RU2336130C1 - Infrasound gas-jet resonance radiator - Google Patents

Abstract

FIELD: mechanics.

SUBSTANCE: infrasound gas-jet resonance radiator incorporates a resonating cylindrical casing housing a coaxially arranged nozzle, con-rod, pipe with a reflector to translate and be locked therein. The aforesaid pipe and nozzle are arranged to move axially, while the aforesaid cylindrical resonating casing is plugged on the nozzle side. Note that a needle passes through the nozzle and the nozzle inlet accommodates a circular diaphragm rigidly attached to the needle. Note also that the aforesaid pipe arranged coaxially in the said cylindrical resonating casing is furnished with a through perforation on the pipe mouth side, while the aforesaid casing and pipe feature the dimensions allowing generating oscillations of a certain frequency.

EFFECT: wider operating range, reduced air consumption, simpler adjustments and higher efficiency of operation.

3 cl, 1 dwg

Description

The invention relates to the field of instrumentation, in particular to heat exchangers such as acoustic gas-jet devices for creating sound fields of discrete frequency in gas media in a wide frequency range, which can be used to intensify heat and mass transfer processes in gas media (combustion, mixing, coagulation, drying, etc. .), as well as for cleaning various active surfaces from loose and other deposits and is used in various industries, for example, for cleaning contaminated surfaces.

A known acoustic device for cleaning and drying active surfaces [1], which is based on the generation of intense acoustic fields. The effect is enhanced due to the backwater of the gas created by a special device made at the outlet end of the tube. However, the known device does not fully realize the conversion of the kinetic energy of the gas flow into acoustic energy, which reduces the intensification of heat and mass transfer processes.

Known gas-jet acoustic emitter, which relates to acoustic heat engineering [2]. It contains a flow resonator with a supersonic receiving part facing the nozzle, and a supersonic exhaust part and a channel connecting the exhaust and receiving parts of the resonator. However, the known device has a sufficiently low efficiency, as a result of which the low efficiency of heating the working fluid to the ignition temperature.

A known installation of sound cleaning [3], which contains ultrasonic piezoelectric transducers and a damper of spurious bending vibrations. The device can be used in various industries for cleaning contaminated surfaces. However, the known device has an uneven intensity of acoustic exposure over the entire surface intended for cleaning.

A known installation of ultrasonic cleaning [4], which differs from the known installation of sound cleaning [3] in that the damper of parasitic bending vibrations in it is made in the form of separate massive steel rings concentrically covering the emitters of the respective transducers, which allows for more uniform cleaning. However, the known device has a low cleaning intensity.

Known gas-jet resonant emitter [5], the closest to the proposed invention, adopted as a prototype. The emitter is designed for sound cleaning of various surfaces from industrial pollution and various deposits. The operation of the known device is based on the conversion of the kinetic energy of gas into acoustic energy in resonance mode.

The disadvantages of the known device are the complexity of the settings, a narrow operating range, high air consumption and some design features that affect the efficiency of the device, and the associated low cleaning level (due to the incomplete conversion of kinetic energy into acoustic).

The technical result of the claimed invention consists in simplifying settings, expanding the operating range, reducing air consumption and increasing the efficiency of the device, especially the quality of cleaning, due to the transition to a lower pressure.

The specified technical result is achieved in that a gas-jet resonant emitter comprising a resonating cylindrical body with a nozzle, rod, pipe coaxially placed therein, in which the reflector, pipe and nozzle are mounted with the possibility of longitudinal movement and fixation, are capable of relative axial movement, the resonant cylindrical body muffled from the nozzle side, a needle passes through the nozzle, and an annular diaphragm is mounted at the entrance to the nozzle, rigidly connected to the needle, in accordance with the invention has in the pipe coaxially placed in the resonant cylindrical body, through perforation from the inlet (mouth) side of the pipe cavity, and the ratio of the length of this pipe to its diameter is not less than 10: 1, while the resonant cylindrical body and the pipe have dimensions that are determined by the formula:

f = Ao / 4L,

where f is the frequency of the self-oscillating process;

Ao is the speed of sound in air (working gas-air);

L is the length of the pipe placed inside the resonating cylindrical body.

Such ratios of the dimensions of the cylindrical body and pipe make it possible to excite oscillations with a frequency below 50 hertz with a transition to the infrasonic region of radiation, which makes it possible to use a gas-jet resonant emitter as an infrasound.

In addition, in the inventive device, the resonant cylindrical body and the pipe located inside it have at least 4 meters dimensions of sound in air in air of 340 m / s.

