RU2532870C1 - Optimisation method of geometric parameters of side semi-spiral supply of centrifugal pump of two-sided inlet - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: in an optimisation process of geometric parameters of side semi-spiral supply of a centrifugal pump of a two-sided inlet there specified is design supply; an average moment of speed at an impeller inlet, a rotation frequency and a radius of the impeller, as well as a law of variation of width of the section of the spiral supply part depending on variation of radius of its section. The carrying capacity of the supply is determined on their basis; a design section of its spiral part is shaped; intermediate sections of the spiral part are shaped considering the angle of contact of the spiral part. The obtained parameters of width of design and intermediate sections are reduced by 15-20%; an outlet radius of the impeller is increased by the value of up to 1%; an angle of contact is increased up to 200…210° and a shape of the cross section of the tongue is changed, thus making it smoothly converging from periphery to the centre of the impeller and a confuser section.

EFFECT: improving uniform distribution of speeds and their moments at the outlet of the supply to the impeller, which allows improving the impeller liquid inlet conditions and reducing cavitation, as well as increasing the efficiency of the pump owing to reducing supply energy losses.

2 cl, 10 dwg

Description

The invention relates to the field of mechanical engineering, namely to the design and manufacture of centrifugal pumps, intended, in particular, for use as oil main pumps.

Currently, the requirements for the characteristics of oil main pumps are constantly being tightened, especially for their energy efficiency and reliability. This is due to the fact that oil main pumps have, as a rule, greater power and, accordingly, consume a lot of energy. Moreover, in the total cost of the life cycle of the pump, the cost of electricity can reach 80%. In this regard, even a slight increase in the efficiency of the pump by 1-2% can give a significant economic effect. Hence, there is a need to improve the energy efficiency of the designed pumps, as well as to optimize the pump parameters.

In this case, the main difficulties arise when optimizing the flow part of the pump, including the inlet, impeller and outlet.

There is a method of optimizing the flow of a centrifugal pump, in which the maximum efficiency is shifted towards higher feeds by increasing the area (expansion) of the entrance to the tapered cone of the outlet (book: High-speed vane pumps. Borovsky B.I. et al. M: Engineering, 1075 p. 125).

There is a method for optimizing the flow part of a multistage centrifugal pump by optimizing the geometric parameters of the impeller and guide vane elements and selecting flow passages for liquid flows, which allows to reduce hydraulic losses and improve the pressure and efficiency parameters (patent RU 2161737 with priority from 02.03.2000).

A known method for optimizing the geometric parameters of the flow channels of the stages of a centrifugal pump, according to which optimization consists in expanding the flow channels of the guide apparatus and the impeller when the nominal mode coincides with the maximum efficiency mode, is not due to the selection of exhaust parameters, as is customary in pump engineering, but due to optimization of parameters the impeller (patent RU 2472973 with priority from 07/01/2011). The specified method allows to increase the pump service life, as well as to increase the pressure and efficiency of the stage by shifting the operating mode with maximum efficiency to the nominal supply area, but it optimizes only the geometric parameters of the flow channels of the centrifugal pump stages.

The closest analogue to the claimed method for optimizing the geometric parameters of the lateral half-helical inlet of a centrifugal pump of a double-sided input, selected as a prototype, is a method for optimizing the geometric parameters of the lateral half-spiral inlet of a centrifugal pump, given in the book: Mikhailov AK, Malyushenko VV Vane pumps. Theory, calculation and construction. M.: Mechanical Engineering, 1977, pp. 95-98. According to this method, the entire supply is conventionally divided into three sections: a confuser section located immediately before the flow inlet to the wheel, a spiral supply section from the confuser section to the transition section, and a section from the transition section to the pump inlet pipe. In the zone adjacent to the confuser section of the spiral supply section, a “tongue” is installed that stabilizes the flow around the shaft and prevents the flow of fluid in the direction against rotation of the impeller. The cross-sectional shape of the spiral supply section is selected depending on the permissible axial dimensions of the pump. The approach is characterized by design and intermediate sections of the spiral supply section and the angle of coverage of the spiral part of the supply. In order to proceed with the calculation and profiling of the approach, the calculated approach feed is set, the average moment of speed at the entrance to the impeller, the rotation frequency and the radius of the impeller, as well as the law of variation of the width of the supply section depending on the change in the radius of the supply section. Then, on their basis, the supply capacity is determined and the calculated cross section of the spiral supply part is profiled, after which, taking into account the angle of the spiral supply part, the intermediate sections of the spiral supply part are profiled. In this case, the angle of coverage of the spiral part of the supply (the angle of the “tongue” to the input flow rate) is not more than 180 ° in the limit, and the cross section of the “tongue” is close to constant. In more detail, this method will be described below. The proposed method allows to significantly optimize the geometric parameters of the lateral half-helical inlet of a centrifugal pump, however, there is a rather uneven distribution of the velocities of the pumped fluid and their moments at the entrance to the impeller, especially at high pump rates, due to the different nature of the fluid flow in the spiral section and the input channel of the supply, which leads to a decrease in the efficiency of the pump and the deterioration of its cavitation qualities.

