CN108853855B - Pneumatic excitation sound fire extinguishing device with cooling effect - Google Patents
Pneumatic excitation sound fire extinguishing device with cooling effect Download PDFInfo
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Abstract
A pneumatic excitation sound fire extinguishing device with a cooling effect comprises an air inlet and a nozzle connected to the outlet of the air inlet. The air inlet end of the air inlet channel is provided with a propeller, and the propeller obtains high-pressure airflow through rotation; and a disturbance device is arranged in the air inlet channel, low-frequency sound wave disturbance is carried out on the high-pressure air flow, the high-pressure air flow with disturbance is generated, and the high-pressure air flow with disturbance enters the nozzle from the outlet of the air inlet channel. The nozzle has a convergent section which is projected by converging the high pressure air stream entering the nozzle at a greater velocity, thereby reducing the temperature of the air stream projected from the nozzle outlet. The sound wave disturbance and the cooling are adopted to synchronously realize the sound cooling and fire extinguishing, and the re-burning can be effectively avoided.
Description
Technical Field
The invention relates to the technical field of acoustic application, in particular to a pneumatic excitation sound fire extinguishing device with a cooling effect.
Background
Fire has always been one of the major disasters threatening the public safety and social development of people. The traditional fire extinguishing modes are various, but with the expansion of user scale and the increase of fire types, the traditional fire extinguisher has many problems in application.
(1) Traditional gas fire extinguishing systems, such as the halon series, use carbon dioxide to extinguish fires, which is often used in a number of special locations for electrical equipment and the like. However, malfunction of the gas fire extinguishing system in the enclosed space threatens the life safety of personnel in the fire.
(2) Most of traditional fire extinguishers are high-pressure containers, so that the traditional fire extinguishers are high in storage conditions, cannot be extruded or collided, and are easy to expand and explode at high temperature.
(3) Traditional fire extinguishers cannot be used in aerospace systems. The fire extinguishing agent used by the traditional fire extinguisher causes pollution and damage to the aerospace on-orbit system. In addition, the fire extinguishing agent in the space microgravity environment belongs to a floating state, and cannot be attached to flame, so that the fire extinguishing effect cannot be realized.
In view of the above problems, researchers have conducted research on sound fire extinguishment. The earliest work utilized shock waves to extinguish fires. The method digests fuel by way of rapid combustion so that combustion cannot be self-sustained. Similar to explosion extinguishment, this method has the disadvantage that the shock waves also severely affect surrounding objects while extinguishing the fire.
Related researchers have proposed ultrasonic fire extinguishing methods that do not require fire extinguishing agents, do not produce fire-extinguishing carryover, and do not introduce environmental noise. The high-frequency sound wave causes the high-frequency vibration of the flame surface, and the fire extinguishing effect can be achieved only by high vibration amplitude.
Related studies have shown that the flame acts like a low pass filter and the high frequency excitation has less effect on its performance, see the iean university of transportation patent for an ultrasonic fire extinguisher (application No.: 2016102822245. inventor: wei yan, yangyi, liushenghua, ludonghua).
Experiments and theoretical researches show that the low-frequency sound waves have obvious influence on the flame surface. In fact, for air, the resonance frequency of oxygen is 60Hz and the resonance frequency of nitrogen is lower than 60 Hz. The relevant literature indicates that the resonant frequency of air is in the range of 20-50 Hz. When low-frequency sound waves act on the flame, the resonance characteristic enables the air to vibrate and strengthen, the movement range of the air is increased, the sparse and dense distribution of oxygen is strengthened, and the flame is extinguished at the sparse part due to insufficient oxygen content. On the other hand, the sound pressure disturbance will disperse the oxygen molecules around the flame, block the oxygen supply channel for flame combustion, and thus extinguish the flame.
The reason why the low-frequency sound wave can effectively extinguish the fire is that the response of the flame to disturbance acts like a low-pass filter through analysis by the courage team at the national defense science and technology university. The low frequency sound wave makes unstable burning strengthen, and the flame face forms large-scale fold and stretches, and when reaching a certain degree, the flame face takes place to collapse, leads to flame to extinguish. The raised flame surface enhances the heat conduction effect, thereby reducing the temperature of the flame surface and leading the combustion to be incapable of self-sustaining. On the other hand, the longer wavelength of low frequency sound waves results in longer duration of low pressure region than high frequency sound waves, and at a constant density, p ═ ρ R according to the ideal gas state equation0T(R0Gas constant) it can be seen that the temperature of the low-pressure zone is constant at a certain density pT also changes.
