The n-type silicon integrated-back contact（IBC） solar cell has attracted much attention due to its high efficiency,whereas its performance is very sensitive to the wafer of low quality or the contamination during hi...The n-type silicon integrated-back contact（IBC） solar cell has attracted much attention due to its high efficiency,whereas its performance is very sensitive to the wafer of low quality or the contamination during high temperature fabrication processing, which leads to low bulk lifetime τbulk. In order to clarify the influence of bulk lifetime on cell characteristics, two-dimensional（2D） TCAD simulation, combined with our experimental data, is used to simulate the cell performances, with the wafer thickness scaled down under various τbulk conditions. The modeling results show that for the IBC solar cell with high τbulk,（such as 1 ms-2 ms）, its open-circuit voltage V oc almost remains unchanged, and the short-circuit current density J sc monotonically decreases as the wafer thickness scales down. In comparison, for the solar cell with low τbulk（for instance, 〈 500 μs） wafer or the wafer contaminated during device processing, the V oc increases monotonically but the J sc first increases to a maximum value and then drops off as the wafer＇s thickness decreases. A model combing the light absorption and the minority carrier diffusion is used to explain this phenomenon. The research results show that for the wafer with thinner thickness and high bulk lifetime, the good light trapping technology must be developed to offset the decrease in J sc.展开更多
The Cl2-sensitive heteropolysiloxanes(HPS) film was formed on the interdigital capacitor based on silicon dioxide by means of sol-gel process and spin-on technique.Measurements of interdigital capacitance were perform...The Cl2-sensitive heteropolysiloxanes(HPS) film was formed on the interdigital capacitor based on silicon dioxide by means of sol-gel process and spin-on technique.Measurements of interdigital capacitance were performed at room temperature for frequencies 100 Hz,1 kHz and 10 kHz.It is shown that there is a linear relationship between the capacitance and the concentration of chlorine gas.Influences of the measurement frequency and film thickness of silicate on the sensitivity of the sensor to C12 gas were discussed.And organically modified N,N-diethylaminopropyl-trimethoxysilane (APMS) had a much higher sensitivity.展开更多
This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,...This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.展开更多
Liquid metal filling flow process in the microscale during the centrifugal casting process was studied by means of similar physical simulation. The research was focused on derived similarity criterion. Based on the tr...Liquid metal filling flow process in the microscale during the centrifugal casting process was studied by means of similar physical simulation. The research was focused on derived similarity criterion. Based on the traditional flow equations, the flow equation and the Bernoulli＇s equation for liquid metal flows in micro-scale space were derived, which provides a mathematical model for numerical simulation of micro-scale flow. In the meanwhile, according to the micro-flow equation and the similarity theory, the similarity criterion for the physical simulation of the mold filling behaviors was presented under centrifugal force field, so as to achieve the visual observation and quantitative analysis of micro-flow process.展开更多
A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was ...A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.展开更多
By means of similar physical simulation, liquid metal filling flow pattern in the microscale during the centrifugal casting process was studied. It was found that, in microscale, the flow channel with the maximum cros...By means of similar physical simulation, liquid metal filling flow pattern in the microscale during the centrifugal casting process was studied. It was found that, in microscale, the flow channel with the maximum cross-sectional area was filled first, and the micro flow channels with 0.1 mm in diameter were filled when the rotational speed was increased to 964 r/min. The total fluid energy remained constant during the mould filling, and the changes of cross-sectional area only occurred in the microflow channels with 0.3 mm in diameter. Filling velocity increased with processing time, and a peak value was achieved rapidly, followed by a gentle increase as the process proceeded further. The time required to achieve the peak filling rate decreased dramatically with increase of rotational speed.展开更多
Micromixing efficiency of viscous media in Y-type micro-channel reactor was studied by using iodide-iodate test reaction as working system.Experiments were carried out in water-glycerin mixtures with 7 different visco...Micromixing efficiency of viscous media in Y-type micro-channel reactor was studied by using iodide-iodate test reaction as working system.Experiments were carried out in water-glycerin mixtures with 7 different viscosities.The experimental results showed that segregation index of the micro-channel reactor increases with the decrease of volumetric flow rate and the increase of solution viscosity.Based on the incorporation model,the micromixing time tm of the micro-channel reactor was estimated in the range of 10-4-10-3s at different viscosities,which indicated that the micro-channel reactor possesses a much better micromixing performance compared to the stirred tank(tm=0.02-0.2s).展开更多
