CN108680497B - Method and system for measuring sliding friction coefficient of micron particles - Google Patents
Method and system for measuring sliding friction coefficient of micron particles Download PDFInfo
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Abstract
The invention relates to a method and a system for measuring a sliding friction coefficient of a micron particle, belonging to the field of particle physical property parameter measurement. The invention comprises the following steps: (1) enabling the micron particles to collide with a horizontal plate to form a continuous parabola, wherein the height of the peak value of the parabola is gradually reduced; (2) measuring the movement track, and recording at least the transverse distance of each parabola and the height of the peak value of each parabola; (3) and (3) calculating the impulse ratio of the tangential direction to the normal direction in the collision process according to the step (2), and equivalently using the impulse ratio of the tangential direction to the normal direction as a sliding friction coefficient, thereby obtaining the sliding friction coefficient. The invention realizes the accurate measurement of the sliding friction coefficient of the micron particles, is beneficial to improving the simulation calculation precision of the flow characteristics of the micron-scale particles and the gas particles, is beneficial to developing the structural design of the related fields of the particle flow and the gas particles, and plays a role in promoting the development of the micron-particle flow and the micron-particle gas particles which are widely applied at present.
Description
Technical Field
The invention relates to a method and a system for measuring a sliding friction coefficient of a micron particle, belonging to the field of particle physical property parameter measurement.
Background
Particle flow and gas particle two-phase flow method theory and numerical simulation research are commonly used in various fields of aerospace, chemical industry, pharmacy, electronics, agriculture, meteorology, medicine and the like, such as transportation and deposition of particles of sand dust, dust and the like in critical parts of an aeroengine, migration and accumulation of sand dust in desert, fluidized bed drying process and the like, particle collision and contact processes are often involved in the relevant theory and simulation calculation process, particle-wall surface and particle-particle collision characteristics determine the dynamic characteristics of particles in the transportation and flowing processes, wherein the sliding and rolling friction of the particles in the collision directly influences the accuracy of particle flow and gas particle two-phase flow characteristic prediction and simulation calculation. Therefore, the measurement of the rolling and sliding friction coefficients of the particulate material is the basis for the development of particle flow and two-phase particle flow studies.
Some methods have been used for measuring the sliding friction coefficient and the rolling friction coefficient of macro particles or materials, but the measurement of the sliding friction coefficient and the rolling friction coefficient of micron-sized particles is extremely difficult, and the friction coefficient is influenced by the particle size characteristics, wall surface roughness, surface adhesion, collision angle and other factors in the collision process, so that no special measuring method or measuring device is available for accurately measuring the sliding friction coefficient of micron particles.
Disclosure of Invention
The invention aims to provide a method and a system for measuring a sliding friction coefficient of a micron particle, which are used for solving the problem that the sliding friction coefficient of the micron particle cannot be accurately measured.
In order to achieve the purpose, the invention provides a method and a system for measuring the sliding friction coefficient of micron particles, and the method for measuring the sliding friction coefficient of the micron particles comprises the following steps:
(1) enabling the micron particles to collide with a horizontal plate to form a continuous parabola, wherein the height of the peak value of the parabola is gradually reduced;
(2) measuring the movement track, and recording at least the transverse distance of each parabola and the height of the peak value of each parabola;
(3) and (3) calculating the impulse ratio of the tangential direction to the normal direction in the collision process according to the step (2), and equivalently using the impulse ratio of the tangential direction to the normal direction as a sliding friction coefficient, thereby obtaining the sliding friction coefficient.
The invention carries out measurement by an experimental means, the experiment only needs the micron particles to carry out specific movement, the accurate measurement of the sliding friction coefficient of the micron particles is realized, the simulation calculation precision of the micron-scale particle flow and the gas particle two-phase flow characteristic is favorably improved, the structural design of the related fields of the particle flow and the gas particle two-phase flow is favorably developed, the development of the micron particle flow and the micron particle gas particle two-phase flow which are widely applied at present is promoted, the measurement is simple and easy to realize, and the measurement result is accurate.
