Intelligent sensing system and method for working medium state in pulsating heat pipe based on temperature monitoring

Abstract

The present application relates to the technical field of heat management and sensing monitoring, in particular to an intelligent sensing system and method for the state of working medium in a pulsating heat pipe based on temperature monitoring, which comprises the following steps: arranging a pipe section composed of friction material and non-friction material on the pulsating heat pipe; attaching a ring-shaped copper electrode to the outer wall of the friction material section and connecting it to an electrometer, and arranging a thermocouple to measure the temperature of the non-friction material section; when the working medium flows through the friction section, solid-liquid (vapor) friction charge signals are generated and transmitted to the processing system synchronously with the temperature signals; through feature extraction and model analysis, the flow state and phase change characteristics of the working medium are sensed in real time, so as to achieve the purpose of intelligently sensing the flow and heat transfer characteristics of the working medium in the pipe. The present application has the advantages of simple structure, strong real-time performance, high sensitivity, non-invasive monitoring, etc., and can be widely applied to the state monitoring and thermal performance analysis and evaluation of working medium in pulsating heat pipes and other phase change heat transfer components.

Description

Technical Field

[0001] This invention relates to the field of thermal management and sensing monitoring technology, and in particular to an intelligent sensing system and method for the working fluid state inside a pulsating heat pipe based on temperature monitoring. Background Technology

[0002] Pulsating heat pipes, as a highly efficient heat transfer device without pump kinetic energy, are widely used in aerospace, LED heat dissipation, and electronic packaging due to their advantages such as simple structure, high thermal conductivity, and small size. Although pulsating heat pipes have a simple structure, the internal process is a very complex unsteady-state flow boiling heat transfer process, which is closely related to factors such as the thermophysical properties of the working fluid, the structure, and technical parameters.

[0003] The flow state and vapor-liquid phase change behavior of the working fluid within a pulsating heat pipe have a crucial impact on its heat transfer performance. However, these states are difficult to observe and provide performance feedback in real time during normal operation, resulting in the lack of a unified mathematical model describing the flow and heat transfer processes within a pulsating heat pipe. Currently, most traditional methods for sensing the working fluid state within a pulsating heat pipe rely on temperature and pressure sensors, infrared thermal imagers, and other means to reveal the heat transfer patterns within a single pulsating heat pipe through experimental analysis. However, these methods cannot directly monitor the flow and phase change behavior characteristics of the vapor-liquid working fluid.

[0004] Triboelectric nanogenerators can convert minute mechanical disturbances into electrical signals, offering advantages such as high sensitivity and flexible, adaptable structures. Therefore, introducing triboelectric nanogenerators into the study of pulsating heat pipes, combined with real-time temperature information on working fluid flow and wall heat transfer, to analyze and perceive their operational status, is of significant importance and holds promising development potential. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose an intelligent sensing system and method for the working fluid state inside a pulsating heat pipe based on temperature monitoring. By using the electrical signal generated by the solid-liquid (vapor) friction material on the pulsating heat pipe and the working fluid temperature signal, and in conjunction with an electrometer, temperature acquisition device, oscilloscope, data analyzer and computer processing system, the internal working fluid flow state can be analyzed and sensed in real time.

[0006] To achieve the above objectives, the technical solution specifically adopted by the present invention is as follows: The intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring includes a pulsating heat pipe, electrodes and leads, a temperature acquisition device, an electrometer, an oscilloscope, a data analyzer, a computer, and a heating section. The pulsating heat pipe comprises multiple experimental sections, each consisting of a composite section of solid-liquid (vapor) frictional and non-frictional materials, used to generate triboelectric signals through contact with the flowing vapor-liquid working fluid. Temperature sensors are arranged in the experimental sections and connected to the temperature acquisition device to monitor pipe wall temperature changes in real time and generate temperature signals. Electrodes and leads of each section are attached to the outer wall surface of the solid-liquid (vapor) frictional material polytetrafluoroethylene (PTFE) pipe section to extract and transmit the triboelectric signals to the electrometer. The electrometer detects and amplifies the triboelectric signals, and the outputs of the temperature acquisition device and the electrometer are connected to the oscilloscope for reorganizing the acquired temperature and triboelectric signals. The computer and data analyzer receive and analyze the characteristics of the triboelectric and temperature signals to obtain the flow state and thermophysical properties of the vapor-liquid working fluid inside the pulsating heat pipe, and present this information graphically on the computer. The heating section is the heat load input area of ​​the pulsating heat pipe.