In addition, in the inventive device, the resonant cylindrical body has a diffuser.

The operation of the inventive infrasonic gas-jet resonant emitter, which relates to powerful sound generators operating in a gaseous medium, is based on the conversion of the kinetic energy of a gas stream into acoustic energy.

The analysis of world-class technology in this area revealed that at present there is a tendency in the power system to use low-grade multi-ash fuels. In this regard, there are problems associated with the drift of convective surfaces of heat exchangers with ash deposits.

However, in addition to ash drift, an urgent problem for heat exchangers is the problem of drift by deposits of technological entrainment in the production of, for example, cement, steelmaking, as well as in a number of other industries. Therefore, the problem of improving the efficiency of heat exchangers and the quality of cleaning removal of ash deposits and deposits of technological entrainment from the surfaces of heat exchangers is of paramount importance.

The inventive device is intended to solve this problem for various industries.

The implementation of the claimed invention is illustrated in the drawing, which shows a diagram of a gas-jet resonant emitter in longitudinal section.

The gas-jet resonant emitter contains: a cylindrical-shaped resonance tube (1), which carries the function of a cylindrical body, which is open on one side and damped on the other by a bottom flange; a nozzle (2) extending from the bottom-flange along the axis of the resonance tube; inner tube (3); near the mouth of the resonant tube, there are through perforated holes in its walls; the inner tube is located along the axis of the resonance tube behind the nozzle at a certain distance from it and faces its mouth with the mouth; bottom reflector (4), drowning out the cavity of the inner pipe; a rod (5) connecting the bottom of the reflector with a mechanism (6) for moving the bottom of the reflector; a mechanism (7) for the relative movement of the nozzle and the inner pipe; retainer-holders (8) of the inner pipe in the resonance pipe; a diaphragm (9) installed at the entrance to the nozzle; a thin needle (10) connected to the diaphragm and placed along the nozzle axis with some departure from it.

The operation of the gas-jet resonant emitter is as follows.

A working gas (air) is supplied under pressure to a gas-jet resonant emitter through a nozzle 2, which flows a subsonic or supersonic jet onto the cavity of the inner pipe 3, interacts with the cavity; at certain parameters, a self-oscillating process characteristic of the first longitudinal vibration mode develops in the interaction of the jet with the cavity. In turn, the developing self-oscillating process contributes to the development of resonance in the resonance tube (1). A needle (10) in a gas-jet resonant emitter significantly facilitates the work of tuning the device to resonance, and in combination with the through holes (perforated) in the inner tube (3), it also makes resonance possible on subsonic jets.

Due to this design, the technical result of the device is achieved by using the effect of applying a powerful sound field of a discrete frequency to the main dusty gas stream (the so-called "sound cleaning").

The indicated effect is based on fracture, the mechanism of which is determined by the autogesionic parameters of deposits, in particular, by the tensile strength index. For some groups of bulk materials, tensile strength with a static application of the load in translation to the sound pressure level lies in the range from 125 to 140 dB (the effect of sound pressure on the deposits is dynamic in nature).

Bulk materials (industrial dust) according to their autogesic ability have their own classification [6]:

1. Non-sticking (free-flowing): open-hearth dust (production without oxygen blasting), blast furnace, sinter, converter (after-burning steel production), electric steel, coke, dolomite, fireclay, dunite, coal, limestone powder, fluorspar (dry production), soil.

2. Weakly sticking (easily flowing): open-hearth dust (production with oxygen blasting), magnesite (sampling after annealing furnaces), dolomite and chamotte (sampling after electrostatic precipitators), coal (with a fraction of 0-60 microns more than 30%), converter ( sampling after recovery boilers, afterburning scheme), limestone, gypsum (coarse building), ash from soda recovery boilers, fuel oil, Karaganda and Kuznetsk coal.

3. Medium sticking (medium flowing): open-hearth dust (production by intense oxygen blasting), magnesite (sampling behind a recovery boiler), coal (with a fraction of 0-60 microns more than 80%), dolomite (sampling behind an electrostatic precipitator), electric steel melting (large furnaces with intensive production), smelter.

To improve the efficiency and quality of the cleaning device claimed resonance tube has a cavity depth, which for infrasound frequency band is selected _and the ratio f = a / 4L; the nozzle exiting from the bottom-flange side along the axis of the resonance tube has a Mach number M _a = 1; the depth of the cavity of the inner tube for the infrasonic frequency range is selected by the ratio f _a = a / 4L and near the mouth there are through perforated holes in its walls.

Examples of experimental studies.

