Method and device for monitoring plasma jet velocity
阅读说明：本技术 等离子体射流速度的监测方法与设备 (Method and device for monitoring plasma jet velocity ) 是由 曹进文 黄河激 孟显 潘文霞 于 2019-09-26 设计创作，主要内容包括：本发明涉及一种等离子体射流速度的监测方法与设备,其方法包括:撷取层流等离子体的多个光图案,基于输出功率与等离子体的浓度正相关由所述光图案的发光边界确定等离子体射流的射流边界;基于所述等离子体射流由射流出口到射流末端的轴向射流边界,确定层流等离子体的射流长度;由所述层流等离子体的射流长度计算出等离子体的射流平均速度,在预定不同的弧电流射流速度保持不变下,建立层流等离子体的射流长度与弧电流的关系。本发明具有等离子体射流速度测量过程简化与降低系测量统设备建置成本的效果。(The invention relates to a method and equipment for monitoring plasma jet velocity, wherein the method comprises the steps of capturing a plurality of light patterns of laminar plasma, determining the jet boundary of plasma jet by the luminous boundary of the light patterns based on the positive correlation between output power and plasma concentration, determining the jet length of the laminar plasma based on the axial jet boundary of the plasma jet from a jet outlet to a jet tail end, calculating the jet average velocity of the plasma by the jet length of the laminar plasma, and establishing the relationship between the jet length of the laminar plasma and arc current under the condition that preset different arc current jet velocities are kept unchanged. The invention has the effects of simplifying the plasma jet velocity measuring process and reducing the construction cost of the system measuring system equipment.)
1. A method of monitoring plasma jet velocity, comprising:
capturing a plurality of light patterns (11) of laminar plasma, and determining a jet boundary (13) of plasma jet from a light emitting boundary of the light patterns (11) based on a positive correlation between output power and plasma concentration;
determining the jet length of the laminar plasma based on an axial jet boundary (13) of the plasma jet from a jet outlet (12) to a jet tip; and
calculating the jet flow average speed of the plasma from the jet flow length of the laminar plasma, wherein the jet flow average speed of the plasma comprises the following steps: and establishing the relationship between the jet length of the laminar plasma and the arc current under the condition that the preset different arc current jet speeds are kept unchanged.
2. The method for monitoring the plasma jet velocity according to claim 1, wherein the relationship between the jet length of the laminar plasma and the plasma jet velocity conforms to the following formula:
Δ L ═ V · Δ t, where Δ L represents jet length, V represents plasma jet velocity, and Δ t represents jet visible time; and the number of the first and second electrodes,
the jet visible time conforms to the following equation:
3. The method for monitoring the plasma jet velocity according to claim 1, wherein the relationship between the jet length and the arc current of the laminar plasma conforms to the following formula:
4. The method for monitoring the plasma jet velocity according to claim 1, wherein the step of calculating the jet average velocity of the plasma from the jet length of the laminar plasma further comprises: determining unknown parameters, and reducing the arc current value to the condition that the jet flow length is zero to meet n0＝K0I0Wherein n is0Indicating the plasma density threshold (usually taken) at a jet length of 0Dependent on the gas pressure), K0Linear coefficient of electron density at jet center to input electric power, I0Represents the arc current value when the jet length is zero; and the relationship of the jet length of the laminar plasma to the arc current conforms to the following equation:
5. The method for monitoring the plasma jet velocity according to claim 1, wherein the extracting of the plurality of light patterns (11) of laminar plasma is performed at different output powers.
6. Method for monitoring the velocity of a plasma jet according to claim 5, characterized in that the axial jet boundary (13) of the plasma jet at the jet tip complies with the following formula:
where n (z ═ 0) denotes the plasma density with z axis dependent on gas pressure, and n0Denotes the plasma density threshold at a jet length of 0, α denotes the plasma recombination coefficient depending on the gas type and gas pressure, and Δ t (i) denotes the jet visibility time at the individual arc current.
7. The method for monitoring the plasma jet velocity according to any one of claims 1 to 6, wherein the plasma concentration of the plasma jet at the outlet is linearly proportional to the output power, and conforms to the following formula:
8. A device for monitoring the plasma jet velocity, characterized by being used for carrying out a method for monitoring the plasma jet velocity according to any one of claims 1 to 7.