Aiming at a low-frequency fire extinguishing mode, the United states department of Defense Advanced Research Program (DARPA) in 2012 successfully extinguishes fire by using two huge sound wave transmitting tubes, but the equipment is heavy and complex to operate.
In 2012, several students at george, meisen university in the united states created a "hand fire extinguisher". The method utilizes a low-frequency sound wave mode to extinguish fire, and researches show that when the sound wave frequency is 30-60Hz, the sound wave has great influence on flame and the fire extinguishing effect is good. The research of the flood transport team of the university officer of east China shows that the sound wave with the sound wave frequency of 20-80Hz can effectively realize the fire extinguishing effect. According to the research results, the officer and the flood transportation team apply for the invention and patente a low-frequency sound wave fire extinguisher (application number: 2016102840597, inventor: luohao, official flood transportation, Zhao Dong Yu, Wan Xue, Lu Bo Xin, in harmony). Shanghai Hai Peng Intelligent science and technology development Co., Ltd also applied for a practical and novel patent based on similar principles, namely an intelligent portable sound wave fire extinguisher (application No. 201620176718.0, inventor: Liuyu, Wuming Hua). The Shandong science and technology university applies for a novel practical low-frequency sound wave fire extinguisher (application number: 2015206801107, inventor: Korean Baokun, Yan Chenghui, Evereijie, Suwei).
The above patent all utilizes low frequency sound wave influence flame face structure to reach fire extinguishing effect. However, the above method can only be used for small flames, and re-ignition is difficult to avoid. The above method is problematic for large flames. Larger flames raise the ambient air temperature and even after the flame extinguishes, there is a possibility that the flame reignites as the ignition point is reached. Therefore, it is necessary to lower the temperature simultaneously while extinguishing the fire with the low frequency sound wave.
On the other hand, because the frequency used for sound fire extinguishing is below 100Hz, the energy conversion efficiency is low for the current mode of electrically driving the horn to obtain sound, and the volume and the weight of the horn are large, which is not beneficial to portable fire extinguishing application occasions.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a pneumatic excitation sound fire extinguishing device with a cooling effect.
In order to achieve the technical purpose, the invention adopts the following specific technical scheme:
the invention relates to a method for obtaining low-frequency sound waves by utilizing a pneumatic method and obtaining low temperature through a nozzle.
Specifically, the invention provides a pneumatic excitation sound fire extinguishing device with a cooling effect, which comprises an air inlet and a nozzle connected to the outlet of the air inlet, wherein the nozzle and the air inlet are hermetically connected and communicated with each other. The air inlet end of the air inlet channel is provided with a propeller, and the propeller obtains high-pressure airflow through rotation. A disturbance device is arranged in the air inlet channel, the disturbance device carries out low-frequency sound wave disturbance on the high-pressure air flow in the air inlet channel to generate disturbed high-pressure air flow, and the disturbed high-pressure air flow enters the nozzle through an outlet of the air inlet channel; the nozzle is provided with a contraction section which enables the high-pressure airflow entering the nozzle to obtain higher speed in a contraction mode and reduces the temperature of the airflow to be sprayed out of the nozzle outlet. The nozzle can be a subsonic shrinkage nozzle or a Laval supersonic nozzle according to specific conditions.
The propeller can adopt a conventional electrically-driven propeller, and comprises more than 2 blades, wherein the more than 2 blades are uniformly distributed on a central rotating shaft of the propeller, the central rotating shaft is driven by a motor to drive all the blades on the central rotating shaft to synchronously rotate, and the rotating speed of the propeller is set to be n.
The disturbing device comprises a plurality of disturbing vanes (not limited to 4 disturbing vanes shown in figure b) distributed in a radial and circumferential manner, and the shape of the disturbing vanes is not limited. Each disturbing blade is connected with power, and each disturbing blade can rotate around a rotating shaft of each disturbing blade (for example, each blade rotates around a central shaft of each disturbing blade) under the driving of the power according to an angular speed of omega 2 pi f, so that frequency disturbance with frequency f is obtained, low-frequency sound wave disturbance of high-pressure air flow in an air inlet channel is realized, and the disturbed high-pressure air flow is generated.
