledge from the researcher, because local resistance reduces the kinetic energy of
the current by affecting the flow rate. We consider this situation in the following
experiment.
It can be seen from these hydrodynamic processes that the velocity of the flow
in the diameters d
1
and d
2
is different, the difference in velocities gives the pressure
lost v
1
- v
2
= ∆v. The pressure lost due to the speed difference can be determined as
follows;
h
мах
=
(𝑉
1
−𝑉
2
)
2
2𝑔
=
∆𝑉
2
2𝑔
where: V
1
- velocity before
expansion of the pressure pipe;
V
2
- the velocity after expansion of the pressure pipe;
d
1
v
1
d
2
v
2
"Science and Education" Scientific Journal / ISSN 2181-0842
December 2021 / Volume 2 Issue 12
www.openscience.uz
239
The difference between these velocities
v
1
-
v
2
=
∆
v
∆𝑉
2
2𝑔
gives the value of local
pressure loss. therefore, it gives incorrect conclusions.
Theoretically, this process can be solved as follows, i.e. the local resistance
coefficient x at the point where the pipe diameter
changes can be calculated
analytically by the flow velocities v
1
and v
2
, the result giving the same conclusion.
For example, let's express the process by v
1
h
мах
=
(𝑉
1
−𝑉
2
)
2
2𝑔
instead of v
2
in the formula
we write by v
1
, that is,
𝜔
1
∗ 𝑣
1
= 𝜔
2
∗ 𝑣
2
=
𝑄
From the equation
𝑣
2
=
𝜔
1
𝜔
2
𝑣
1
conditionally, а
𝜔
2
=
𝑣
1
𝑣
2
𝜔
2
) where h
мах
=
(1 −
𝑉
2
𝑉
1
)
𝑉
1
2
2𝑔
if we define
𝜉
′
=
(1 −
𝑉
2
𝑉
1
)
2
or h
мах
=
𝜉
′ 𝑉
1
2
2𝑔
from h
мах
=
(1 −
𝜔
1
𝜔
2
)
2 𝑉
1
2
2𝑔
if
𝜉
′
=
(1 −
𝜔
1
𝜔
2
)
2
and
𝜉
′
=
(1 −
𝜔
1
𝜔
2
)
2
are
equal to each other.
In the same way, if we take the velocity v
2
behind the local resistance, then we
define it as
𝜉
′′
=
(1 −
𝑉
1
𝑉
2
)
2
then h
мах
=
𝜉
′′ 𝑉
2
2
2𝑔
or if h
мах
=
(1 −
𝜔
2
𝜔
1
)
2 𝑉
2
2
2𝑔
h
мах
=
𝜉
′′ 𝑉
2
2
2𝑔
.
𝜉
′′
=
(1 −
𝑉
1
𝑉
2
)
2
=
(1 −
𝜔
2
𝜔
1
)
2
, h
мах
=
𝜉
′′ 𝑉
2
2
2𝑔
We
expressed the lost
pressure by velocity v
2
. The results obtained give the same value.
h
мах
=
𝜉
′ 𝑉
1
2
2𝑔
=
𝜉
′′ 𝑉
2
2
2𝑔
due to the difference in velocities
𝜉
′
and
𝜉
′′
. The analytical solution fully
confirms the experimental data.
Conclusion. If we examine the research in this area in relation to the Reynolds
number, there are changes in the values of
𝜉
′
and
𝜉
′′
, the main reason being that the
Reynolds number increases at high flow velocities, which in turn affects the
coefficients
𝜉
′
and
𝜉
′′
. Research in this area is awaiting a solution, both theoretically
and practically.
Do'stlaringiz bilan baham: 