[0007] Furthermore, the solid-liquid (vapor) friction material pipe section is made of polytetrafluoroethylene or a composite material that meets the requirements for triboelectric power generation.

[0008] Furthermore, the solid-liquid (vapor) friction material pipe segments are arranged at intervals along the experimental section, and non-friction material isolation sections are set between adjacent pipe segments. The non-friction material isolation sections are mainly used to isolate the mutual influence between the electrical signals of each friction material segment. The length of this section should be as short as possible while meeting the processing requirements. The length of the solid-liquid (vapor) friction material pipe segments is 10~20mm, and the number is 5~10 segments. The shorter the length of this section and the more segments there are, the closer the perception result is to the real situation.

[0009] Furthermore, the electrode is a copper thin-film electrode attached to the outer wall of the solid-liquid (vapor) friction material pipe section and led out through a high-temperature resistant wire.

[0010] Furthermore, the oscilloscope includes a signal processing module, which is used to filter and denoise the acquired signal, extract characteristic parameters such as frequency, amplitude and pulse interval of the waveform, and calculate the working fluid temperature and flow pattern according to the pre-calibrated correspondence.

[0011] This invention also provides an intelligent sensing method for the working fluid state inside a pulsating heat pipe based on temperature monitoring. The method employs the aforementioned intelligent sensing system to monitor the working fluid state inside the pulsating heat pipe, and includes the following steps: Step 1: Signal Generation When the working fluid in the pulsating heat pipe flows through multiple sections of solid-liquid (vapor) friction material, a triboelectric signal containing geometric information of vapor bubbles and liquid columns is generated through solid-liquid (vapor) contact friction. Step 2: Signal Acquisition The triboelectric signal is exported to the electrometer through electrodes and leads, and the pipe wall temperature signal containing phase change heat transfer information is collected to the temperature acquisition unit through the temperature sensor. Step 3: Signal Processing The computer and data analyzer synchronously receive and process triboelectric signals and temperature signals, and extract the frequency, amplitude and pulse interval characteristic parameters of the triboelectric signals. Step 4: Status Analysis Based on the pre-calibrated feature mapping relationship, the flow state and thermophysical properties of the working fluid are analyzed.

[0012] Furthermore, step 3 specifically includes: Step 3.1: Filter and denoise the triboelectric signal; Step 3.2: Identify the pulse waveform boundaries in the triboelectric signal; Step 3.3: Calculate the time interval and amplitude change rate between adjacent pulses; Step 3.4: Correlate the temperature signal abrupt change point with the triboelectric signal pulse sequence. This invention has the following characteristics and beneficial effects:

[0013] 1) This invention combines triboelectric nanogenerator technology with pulsating heat pipes, and the triboelectric nanogenerator signal is extremely sensitive to the interaction between the working fluid and the pipe wall. Polytetrafluoroethylene (PTFE) material has strong electronegativity and can generate significant charge transfer in solid-liquid (vapor) friction. Even under low flow rates or with a small amount of vapor movement, it can still generate a detectable electrical signal, ensuring detection sensitivity.

[0014] 2) The friction signal features of this invention are very rich. The amplitude, frequency, and waveform of the triboelectric signal can all reflect the characteristics of the working fluid in different states. Through signal feature analysis, flow patterns such as liquid plug flow, vapor plug flow, bubbly flow, and mixed flow can be effectively distinguished, thereby revealing the internal heat transfer mechanism of the pulsating heat pipe more comprehensively.