Example 1

On the basis of the gas-dynamic laboratory of St. Petersburg State University, an experimental test was performed of the gas-jet resonant emitter of the prototype device to identify its shortcomings and analyze the reasons for their further elimination in the claimed invention.

The test results showed that the adjustment of the determining parameters of the emitter to the resonance is significantly difficult mainly due to the geometric and operational parameters of the device, affecting the positive effect obtained from the resonance.

The following are the main geometric and operational parameters of a gas-jet resonant emitter that determine the setting for the resonance phenomenon:

- d _a - diameter of the outlet section of the nozzle;

- d ₁ - the diameter of the cavity of the inner pipe;

- d _and - the diameter of the thin needle (rod);

- d ₂ - the diameter of the cavity of the resonant tube;

- l ₀ - the departure of the nozzle with respect to the flange-bottom of the resonance tube;

- l _and - the needle stick out in relation to the nozzle exit (with a + or - sign);

- l ₁ - the distance between the nozzle exit and the mouth of the cavity of the inner pipe;

- L ₁ - the depth of the cavity of the inner pipe;

- L ₂ - the depth of the cavity of the resonant tube;

- θ _a is the half-angle of the nozzle;

- M _a is the geometric Mach number of the nozzle;

- n is the off-design of the supersonic stream;

- Re is the Reynolds number;

- γ is the ratio of specific heat capacities (γ = 1.4 for air).

The results of experimental studies have revealed that the determined parameter is the level of sound pressure at the fundamental (discrete) frequency of the resonant tube to simplify the tuning and increase the efficiency of the emitter.

An experimental assessment of the influence of the nozzle geometric Mach number M _a showed that the maximum sound pressure level at the fundamental frequency of the resonance tube remains constant at numbers M _a > 1, the range of variation of the off-design n of the supersonic jet is in the range from 1.2 to 1.4, t. e. Resonance in the device is manifested when supersonic jets from the nozzle flow in under-expansion modes.

Example 2

For the inventive infrasound gas-jet resonant emitter, the depth of the cavity of the resonant tube is optimal to choose equal to the length of the resonant tube of the infraphone (for example, equal to 4-4.5 m.). The ratio L ₂ / d ₂ (known from physics textbooks) ranges from 10 to 12.

From the determined parameter (the off-design of the jet n) and the known number M _a, we can proceed to determine the total pressure p ₀ in front of the nozzle. It should be borne in mind that maintaining the off-design of the jet n in the range from 1.2 to 1.4 (with an increase in the number М _a ) leads to an unjustified increase in the total pressure in front of the nozzle, which practically excludes the possibility of efficient operation of the claimed device and which is unacceptable substantiation of the choice of design of the inventive emitter. Therefore, when choosing a nozzle, it is easier to dwell on its design with a geometric number M _a = 1 (the so-called “nozzle-point”, that is, a nozzle with a diameter of the critical section equal to the diameter of the outlet section). With such an optimal choice of the determined parameters that affect the resonance effect, the parameter θ _a is excluded - the nozzle half-angle.

The determined needle parameter d _and (needle diameter) can be selected taking into account that it is always thin, constant and equal to 3-5 mm.

In the claimed device, when an air stream flows onto the cavity of the inner pipe, the self-oscillating process is realized with the adjustable parameters determining this process. This process has been studied in sufficient detail [7] and is interesting, in particular, because for relatively short pipes (L ₁ / d ₁ = 1-3), acoustic radiation with a pronounced discrete tone is observed. This effect is widely exploited in the construction of gas-jet emitters of the ultrasonic range

In [7], it was shown and justified the existence in the phenomenon of odd (2m + 1) longitudinal modes of oscillations at relatively deep cavities: m = 0, 1, 2, 3, ... m = 0 — the first longitudinal mode; m = 1 - third longitudinal mode, etc. The modes differ in the flow structure and frequencies, which form a nonequidistant spectrum in ratios close to f _i / f _a = (2 / m + 1). f _i is the mode frequency, f _a = a / 4L is the acoustic frequency of the tube cavity. This means that for very short cavities, “resonance” is observed when transverse or rotational vibrational modes occur in the phenomenon, and in the phenomenon of interaction of gas jets with deep cavities, the acoustic energy maxima shift to the region of turbulent pulsations.

In the claimed infrasound gas-jet resonant emitter, it is important that in the interaction of the air stream with the cavity of the inner tube, a self-oscillating process characteristic of the first longitudinal mode is observed. Then a resonance phenomenon can be expected in the external resonance tube, one of the conditions for it should be the ratio L ₁ / L ₂ ~ 1 (the depth of the cavity of the inner tube is close to the depth of the resonance tube).

