RU2260716C1 - Method of and device for reducing cavitation in hydraulic machines - Google Patents

Abstract

FIELD: mechanical engineering.

SUBSTANCE: invention relates to devices aimed at reduction of cavitation in hydraulic machines. Method precludes break of liquid flow at striking of liquid against parts of hydraulic machines by forming controllable flow in near the boundary areas of hydraulic machines and increasing kinetic energy owing to imparting rotating component to flow in direction of movement of pump impeller. Plasticity is imparted to liquid flow by delivering air in amount of 2-5% of amount of supplied water. Device to reduce cavitation includes section of hydraulic machine pipeline made straight and eccentrically narrowing with profiled resistance elements in form of fragments of Archimedean spiral installed on its walls along passage part with inclination in flow. Section is arranged before centrifugal pump. Ratio of larger diameter of pipeline section to its smaller diameter is 1.8-1.5, and ratio of length of section to larger diameter is 1.5-2.0. Section is furnished with cylindrical rarefaction chamber installed before pump and with device to feed air into rarefaction chamber.

EFFECT: provision of reduction of cavitation in hydraulic machines.

3 cl, 1 dwg

Description

The invention relates to mechanical engineering, in particular to methods and devices for reducing the level of cavitation in hydraulic machines, namely in centrifugal pumps. The invention can also be applied in methods and devices using a controlled level of cavitation to purify water and sediments.

There is a method of reducing cavitation in hydraulic machines, which consists in preventing a flow break from a collision of a liquid with a moving impeller of the pump by reducing the angle of incidence of the moving stream on the impeller blade [see Japanese Application 2002, 195144, F 03 B 3/02; 3/18; 11/04, publ. 07/10/2002].

There is a method of reducing cavitation in hydraulic machines, which consists in preventing flow disruption arising from the collision of the direct flow of water and the reverse flows in the Francis pump and its cavitation effect on the pump impeller by forming their collision at the required angles [see Japan patent No. 4041977, F 03 In 11/04, F 03 In 11/00, publ. 02/12/1992].

The disadvantages of the above analogues is the low degree of cavitation suppression, which does not prevent the erosion of machine parts caused by cavitation.

A known method of reducing cavitation in hydraulic machines, including preventing a flow break from a fluid collision with parts of hydraulic machines by forming controlled flow movement in areas adjacent to parts of hydraulic machines and increasing its kinetic energy [see Russian patent No. 2188965, F 03 11/04, publ. 09/10/2002]. Cavitational erosion of the convex wall of the curved bend of a suction pipe of a hydraulic turbine is reduced by reducing the pulsation of water flows in the flowing part by supplying kinetic energy to the boundary layer of fluid adjacent to the convex wall and increasing the resistance to the pulsating velocity components directed upstream.

Closest to the proposed method for reducing cavitation in hydraulic machines is a method that includes preventing a rupture of the fluid flow with parts of the hydraulic machines by forming a controlled flow movement in areas adjacent to the parts of the hydraulic machines and increasing its kinetic energy due to the fact that the flow is imparted a rotational movement in the direction impeller movements [see USSR copyright certificate No. 1290012, F 04 D 9/04, publ. 02/15/1987].

However, this method does not allow to the necessary degree to prevent the erosion of machine parts caused by cavitation. In addition, when using pumps for pumping treated water when cleaning it with biological methods, the cavitation level created during pump operation is unfavorable for the useful microflora used and inhibits its effect. At the same time, a low level of cavitation is a factor contributing to a more effective treatment of water and effluents [see Russian patent No. 1798332, C 02 F 11/00, publ. 1998, patent of Russia No. 2146231, C 02 F 3/12, publ. 2000, I. Pigal “Cavitation”. M., Mir, 1975, p. 70). It is also known that imparting plasticity to a fluid flow by supplying air to it reduces cavitation [see German patent No. 1503273, F 03 B 11/04, publ. 05/31/1972]. However, with uncontrolled air supply, there are complications associated with the stratification of the flow into layers of air and water, which interferes with the normal operation of the pump or the level of achieved reduction in cavitation is insufficient.

A device for reducing cavitation in hydraulic machines is known, in which the pump contains a cochlear-shaped casing forming a cavity directing the flow of high-pressure water to the impeller for interaction with it at the required angle [see Japanese Application 2002, 195144, F 03 B 3/02; 3/18; 11/04, publ. 07/10/2002].