The scheme is that the propeller and the disturbance device are separately and independently arranged. In the invention, the propeller and the disturbance device can also be integrated into a whole, the propeller comprises a plurality of blades which are distributed on the central rotating shaft of the propeller, and the central rotating shaft is driven by a motor to drive all the blades on the central rotating shaft to synchronously rotate so as to obtain high-pressure airflow; each blade is respectively provided with power, namely each blade is respectively connected with independent power, and each blade can rotate around a rotating shaft on the blade under the driving of the power, so that frequency disturbance with the frequency of f is obtained, low-frequency sound wave disturbance on high-pressure air flow is realized, and the high-pressure air flow with disturbance is generated.
It should be noted that the length and shape of the air inlet are not constrained and are configured according to the application scenario. The larger the radius of the air inlet channel is, the longer the length of the blade of the corresponding propeller is, and the pressure p of high-pressure air flow obtained by the rotation of the propelleraThe larger. The larger the length and width of a disturbance blade of the disturbance device are, the obtained pressure disturbance p'aThe larger.
Pressure p of high pressure air flow obtained by rotation of propelleraCan be obtained by the following formula
pa＝Cpρ0n2D4. (1)
In the above formula, CpThe coefficient of tension is determined by the geometrical parameters of the propeller; n is the rotational speed at which the propeller rotates; rho0Is the density of the air flow at the inlet of the air inlet; d is the diameter of the propeller.
The disturbance device realizes low-frequency sound wave disturbance on the high-pressure airflow, so that the airflow volume and the pressure of the high-pressure airflow flowing through the disturbance device are periodically changed to form low-frequency noise, and the generated pressure disturbance is p'a。
Let the radius at the nozzle inlet be RA，RCThe radius of the outlet of the nozzle is the radius of the outlet of the nozzle, and the nozzle accelerates the high-pressure airflow in a contraction mode, so that the high-pressure airflow with higher speed is obtained. The pressure and temperature at the inlet of the nozzle are respectively denoted as pA(＝pa+p′a) And TAThe flow velocity of the air flow is VA. The energy enthalpy h at the inlet of the nozzleAComprises the following steps:
wherein γ represents the specific heat ratio; c. CpRepresents the constant pressure heat capacity; rhoARepresents the density at the nozzle inlet; c. CARepresenting the speed of sound at the nozzle inlet.
Since the flow of the gas stream is isentropic, the energy is not dissipated in the nozzle and the enthalpy of the energy is not changed, for which purpose the total enthalpy can be defined
h0＝hA (3)
The gas in the nozzle is ideal gas, so that the total pressure (p) of the system can be obtained under the concept of total enthalpy0) Total temperature (T)0) And velocity of stagnant sound (c)0)
Where ρ is0Representing the corresponding density at the total system pressure;
according to the isentropic ideal gas state equation, the pressure p, the temperature T and the Mach number M at any position in the nozzle can be characterized as
The temperature at any location in the nozzle can be characterized as
It is known that as the nozzle flow mach number increases, the corresponding temperature decreases; from equation (6), the ratio of the temperature at the nozzle inlet to the temperature at the nozzle outlet can be characterized as
Wherein the pressure at the nozzle outlet is equal to the ambient pressure PEnvironment(s)Coincidence, i.e. PC＝PEnvironment(s)The Mach number M at the nozzle exit can be obtained from equation (5)CIs composed of
When Mach number M at the nozzle outlet is calculated by equation (8)CWhen the flow velocity is less than 1, the airflow at the outlet of the nozzle flows in a subsonic velocity mode, at the moment, the nozzle adopts a subsonic velocity contraction type nozzle, the radius from the inlet of the nozzle to the radius from the outlet of the nozzle is gradually reduced, and along with the gradual reduction of the radius of the nozzle from the inlet of the nozzle to the outlet of the nozzle, namely the continuous reduction of the cross section area of the nozzle, the increase of the airflow velocity in the nozzle and the reduction of the airflow pressure and temperature in the nozzle can be brought.