Thus, the depth of the cavity of the inner tube for the upper boundary of the infrasound should be L ₁ ~ 4 m. With such deep cavities (L ₁ / d ₁ >> 10), the influence of the Reynolds number Re is significant on the process, this effect (negative) will increase when introduced into the design of the rod. The rod should be removed from the design of the resonant emitter and the influence of the Reynolds number Re should not be considered if the first longitudinal mode appears in the interaction of the jet with the cavity of the inner tube (this mode also exists in deeper cavities).

Taking into account the above remarks, the number of parameters determining the resonance phenomenon only slightly decreased. We give these parameters in a dimensionless form:

- относительный диаметр выходного сечения сопла;-

- the relative diameter of the output section of the nozzle;

- относительный диаметр полости внутренней трубы;-

- the relative diameter of the cavity of the inner pipe;

- относительный вылет сопла;-

- relative overhang of the nozzle;

- относительный вылет иглы;-

- relative reach of the needle;

- относительная глубина полости внутренней трубы;-

- the relative depth of the cavity of the inner pipe;

- полное давление перед соплом (р_н - наружное давление).-

- total pressure in front of the nozzle (p _n - external pressure).

в явлении существуют протяженные зоны, в которых искомый уровень звукового давления остается практически постоянным. Но даже в упрощенном варианте анализ влияния определяющих параметров на резонанс может быть дан лишь на основе объемного и трудоемкого экспериментального исследования.The search for local maxima of the sound pressure level at the fundamental frequency of the resonance tube during the resonance phenomenon (depending on the above parameters) was significantly simplified, since it turned out that the parameter

there are extended zones in the phenomenon in which the desired sound pressure level remains almost constant. But even in a simplified version, an analysis of the influence of determining parameters on resonance can be given only on the basis of a voluminous and laborious experimental study.

.) Уровень звукового давления на основной частоте резонансной трубы растет с увеличением скорости истечения дозвуковой струи, а с переходом к сверхзвуковому истечению практически остается постоянным.In the claimed infrasound gas-jet resonant emitter, resonance at the main acoustic frequency of the resonant tube is achieved when both subsonic and supersonic jets flow from the nozzle. (Moreover, if we take into account the resonance zone for the total pressure in front of the nozzle, the zone starts from low subcritical pressure in front of the nozzle to full pressure

.) The sound pressure level at the fundamental frequency of the resonance tube grows with an increase in the subsonic jet outflow rate, and with the transition to supersonic outflow it remains practically constant.

This result is achieved by the following design changes:

- the nozzle is made with the geometric Mach number of the nozzle M _a = 1, i.e. a so-called nozzle-point is used, in which there is no expanding part beyond the critical section (the diameter of the critical section of the nozzle is equal to the diameter of the output section of the nozzle);

- a thin needle connects to the diaphragm, passes through the nozzle along its axis and can go beyond the nozzle a certain distance beyond the nozzle exit;

- the inner pipe is made with through holes in the walls of the pipe near the mouth of its cavity;

- the mouth of the cavity (there is an inlet in the cavity);

- the depth of the cavity of the resonant tube is calculated by its main acoustic frequency; this frequency is the frequency of the infrasound range. (It is possible to build a low-frequency resonant emitter with a fundamental frequency in the frequency range above the infrasound frequency, up to a frequency of ~ 100 Hz.)

In laboratory conditions, due to existing restrictions, a resonance tube with a diameter of d ₂ = 200 mm and a cavity depth of L ₂ = 2000 mm was chosen. The main acoustic frequency expected at resonance for this tube may be less than 40 Hz, i.e. the frequency is close enough to the infrasonic range.

Example 3

During experimental studies, sound pressure levels were measured using the VSHV-003 sound level meter, the microphone was installed at a distance of 6 m from the emitters. The experimental box used was a concrete room measuring 16 × 9 × 6 m ³ . In the process of experimental studies were carried out:

- Oscillographic recording of temporary signals of sensors recording pressure changes in the cavities of the internal and resonant pipes;

;- oscillographic recording of microphone signals in an octave with a geometric mean frequency f _cp = 31.5 Hz at a resonance depending on pressure

;

.- oscillographic recording of pressure pulsations in the cavity of the inner pipe depending on the pressure

.

It should be noted that the choice of the length of the resonance tube is also due to the possibility of acoustic measurements in the infrasonic range.