Further, the impulse ratio of the tangential direction and the normal direction in the collision process is calculated through the normal recovery coefficient and the tangential recovery coefficient of each collision point, and the calculation formula is as follows:
wherein f iskIs the impulse ratio of tangential direction to normal direction, enkFor normal restitution of coefficient, etkIs a tangential recovery coefficient, theta is an included angle between the incident direction and the vertical direction and can be represented by an incident normal speed and an incident tangential speed;
wherein k is the number of collisions, l is the lateral distance of the parabola, and h is the peak height of the parabola.
The normal recovery coefficient of the collision point is related to the normal speed of the collision point, the tangential recovery coefficient of the collision point is related to the tangential speed of the collision point, and the normal speed and the tangential speed can be obtained according to the transverse distance between the two ends of the parabola and the height of the peak value of the parabola, so that the impulse ratio of the tangential direction to the normal direction is simple, convenient and accurate.
Further, the environment in which the microparticles move is a vacuum environment or a high vacuum environment.
The particle is less, and the air resistance and the aerodynamic force that receive in the motion process are great, adopt vacuum environment or high vacuum environment, avoid air resistance and aerodynamic force to the influence of micron granule, and measuring result is more accurate.
Further, the environment in which the microparticles move is a darkroom environment.
In a darkroom, the motion track of the captured micron particles is ensured to be clear enough, and the measurement and calculation are convenient.
Further, the movement locus of the micrometer particles is measured by a high-speed camera device.
The higher the resolution of the camera is, the smaller the size of the measured particles is, and the motion trail of the micron particles can be clearly captured by using a high-speed video camera, so that the accuracy of measurement and calculation is ensured.
A system for measuring the sliding friction coefficient of microparticles comprises a microparticle launching device, a trajectory acquisition device, at least one processor and a memory, wherein the microparticle launching device, the trajectory acquisition device, the processor and the memory are arranged in a box body, and the processor runs a computer program stored in the memory to realize the following steps:
(1) enabling the micron particles to collide with a horizontal plate to form a continuous parabola, wherein the height of the peak value of the parabola is gradually reduced;
(2) measuring the movement track, and recording at least the transverse distance of each parabola and the height of the peak value of each parabola;
(3) and (3) calculating the impulse ratio of the tangential direction to the normal direction in the collision process according to the step (2), and equivalently using the impulse ratio of the tangential direction to the normal direction as a sliding friction coefficient, thereby obtaining the sliding friction coefficient.
Further, the impulse ratio of the tangential direction and the normal direction in the collision process is calculated through the normal recovery coefficient and the tangential recovery coefficient of each collision point, and the calculation formula is as follows:
wherein f iskIs the impulse ratio of tangential direction to normal direction, enkFor normal restitution of coefficient, etkIs a tangential recovery coefficient, theta is an included angle between the incident direction and the vertical direction and can be represented by an incident normal speed and an incident tangential speed;
wherein k is the number of collisions, l is the lateral distance of the parabola, and h is the peak height of the parabola.
Further, the box body is a vacuum environment box.
Further, the device also comprises an illumination system, wherein the illumination system is used for illuminating the micron particle moving area.
Further, the track acquisition device is a high-speed camera device.
Drawings
FIG. 1 is a schematic diagram of the principles of the present invention;
FIG. 2 is a schematic view of a measurement system of the present invention.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
Examples of measurement systems for the sliding friction coefficient of microparticles:
the system for measuring the sliding friction coefficient of microparticles, as shown in fig. 2, comprises a vacuum environment box 1, a support frame system 2, a microparticle emitting device 3, a laser lighting system 4, a strip-shaped target material plate 5 (horizontal plate), a vertical wall surface 6, a particle adsorbing material 7, a high-speed camera 8 (high-speed camera device), an image analyzing and processing device 9, wherein the image analyzing and processing device 9 comprises a processor and a memory.
The environment in the vacuum environment box 1 is a vacuum environment or a high vacuum environment, wherein vacuum refers to a state in a given space when gas molecules in the space are pumped to be thin and the pressure is lower than an atmospheric pressure, the thin degree of the gas is called vacuum degree, and when the vacuum degree is lower than 1.333 × 10-1～1.333×10-6Pa, high vacuum.