Substituting equation (8) into equation (7) can obtain a temperature ratio of nozzle inlet to nozzle outlet of
Mach number M at the nozzle outlet when calculated from equation (8)CWhen the flow rate is more than 1, the flow Mach number at a certain cross section of the nozzle is 1, and the cross section is defined as a critical cross section; the nozzle adopted at the moment is a Laval supersonic nozzle, the middle section of the Laval supersonic nozzle is contracted, and the radius of the inlet of the nozzle is RARadius at nozzle outlet is RCThe critical cross section, i.e. the position of the minimum cross section in the middle of the nozzle, has a corresponding cross section radius of RB，RAGreater than RB，RCGreater than RB. The radius of the Laval supersonic nozzle from the nozzle inlet to the minimum cross section of the nozzle middle part is gradually reduced, and the radius of the minimum cross section of the nozzle middle part to the radius of the nozzle outlet is gradually increased. The change rule of the radius of the nozzle in the nozzle structure is not restricted. Such as the radius from the nozzle inlet to the smallest cross-section in the middle of the nozzleThe radius from the minimum cross section of the middle part of the nozzle to the outlet of the nozzle is increased linearly, which is not limited in practical application.
For Laval supersonic nozzle, according to the conservation of mass in the flow process, the radius R of the inlet of the nozzleAThe following mass conservation formula exists at the radius R of any cross section of the nozzle
Wherein, VA、ρAFlow velocity and density at the nozzle inlet, respectively; v and p are respectively the flow speed and the density of any cross section of the nozzle
Defining the propagation velocity of the sound wave at the entrance of the nozzle and at any cross section of the nozzle as cAAnd c, then exist
At critical cross section, corresponding to a Mach number MB1, the radius R of the critical cross sectionBAnd RAThe relationship of (c) can be characterized as:
equation (5) taken into equation (12) may result in the following equation
Radius R at the nozzle outletCRelative to the critical cross-sectional radius RBIs as follows
At this time, the temperature T at the nozzle outletCAnd the temperature T at the nozzle inletAThe relationship of (c) is shown in equation (7).
Compared with the subsonic flow, the exit gas flow in supersonic flow has Mach number exceeding 1 limit, and can obtain better low temperature.
The invention has the following beneficial effects:
the technical scheme of the invention can solve two technical problems faced by the existing sound fire extinguishing:
(1) the electrodynamic transducer has a low efficiency of conversion into low frequency sound waves (below 100 Hz), and the volume and weight of the device do not correspond to portable applications.
(2) The traditional sound fire-extinguishing equipment does not have a cooling effect, the occurrence of re-combustion cannot be avoided, and the practical range is restricted.
The portable gas stove is light in structure, convenient to carry, good in cooling effect and capable of effectively avoiding re-combustion.
Drawings
FIG. 1 is a schematic structural view of the present invention;
in fig. 1: 1. an air inlet channel; 2. a nozzle; a. a propeller; b. a perturbation device;
FIG. 2 is a schematic view of a propeller and a perturbation device; wherein (a) is a schematic diagram of the structure and the movement mode of the propeller; (b) is a schematic diagram of the structure and the motion mode of the perturbation device.
FIG. 3 is a schematic view of the structure and movement of the propeller and the perturbation device integrated together;
FIG. 4 is a schematic view of the construction of a subsonic convergent nozzle;
FIG. 5 is a schematic diagram of the structure of a fire suppression apparatus provided by the present invention in a subsonic flow condition;
FIG. 6 is a schematic view of the structure of a Laval supersonic nozzle;
fig. 7 is a schematic structural diagram of a fire extinguishing apparatus provided by the present invention in a supersonic flow condition.
Detailed Description
In order to make the technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention relates to a method for obtaining low-frequency sound waves by utilizing a pneumatic method and obtaining low temperature through a nozzle.
Referring to fig. 1, a schematic structural diagram of an embodiment of the present invention includes an air inlet 1 and a nozzle 2 connected to an outlet of the air inlet, where the nozzle 2 and the air inlet 1 are hermetically connected and communicated with each other. The air inlet end of the air inlet channel 1 is provided with a propeller a, and the propeller a obtains high-pressure air flow through rotation. A disturbance device b is arranged in the air inlet channel 1, the disturbance device b carries out low-frequency sound wave disturbance on high-pressure air flow in the air inlet channel to generate disturbed high-pressure air flow, and the disturbed high-pressure air flow enters the nozzle 2 through an outlet of the air inlet channel; the nozzle 2 has a constriction section which makes the high-pressure air flow entering the nozzle 2 obtain higher speed in a constriction mode and is sprayed out from the nozzle outlet after the temperature of the air flow is reduced. The whole air inlet channel, the propeller and the disturbance device arranged in the air inlet channel form a pneumatic sound production part of the pneumatic excitation sound fire extinguishing device with the cooling effect. The nozzle 2 can be a subsonic convergent nozzle or a Laval supersonic nozzle according to specific conditions.
