Metallised film capacitors(MFCs)are renowned for their unique self-healing(SH)properties,which bestow them with exceptional reliability and stability in the face of intense electric fields,high voltages,and pulse powe...Metallised film capacitors(MFCs)are renowned for their unique self-healing(SH)properties,which bestow them with exceptional reliability and stability in the face of intense electric fields,high voltages,and pulse power applications.Nonetheless,the exploration of SH characteristics concerning single-layer dielectric film remains insufficient for advancing MFC reliability evaluation.To establish the theoretical correlation of SH characteristics from the device to the film in the MFCs,this work developed a simulation model to analyse the SH dynamic behaviour in the MFCs.The effects of coupling capacitors,arc resistance and insulation resistance on the macroscopic characteristics(voltage drop and pulse current)are focused during the SH process in MFCs.The results indicate that SH is primarily associated with the voltage drop duration rather than the sampling current.Consequently,the SH process in MFC is characterised as an abrupt decrease in voltage to its minimum value.This refinement enhances the SH energy dissipation model of MFC.The quantified relationship between the macroscopic characteristics and microstructure evolution(polypropylene decomposition and aluminium electrode vaporisation)is established in MFCs under diverse SH energy levels.As SH energy and duration increase,the proportion of energy attributed to polypropylene decomposition increases,resulting in multi-layer ablation and adhesion within the metallised film and a pronounced deterioration in MFC electrical performance.The examination of macro-micro perspectives sheds new light on the intricate mechanisms governing the SH behaviour in MFCs,offering valuable insights for the advancement of their design,reliability evaluation,and performance optimisation in diverse electrical applications.展开更多
The printed circuit heat exchanger(PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the...The printed circuit heat exchanger(PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm.Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features.The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleateboiling-like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed.In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover,heat transfer deterioration will always appear, since the supercritical flow will finally develop into a filmboiling-like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE.展开更多
We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was fi...We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.展开更多
The concept of micro-total analysis systems(µTAS)introduced in the early 1990s revolutionized the development of lab-on-a-chip(LoC)technologies by miniaturizing and automating complex laboratory processes.Despite...The concept of micro-total analysis systems(µTAS)introduced in the early 1990s revolutionized the development of lab-on-a-chip(LoC)technologies by miniaturizing and automating complex laboratory processes.Despite their potential in diagnostics,drug development,and environmental monitoring,the widespread adoption of LoC systems has been hindered by challenges in scalability,integration,and cost-effective mass production.Traditional substrates like silicon,glass,and polymers struggle to meet the multifunctional requirements of practical applications.Lab-on-Printed Circuit Board(Lab-on-PCB)technology has emerged as a transformative solution,leveraging the cost-efficiency,scalability,and precision of PCB fabrication techniques.This platform facilitates the seamless integration of microfluidics,sensors,and actuators within a single device,enabling complex,multifunctional systems suitable for real-world deployment.Recent advancements have demonstrated Lab-on-PCB’s versatility across biomedical applications,such as point-of-care diagnostics,electrochemical biosensing,and molecular detection,as well as drug development and environmental monitoring.This review examines the evolution of Lab-on-PCB technology over the past eight years,focusing on its applications and impact within the research community.By analyzing recent progress in PCB-based microfluidics and biosensing,this work highlights how Lab-on-PCB systems address key technical barriers,paving the way for scalable and practical lab-on-chip solutions.The growing academic and industrial interest in Lab-on-PCB is underscored by a notable increase in publications and patents,signaling its potential for commercialization and broader adoption.展开更多
Electrowetting-on-dielectric(EWOD)is to directly control the wettability of liquids on the solid surface by applying the electric potential to the microelectrode array under the dielectric layer.The prototype of the E...Electrowetting-on-dielectric(EWOD)is to directly control the wettability of liquids on the solid surface by applying the electric potential to the microelectrode array under the dielectric layer.The prototype of the EWOD droplet creator with the sandwiched structure is used:the droplet is sandwiched between the top and bottom plates;the bot-tom plate consists of silicon used as the substrate of the microelectrode array,nitride sili-con film deposited by low pressure chemical vapor deposition as the dielectric layer and the fluorocarbon polymer film deposited by inductively coupled plasma chemical vapor deposition as the hydrophobic layer;and the top plate is the transparent electrode covered with the hydrophobic layer.To obtain the required minimum voltage,the process and the criterion of creating droplets are analyzed.At the voltage of 35 V the deionized water droplet surrounded in silicone oil is successfully created.展开更多
基金Major Research Plan of the National Natural Science Foundation of China,Grant/Award Numbers:92166206,92366302Science and Technology Projects of Hunan Province,Grant/Award Number:2024JJ6051。
文摘Metallised film capacitors(MFCs)are renowned for their unique self-healing(SH)properties,which bestow them with exceptional reliability and stability in the face of intense electric fields,high voltages,and pulse power applications.Nonetheless,the exploration of SH characteristics concerning single-layer dielectric film remains insufficient for advancing MFC reliability evaluation.To establish the theoretical correlation of SH characteristics from the device to the film in the MFCs,this work developed a simulation model to analyse the SH dynamic behaviour in the MFCs.The effects of coupling capacitors,arc resistance and insulation resistance on the macroscopic characteristics(voltage drop and pulse current)are focused during the SH process in MFCs.The results indicate that SH is primarily associated with the voltage drop duration rather than the sampling current.Consequently,the SH process in MFC is characterised as an abrupt decrease in voltage to its minimum value.This refinement enhances the SH energy dissipation model of MFC.The quantified relationship between the macroscopic characteristics and microstructure evolution(polypropylene decomposition and aluminium electrode vaporisation)is established in MFCs under diverse SH energy levels.As SH energy and duration increase,the proportion of energy attributed to polypropylene decomposition increases,resulting in multi-layer ablation and adhesion within the metallised film and a pronounced deterioration in MFC electrical performance.The examination of macro-micro perspectives sheds new light on the intricate mechanisms governing the SH behaviour in MFCs,offering valuable insights for the advancement of their design,reliability evaluation,and performance optimisation in diverse electrical applications.