The objective of the invention is to increase the uniformity of the distribution of velocities of the pumped liquid and their moments and reduce vortex formation in the inlet at the entrance to the impeller, which leads to an increase in the efficiency of the pump and improvement of its cavitation characteristics.

The problem is solved in that in the known method for optimizing the geometric parameters of the lateral half-helical inlet of a centrifugal pump of a double-sided inlet, consisting of an inlet channel, a spiral part, a confuser section in front of the flow inlet of the pump impeller and a partition - a "tongue" of supply that separates the fluid flows through the inlet channel and the spiral part of the supply, and characterized by the calculated and intermediate sections of the spiral part of the supply and the angle of coverage of the spiral part of the supply, at which They specify the estimated feed rate of the supply, the average moment of speed at the entrance to the impeller, the rotational speed and radius of the impeller, as well as the law of variation of the width of the supply section depending on the change in the radius of the supply section, on the basis of this determine the delivery capacity and profile the calculated cross section of the spiral part supply, after which, taking into account the angle of coverage of the spiral supply part, the intermediate sections of the spiral supply part are profiled, new is that the parameters of width p obtained on the basis of the initial data of counting and intermediate sections of the spiral part of the supply is reduced by 15-20%, the output radius of the impeller of the pump is increased by 1%, the angle of coverage of the spiral part of the supply is increased to 200 ... 210 ° and the cross-sectional shape of the “tongue” is changed, making it gradually tapering from the periphery to the center of the impeller and the confuser supply section.

A decrease in the supply capacity due to a 15-20% reduction in the width of the calculated and intermediate sections of the spiral part of the supply, respectively, increases the peripheral flow rate at the entrance to the impeller and improves the uniformity of the fluid flow at the entrance to the wheel and the cavitation qualities of the wheel and pump.

An increase in the output radius of the pump impeller by up to 1% compensates for a decrease in the pump head with a 15–20% decrease in the supply capacity.

Increasing the coverage of the spiral part of the supply up to 200 ... 210 ° and changing the cross-sectional shape of the “tongue” made smoothly tapering from the periphery to the center of the impeller and the confuser portion of the supply improves the uniformity of the flow inlet to the impeller and reduces energy loss in the supply.

The essence of the present invention is illustrated by the following drawings.

Figure 1 - appearance of the upgraded oil pump of a bilateral entrance type NM with optimized lateral half-spiral inlet;

Figure 2 is a schematic 3-D model of lateral half-spiral inlets and a spiral outlet of a centrifugal pump of a double-sided inlet;

Figure 3 - diagram of the semi-spiral supply;

Figure 4 - calculated cross-section of the semi-spiral supply;

Figure 5 - calculated last section of the known (prototype) and the proposed semi-spiral supply;

6 is a vector diagram of the flow rates of the pumped liquid at the entrance to the impeller of the known and proposed semi-spiral supply;

7 is a supply diagram with a coverage angle of the spiral part of 180 °;

Fig. 8 is a supply diagram with a coverage angle of the spiral portion of 210 °;

Fig.9 - calculation of the velocity fields of the fluid flow at the entrance to the impeller in a known supply (distribution of the speed module in a known supply);

Figure 10 - calculation of the velocity fields of the fluid flow at the entrance to the impeller in the proposed supply (distribution of the speed module in the proposed supply).