The system comprises a supporting frame system 2, a micron particle emitting device 3, a laser lighting system 4, a strip-shaped target material plate 5, a vertical wall surface 6, a particle adsorbing material 7 placed in a vacuum environment box 1, the supporting frame system 2 is fixed at a specific position and used for installing the micron particle emitting device 3 and the laser lighting system 4, the micron particle emitting device 3 can adjust the installation height and the nozzle angle according to requirements, the strip-shaped target material plate 5 is used for colliding and rebounding with micron particles at the bottom of the vacuum environment box 1, the particle adsorbing material 7 is arranged on the inner side of the vertical wall surface 6, a high-speed camera 8 is connected with an image analysis processing device 9, the high-speed camera 8 and the image analysis processing device 9 are placed outside the vacuum environment box 1, the motion track of the micron particles is captured, and the sliding friction coefficient of the micron particles is calculated.
The specific process is that, in order to capture the motion trail of the microparticles clearly, the measurement process of the whole measurement system is carried out in a darkroom, before the microparticles are emitted, the laser illumination system 4, the high-speed camera 8 and the image analysis processing device 9 are in working states, the angle of the microparticle emission device 3 is adjusted, the motion trail of the microparticles is in a vertical plane, the microparticles are in a vacuum or high-vacuum environment, the influence of air resistance and aerodynamic force on the motion trail is avoided, after the microparticles are emitted by the microparticle emission device 3, the microparticles collide with the strip-shaped target material plate 5 for the first time, the second time, the third time and the like at a certain initial speed under the action of gravity for a period of time until the microparticles are adhered to the particle adsorption material 7 or stand still on the target material plate 5, the high-speed camera 8 captures and records the whole motion trail of the microparticles, the recorded motion trajectory is sent to the image analysis processing device 9, the rebound height and the collision point distance after the first and second collisions are obtained through image analysis through analysis and calculation of the image analysis processing device 9, and the particle sliding friction coefficient can be directly calculated by using the proposed theoretical formula. According to the testing principle, the particle sliding friction coefficient measurement with different sizes and different components can be realized, an image recognition system is matched, a plurality of particles can be emitted at one time to realize simultaneous measurement, and the measuring efficiency and feasibility are improved.
The specific calculation process and principle is as follows, the collision contact process of the micron particles and the strip-shaped target material plate 5 can be divided into two states of sliding and rolling. The microparticles collide with the strip-shaped target material plate 5 at a certain normal (vertical) speed and tangential (horizontal) speed, and will collide with the strip-shaped target material plate 5 again under the action of gravity after rebounding, and the process is repeated continuously until the microparticles stop or move outside the measurement range, and the movement track is as shown in fig. 1. The sliding friction coefficient of the microparticles can be measured by multiple collisions of the microparticles under the action of gravity.
The micron particles are released from a high position at a certain speed, the particle outlet speed can be horizontal, obliquely downward or obliquely upward, the particles are guaranteed to move in a vertical plane, the particles fall and collide and rebound with the bottom surface, and the collision frequency of the particles and the strip-shaped target material plate 5 is determined by the particle launching height and the initial speed. Recording the rebound height and the collision position of each collision of the particles, wherein the distance between each rebound height and each collision position is hkAnd lkDenotes (k ═ 1,2, …) that the collision point rebound normal velocity and tangential velocity are respectively represented by VnkAnd VtkIndicating that the time interval between the collision points is tk. The testing device is implemented in a vacuum environment and comprises the following components:
rebound normal speed of each collision point and time interval of collision points
Horizontal velocity of impact point rebound
The normal recovery coefficient of each collision point is
Corresponding to a tangential recovery coefficient of
There is a ratio of tangential to normal momentum during collision
Where θ is the angle between the incident direction and the vertical direction, and has tan θ ═ Vt(k-1)/Vn(k-1)The impulse ratio can then be expressed again as a function of the rebound height and the distance between the impact points
During collision, the tangential impulse ratio and the normal impulse ratio are equivalent friction coefficients, but during collision, due to the change of the sliding and rolling states of the particles and the wall surface, the collision process changes from the sliding state to the rolling state, and therefore, the obtained impulse ratio is changed from the sliding friction coefficient to the rolling friction coefficient. According to the impulse ratio of each collision point, the sliding and rolling state change of each collision process can be judged, and under the condition that the tangential speed is large enough, the sliding state of the previous collision contact processes can be ensured.