[0015] 3) This invention requires no external power supply. Triboelectric nanogenerator technology is a self-driven sensing technology, with the signal originating directly from the contact between the working fluid and the friction layer. It can operate for extended periods without additional power, making it particularly suitable for applications in enclosed, high-temperature environments. Attached Figure Description

[0016] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a three-dimensional front view of the intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring, according to an embodiment of the present invention. Figure 2This is an experimental section diagram of the intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring, as described in an embodiment of the present invention. Figure 3 This is a diagram of the friction material of the polytetrafluoroethylene pipe section in the intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring, as described in an embodiment of the present invention. Explanation of reference numerals in the attached diagram: 1. Pulsating heat pipe; 2. Experimental section; 3. Composite section of frictional and non-frictional materials; 3-1. Frictional material tube section; 3-2. Non-frictional material isolation section; 4. Electrode and lead wire; 5. Temperature acquisition device; 6. Electrometer; 7. Oscilloscope; 8. Data analyzer; 9. Computer; 10. Heating section. Detailed Implementation

[0017] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0018] In a first aspect, this invention provides an intelligent sensing system for the working fluid state within a pulsating heat pipe based on temperature monitoring. The core of this system is a solid-liquid (vapor) friction material section 3-1, arranged in alternating layers of a frictional material (such as micro-roughened polytetrafluoroethylene) and a non-frictional material (such as copper tubing), on the experimental section 2 of the pulsating heat pipe 1. A copper thin film is deposited on the outer wall of the solid-liquid or solid-vapor friction material section 3-1 as an electrode, which is then led out using high-temperature resistant silver-plated copper wire. The solid-liquid (vapor) friction material section 3-1 is made of polytetrafluoroethylene or a composite material that meets the requirements for triboelectric power generation (e.g., fluorinated ethylene propylene copolymer and perfluoroalkoxy resin). When the working fluid flows in this section, a triboelectric signal is generated through solid-liquid (vapor) contact, and a temperature signal is generated through a temperature sensor and a temperature acquisition device, thereby achieving real-time monitoring and intelligent sensing of the working fluid state.

[0019] See attached document Figure 1 -Appendix Figure 3The intelligent sensing system for the working fluid state inside the pulsating heat pipe includes a pulsating heat pipe 1, electrodes and leads 4, a temperature acquisition device 5, an electrometer 6, an oscilloscope 7, a data analyzer 8, a computer 9, and a heating section 10. The pulsating heat pipe 1 includes multiple experimental sections 2, each consisting of a solid-liquid (vapor) friction material tube section 3-1, used to generate triboelectric signals by contacting the flowing vapor-liquid working fluid. Temperature sensors are arranged in the experimental sections 2 and connected to the temperature acquisition device 5 to monitor changes in the pipe wall temperature in real time and generate temperature signals. The electrodes and leads 4 of each section are attached to the outer wall surface of the solid-liquid (vapor) friction material tube section 3-1. The electrometer 6 is used to extract and transmit the triboelectric signal to the electrometer 5; the electrometer 6 is used to detect and amplify the triboelectric signal, and the output terminals of the temperature acquisition device 5 and the electrometer 6 are respectively connected to the oscilloscope 7 for reshaping the acquired temperature signal and triboelectric signal; the computer 9 and the data analyzer 8 receive and analyze the characteristics of the triboelectric signal and the temperature signal to obtain the flow state and thermophysical properties of the vapor-liquid working fluid in the pulsating heat pipe. The thermophysical properties refer to the temperature distribution characteristics and phase change heat transfer characteristics, which are presented as graphical information on the computer 9; the heating section 10 is the heat load input area of ​​the pulsating heat pipe 1.