The proposed method can be implemented using operations to optimize the geometric parameters of the lateral half-helical inlet of a centrifugal pump of a double-sided inlet, disclosed in the book: Vane pumps. Theory, calculation and construction. M .: Engineering, 1977, pp. 95-98 (prototype), with the introduction of appropriate changes and additions. A general view of the double-sided centrifugal pump and the schematic 3-D model of the lateral half-spiral inlets and the spiral outlet of the double-sided centrifugal pump are shown in Figs. 1, 2. The half-spiral lateral inlet 9 of the centrifugal pump, as noted above, consists of an input channel 10 (section from the inlet pipe 11 to the cross-section GH), the spiral part 12 (the supply section from 1-8 to the transitional cross-section GH), the confuser section 13 (inlet or funnel) located immediately in front of the flow inlet pump 14, and the partition - the "tongue" 15 of the inlet, dividing the fluid flows through the inlet channel 10 and the spiral part of the inlet 12 (Figure 3). The “tongue” 15 is usually set in section 0, located at an angle of 45 ° to the direction of flow, but if necessary, it can be moved to section 2, i.e. set at an angle of 90 ° to the direction of the input flow rate without significant changes in the characteristics and efficiency of the pump. Further displacement of the tongue is not recommended. Such fluid supply devices make it possible to circulate the flow around the pump shaft and thereby reduce vortex losses at the inlet to the pump impeller.

Profiling of the supply is carried out by determining the geometric parameters of the last and intermediate sections of the spiral section of the supply. As the last section of the spiral supply section, section 8 is selected (Figure 3). In order to proceed with the calculation and profiling of a half-spiral supply, it is necessary to select the pump design and set the parameters Q, H, n, where: Q - pump flow, m ³ / s; N - pump head, m; n is the impeller rotation frequency, rpm and R is the radius of the entrance to the inlet, m. Then, the inlet capacity is determined for the calculated cross section of the spiral supply section (section A ₈ ), m, using the formula:

Where:

K _p = 1.6 ... 3.0 - coefficient obtained by experimental data.

For wheels with two-way entry:

The velocity distribution in sections 1-8 is taken based on the fact that the moment of speed:

V _u r = const

Where:

V _u - peripheral speed at the entrance to the wheel, m / s;

r is the radius of the section, m

Then the cross-sectional capacity (Figure 4):

Where:

b - section width, m;

r _8max is the maximum radius of the calculated section, m;

r ₀ - radius of exit from the supply, m.

bi = f (ri) - the law of change b _i , is determined by the known design of the pumps.

Then, the width parameters of the last and intermediate sections of the spiral part of the supply are reduced by 15-20% (Figure 5), then

Where:

To _P = 0.8 ... 0.85 - correction factor.

Respectively

Profiling of intermediate sections of the spiral part of the supply is carried out on the basis of the ratio:

Where:

A _pi is the supply capacity for the calculated cross section of the spiral supply section for wheels with a two-sided input, m;

r _imax is the maximum radius of the calculated section, m;

The intermediate sections i of the spiral supply section are constructed so that the throughput decreases in proportion to the angle of the section in the plan

Where:

φ _i - the angle of the section (measured from the tongue), degrees;

φ ₈ - the angle of the estimated cross-section of the spiral supply section (measured from the tongue), deg.

Inlet contours, axial dimensions b ₀ and the law of change b _i = f (r _i ) are selected according to the completed pump designs. Then carry out a graphical construction of the spiral part of the pump.

The output radius of the impeller of the pump is increased by up to 1%, the angle of coverage of the spiral part of the inlet is increased to 200 ... 210 ° and the cross-sectional shape of the “tongue” is changed, making it gradually tapering from the periphery to the center of the impeller and the confuser portion of the inlet.

When constructing cross-sections of the flowing part of a semi-spiral inlet of a centrifugal pump of a double-sided inlet, 3-D modeling methods can be used, in particular Bezier curves, see, for example: Rogers D., Adams J. Mathematical foundations of computer graphics. M .: Mir, 2001.