A device for reducing cavitation is known, which contains an annular deflecting wall in front of the outlet of the transfer water to the direct flow in the Francis pump [see Japan patent No. 4041977, F 03 In 11/04, 11/00, publ. 02/12/1992].

A device for reducing cavitation in hydraulic machines is known [see Russian patent No. 2188965, F 03 11/04, publ. September 10, 2002], which includes a number of profiled wall blades installed downstream and pipelines transferring fluid from the interscapular border zone of high pressure near the concave wall to the interscapular zone of low pressure adjacent to the convex wall. In this case, the blades and pipelines are installed in the curved elbow of the suction pipe of the turbine.

The disadvantage of this device is the low degree of reduction in cavitation.

Closest to the proposed device is a device that includes a section of the pipeline of a hydraulic machine located in front of a centrifugal pump and made straight and narrowed, with profiled resistance elements installed on its walls along the flow part with an inclination in the flow [see USSR copyright certificate No. 1290012, F 04 D 9/04, publ. 02/15/1987].

However, the known device does not provide a sufficient level of cavitation reduction.

The objective of the proposed group of inventions, which form a single inventive concept, is to reduce cavitation by optimizing the amount of air supplied to the flow to the cavitation number of 0.01-0.05 and lower, i.e. to a level useful in water treatment, without stratification of the flow and disruption of the pump, and to prevent the destruction of machines caused by cavitation.

The technical result of the proposed technical solution is to reduce cavitation to cavitation numbers of 0.01-0.05 and below.

The specified technical result in terms of the method is achieved by the fact that in the known method of reducing cavitation in hydraulic machines, which includes preventing flow disruption from a fluid collision with parts of hydraulic machines by forming controlled flow movement in areas adjacent to parts of hydraulic machines and increasing its kinetic energy, for which the rotational component is attached to the flow in the direction of movement of the impeller of the pump, according to the invention, the fluid flow is plasticized by flow into the air stream, and air is supplied 2-5% of the volume of water supplied.

The technical result in terms of the device is achieved by the fact that in the known device, including the pipeline section of the hydraulic machine, located in front of the centrifugal pump and made straight and narrowed, with filtered resistance elements mounted on its walls with an inclined flow, according to the invention, the pipe section is narrowed eccentrically at a ratio the larger diameter of the said section to its smaller diameter is 1.8-1.5, and the ratio of the length of the section to the larger diameter is 1.5-2, while OK is equipped with a cylindrical rarefaction chamber located in front of the pump, and a device supplying air to the rarefaction chamber, and each profiled resistance element is made in the form of a fragment of an Archimedes spiral.

The method is as follows

They prevent the flow of fluid from breaking off from a collision of fluid with parts of hydraulic machines by forming a controlled movement of the flow of areas bordering the parts of the hydraulic machines and increasing its kinetic energy, for which the flow is given a rotational movement in the direction of rotation of the impeller, and further according to the invention, the fluid flow is plasticized by supplying air to the water stream in an amount of 2-5% of the volume of water supplied. As a result of the impact on the flow, it moves along a spiral trajectory accelerated, and instead of being “chopped” by the impeller blades, it is “screwed” into the hydraulic machine. The air supplied in the indicated quantities helps the medium to stretch, as it were, and the cavitation number can be reduced to 0.001-0.005.

When the air supply is less than 2% of the volume of the supplied water, the cavitation level does not decrease to the required values of cavitation numbers. With a greater than 5% air supply, the pump is disturbed due to the stratification of the fluid flow into water and air, and the cavitation number again increases due to the occurring vibrations.

Example

When a fluid stream is fed into the working cavity of a hydraulic machine at a speed of 1 m / s and the amount of air supplied is 2%, the number of cavitation decreases from 6 units to 0.001. This is because the fluid flow rate increases to 16 m / s. Due to the increasing volume of the water-air mixture and the acquisition of the quality of plasticity, the possibility of breaking the fluid flow and creating cavitation cavities is excluded. This helps to increase the pump life up to 30 years.

The drawing shows a device to reduce cavitation.

A device for reducing cavitation in hydraulic machines is a straight section eccentrically narrowed to a diameter d of a section 1 of length L of a pipe 2 of diameter D installed in front of a centrifugal pump 3. Section 1 is equipped with a cylindrical rarefaction chamber 4 installed directly in front of the impeller (not shown) of pump 3, and a device 6 for supplying air, for example, a pitot tube, the output of which is installed in the vacuum chamber 4. On the inner walls of section 1, resistance elements are installed in the form of fragments 5 of the Archimedes spiral.