[0020] Specifically, the pulsating heat pipe 1 is a metal pipe with an inner diameter of less than 6 mm, which is bent in a serpentine manner to form a heating section 10, an insulation section, and a condensation section. The working fluid is deionized water (other working fluids, such as ethanol, can also be used), and the liquid filling rate is generally 30%~80%. Solid-liquid (vapor) friction material pipe sections 3-1 with an inner diameter similar to that of the main pipe section are arranged on the pulsating heat pipe (the position and length of the pipe sections can be determined as needed). The solid-liquid (vapor) friction material pipe sections 3-1 are fixed to the main pipe section of the pulsating heat pipe with high-temperature resistant and hydrolysis-resistant silicone rubber adhesive to ensure long-term operational stability. Furthermore, the solid-liquid (vapor) friction material pipe segments 3-1 are arranged at intervals along the experimental section 2, and non-friction material isolation sections 3-2 are set between adjacent pipe segments. The non-friction material isolation sections 3-2 are mainly used to isolate the mutual influence between the electrical signals of each friction material segment. The shorter the length of this section is, the better, under the premise of meeting the processing technology. The length of the solid-liquid (vapor) friction material pipe segments 3-1 is 10~20mm, and the number is 5~10 segments. The length of the non-friction material isolation sections 3-2 is 10~15mm, and the number is 4~9 segments. The smaller the length and the more segments, the closer the perception result is to the real situation.

[0021] Electrodes, leads 4, and temperature sensor leads are installed at corresponding positions on the outer wall of the solid-liquid (vapor) friction material pipe section 3-1. The electrometer 6 and temperature acquisition device 5 transmit the collected triboelectric and temperature signals to the oscilloscope 7 for analysis and processing. The processed signals are then transmitted to the data analyzer 8 for analysis and uploaded to the computer 9 to generate a visualized dynamic information image, which is used to identify different flow states of the working fluid in this area.

[0022] During the operation of a pulsating heat pipe, the working fluid inside the pipe constantly undergoes reciprocating oscillating motion between the liquid column and bubbles. Simultaneously, the heating section continuously generates, grows, and merges bubbles, while the condensation section experiences a cycle of bubble shrinking, splitting, and disappearing. This process is extremely complex, but it is precisely the differences in these processes—such as the oscillating motion of the working fluid, the speed of bubble generation and disappearance, and the morphology and size of the bubbles—that determine the heat transfer performance of the pulsating heat pipe. When different forms of working fluid come into contact with the surface of the solid-liquid (vapor) friction material section 3-1 through the friction material region, the friction material, such as micro-roughened polytetrafluoroethylene, has strong electronegativity and can generate significant charge transfer during solid-liquid (vapor) friction. Even under low flow rates or with a small amount of bubble movement, a detectable electrical signal can still be generated, ensuring detection sensitivity. Then, the frequency, amplitude, and pulse interval characteristic parameters of the triboelectric signals carrying different information are analyzed. Different flow patterns correspond to different triboelectric signal characteristics. When the working fluid is in a slug flow pattern, the triboelectric signal typically exhibits high amplitude, low frequency, and wide pulse characteristics due to the large contact area between the liquid column and the friction material. When the working fluid is in a bubbly flow pattern, the triboelectric signal typically exhibits low amplitude and high frequency pulse characteristics due to the rapid passage of bubbles through the friction region. When the working fluid is in a mixed flow state, the triboelectric signal waveform shows irregular pulse changes. By analyzing the amplitude, frequency, and pulse interval of the triboelectric signal, the internal flow pattern of the pulsating heat pipe can be identified.

[0023] This embodiment enables real-time monitoring of the working fluid flow state inside the pulsating heat pipe 1 without altering its main structure and heat transfer performance. Visual experimental research and analysis show that the obtained signal information is essentially consistent with the actual flow state of the working fluid, thus verifying the feasibility and effectiveness of the method.

[0024] In a second aspect, this invention provides an intelligent sensing method for the working fluid state inside a pulsating heat pipe based on temperature monitoring. The method works by utilizing the contact electrostatic effect when a liquid column or vapor bubble flows through a friction material section, resulting in charge transfer between the liquid (gas) and solid surfaces, creating a potential difference. The periodicity of the flow and the changes in contact patterns caused by phase transitions are reflected in the output signal as specific frequency and amplitude characteristics. Simultaneously, changes in the evaporation or condensation state of the working fluid inside the pipe lead to changes in the wall temperature, exhibiting a regular characteristic signal pattern. Finally, the state change characteristics of the internal working fluid can be deduced by utilizing the relationship and calibration between the triboelectric signal and the temperature signal. Specifically, the method includes the following steps: Step 1: Signal Generation When the working fluid in the pulsating heat pipe 1 flows through the multiple segments of solid-liquid (vapor) friction material pipe 3-1 arranged at intervals, a triboelectric signal containing geometric information of vapor bubbles and liquid columns is generated through solid-liquid (vapor) contact friction.