The advantages of the proposed technical solution are confirmed by the analysis of vector plans for the flow rates of the pumped liquid at the entrance to the impeller of the known and proposed semi-spiral supply, Fig.6, where:

- абсолютная скорость потока на входе в рабочее колесо (V₁ - прототип, $$V_1{}^{\prime }$$

- предлагаемый подвод), м/с;V ₁ $$V_{\mathrm{one}}{}^{\prime }$$

- absolute flow rate at the entrance to the impeller (V ₁ - prototype, $$V_{\mathrm{one}}{}^{\prime }$$

- proposed supply), m / s;

- окружная составляющая абсолютной скорости потока на входе в рабочее колесо, м/с;V _u1 , $$V_{u\mathrm{one}}{}^{\prime }$$

- circumferential component of the absolute flow velocity at the entrance to the impeller, m / s;

- радиальная составляющая скорости потока на входе в рабочее колесо, м/с;V _u $$V_u{}^{\prime }$$

- the radial component of the flow velocity at the entrance to the impeller, m / s;

- относительная скорость потока на входе в рабочее колесо, м/с;W ₁ $$W_{\mathrm{one}}{}^{\prime }$$

- relative flow rate at the entrance to the impeller, m / s;

- переносная скорость потока на входе в рабочее колесо, м/с.U ₁ $$U_{\mathrm{one}}{}^{\prime }$$

- portable flow rate at the entrance to the impeller, m / s.

According to the Euler equation from the theory of paddle hydraulic machines, the specific work of the paddle wheel is equal to

Where:

ω is the angular speed of rotation of the impeller;

g is the acceleration of gravity;

R ₁ is the radius of the entrance to the impeller;

R ₂ is the radius of the exit of the impeller;

V _u1 is the peripheral component of the velocity at the entrance to the impeller;

V _u2 is the peripheral component of the velocity at the exit of the impeller.

в предлагаемом подводе по сравнению с окружной составляющей абсолютной скорости на входе в рабочее колесо V_u1 подвода прототипа, при котором $$V_{u1}{}^{\prime }>U_{u1}$$

. Увеличение $$V_{u1}{}^{\prime }$$

улучшает равномерность потока жидкости на входе в рабочее колесо и кавитационные качества колеса и насоса. На Фиг.7, 8 представлены схемы подвода с углом охвата спиральной части 180° (геометрия подвода прототипа) и углом охвата спиральной части 210° (геометрия предлагаемого подвода) и с разными формами языка 15. Данные выводы подтверждаются результатами расчетного моделирования в компьютерном пакете STAR ССМ+ течения жидкости в конфузорных участках 13 предлагаемого подвода и подвода прототипа. Моделировалось течение жидкости в полуспиральных подводах нефтяного магистрального насоса типа НМ 3600-230 (подача 3600 м³/с, напор 230 м, частота вращения вала 3000 об/мин). Степень равномерности моментов скорости потоков жидкости можно визуально оценить по степени однородности цветовых оттенков компьютерных рисунков на Фиг.9, 10. Чем равномернее распределение моментов скоростей, тем однороднее оттенок полученного рисунка. При этом в числовых данных среднее значение момента скорости жидкости на выходе из подвода прототипа составило 0,6 м²/с, а относительное среднеквадратичное отклонение момента скорости около 40%, для предлагаемого в результате оптимизации подвода те же величины составили 1,41 м²/с и 10%, т.е. степень равномерности момента скорости увеличивается в среднем в 4 раза, а величина скорости момента более чем в 2 раза.Based on this equation, increasing V _{u1 the} peripheral component of the flow rate at the entrance to the impeller in the proposed supply (by reducing the capacity of the calculated and intermediate supply sections, Figure 5) at the same time slightly reduces the pump head. However, as is known from the theory of blade hydraulic machines, it should also be taken into account that the pump head depends linearly on the peripheral speed at the inlet, and the dependence is quadratic on the radius of the wheel at the output. Therefore, a small (estimated less than 1%) increase in the output radius of the impeller can compensate for the decrease in pressure of the wheel, which occurred due to a change in the geometry of the design of the supply device. In Fig. 5, for example, the calculated last section of the spiral supply section shows a decrease in the indicated section 16 in the proposed supply as compared with the prototype supply section 17, and Fig. 6 on the vector plans of flow velocities shows a corresponding increase in the peripheral component of the absolute flow velocity at the input to the working wheel $$V_{u\mathrm{one}}{}^{\prime }$$

in the proposed supply in comparison with the peripheral component of the absolute speed at the entrance to the impeller V _u1 supply of the prototype, in which $$V_{u\mathrm{one}}{}^{\prime }>U_{u\mathrm{one}}$$