The number of fragments 5 of the Archimedes spiral mounted on the walls depends on the volume of water supplied and, therefore, on the diameter of the pipeline, and should be at least two. The ratio of the larger diameter D of the plot 1 to its smaller diameter d is 1.8-1.5, and the ratio of the length L of the plot 1 to the larger diameter D is 1.5-2. In this case, a cavitation level of 0.01-0.05 is achieved.

The device operates as follows. The water supplied to the pipeline 2, getting into the tapering section 1, acquires acceleration, in addition, the resistance elements installed in the walls of the tapering section 1 in the form of fragments 5 of the Archimedes spiral give the fluid flow a rotational component of motion. The water twisted by the impeller of the pump 3 is, as it were, screwed into the interscapular space of the impeller of the pump 3 as much as possible due to the selected geometric proportions of the sizes of the tapering section 1, adapting to the movement of the impeller. In areas bordering with the blades, the flow moves with speed and in the direction of movement of the impeller of the pump 3, flowing around it. This prevents breaks in the fluid flow from a collision of the liquid with the blades of the impeller of the pump 3, and cavitation is reduced. When air is supplied to the rarefaction chamber 4 from the device 6, dense streams push the air-water mixture to the periphery and reduce the cavitation effect on the impeller vanes of the pump 3. Installation of fragments 5 of the Archimedes spiral in an eccentrically tapering pipe section 1 with the indicated ratio of diameters d, D of section 1 and its length L allows you to give the water flow along with the translational motion of the rotational component of the movement in the direction of rotation of the impeller of the pump 3 without reducing the flow rate. This prevents a rupture of the fluid flow from a collision with the impeller blades. The narrowing of the pipe section 1 gives the stream acceleration, thereby increasing the kinetic energy of the stream. These factors prevent flow disruption from fluid collisions with parts of hydraulic machines, namely, centrifugal pump vanes. The presence of a rarefaction chamber 4 with a device 6 for introducing air into the stream allows the creation of a plastic medium consisting of a water-air mixture that is not “chopped” by the impeller blades, but flows around it. The eccentric narrowing of section 1 of the pipeline 2 allows avoiding the accumulation of air in the upper part of section 1 when introducing air into the flow, which could lead to a decrease in the flow rate and complete “locking” of section 1. The device allows to reduce the cavitation number to 0.001-0.005 and cavitation wear of parts cars.

Device execution example

For pumping liquid in an amount of 150 m ³ / h, a device with section 1 in the form of an eccentrically narrowed cone is used for reasons of preventing air accumulation in its upper part. The input diameter D is 230 mm, the output diameter d is 115 mm. The length of the conical part L is 414 mm. The total length of the device is 439 mm. The length of the rarefaction chamber 4 is 25 mm. Fragments 5 of the spinning spiral have a variable inclination with respect to the axis of the suction pipe of pump 3. The initial part of the spiral, which is up to 10% of the length of the cone, is parallel to its axis, then, according to the principle of the Archimedean spiral, smoothly twists in the direction of movement of the impeller. The length and number of fragments 5 of the spiral are calculated based on the discrete coefficient Kq of the spiral. To reduce the number of cavitation to 0.001, the device contains a pitot tube through which air is supplied to the rarefaction zone. A swirling flow pushes the water-air mixture to the periphery, where a plastic medium is created, which prevents flow breaks from collision with the impeller and the phenomenon of cavitation.

Claims (2)

1. A method of reducing cavitation in hydraulic machines, including preventing a break in the fluid flow from a collision of the fluid with parts of the hydraulic machines by forming a controlled flow movement in areas adjacent to the parts of the hydraulic machines and increasing its kinetic energy, for which the rotational component of the movement is imparted to the flow in the direction of movement of the worker pump wheels, characterized in that plasticity is imparted to the fluid flow by feeding into the air flow, wherein 2-5% of the volume under the air is supplied water collection. 2. A device for reducing cavitation in hydraulic machines, including a section of the pipeline of the hydraulic machine located in front of the centrifugal pump and made straight and narrowed, with profiled resistance elements installed on its walls along the flow section with an inclined flow, characterized in that the section is narrowed eccentrically when the ratio of its larger diameter to the said portion to its smaller diameter equal to 1.8-1.5, and the ratio of the length of the portion to its larger diameter is 1.5-2, while the drain is equipped with a cylindrical rarefaction chamber located in front of the pump and a device supplying air to the rarefaction chamber, and each profiled resistance element is made in the form of a fragment of an Archimedes spiral.