[0025] Step 2: Signal Acquisition The triboelectric signal is transmitted to the electrometer 6 via the electrode and lead wire 4, while the pipe wall temperature signal containing phase change heat transfer information is collected by the temperature sensor and transmitted to the temperature acquisition unit 5.

[0026] Step 3: Signal Processing The computer 9 and the data analyzer 8 synchronously receive and process the triboelectric signal and temperature signal, and extract the frequency, amplitude and pulse interval characteristic parameters of the triboelectric signal.

[0027] Step 3.1: Apply wavelet denoising to the triboelectric signal to reduce the impact of environmental electromagnetic interference and high-frequency noise on the triboelectric signal.

[0028] Step 3.2: The pulse waveform boundary in the triboelectric signal is identified by setting a voltage threshold and time window on an oscilloscope. When the signal amplitude exceeds the preset threshold, it is determined to be a valid pulse.

[0029] Step 3.3: Calculate the time interval and amplitude change rate of adjacent pulses.

[0030] Step 3.4: Correlate the temperature signal abrupt change point with the triboelectric signal pulse sequence. When the temperature in the evaporation section rises rapidly, it indicates that the phase change inside the pipe is enhanced and more bubbles are generated. At this time, the liquid plug oscillation intensifies, and the corresponding triboelectric signal amplitude increases. When local areas dry out, the contact between the liquid and the friction material weakens, and the triboelectric signal will show pulse interruption or amplitude decrease.

[0031] Step 4: State Analysis. Based on the pre-established characteristic mapping relationship between the triboelectric signal and the temperature signal, the flow state and thermophysical properties of the working fluid are analyzed. Specifically, the computer 9 and the data analyzer 8 do not directly and automatically identify the working fluid state, but rather determine the state by performing correlation analysis on the characteristic parameters of the triboelectric signal and the temperature signal. These characteristic parameters include the amplitude, frequency, pulse interval, and pulse width variation of the triboelectric signal, as well as the rate of change and abrupt changes in the temperature signal. The pre-established characteristic mapping relationship between the triboelectric signal and the temperature signal is as follows: when the working fluid is in a slug flow, due to the large contact area between the liquid column and the friction material, the triboelectric signal typically exhibits high amplitude, low frequency, and wide pulse characteristics; when the working fluid is in a bubbly flow, due to the rapid passage of bubbles through the friction area, the triboelectric signal typically exhibits low amplitude and high frequency pulse characteristics; when the working fluid is in a mixed flow state, the triboelectric signal waveform shows irregular pulse changes. By analyzing the amplitude, frequency, and pulse interval of the triboelectric signal, the internal flow pattern of the pulsating heat pipe can be identified.

[0032] In summary, the method of this invention, during signal analysis, uses an electrometer to measure the instantaneous voltage, current, or charge output by each friction material segment due to the triboelectric nano-power generation principle, and a temperature acquisition device to collect temperature signals. The collected friction and temperature signals are then aggregated using an oscilloscope and transmitted in real time to a data analyzer. Finally, these signals are extracted and processed by a computer, transforming the friction and temperature signals into characteristic signals for analysis. Then, by utilizing the correspondence between signal characteristics and phase transitions and temperature changes, a visualized dynamic information image of the working fluid state inside the pulsating heat pipe is generated, thereby achieving the purpose of intelligent sensing of the flow and heat transfer characteristics of the working fluid inside the pipe.

