RU2585029C2 - Mixer - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to mixing devices and can be used for mixing fluid flows, in particular, gases or liquids, in different industries and in oil refining and petrochemical, gas and power industry. Mixer for fluid flows comprises a mixing chamber, connected to it at least two coaxially arranged cylindrical pipe, through which fluid flows are supplied for mixing, vortex installed at least in one of pipes, and mix discharge union, mixing chamber diameter more than 1.7 times larger than outer diameter of pipes, and ratio between length of mixing chamber and its diameter is larger than or equal to 1.5. At that, vortex is arranged to swirled flow supply to input of mixing chamber with intensity which is determined from ratio of moment of momentum of fluid medium flow to axial number of flow at inlet into mixing chamber, which is equal to or greater than 0.7.

EFFECT: high efficiency of mixing of supplied fluid flows.

1 cl, 3 dwg

Description

The invention relates to mixing devices and can be used to mix fluid flows, in particular gases or liquids, in various industries and mainly in oil refining and petrochemicals, gas and energy industries.

A known static mixer (RF patent No. 20144879, IPC B01F 5/00), comprising a housing with nozzles for introducing components and outputting the mixture, two groups of truncated hollow perforated cones facing large bases to the nozzles for introducing components. On the periphery of the housing, as well as on the axis, swirlers are installed.

The specified mixer cannot work effectively due to the design solution. The entire fluid flow is blocked by a number of elements representing high hydraulic resistance. In addition, the elements of the mixer are represented by rather complex details, which also reduces the efficiency of the device as a whole.

Known direct-flow vortex mixer (RF patent No. 2414283, IPC B01F 5/00), containing two coaxially arranged cylindrical pipes, one-way twisting devices installed in the inner tube and annulus, as well as fittings for input components and output mixture. The operation of the device is organized in such a way that the mixed flows (gases or liquids) are fed through parallel fittings to the area of the screw mixing device, and the mixture of components passes first through the internal screw and then, after turning, through the external one.

The obvious disadvantages of the mixing device include its high metal consumption, the difficulty of manufacturing, and, probably, significant hydraulic resistance.

Mixing devices of other types (Abramovich G.N. et al. Theory of turbulent jets. M., Nauka, 1984, p. 715), based on the distributed entry of one stream into another, have the disadvantage of having to place structural elements in the stream, resulting in total pressure loss. In addition, this can be difficult in the case of a high flow temperature. The supply of one stream to another by jets from the channel wall does not allow for a high uniformity in the distribution of the concentration of the supplied fluid in the stream.

Closest to the proposed technical solution is a mixing device according to international application No. WO 2011101038, IPC B01F 3/02, B01F 5/00, B01F 5/04, consisting of two or more coaxial pipes for feeding the mixed flows into the inside of the mixer, a twisting device and mixing zones. In the device for the purpose of controlled mixing, the peripheral flow is twisted with the help of a blade and / or tangential inlet and forms a vortex rotating around the central flow. An additional effect achieved is that the inner surface of the pipe for some extent from the mixing zone of the two streams is protected from the internal, more corrosive stream, external, inert with respect to the pipe material.

Modeling the flow regimes for the conditions given in the indicated application shows that the flow in the mixing zone, sufficiently remote from the internal outlet pipe, is characterized by significant heterogeneity both in the velocity vector fields - axial and tangential, and in the composition of the flow. In FIG. Figure 1 shows the distribution of the concentrations of two mixing gases at a distance of two calibers from the point of mixing of the jets in a plane perpendicular to the axis of the pipes. The flow is characterized by significant heterogeneity, and to equalize the flow characteristics, a significant extension of the mixing zone is required. Thus, this device cannot be considered as an efficient mixer.

The technical problem that the proposed mixing device solves is to increase the mixing efficiency of the supplied fluid flows (gases or liquids, including in the form of aerosols, emulsions and suspensions) by achieving consistency between the geometric dimensions of the device and the rate of swirling flow.

The specified technical problem is solved in that in a mixing device for fluid flows, which contains a mixing chamber, at least two coaxially placed cylindrical pipes connected to it by which the fluid flows are mixed with at least one of them installed a swirler, and a fitting for withdrawing the mixture of components, the diameter of the mixing chamber exceeds the diameter of the outer pipe by more than 1.7 times, and the ratio between the length of the mixing chamber and its diameter is greater than or equal to 1.5. In this case, the swirler is installed with the possibility of supplying a swirling flow to the input of the mixing chamber with a swirl intensity, which is determined from the ratio of the momentum of the fluid flow to the axial amount of motion of the flows at the inlet of the mixing chamber, equal to or greater than 0.7.