9. A device for monitoring the velocity of a plasma jet, comprising:
an extraction unit (10) configured to extract a plurality of light patterns (11) of a laminar plasma, determining a jet boundary (13) of a plasma jet from a light emitting boundary of the light patterns (11) based on a positive correlation of an output power with a concentration of the plasma;
a determination unit (20) configured to determine a jet length of the laminar plasma based on an axial jet boundary (13) of the plasma jet from a jet outlet (12) to a jet tip; and
a calculation unit (30) configured to calculate a jet average velocity of the plasma from the jet length of the laminar plasma, wherein the jet length of the laminar plasma has been established in relation to the arc current with a predetermined different arc current jet velocity remaining unchanged.
Technical Field
The invention relates to the technical field of plasma jet measurement, in particular to a method and equipment for monitoring plasma jet velocity.
Background
At present, plasma spraying is widely applied to the industrial fields of aerospace, navigation, mechanical manufacturing, electronic part manufacturing and the like for forming a coating, is used for producing various functional materials required by heat resistance, wear resistance, corrosion resistance and the like, and the adoption of a plasma spraying method such as direct current arc plasma spraying and the like is a key technology for material coating. In dc arc plasma applications, the process material is heated and accelerated as a particulate powder or gas injected into a laminar plasma jet. Therefore, real-time monitoring of the velocity of the plasma jet is an integral part of process control. The conventional plasma jet velocity measurement process is complex, and the system equipment construction cost is high.
The 5-month engineering thermophysics journal of 2004,
Disclosure of Invention
One of the objectives of the present invention is to provide a method for monitoring plasma jet velocity, so as to solve the problems of complex process of measuring plasma jet velocity and high cost of system equipment construction.
Another object of the present invention is to provide a plasma jet velocity monitoring device, which is used to simplify the plasma jet velocity measurement process and reduce the cost of system equipment.
One of the purposes of the invention is realized by the following technical scheme:
a method for monitoring the speed of plasma jet is provided, which comprises the following steps: capturing a plurality of light patterns of laminar plasma, and determining the jet flow boundary of plasma jet flow by the luminous boundary of the light patterns based on the positive correlation between the output power and the concentration of the plasma; determining a jet length of laminar plasma based on an axial jet boundary of the plasma jet from a jet outlet to a jet tip; and calculating the jet flow average speed of the plasma according to the jet flow length of the laminar plasma, wherein the method comprises the following steps: and establishing the relationship between the jet length of the laminar plasma and the arc current under the condition that the preset different arc current jet speeds are kept unchanged. In addition, a monitoring device corresponding to the monitoring method is provided.
By adopting the technical scheme, the plasma jet velocity is obtained by utilizing the captured plasma jet pattern and the matched calculation, the jet average velocity value can be obtained based on the measurable plasma jet length, the received arc current value, the voltage and the external/actual environmental conditions, the temperature or the pressure of the plasma jet does not need to be measured additionally in the process, and the plasma jet velocity can be detected more quickly.
The invention may be further arranged to: the relationship between the jet length of laminar plasma and the jet speed of the plasma conforms to the following formula:
Δ L ═ V · Δ t, where Δ L denotes the jet length, V denotes the plasma jet velocity, Δ t denotes the jet visibility time (i.e. the time required for the plasma jet to reach the light emission boundary from the exit) and,
the jet visible time conforms to the following equation:
By adopting the technical scheme, the values of the jet flow length delta L, the jet flow visible time delta t and the like can be effectively obtained, the jet flow length value can be favorably calculated and converted into the average speed of the jet flow of the electric electrons, and the temperature and the pressure of the plasma can be not required to be additionally measured.
The invention may be further arranged to: the relationship between the jet length of the laminar plasma and the arc current conforms to the following formula:
By adopting the technical scheme, the visible time delta t (I) of the jet flow can be confirmed to correspond to alpha and n when the jet flow length is zero0、K0After measuring the jet length delta L (I), combining the known arc current value I with alpha and n corresponding to the jet length being zero0、K0The jet visible time delta t (I) obtained by the environmental coefficient and the like can be used for calculating the average speed V (I) of the electron body jet.
The invention may be further arranged to: calculating the jet flow average speed of the plasma from the jet flow length of the laminar plasma, and further comprising: determining unknown parameters by reducing the arc current value to a condition where the jet length is zero, wherein n is0Denotes the plasma density threshold, K, at a jet length of 00Linear coefficient of electron density at jet center to input electric power, I0Represents the arc current value when the jet length is zero; and the relationship of the jet length of the laminar plasma to the arc current conforms to the following equation:
where Δ l (I) represents the jet length at a known arc current value, α represents the plasma recombination coefficient depending on the gas type and gas pressure, v (I) represents the plasma jet average velocity at a known arc current value, and I represents the arc current value at the time of measurement.