[0033] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A temperature-monitoring-based intelligent sensing system for the working fluid state inside a pulsating heat pipe, comprising a pulsating heat pipe (1), electrodes and leads (4), a temperature acquisition device (5), an electrometer (6), an oscilloscope (7), a data analyzer (8), a computer (9), and a heating section (10); characterized in that, The pulsating heat pipe (1) includes multiple experimental sections (2) whose main body is a composite section of solid-liquid or solid-vapor friction and non-friction materials (3), which are used to generate triboelectric signals by contacting the flowing vapor-liquid working fluid. The experimental section (2) is equipped with a temperature sensor connected to a temperature acquisition unit (5) to monitor the pipe wall temperature change in real time and generate a temperature signal. The electrode and lead wire (4) are connected to each solid-liquid or solid-vapor friction material pipe section (3-1) for outputting triboelectric signals to the electrometer (6); The electrometer (6) is used to detect and amplify the triboelectric signal, and the output terminals of the temperature acquisition unit (5) and the electrometer (6) are respectively connected to an oscilloscope (7) for reshaping the acquired temperature and triboelectric signals; The computer (9) and the data analyzer (8) receive and analyze the characteristics of triboelectric signals and temperature signals to obtain the flow state and thermophysical properties of the vapor-liquid working fluid in the pulsating heat pipe, and present them in the computer (9) as graphic information. The heating section (10) is the heat load input area of ​​the pulsating heat pipe (1).

2. The intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 1, characterized in that: The solid-liquid or solid-vapor friction material pipe section (3-1) is made of polytetrafluoroethylene or a composite material that meets the requirements of triboelectric power generation.

3. The intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 1, characterized in that: The solid-liquid or solid-vapor friction material pipe section (3-1) is arranged at intervals along the experimental section (2), and a non-friction material isolation section (3-2) is provided between adjacent pipe sections. The length of the solid-liquid or solid-vapor friction material pipe section (3-1) is 10~20mm, and the number is 5~10 sections.

4. The intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 1, characterized in that: The electrode is a copper thin film electrode that is attached to the outer wall of the solid-liquid or solid-vapor friction material pipe section (3-1) and led out through a high-temperature resistant silver-plated copper wire.

5. The intelligent sensing system for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 1, characterized in that: The oscilloscope (7) includes a signal processing module, which is used to filter and denoise the acquired signal, extract the frequency, amplitude and pulse interval of the waveform, and calculate the working fluid temperature and flow pattern according to the pre-calibrated correspondence.

6. A method for intelligent sensing of the working fluid state inside a pulsating heat pipe based on temperature monitoring, characterized in that: The intelligent sensing system described in any one of claims 1-5 is used to monitor the working fluid state inside the pulsating heat pipe.

7. The intelligent sensing method for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 6, characterized in that: Includes the following steps: Step 1: Signal Generation When the working fluid in the pulsating heat pipe (1) flows through multiple sections of solid-liquid or solid-vapor friction material pipes (3-1) arranged at intervals, a triboelectric signal containing geometric information of vapor bubbles and liquid columns is generated through solid-liquid or solid-vapor contact friction. Step 2: Signal Acquisition The triboelectric signal is exported to the electrometer (6) through the electrode and lead wire (4), and the pipe wall temperature signal containing phase change heat transfer information is collected by the temperature sensor and sent to the temperature acquisition unit (5). Step 3: Signal Processing The computer (9) and the data analyzer (8) synchronously receive and process the triboelectric signal and temperature signal, and extract the frequency, amplitude and pulse interval characteristic parameters of the triboelectric signal; Step 4: Status Analysis Based on the pre-calibrated feature mapping relationship, the flow state and thermophysical properties of the working fluid are analyzed.

8. The intelligent sensing method for the working fluid state inside a pulsating heat pipe based on temperature monitoring as described in claim 7, characterized in that: Step 3 specifically includes: Step 3.1: Filter and denoise the triboelectric signal; Step 3.2: Identify the pulse waveform boundaries in the triboelectric signal; Step 3.3: Calculate the time interval and amplitude change rate between adjacent pulses; Step 3.4: Correlate the temperature signal abrupt change point with the triboelectric signal pulse sequence.

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