An additional effect achieved in the proposed device is that under conditions when one of the fluid flows is corrosive, efficient mixing of the fluid flows in the volume of the mixing chamber avoids problems with corrosion of the internal parts of the mixing device due to dilution with an inert stream. For this, the corrosion-active component is fed into the central pipe, and the inert component is fed into the annular space between the outer and central pipes.

The essence of the proposed device lies in the fact that the fluid flows into the mixing device through pipes, which are located coaxially with the mixing chamber and the fitting for outputting the mixture of components. The diameter of the mixing chamber exceeds the diameter of the outer inlet pipe. The incoming flows (at least one), in addition to the translational component, also have a rotational component, that is, they are twisted relative to the axis of the pipe. After exiting the pipe into the mixing chamber, the flow expands and slows down the axial component of the velocity. Moreover, the expansion of the flow, according to the law of conservation of angular momentum, causes a decrease in the average angular velocity of the flow, on the one hand, and due to the action of centrifugal forces, it causes a redistribution of the mass of the rotating flow from the center to the periphery. The combination of these movements (actions) leads to the twisting of the expanding flow in the axial direction and the formation of a reverse vortex directed from the periphery of the flow to its axis. The interaction of this vortex with oncoming fluid flows leads to their intensive mixing.

A study of the work of the proposed mixing device using computational fluid dynamics showed that this effect occurs if the ratio of the diameter of the mixing chamber to the diameter of the outer inlet pipe is from 1.7 to 3.4, and the ratio between the length of the mixing chamber and its diameter is in the range from 1.5 to 3.0. Moreover, the upper limit of relations is determined from constructive and economic considerations.

The mixing effect is achieved when the flow at the inlet to the mixing chamber is twisted with a certain intensity. To characterize the flow swirl intensity, an integral swirl parameter was selected, characterized by the ratio of the angular momentum of the flow M to the axial angular momentum of the flows K. As follows from the scientific literature (Abramovich GN Theory of turbulent jets. M., Nauka, 1984), at the expiration A swirling jet in the axis region causes a return flow if U _tst ≥ U _x , where U _tst is the tangential velocity at the periphery, and U _x is the average axial velocity.

We write this through the integral parameters of the flow. We assume that the flow velocity over the cross section is constant and the angular velocity from all particles in the outlet cross section is also constant, i.e. fluid rotates like a solid.

The amount of fluid motion will be written as

,

,

where r is the current radius;

ρ is the density of the fluid.

The moment of momentum is written as

,

,

where ω is the angular velocity;

r _article - the radius of the pipe in which the flow swirls.

,Given that

,

where U _tst is the tangential velocity at the pipe wall.

получаемHence, with equality

we get

as a condition for the occurrence of a return flow.

The use of the integral parameter is most convenient in view of the fact that expressions are derived for the main types of swirling devices that allow, based on the characteristic design dimensions, to determine the integral parameter of the flow swirl obtained at the input to the mixing chamber.

In our case, the optimal effect of the mixing device was achieved when the ratio of the angular momentum of the flow to the axial angular momentum of the flows was 0.5 · r _st . With an increase in this ratio, the effect is preserved, however, the efficiency of the device decreases, since with an increase in the ratio, the fraction of the energy of the flow increases, which is wasted on its useless twisting.

The proposed technical solution will be better understood when reading the description of the device below, a diagram of which is shown in the attached FIG. 2.

The mixing device comprises a mixing chamber 1 with inlet pipes 2, 3 and 4 and an outlet pipe 5. Fluid flows into the mixer through a central channel 6 and ring channels 7 and 8. At least one of the flows is swirled with a certain intensity by any twisting device . In the diagram (Fig. 2), as an example, a twisting device 9 is shown, which is made in the form of blades mounted at an angle to the axis of the pipe.

The device operates as follows. Mixed fluid streams enter the mixing chamber 1 through the central channel 6 and through concentric channels 7 and 8. In the channel 7 means for swirling the flow 9 are installed. The input streams are pre-twisted in one of the known ways so that the ratio of the angular momentum of the flow to the axial amount the movement of flows was 0.5 · r _Art . For swirling, for example, tangential-blade, axial-blade, or any other of the known methods of swirling can be used (Aerodynamics of a swirling medium. / Ed. By R.V. Akhmedov. M., Energy, 1977, 240 p.) Flowing flows the medium enters the mixer, the diameter of the mixing chamber of which D exceeds the diameter of the external inlet pipe D _ST at least 1.7 times. In this case, the fluid flow expands and fills the cross section of the mixing chamber. As a result of the addition of the translational and rotational movements of the expanding jet, a powerful reverse vortex arises, which provides intensive mixing of gases. The consequence of this is a high degree of uniformity of the jet already at a distance equal to 2.6 D _CT from the gas inlet. FIG. 3 illustrates the operation of a mixer for mixing two gases of different composition. The drawing shows the field of concentrations of the components of the mixed gases in section along the axis of the proposed device. From the drawing it can be seen that at a distance of less than 2.6 D _{CT of the} input channel, the flow is almost uniform.