By adopting the technical scheme, alpha and n when the jet flow length is zero can be more practically eliminated0、K0And the accuracy of the calculated average speed V (I) of the plasma jet is improved under the influence of the environmental coefficient.
The invention may be further arranged to: the extracting of the plurality of light patterns of the laminar plasma is performed at different output powers.
By adopting the technical scheme, more adaptive analysis data can be established for calculating the average speed V (I) of the plasma jet according to different actual working conditions.
The invention can be further configured as follows: the axial jet boundary of the plasma jet at the jet tip conforms to the following equation:
By adopting the technical scheme, the axial jet flow boundary of the plasma jet flow at the jet flow end can be effectively confirmed, and the interference factor when the jet flow length is zero is considered.
The invention may be further arranged to: the plasma concentration of the plasma jet at the outlet is in linear direct proportion to the output power, and the following formula is met:
wherein n is0Denotes the plasma density threshold, K, at a jet length of 00A linear coefficient representing the electron density at the center of the jet and the input electric power, α represents a plasma recombination coefficient depending on the gas type and gas pressure, and Δ t represents a jet visible time.
By adopting the technical scheme, the linear proportional relation of concentration and power and the calculation consideration of the environmental conditions such as the gas pressure coefficient, the gas type, the gas pressure, the linear constant of the plasma torch and the like when the jet length is zero are increased, and the method is particularly favorable for establishing an artificial intelligent calculation model for calculating the average speed of the plasma jet.
The other purpose of the invention is realized by the following technical scheme:
a monitoring device for plasma jet velocity is provided, which comprises an acquisition unit, a determination unit and a calculation unit. The extraction unit is configured to extract a plurality of light patterns of laminar plasma, and determine a jet boundary of a plasma jet from a light emitting boundary of the light patterns based on a positive correlation of output power and a concentration of the plasma. The determination unit is configured to determine a jet length of the laminar plasma based on an axial jet boundary of the plasma jet from the jet outlet to the jet tip. The calculation unit is configured to calculate an average jet velocity of the plasma from the jet length of the laminar plasma, wherein the relationship of the jet length of the laminar plasma to the arc current has been established with predetermined different arc current jet velocities remaining unchanged.
By adopting the technical scheme, under the operation of the acquisition unit, the determination unit and the calculation unit, the average speed value of the emergent flow is calculated by the light pattern, and a temperature measurement device or/and a pressure measurement device of the plasma jet flow does not need to be additionally built in the measurement equipment, so that the measurement process is simplified, and the speed of the plasma jet flow is rapidly detected.
In summary, the invention includes at least one of the following beneficial technical effects:
1. the plasma jet velocity can be detected more quickly without additionally measuring the temperature or/and the pressure of the plasma jet in the process of measuring the plasma jet velocity;
2. the temperature measuring device or/and the pressure measuring device for measuring the plasma jet flow do not need to be built in the device for measuring the plasma jet flow speed, so that the building cost of the plasma jet flow speed measuring system device can be reduced;
3. the influence of the environmental coefficient is fully considered, and the average speed of the isoelectric electron jet can be calculated and converted according to the current input electric power of the jet and the jet length value derived from the captured light pattern;
4. the influence of the environmental coefficient is fully considered, and the average speed of the electron plasma jet can be calculated and converted according to the arc current value of the corresponding jet at the time and the jet length value derived from the captured light pattern;
5. the influence of the environmental coefficient when the jet length is zero can be eliminated more practically, and the calculation accuracy of the average speed V (I) of the plasma jet is improved;
6. the axial jet boundary of the plasma jet at the jet end can be more accurately confirmed;
7. an artificial intelligence calculation model for calculating the average speed of the plasma jet can be established for different working conditions, so that artificial intelligence learning and training can be achieved, and further calculation errors influenced by possible unknown parameters can be eliminated.
Drawings
Fig. 1 is a schematic flow chart illustrating a method for monitoring a plasma jet velocity according to a preferred embodiment of the invention.
Fig. 2 is a schematic diagram illustrating a plurality of light patterns for extracting laminar plasma in step S1 according to a preferred embodiment of the invention.
FIG. 3 is a graph showing the relationship between the arc current of the laminar plasma jet and the thermal efficiency of (a) the jet length, (b) the output power, and (c).
Fig. 4 is a schematic diagram illustrating the relationship between the jet length and the arc current of the laminar plasma in step S3 according to a preferred embodiment of the present invention.
