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Rustamov Sherzod Rustamovich, assistant, at the department "Using water energy and pumping stations", Tashkent institute of irrigation and agricultural mechanization engineers (TIIAME), Uzbekistan E-mail: [email protected] Nasirova Naira Ravilevna, Junior resercher, Tashkent institute of irrigation and agricultural mechanization engineers (TIIAME), Uzbekistan E-mail: [email protected]
CONSTRUCTIVE PECULIARITIES OF MODERNIZED CENTRIFUGAL PUMP
Abstract: Theoretical basis for calculating the new design of a centrifugal pump. The article describes the design and design efficiency factor of the new pump on the geometric dimensions of the working part and is compared with the real value. When testing the model, a high efficiency factor of the new pump was fixed 80.7 ... 86.4%.
Keywords: centrifugal pump, operating characteristics, cavitation and abrasive wear. In the Republic there were problems with the opera- where Q is a real feed; QT is the theoretical feed.
tion of systems with mobile and stationary means of water lifting. By 2015, the capacity of the main pumping and energy equipment, spent park (factory) resource, was more than 70% of the installed capacity at large pumping stations (PS). In the context of urgent renovation, an operational strategy must be defined, aimed at maintaining the necessary reliability and economic parameters of their basic elements. The definition of «limiting» elements of the main equipment in the changed operating conditions is an extremely urgent task at the beginning of the XXI st century [1].
More than half of accidents and failures are caused by physical wear ofthe impeller units (IU), chamber IU, bearings, i.e. the main nodes, the restoration ofwhich requires complete disassembly with the withdrawal of them from operation for a long period. The average weighted efficiency is reduced, the operating characteristics deteriorate, the supply and pressure of the pumps is reduced.
The volumes of reverse water leakage (flow from the pressure part to the suction through the design gaps, valves, etc.) are increasing. For a comparative evaluation of these leaks, the concept of a volumetric efficiency
n = Q / Qt ,
The concepts of theoretical useful power NT = 0,001 pgQTHT and mechanical efficiency of the pump
nM = Nt / N
These parameters completely characterize the individual elements in terms of their functionality and dependency with other pump units. The main disadvantages of the previously created pumps are:
• Large mechanical wear of the body parts of the sealing elements, friction pairs;
• Erosion, cavitation and abrasive wear of the IU and hulls;
• Application oflow-grade, low-quality sealing gaskets.
When designing modern centrifugal pumps, it is possible to complicate their designs. For example, the European centrifugal pump contains a casing with an engine and suction nozzle and a device for twisting the flow at the inlet to the IU [1, 2]. The disadvantage of such pumps is that not all of the peripheral flow is curled, which creates reverse vortex zones. The authors created a number of new centrifugal pumps with high demands on cavitation qualities [3].
CONSTRUCTIVE PECULIARITIES OF MODERNIZEDCENTRIFUGAL PUMP
In order to increase the uniformity of the twist of the flow along the periphery in one design, the channel is annular and the chamber has an area of flow that decreases in the direction in which the flow of water flows therein. In (Fig. 1) shows a longitudinal section of the pump.
Figure 1. Centrifugal pump with pressure and suction nozzles
The centrifugal pump comprises a body 1 with a delivery and suction nozzles 2 and 3, a device for swirling the flow at the wheel 4 in the form of a chamber 5 connected to a delivery nozzle 2 surrounding the suction pipe 3 and a channel 6 located at an acute angle to the pump axis 7 and oriented to the IU4, the duct 6 being annular and the chamber 5 having a cross-sectional area S decreasing in the direction of movement of the water flow therein.
When the pump is running at partial feeds, water flowing through channel 6 twists the peripheral flow region at the inlet of the wing 8. This is achieved by varying the supply of a constant flow angle on the wing blade 8, which ensures the absence of cavitation damages.
The efficiency of the working process of the new pump is determined
n =
Q_ Sa
(i)
where Q - water flow in the side channel (pump feed);
S - static moment of the lateral channel area relative to the IU axis;
mK - is the angular velocity of the IU.
Calculating the efficiency of new pumps according to the geometric characteristics of the working elements and compar-
ing them with actual values show that the actual efficiency is less by 3-10% calculated by formula (1). Thus, according to formula (1), the maximum achievable (theoretical) value of the efficiency of the new pump is determined [2].
If we represent the motion of water in a lateral channel with a circumferential velocity ml as a rotation with respect to the axis of the pump with angular velocity w , i.e. u = w , where r - is the radius of the center of gravity of the side channel area, we obtain Q = Fu and S = Fr, which coincides with the hydraulic efficiency.
The pressure increase in the side channel of the new pump is determined only by the energy losses in the water stream. This conclusion is now used in the construction of models and design schemes for a new pump with holes in the plates (Figure 2).
Figure 2. Diagram of the modernized pump with holes in the plates
In a real pump, due to the increase in leakage over the plates, the actual efficiency is less than the volume efficiency: n<nv, i.e. n = nv.
We construct the characteristics of a pump with holes in the plates. We use the following notation: Q - supply of the ideal pump (without holes in the plates): Q = (3 , + Q (Q i , - supply to the net-
L / network ^-inversev network -LA '
work, Q - leakage through the holes.) When the
inverse O O '
pump is operated on the open discharge pipe (head is zero), the pump Qnetwork slightly lower than Q, due to the presence of holes in the plates. The pump head will equal the sum of the hydraulic losses in the backflow:
- Pl =£K,
H =
Y
(2)
where Pp P2 - pressure in the suction and discharge nozzles; 2h - hydraulic losses in the return flow on the holes in the plates.
The leakage value is defined as
Qc6p = »/V2gH, (3)
wheref - is the area of the hole; y - equivalent flow coefficient; H - pump head.
Tests of the new pump were carried out on the test stand IS-1, in accordance with the method of periodic tests based on ISO 9906: 1999.
The characteristics of the pump D2000-21 were taken in the feed interval from 0 to the maximum flow, with
a submerged pump IU of 2.0 m, excluding cavitation, in accordance with TSh 46.31-16: 2002.
Conclusions:
1. Performance characteristics of the new pump with impeller diameter D.u = 425 mm showed the value of efficiency n% calculated 80.1 ... 83.0, actual 80.7 ... 86.4, deviation + 3.4 ... + 0.6. During the tests, vibration and noise were not observed. The working range of water supply at the rotor speed n = 985 min1 is from 1188 m3/h to 2125 m3/h.
2. These characteristics show the need to apply the designs of new advanced parameter pumps for the modernization of irrigation pumping stations.
References:
1. Dzhurabekov A., Rustamov Sh., Glovatsky O. Mechanism of cavitation and hydroabrasive wear of centrifugal pumps of irrigation pumping stations // Collected papers, SIC ICWC of Central Asia,- Tashkent, - 2017.-P. 153-159.
2. Glovatsky O., Ergashev R., Rustamov S.H. Improvement to usages and studies large pumping station // Monograph. LAP LAMBERT Academic Publishing.- Saarbruken.- 2013.- 170 p.
3. Glovatsky O., Nasyrova N., Saparov A. New methods of weakening cavitation modes during operation of pumping equipment of the pump station «Bek-Yab» // Bulletin of the Karakalpak Branch of the Academy of Sciences of Uzbekistan, Nukus,- 2016.- P. 28-32 p.