基金provided by Science and Technology Development Project of Jilin Province(No.20230101338JC)。
文摘The printed circuit heat exchanger(PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm.Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features.The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleateboiling-like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed.In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover,heat transfer deterioration will always appear, since the supercritical flow will finally develop into a filmboiling-like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE.
基金the National Natural Science Foundation of China(50405001).
文摘We study here effects of nozzle layout on the droplet ejection of a micro atomizer, which was fabricated with the arrayed nozzles by the MEMS technology and actuated by a piezoelectric disc. A theoretical model was first built for this piezoelectric-liquid-structure coupling system to characterize the acoustic wave propagation in the liquid chamber, which determined the droplet formation out of nozzles. The modal analysis was carried out numerically to predict resonant frequencies and simulate the corresponding pressure wave field. By comparing the amplitude contours of pressure wave on the liquid-solid interface at nozzle inlets with the designed nozzle layout, behaviors of the device under different vibration modes can be predicted. Experimentally, an impedance analyzer was used to measure the resonant frequencies of the system. Three types of atomizers with different nozzle layouts were fabricated for measuring the effect of nozzle distribution on the ejection performance. The visualization experiment of droplet generation was carried out and volume flow rates of these devices were measured. The good agreement between the experiment and the prediction proved that only the increase of nozzles may not enhance the droplet generation and a design of nozzle distribution from a view-point of frequency is necessary for a resonant related atomizer.
文摘The concept of micro-total analysis systems(µTAS)introduced in the early 1990s revolutionized the development of lab-on-a-chip(LoC)technologies by miniaturizing and automating complex laboratory processes.Despite their potential in diagnostics,drug development,and environmental monitoring,the widespread adoption of LoC systems has been hindered by challenges in scalability,integration,and cost-effective mass production.Traditional substrates like silicon,glass,and polymers struggle to meet the multifunctional requirements of practical applications.Lab-on-Printed Circuit Board(Lab-on-PCB)technology has emerged as a transformative solution,leveraging the cost-efficiency,scalability,and precision of PCB fabrication techniques.This platform facilitates the seamless integration of microfluidics,sensors,and actuators within a single device,enabling complex,multifunctional systems suitable for real-world deployment.Recent advancements have demonstrated Lab-on-PCB’s versatility across biomedical applications,such as point-of-care diagnostics,electrochemical biosensing,and molecular detection,as well as drug development and environmental monitoring.This review examines the evolution of Lab-on-PCB technology over the past eight years,focusing on its applications and impact within the research community.By analyzing recent progress in PCB-based microfluidics and biosensing,this work highlights how Lab-on-PCB systems address key technical barriers,paving the way for scalable and practical lab-on-chip solutions.The growing academic and industrial interest in Lab-on-PCB is underscored by a notable increase in publications and patents,signaling its potential for commercialization and broader adoption.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.10472055 and 60411009)the Fundamental Research Foundation of Tsinghua University(Grant Nos.JC2003060 and JC2003061).
文摘Electrowetting-on-dielectric(EWOD)is to directly control the wettability of liquids on the solid surface by applying the electric potential to the microelectrode array under the dielectric layer.The prototype of the EWOD droplet creator with the sandwiched structure is used:the droplet is sandwiched between the top and bottom plates;the bot-tom plate consists of silicon used as the substrate of the microelectrode array,nitride sili-con film deposited by low pressure chemical vapor deposition as the dielectric layer and the fluorocarbon polymer film deposited by inductively coupled plasma chemical vapor deposition as the hydrophobic layer;and the top plate is the transparent electrode covered with the hydrophobic layer.To obtain the required minimum voltage,the process and the criterion of creating droplets are analyzed.At the voltage of 35 V the deionized water droplet surrounded in silicone oil is successfully created.