The propeller can adopt a conventional electrically-driven propeller, and comprises more than 2 blades, wherein the more than 2 blades are uniformly distributed on a central rotating shaft of the propeller, the central rotating shaft is driven by a motor to drive all the blades on the central rotating shaft to synchronously rotate, and the rotating speed of the propeller is set to be n.
The disturbing device comprises a plurality of disturbing vanes (not limited to 4 disturbing vanes shown in figure b) distributed in a radial and circumferential manner, and the shape of the disturbing vanes is not limited. Each disturbing blade is connected with power, and each disturbing blade can rotate around a rotating shaft of each disturbing blade (for example, each blade rotates around a central shaft of each disturbing blade) under the driving of the power according to an angular speed of omega 2 pi f, so that frequency disturbance with frequency f is obtained, low-frequency sound wave disturbance of high-pressure air flow in an air inlet channel is realized, and the disturbed high-pressure air flow is generated.
It should be noted that the length and shape of the air inlet are not constrained and are configured according to the application scenario. The larger the radius of the air inlet channel is, the larger the length of the blade of the corresponding propeller is, and the larger the pressure intensity of the high-pressure air flow obtained by the rotation of the propeller is.
In fig. 2(a), the design of the propeller structure will affect the airflow pressure in the air intake channel, and thus affect the airflow speed, and the propeller structure can be designed by the propeller lift formula (the propeller lift formula is more complete, refer to formula (1)), and the designed pressure is determined according to the specific application background.
In the disturbance device in fig. 2(b), each disturbance blade rotates around its own rotation axis, and in order to obtain strong pressure disturbance, the length and width of the disturbance blade are large, and the disturbance frequency is determined by ω 2 π f.
The pressure of the high-pressure air flow obtained by the rotation of the propeller can be obtained by the following formula
pa＝Cpρ0n2D4. (1)
In the above formula, CpThe coefficient of tension is determined by the geometrical parameters of the propeller; n is the rotational speed at which the propeller rotates; rho0Is the density of the air flow at the inlet of the air inlet; d is the diameter of the propeller.
In fig. 2(b), the disturbing device includes a plurality of disturbing blades distributed in a radial circumferential direction, each disturbing blade is connected with power, and each disturbing blade can rotate around its own rotation axis (for example, each blade rotates around its own central axis) under the driving of power according to an angular velocity of ω ═ 2 π f, so that the airflow volume and the pressure of the high-pressure airflow flowing through the disturbing device are changed periodically, and low-frequency noise is formed, i.e. the pressure disturbance is p'a。
The rotation of the propeller and the rotation of the blades of the disturbance device can be driven in a motor mode, so that electric energy is directly converted into mechanical energy.
In the scheme, the propeller and the disturbance device are separately and independently arranged, and further, the propeller and the disturbance device can be integrated together, as shown in fig. 3. The propeller comprises a plurality of blades, the blades are distributed on a central rotating shaft of the propeller, and the central rotating shaft is driven by a motor to drive all the blades on the central rotating shaft to synchronously rotate at the rotating speed of n so as to obtain high-pressure airflow. Each blade is respectively provided with power, namely each blade is respectively connected with independent power, and each blade can rotate (namely autorotation) around a rotating shaft on the blade under the driving of the power, so that frequency disturbance with the frequency of f is obtained, low-frequency sound wave disturbance on high-pressure air flow is realized, and the high-pressure air flow with the disturbance is generated.
Let the radius at the nozzle inlet be RA，RCThe radius of the outlet of the nozzle is the radius of the outlet of the nozzle, and the nozzle accelerates the high-pressure airflow in a contraction mode, so that the high-pressure airflow with higher speed is obtained. The pressure and temperature at the inlet of the nozzle are respectively denoted as pA(＝pa+p′a) And TAThe flow velocity of the air flow is VA. The energy enthalpy h at the inlet of the nozzleAComprises the following steps:
wherein γ represents the specific heat ratio; c. CpRepresents the constant pressure heat capacity; rhoARepresents nozzle inlet density? c. CARepresenting the speed of sound at the nozzle inlet.