The operation of the invention will be better understood when considering an example of the implementation of a technical device, a diagram of which is presented in FIG. 2. The device is a mixer in which it is required to mix the flows of hot and cold water. Hot water is supplied to the central channel 4 with a diameter of d = 0.01 m with a temperature t _Г = 90 ° C and a velocity U _Г = 0,8 m / s. Cold water is supplied through a peripheral channel 3 with a diameter of D _CT = 0.05 m, in which twisting vanes are installed at an angle of 50 ° to the installation axis (flow direction), with a temperature t _X = 10 ° C and a speed U _X = 1.1 m /from. Mixing chamber 1 has a diameter D = 0.076 m and a length L = 0.13 m.

The ratio of the size of the device: D / D _CT = 1.51, L = 1.71D.

Such a device provides high-quality mixing of hot and cold liquids. We show this using the estimated calculation.

The density of water we take ρ _W = 1000 kg / m ³ . Mass costs through the central channel and external respectively

m _c = 0.063 kg / s and m _p = 2.072 kg / s.

The tangential velocity in the external channel is

U _t = U _x tg50 ° = 1.31 m / s.

For the estimated calculation of the angular momentum of the swirling flow, we apply the simplified formula

M = U _t · m _p · r _cp ,

- средний радиус вращения закрученного потока.Where

- the average radius of rotation of the swirling flow.

From here we get

which is more than 0.5 · r _article = 0.0125.

Thus, a mixer with the indicated proportions of the structure, into which liquids with the parameters indicated in the example are supplied, ensures efficient mixing of liquids so that at the outlet of the mixing chamber 0.13 m from the inlet, the flow will have a constant temperature of 12.4 ° C throughout the cross section mixer.

Consider another design of a water mixer with the following characteristics: a central channel for hot water with a temperature of t _Г = 80 ° C and a diameter of d = 0.1 m and a hot water feed rate of U _Г = 0.8 m / s. Cold water is supplied through a peripheral channel 3 with a diameter of D _CT = 0.4 m. The speed of cold water U _X = 1.1 m / s, temperature t _X = 5 ° C. Twisting vanes are installed in the channel at an angle of 30 ° to the installation axis (flow direction). The aspect ratio of the device: D / D _CT = 1.51, L = 1.71D, so that the mixing chamber 1 has a diameter D = 0.6 m and a length L = 1.03 m.

, в то время как 0,5·r_ст=0,1. Это означает, что смеситель не обеспечивает удовлетворительного смешения потоков воды и на выходе из него эпюра температуры по сечению потока будет крайне неоднородной.The calculation shows that for this device, the ratio

, while 0.5 · r _article = 0.1. This means that the mixer does not provide satisfactory mixing of the water flows and at the outlet from it the temperature plot along the flow cross section will be extremely heterogeneous.

, т.е. смеситель работает эффективно так, что температура воды в каждой точке выходного сечения смесителя постоянна и равна 8,5°C.When changing the angle of installation of the twisting blades from 30 to 45 °, the ratio

, i.e. The mixer works effectively so that the water temperature at each point of the outlet section of the mixer is constant and equal to 8.5 ° C.

Thus, due to the consistency between the geometric dimensions of the device and the intensity of the swirling flow, effective mixing of fluids is achieved. An additional effect is the reduction in the metal consumption of the mixer and the simplicity of its manufacture.

Claims (1)

A mixing device for fluid flows, comprising a mixing chamber, at least two coaxially placed cylindrical pipes connected to it, through which the fluid flows into the mixture, a swirler installed in at least one of the pipes, and a fitting for discharging the mixture, characterized the fact that the diameter of the mixing chamber is more than 1.7 times the diameter of the outer pipe, and the ratio between the length of the mixing chamber and its diameter is greater than or equal to 1.5, while the swirl is installed with the possibility of supplying twist flow to the input of the mixing chamber with an intensity determined from the ratio of the angular momentum of the fluid flow to the axial amount of motion of the flows at the inlet to the mixing chamber, which is equal to or greater than 0.7.

Images