FIG. 5 is a block diagram of an apparatus for monitoring the plasma jet velocity according to a preferred embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Referring to fig. 1, a method for monitoring a plasma jet velocity disclosed in an embodiment of the present invention includes:
step S1, capturing a plurality of light patterns of laminar plasma, and determining the jet flow boundary of plasma jet flow by the luminous boundary of the light patterns based on the positive correlation between the output power and the plasma concentration;
step S2, determining the jet length of laminar plasma based on the axial jet boundary of the plasma jet from the jet outlet to the jet tail end; and a process for the preparation of a coating,
and step S3, calculating the jet flow average speed of the plasma according to the jet flow length of the laminar plasma, wherein the step comprises the following steps: and establishing the relationship between the jet length of the laminar plasma and the arc current under the condition that the preset different arc current jet speeds are kept unchanged.
The implementation principle of the embodiment is as follows: the plasma jet is photographed to capture a plurality of light patterns, the plasma jet length is calculated, and then the relation between the jet velocity and the arc current and the jet length is deduced according to the compound theory of electrons and ions in the plasma, so that the plasma jet average velocity is obtained. In the speed measurement method, a fixed coefficient after learning in a specific environment exists, and various coefficients are kept unchanged under the condition that working gas, working air pressure and a plasma generator are unchanged.
In addition, another embodiment of the present invention discloses another monitoring device corresponding to the above monitoring method, for performing the above plasma jet velocity monitoring method.
Fig. 2 shows that in step S1, a plurality of
The following description is given for the sake of facilitating understanding of the technical aspects of the present invention, but not for limiting the present invention. Laminar plasma undergoes a process of attenuation of diffusion and recombination from the exit to the end of the jet. The slower the decay rate and the longer the jet, the greater the initial (jet outlet) plasma concentration. In one example, according to experimental results, the concentration of the plasma is almost linearly proportional to the power. Fig. 3 shows that the output power is almost linearly proportional to the arc current. Therefore, the following mathematical relationship can be confirmed to be reasonably feasible:
wherein Δ l (i) represents the jet length at a known arc current value, v (i) represents the plasma jet average velocity at a known arc current value, and Δ t represents the jet visible time at a known arc current value; and the number of the first and second electrodes,
wherein α represents a plasma recombination coefficient depending on the kind of gas and the gas pressure, K0Linear coefficient of electron density at jet center to input electric power, I0The value of the arc current value when the visible length of the jet flow is reduced to 0 is shown, and I represents the arc current value of the corresponding jet flow at that time.
Therefore, the average velocity v (i) of the plasma jet at a known arc current value can be deduced from the jet length Δ l (i) at the known arc current value.
It is known from fig. 3 that the output power is almost linearly proportional to the arc current. Therefore, it can also be confirmed that the jet visible time Δ t is in the following formula:
wherein alpha represents the recombination coefficient of the plasma, and can be obtained by inquiring publicly published data depending on the gas type and the gas pressure; k0Linear system of electron density and input electrical power representing jet centerThe linear relation between the electron density in the jet flow and the input power can be obtained through experimental measurement; p0A threshold value representing the input power when the visible length of the jet flow is reduced to 0, and the visible length of the jet flow is reduced to 0 after the input electric power P is reduced to the threshold value; p denotes the input electrical power to the torch, readable from the power supply equipment, it being noted that reference herein to input electrical power refers to the available discharge power, e.g., for a dc arc plasma torch, P equals the current output by the power supply multiplied by the voltage; for the rf plasma torch, P is equal to the actual feed power.
In addition, regarding the linear coefficient K0The determination method of (2) includes the following two methods:
(1) obtaining two input electric powers P by a plasma density measuring device (such as an electrostatic probe) under actual working conditions1And P2Plasma density n1And n2From this, the linearity coefficient K can be calculated0：
(2) Measuring power (e.g. pitot tube) by means of other jet velocities under actual conditions, obtaining power at a certain input electric power P3Lower jet velocity V3Simultaneously recording the jet length L3From this, the linear coefficient K can be calculated by combining the formula for calculating the average velocity of the jet0：
In addition, it can be seen that the equation of the time Δ t and the input electric power P is derived and further explained as follows:
the relationship between electron and ion recombination in plasma over time is described in the document "An Introduction to plasma Physics and Controlled Fusion, vol.1, by chen, with the trade name: the plasma physics introduction, section 5.4, pp97, has been described as follows:
the electron density at the radial position r at time t is represented, and the electron density at the radial position r at time t — 0 is represented.