In the experiments, it is best to use: and measuring data of the first few collisions and the last few collisions to guarantee the accuracy of the result. The reason for adopting the data after the first time is that the first time of collision is related to the emitting device, and an accurate test result can be obtained only by strictly ensuring that the emergent direction of the particles is horizontal, otherwise, the data is not suitable for being adopted as the data, but the difficulty of realizing the complete horizontal of the emergent speed of the particles is extremely high; the reason for using the former data is that the peak height of the parabola gradually decreases in the latter movements, and rolling friction is generated besides sliding friction, so that the measurement result has a larger deviation (even in the latter movements, the rolling friction is completely equivalent).
In the above system, the measurement is performed on the micron particles, and as other embodiments, the measurement of the sliding friction coefficients of particles with different sizes and different compositions can be realized.
In the measurement system of the sliding friction coefficient of the micrometer particles in the above embodiment, the normal recovery coefficient and the tangential recovery coefficient of each collision point are obtained through the lateral distance of the parabola and the peak height of the parabola, and then the impulse ratio of the tangential direction and the normal direction is calculated.
The method for measuring the sliding friction coefficient of the microparticle is coded and stored in the memory of the system for measuring the sliding friction coefficient of the microparticle, and is implemented in the system for measuring the sliding friction coefficient of the microparticle.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that the foregoing and various other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention as defined in the appended claims.
Claims (3)
1. A system for measuring the sliding friction coefficient of microparticles, comprising at least one processor and a memory, wherein said processor runs a computer program stored in said memory to implement the steps of:
(1) enabling the micron particles to collide with a horizontal plate to form a continuous parabola, wherein the height of the peak value of the parabola is gradually reduced;
(2) measuring the movement track, and recording at least the transverse distance of each parabola and the height of the peak value of each parabola;
(3) calculating the impulse ratio of the tangential direction and the normal direction in the collision process according to the step (2), and equivalently using the impulse ratio of the tangential direction and the normal direction as a sliding friction coefficient so as to obtain the sliding friction coefficient;
specifically, the measuring system comprises a vacuum environment box, a supporting frame system, a micron particle emitting device, a laser lighting system, a strip-shaped target material plate, a vertical wall surface, a particle adsorbing material, a high-speed camera and an image analysis processing device, wherein the image analysis processing device comprises at least one processor and a memory;
the system comprises a support frame system, a micron particle emitting device, a laser lighting system, a strip-shaped target material plate, a vertical wall surface and a particle adsorption material, wherein the support frame system is fixed at a specific position and used for mounting the micron particle emitting device and the laser lighting system;
the measurement process of the whole measurement system is carried out in a darkroom, before the micron particles are emitted, the laser illumination system, the high-speed camera and the image analysis processing device are in working states, the angle of the micron particle emitting device is adjusted, the motion track of the micron particles is in a vertical plane, the micron particles are in a vacuum or high-vacuum environment, the motion track is prevented from being influenced by air resistance and aerodynamic force, after the micron particles are emitted by the micron particle emitting device, the micron particles collide with a strip-shaped target material plate for multiple times under the action of gravity until the micron particles are adhered to a particle adsorption material or are still on the target material plate, the whole motion track of the micron particles is captured and recorded by the high-speed camera, and the recorded motion track is sent to the image analysis processing device.
2. The measurement system of claim 1, wherein the tangential to normal impulse ratio during a collision is calculated from the normal restitution coefficient and the tangential restitution coefficient of each collision point by the formula:
wherein f iskIs the impulse ratio of tangential direction to normal direction, enkFor normal restitution of coefficient, etkIs a tangential recovery coefficient, theta is an included angle between the incident direction and the vertical direction and can be represented by an incident normal speed and an incident tangential speed;
wherein k is the number of collisions, l is the lateral distance of the parabola, and h is the peak height of the parabola.
3. The measurement system of claim 1, wherein the laser illumination system is configured to illuminate a microparticle movement region.
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