Since the flow of the gas stream is isentropic, the energy is not dissipated in the nozzle and the enthalpy of the energy is not changed, for which purpose the total enthalpy can be defined
h0＝hA (3)
The gas in the nozzle is ideal gas, so that the total pressure (p) of the system can be obtained under the concept of total enthalpy0) Total temperature (T)0) And velocity of stagnant sound (c)0)
Where ρ is0Total pressure of the systemThe corresponding density.
According to the isentropic ideal gas state equation, the pressure p, the temperature T and the Mach number M at any position in the nozzle can be characterized as
Further, the temperature at any location in the nozzle may be characterized as
It can be seen that as the nozzle flow mach number increases, the corresponding temperature decreases. According to the above formula, the ratio of the temperature at the nozzle inlet (at A) to the nozzle outlet (at C) can be characterized as
Then increasing the mach number M at the nozzle exit may be usedCTo achieve a temperature T of the gas stream at the nozzle outletCIs reduced. To achieve Mach number M at the nozzle outletCThe increase in cross-section can be obtained by using a varying cross-section.
First consider the Mach number M at the nozzle exit (at C)C. The pressure at the nozzle outlet (C) is in accordance with the external pressure (external pressure P)Environment(s)Is defined as PEnvironment(s)) I.e. PC＝PEnvironment(s). In this case, the Mach number M at the nozzle outlet can be obtained from the formula (5)CIs composed of
Mach number M at nozzle exitCWhen the flow rate is less than 1, the air flow at the outlet of the nozzle flows at subsonic speed, at the moment, the nozzle adopts a subsonic speed contraction-shaped nozzle, and the inlet of the nozzleThe radius decreases gradually to the exit radius of the nozzle as shown in figure 4.
Substituting equation (8) into equation (7) yields a temperature ratio of nozzle inlet (at A) to nozzle outlet (at C) of
Fig. 5 is a schematic view of the structure of the fire extinguisher in the subsonic condition.
In the subsonic velocity, the radius of the inlet of the nozzle decreases gradually from the radius of the outlet of the nozzle, which results in an increase in the velocity of the gas flow and a decrease in the pressure and temperature as the radius decreases, i.e. the cross-sectional area decreases. When the critical value is reached, i.e. the flow mach number at a certain cross section of the nozzle is 1, the velocity of the gas flow will reach sonic velocity, defining the cross section as the critical cross section. Passing through the critical cross-section will enter supersonic flow, where the nozzle needs to be added with an expansion duct in order to obtain a greater velocity, i.e. increasing the cross-sectional area of the nozzle after the critical cross-section will cause an increase in the velocity of the gas flow, a decrease in the pressure and a decrease in the temperature.
Mach number M at the nozzle outlet when calculated from equation (8)CAbove 1, the flow mach number is 1 at a certain cross section of the nozzle, which is defined as the critical cross section. At this time, the nozzle is a Laval supersonic nozzle, and as shown in fig. 6, the middle section of the Laval supersonic nozzle is contracted, and the radius at the inlet of the nozzle is RARadius at nozzle outlet is RCThe critical cross-section, i.e. the position of the minimum cross-section B in the middle of the nozzle in FIG. 6, corresponds to a cross-sectional radius RB。RAGreater than RB，RCGreater than RB. The radius of the Laval supersonic nozzle from the nozzle inlet to the minimum cross section of the nozzle middle part is gradually reduced, and the radius of the minimum cross section of the nozzle middle part to the radius of the nozzle outlet is gradually increased. The change rule of the radius of the nozzle in the nozzle structure is not restricted. For example, the radius between the inlet of the nozzle and the minimum cross section of the middle part of the nozzle is reduced linearlyThe radius from the minimum cross section of the middle part of the nozzle to the outlet of the nozzle is increased linearly, which is not limited in practical application.
For Laval supersonic nozzle, according to the conservation of mass in the flowing process, the radius R of the nozzle inlet (A position)AThe following mass conservation formula exists at the radius R of any cross section of the nozzle
Wherein, VA、ρAFlow velocity and density at the nozzle inlet a, respectively; v and p are respectively the flow speed and the density at any cross section of the nozzle.