In table 1, for absolutely equal values that determine the resonance parameters, the octave distribution of sound pressure levels for a gas-jet resonant emitter (GRI) and a gas-jet (no resonance tube) emitter (GI) is shown. In this case, in the interaction of the air stream with the cavity of the pipe for HI or with the cavity of the inner pipe for HMI, the same process is observed in the first longitudinal mode.

Table 1 f _cp , Hz 31.5 63 125 250 500 1000 2000 4000 8000 GI I, dB 112 105 one hundred 113 113 113 118 94 113 GRI I, dB 129.5 119 97 119 118 115 115 94 104

Table 1 shows the parameters: - f _cp - geometric mean octave frequency;

- I - sound pressure level in this octave.

The data presented in Table 1 show that a gas-jet emitter (GI) with a deep cavity has a maximum of acoustic energy, despite the fact that in the interaction of the jet with the cavity there is a self-oscillating process in the first longitudinal mode (process frequency ~ 37 Hz; pressure sensor readings) , is shifted to the high-frequency region of the spectrum of the acoustic signal. In the new scheme, the scheme of a gas-jet resonant emitter, a pronounced maximum of acoustic energy is observed in the first octave (f _cp = 31.5 Hz). The readings of the pressure sensors also indicate that processes occur at the same frequency of ~ 37 Hz in the cavities of the resonant and inner tubes. Thus, the conducted research in practice confirms theoretical calculations and substantiation of the functionality of the claimed invention. In practice, in a resonant tube, a process can be excited at a frequency of any overtone of the same if the frequency of the longitudinal mode of the gas-jet emitter coincides with this frequency. In this sense, a jet with an internal tube placed in a resonant tube acts as a self-oscillating energy source.

The advantages of using the claimed device in the “sound” cleaning range are based on the following provisions: infrasound generators have a spherical radiation pattern, and the sound therefore almost reaches all hidden and remote places in the voiced volume; in infrasound, the fraction of reflected sound energy is much higher when scoring internal volumes with insulated walls; the sound wavelength for infrasound is comparable in most cases with the characteristic dimensions of technological devices.

The claimed infrasound gas-jet resonant emitter can be used, taking into account the results of testing this design in laboratory and industrial conditions, both for “sound” cleaning and for intensification of heat and mass transfer processes in gas environments by sound waves; as well as for acoustic coagulation of aerosols (in particular, as an effective fire extinguishing agent in closed and semi-closed volumes, where it is necessary to extinguish the fire and coagulate aerosols in a short time); as a psychotropic weapon in the fight against rodents and mice in agriculture (with sound irradiation of large areas), etc.

References

1. Description of the invention to the copyright certificate (SU) No. 1568340 A1.

2. Application RU No. 92011173 A.

3. RF patent No. 2175274.

4. RF patent No. 2181635.

5. Description of the invention to the copyright certificate (SU) No. 1587765 A1 (prototype).

6. Schelokov Y.M., Avvakumov A.M., Sazykin Yu.K. Cleaning the heating surfaces of waste heat boilers. - M.: Energoatomizdat, 1987 .-- 223 p.

7. Poluboyarinov AK, Tsvetkov AI. Experimental study of longitudinal modes during the Hartmann // Applied aerodynamics and thermal processes. - Novosibirsk: Publishing House ITPM SB AS USSR, 1980. p. 99-112.

Claims (3)

1. An ultrasonic gas-jet resonant emitter comprising a cylindrical resonant body with a nozzle, rod, pipe coaxially placed in it and a reflector, a pipe and a nozzle mounted with the possibility of longitudinal movement and fixation thereof, with relative axial movement, the resonant cylindrical housing is muffled from the nozzle side , a needle passes through the nozzle, and an annular diaphragm is mounted rigidly connected to the needle at the entrance to the nozzle, characterized in that the pipe is coaxially placed in the resonating m cylindrical body, has through perforation from the side of the mouth of the pipe cavity, the resonating cylindrical body and pipe have dimensions that allow you to excite vibrations with a frequency below 50 Hz with the transition to the infrasonic region of radiation and are determined by the formula f = A _o / 4L, where f is the frequency of the self-oscillating process; And _o is the speed of sound in air (working gas-air); L is the length of the pipe placed inside the resonating cylindrical body. 2. The ultrasonic gas-jet resonant emitter according to claim 1, characterized in that the resonating cylindrical body and the pipe located inside it have a sound speed in air of 340 m / s, dimensions of at least 4 m. 3. The ultrasonic gas-jet resonant emitter according to claim 2, characterized in that the resonant cylindrical body has a diffuser.