Each plasma cell in the center of the jet, the plasma density at the outlet being equal to
n(r＝0,0)＝K0P
(2)
As the plasma cell moves forward, recombination of ions and electrons occurs within the plasma cell, resulting in a gradual drop in electron density. When the electron density decreases to a certain critical value n0The plasma cell then emits light too weakly and invisible, here the foremost boundary of the jet. The critical value n0With threshold value P of input power0The relationship of (1) is:
n(r＝0,t＝Δt)＝K0P0
(3)
the meaning of the expression is: when the input power is gradually reduced to P0In time, the visible boundary of the jet recedes gradually to the outlet, i.e. the jet is not visible.
Substituting equation (2) and equation (3) into equation (1) yields:
the transit time of the plasma cell within the jet can be derived from equation (4):
therefore, the mathematical relationship of the visible time Δ t and the input electric power P can be determined.
Of particular note is the linear coefficient K0The determination process of (2) can be obviously executed outside the monitoring time of the plasma jet velocity, and the monitoring efficiency of the plasma jet velocity is not influenced or slowed. Alternatively, the plasma jet velocity can be monitoredIn-process linear coefficient K0Random authentication or adjustment.
Referring to fig. 4, a schematic diagram of the jet length versus arc current for laminar plasma in an exemplary experiment at step S3 is shown. It can be seen from the curves that the trend of the plasma jet length and the experimental data are not completely linearly proportional based on different working conditions. The trend in the experimental data shows that the jet length grows more and more rapidly as the current in the middle section increases. The reason for this can be assumed that the jet velocity is a non-perfectly linear positive correlation with current change. From the deviation of the data from the analysis it can be qualitatively seen that the velocity of the plasma jet increases significantly with increasing arc current, written as v (i). Thus, in another example, based on established experiments, a computational model can be established in which the relationship between the jet length and the arc current for laminar plasma conforms to the following equation:
wherein, as described above, Δ L (I) represents the jet length at a known arc current value, V (I) represents the plasma jet average velocity at a known arc current value, Δ t (I) represents the jet visibility time, n0Denotes the plasma density threshold, K, at a jet length of 00And I represents the current value of the arc current corresponding to the jet current at the time. In the above formula, α and n0Depending only on the type of gas and pressure, K0Depending on the gas type, gas pressure and plasma torch. Under the condition that the three main influencing factors are not changed, the method for estimating the jet velocity by the laminar plasma jet length can be obtained.
The calculation formula for the jet visible time Δ t (i) can be deduced as follows:
first, according to the mass conservation equation of plasma:
the first term on the right is the diffusion term, which should be negative, and the second term is the recombination term of electrons and ions, which is also negative. Written as conservation equation under satellite coordinates (Lagrange form):
when the speed of the jet is mainly axial and the radial direction and the angular direction are negligible, the following solution is obtained:
for plasma at the most distal boundary of the jet, then:
where n (z ═ 0) represents the plasma density with z axis dependent on gas pressure.
From the foregoing, the plasma concentration at the outlet is linearly proportional to the power (i.e., the arc current), with the linear constant K0Then, there are:
the time at which the jet is visible can thus be obtained as:
the jet velocity remains constant for different arc currents, the jet length versus current is similar to:
when a is 49.5 and b is 3412.5 calculated from the two sets of data in fig. 3, a relationship is shown in fig. 4.
A preferred embodiment of the present invention may further compriseThe steps are as follows: the step S3 of calculating the average jet velocity of the plasma from the jet length of the laminar plasma further includes: determining unknown parameters, and reducing the arc current value to the condition that the jet flow length is zero to meet n0＝K0I0Wherein n is0Denotes the plasma density threshold, K, at a jet length of 00Linear coefficient of electron density at jet center to input electric power, I0Represents the arc current value when the jet length is zero; and the relationship of the jet length of the laminar plasma to the arc current conforms to the following equation:
An example of the determination of an unknown parameter is as follows:
when the used gas of the plasma is Ar (argon), the recombination coefficient alpha of the plasma is approximately equal to 2 multiplied by 10-10cm3The threshold plasma density n0 and the linear coefficient K0 can be obtained from experimental data. The parameters may be determined in a calibrated manner by reducing the current to Δ L (I)0) When equal to 0, i.e. according to the above formula n0＝K0I0And is based on
Then the data I of the experiment speed measurement1,ΔL(I1),V(I1) The previous coefficients are determined.
Referring to fig. 5, the present invention further discloses a plasma jet velocity monitoring apparatus, which includes an
The embodiments of the present invention are merely preferred embodiments for easy understanding or implementing of the technical solutions of the present invention, and not intended to limit the scope of the present invention, and all equivalent changes in structure, shape and principle of the present invention should be covered by the claims of the present invention.
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