Defining the propagation velocity of the sound wave at the nozzle inlet (A) and at any cross section of the nozzle as cAAnd c, then exist
At the critical cross section B, the Mach number is MB1, the radius R of the critical cross section BBAnd RAThe relationship of (c) can be characterized as:
equation (5) taken into equation (12) may result in the following equation
Radius R at the nozzle outletCRelative to the critical cross-sectional radius RBIs as follows
At this time, the temperature T at the nozzle outletCAnd the temperature T at the nozzle inletAIs represented by the following formula:
compared with the subsonic flow, the exit gas flow in supersonic flow has Mach number exceeding 1 limit, and can obtain better low temperature. The structure of the pneumatic sound fire extinguishing device under supersonic flow is shown in figure 7.
In summary, although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the invention.
Claims (4)
1. A pneumatic excitation sound fire extinguishing apparatus with a cooling effect, characterized in that: the device comprises an air inlet and a nozzle connected to the outlet of the air inlet, wherein the nozzle and the air inlet are hermetically connected and communicated with each other; the air inlet end of the air inlet channel is provided with a propeller, and the propeller obtains high-pressure airflow through rotation; a disturbance device is arranged in the air inlet channel, the disturbance device carries out low-frequency sound wave disturbance on the high-pressure air flow in the air inlet channel to generate disturbed high-pressure air flow, and the disturbed high-pressure air flow enters the nozzle through an outlet of the air inlet channel; the nozzle is provided with a contraction section, and the contraction section enables the high-pressure airflow entering the nozzle to obtain higher speed in a contraction mode and reduces the temperature of the airflow and then the airflow is sprayed out from the nozzle outlet; the propeller and the disturbance device are integrated into a whole, the propeller comprises a plurality of blades, the blades are distributed on a central rotating shaft of the propeller, the central rotating shaft is driven by a motor to drive all the blades on the central rotating shaft to synchronously rotate so as to obtain high-pressure airflow, and the rotating speed of the propeller is set to be n; each blade is respectively provided with power, namely each blade is respectively connected with independent power, and each blade can be driven by the power to surround the bladeThe rotating shaft rotates at an angular speed of omega 2 pi f, so that frequency disturbance with the frequency f is obtained, low-frequency sound wave disturbance on the high-pressure airflow is realized, and the high-pressure airflow with disturbance is generated; pressure p of high pressure air flow obtained by rotation of propelleraObtained by the following formula
pa＝Cpρ0n2D4. (1)
In the above formula, CpThe coefficient of tension is determined by the geometrical parameters of the propeller; n is the rotational speed at which the propeller rotates; rho0Is the density of the air flow at the inlet of the air inlet; d is the diameter of the propeller;
the disturbance device realizes low-frequency sound wave disturbance on the high-pressure airflow, so that the airflow volume and the pressure of the high-pressure airflow flowing through the disturbance device are periodically changed to form low-frequency noise, and the generated pressure disturbance is p'a；
Let the radius at the nozzle inlet be RA，RCThe radius of the outlet of the nozzle is the radius, and the nozzle accelerates the high-pressure airflow in a contraction mode, so that the high-pressure airflow with higher speed is obtained; the pressure and temperature at the inlet of the nozzle are respectively denoted as pA(＝pa+p′a) And TAThe flow velocity of the air flow is VA(ii) a The energy enthalpy h at the inlet of the nozzleAComprises the following steps:
wherein γ represents the specific heat ratio; c. CpRepresents the constant pressure heat capacity; rhoARepresents the density at the nozzle inlet; c. CARepresenting the speed of sound at the nozzle inlet;
since the flow of the gas is isentropic, the energy is not dissipated in the nozzle and the enthalpy of the energy is not changed, for which purpose the total enthalpy is defined
h0＝hA (3)
The gas in the nozzle is ideal gas, and the total pressure p of the system can be obtained under the concept of total enthalpy0Total temperature T0And velocity of stagnation c0
Where ρ is0Representing the corresponding density at the total system pressure;
according to an isentropic ideal gas state equation, the pressure p, the temperature T and the Mach number M at any position in the nozzle are characterized by
The temperature at any position in the nozzle is characterized by