. Increase $$V_{u\mathrm{one}}{}^{\prime }$$

improves the uniformity of fluid flow at the entrance to the impeller and the cavitation properties of the wheel and pump. 7, 8 are diagrams of the approach with the angle of coverage of the spiral part 180 ° (geometry of the supply of the prototype) and the angle of coverage of the spiral part of 210 ° (geometry of the proposed approach) and with different forms of language 15. These conclusions are confirmed by the results of computational modeling in the STAR computer package CCM + fluid flow in the confuser sections 13 of the proposed supply and supply of the prototype. The fluid flow was simulated in the semi-helical inlets of an oil main type pump НМ 3600-230 (supply 3600 m ³ / s, pressure 230 m, shaft rotation speed 3000 rpm). The degree of uniformity of the moments of the velocity of fluid flows can be visually assessed by the degree of uniformity of the color shades of the computer drawings in Figures 9, 10. The more uniform the distribution of the moments of velocities, the more uniform the shade of the resulting pattern. Moreover, in the numerical data, the average value of the moment of fluid velocity at the outlet of the prototype inlet was 0.6 m ² / s, and the relative standard deviation of the velocity moment was about 40%, for the proposed supply as a result of optimization, the same values were 1.41 m ² / s and 10%, i.e. the degree of uniformity of the moment of speed increases on average 4 times, and the magnitude of the speed of the moment is more than 2 times.

The present invention was practically used in the framework of the project of LLC "NKMZ" innovative modernization of main oil pumps of the NM series (Figure 1).

Thus, the proposed method for optimizing the geometric parameters of the lateral half-helical inlet of a centrifugal pump of a double-sided inlet allows one to obtain a much more uniform distribution of velocities and their moments at the outlet of the inlet to the wheel, which improves the conditions for liquid to enter the impeller and reduces energy loss in the inlet, thereby increasing Pump efficiency (approximately 1%, which is a significant value for oil pumps) and its cavitation properties are improved.

Claims (2)

1. A method for optimizing the geometric parameters of a lateral half-helical inlet of a double-sided centrifugal pump, consisting of an inlet channel, a spiral part, a confuser section in front of the flow inlet of the pump impeller and a partition - the “tongue” of the inlet separating the fluid flows through the inlet channel and the spiral part supply, and characterized by the calculated and intermediate sections of the spiral part of the supply and the angle of coverage of the spiral part of the supply, at which the calculated supply of the supply is set, the average moment t is the velocity at the entrance to the impeller, the rotational speed and radius of the impeller, as well as the law of changing the width of the cross section of the spiral supply part, depending on the change in the radius of the supply cross section, based on them, determine the supply capacity and profile the calculated cross section of the spiral supply part, after which taking into account the angle of coverage of the spiral part of the supply, intermediate sections of the spiral part of the supply are profiled, characterized in that the parameters of the width of the calculated and intermediate sections obtained on the basis of the initial data th spiral part of the supply is reduced by 15-20%, the output radius of the impeller of the pump is increased by 1%, the coverage angle of the spiral part of the supply is increased to 200 ... 210 ° and the cross-section of the “tongue” is changed, making it gradually tapering from the periphery to the center of the impeller and the confusion section of the supply. 2. The optimization method according to claim 1, characterized in that the throughput for the calculated cross-section of the spiral supply section for wheels with a two-way input is determined from the ratio:

Where:
A _p8 is the supply capacity for the calculated cross-section of the spiral supply section for wheels with a two-sided entrance, m;
Kp = 1.6 ... 3.0 - coefficient obtained from experimental data;
Kp = 0.8 ... 0.85 - correction factor;
while profiling the calculated cross section of the spiral part of the supply is carried out on the basis of the ratio:

Where:
r is the radius of the section, m;
r _8max is the maximum radius of the calculated section, m;
r ₀ is the radius of the exit from the supply, m;
and profiling of the intermediate sections of the spiral part of the supply is carried out on the basis of the ratio:

Where:
A _pi is the supply capacity for the calculated cross section of the spiral supply section for wheels with a two-sided input, m;
r _imax is the maximum radius of the calculated section, m;
moreover, the intermediate sections i of the spiral supply section are constructed so that the throughput decreases in proportion to the angle of the section in the plan

Where:
φ _i - the angle of the section (measured from the tongue), degrees;
φ ₈ - the angle of the calculated cross-section of the spiral supply section (the angle covered is measured from the tongue), equal to 200 ... 210 °.

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