It is known that as the nozzle flow mach number increases, the corresponding temperature decreases; from equation (6), the ratio of the temperature at the nozzle inlet to the temperature at the nozzle outlet is characterized by
Wherein the pressure at the nozzle outlet is equal to the ambient pressure PEnvironment(s)Coincidence, i.e. PC＝PEnvironment(s)The Mach number M at the nozzle outlet is obtained according to the formula (5)CIs composed of
When Mach number M at the nozzle outlet is calculated by equation (8)CWhen the flow rate is less than 1, the air flow at the outlet of the nozzle flows at subsonic speed, at the moment, the nozzle adopts a subsonic speed shrinkage nozzle, the radius of the inlet of the nozzle to the radius of the outlet of the nozzle is gradually reduced, and the flow rate is gradually reduced along with the flow rate from the inlet of the nozzle to the outlet of the nozzleThe gradual reduction of the radius of the nozzle, namely the continuous reduction of the cross section area of the nozzle, brings about the increase of the airflow speed in the nozzle and the reduction of the airflow pressure and temperature in the nozzle;
substituting equation (8) into equation (7) to obtain a temperature ratio of nozzle inlet to nozzle outlet of
Mach number M at the nozzle outlet calculated by equation (8)CWhen the flow rate is more than 1, the flow Mach number at a certain cross section of the nozzle is 1, and the cross section is defined as a critical cross section; the nozzle adopted at the moment is a Laval supersonic nozzle, the middle section of the Laval supersonic nozzle is contracted, and the radius of the inlet of the nozzle is RARadius at nozzle outlet is RCThe critical cross section, i.e. the position of the minimum cross section in the middle of the nozzle, has a corresponding cross section radius of RB，RAGreater than RB，RCGreater than RB(ii) a The radius of the Laval supersonic nozzle from the nozzle inlet to the minimum cross section of the nozzle middle part is gradually reduced, and the radius of the minimum cross section of the nozzle middle part to the radius of the nozzle outlet is gradually increased.
2. The pneumatically excited sound fire extinguisher with a cooling effect according to claim 1, wherein: the larger the radius of the air inlet channel is, the longer the length of the blade of the corresponding propeller is, and the pressure p of high-pressure air flow obtained by the rotation of the propelleraThe larger;
the larger the length and width of a disturbance blade of the disturbance device are, the obtained pressure disturbance p'aThe larger.
3. The pneumatically excited sound fire extinguisher with a cooling effect according to claim 1, wherein: for Laval supersonic nozzle, according to the conservation of mass in the flow process, the radius R of the inlet of the nozzleAThe mass exists at the radius R at any cross section of the nozzleConservation formula
Wherein, VA、ρAFlow velocity and density at the nozzle inlet, respectively; v and rho are respectively the flow speed and the density of any cross section of the nozzle;
defining the propagation velocity of the sound wave at the entrance of the nozzle and at any cross section of the nozzle as cAAnd c, then exist
At critical cross section, corresponding to a Mach number MB1, the radius R of the critical cross sectionBAnd RAThe relationship of (c) can be characterized as:
equation (5) taken into equation (12) may result in the following equation
Radius R at the nozzle outletCRelative to the critical cross-sectional radius RBIs as follows
At this time, the temperature T at the nozzle outletCAnd the temperature T at the nozzle inletAThe relationship of (c) is shown in equation (7).
4. A method of extinguishing a fire using the pneumatically excited sound fire extinguishing apparatus with a temperature reducing effect according to any one of claims 1 to 3.
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|---|---|---|---|---|
| CN205460603U (en) * | 2016-03-11 | 2016-08-17 | 中国空气动力研究与发展中心高速空气动力研究所 | Even stable supersonic extinguishing device in flow field |
| CN105903137A (en) * | 2016-04-29 | 2016-08-31 | 东华大学 | Low-frequency sound wave fire extinguisher |
| WO2016176345A1 (en) * | 2015-04-30 | 2016-11-03 | Task Force Tips, Inc. | Firefighting nozzle with trigger operated slide valve |
| KR20180002453A (en) * | 2016-06-29 | 2018-01-08 | 배병채 | wave fire subjugation |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2016176345A1 (en) * | 2015-04-30 | 2016-11-03 | Task Force Tips, Inc. | Firefighting nozzle with trigger operated slide valve |
| CN205460603U (en) * | 2016-03-11 | 2016-08-17 | 中国空气动力研究与发展中心高速空气动力研究所 | Even stable supersonic extinguishing device in flow field |
| CN105903137A (en) * | 2016-04-29 | 2016-08-31 | 东华大学 | Low-frequency sound wave fire extinguisher |
| KR20180002453A (en) * | 2016-06-29 | 2018-01-08 | 배병채 | wave fire subjugation |
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