Lamb waves are used to detect fouling in food vessels. The propagation of the Lamb waves in plates exhibits many modes and dispersion characteristics, which have great influence on fouling detection. The relative dist...Lamb waves are used to detect fouling in food vessels. The propagation of the Lamb waves in plates exhibits many modes and dispersion characteristics, which have great influence on fouling detection. The relative distribution of the in-plane and out-of-plane displacement of the mode across the thickness of the plate will determine the sensitivity of the mode to a particular loading condition. By considering the dispersion and multi-mode characteristics of guided waves, an interdigital polyvi- nylidene fluoride （PVDF） transducer is designed to realize the mode selection of gnided waves, and a single a0 mode is used for guided wave detection. Fouling detection experiments are conducted in the laboratory using epoxy adhesive on a thin plate. Using the interdigital PVDF transducer, three fouled areas are detected. Using one of the time-frequency analysis methods, the waveforms are further processed. This also demonstrates the validity of this method of fouling detection.展开更多
Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attenti...Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon （SIC） was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.展开更多
The algorithm of gaseous flow in bi-dimensional micro-channels is set up andthe corresponding program based on micro-flow theory is presented. Gaseous flow in micro-channels isnumerically analyzed and the pressure dro...The algorithm of gaseous flow in bi-dimensional micro-channels is set up andthe corresponding program based on micro-flow theory is presented. Gaseous flow in micro-channels isnumerically analyzed and the pressure drop along the duct as well .as the velocity profile in themicro-channels is obtained. The numerical results agreed well with the experimental results in thereferences. Moreover, the effects of Kn, sigma_v and Re on the velocity profiles are analyzed. It isfound that for Kn>0.001, with increasing Kn number, the slip velocity on the wall boundaryincreases; the tangential momentum coefficient sigma_v affects the slip velocity greatly. The slipvelocity increases with decreasing a, In the slip flow regime and for low Re numbers, the slipvelocity is little influenced by the Re number.展开更多
Numerical simulation using the finite differential method was carried out to analyze the diffusion of an impulse sample in the micro-channel driven by electroosmosis. The results show that the electrical field strengt...Numerical simulation using the finite differential method was carried out to analyze the diffusion of an impulse sample in the micro-channel driven by electroosmosis. The results show that the electrical field strength applied externally and the concentration of buffer solution play a significant role in the diffusion of sample, however, hydraulic diameter and aspect ratio of height to width of channel play a small role in it. Weakening the electrical field strength applied externally and the concentration of buffer solution properly can prevent the sample band from broadening effectively, and promote the efficiency of testing and separation as well as keep a faster speed of transport. The conclusions are helpful to the optimal design for micro-channel.展开更多
Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stab...Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stability have hindered their large-scale commercial application.Herein,aflexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays(MNAs)is pro-posed.The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3.Due to its porous and interdigital structure,the maximum sensitivity(0.07 kPa-1)of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor,and it was much greater than that of aflat pressure sensor without a porous MNA structure.Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sen-sor.In addition,the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure.Most importantly,it was found that the sensor could accurately monitor the motion of afinger,wrist joint,arm,face,abdomen,eye,and Adam’s apple.Furthermore,preliminary semantic recognition was achieved by monitoring the movement of the Adam’s apple.Finally,multiple pressure sensors were integrated into a 33 array to detect a spatial pressure distribu-×tion.Compared to the sensors reported in previous works,the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.展开更多
A novel highly porous 3-D poly（e-caprolactone） （PCL） scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed ...A novel highly porous 3-D poly（e-caprolactone） （PCL） scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed to form the microchannel in PCL matrix. The morphology, porosity and mechanical properties of the scaffolds were studied and calculated. It was found that the larger the content of chitosan fiber is, the higher the porosity would be, due to the volumetric expansion of chitosan fiber in PCL matrix during it being leached. In addition, the less the content of chitosan fiber is, the higher the compressive modulus would be.展开更多
With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is pro...With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment.In this study,thermal resistance theoretical model of the micro-channel heat sink was first established.Then,fabrication process of the micro-channel heat sink was introduced.Subsequently,heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform.Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application.Moreover,the micro-channel structures in the heat sink were optimized by orthogonal test.Based on the orthogonal optimization,heat dissipation performance of the micro-channel radiator was further improved.展开更多
Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a microflow is the direct simulation Monte Carlo(DSMC) method, which is used in this paper to investigate primary...Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a microflow is the direct simulation Monte Carlo(DSMC) method, which is used in this paper to investigate primary flow properties of supersonic gas in a circular micro-channel for different inflow conditions, such as free stream at different altitudes, with different incoming Mach numbers, and with different angles of attack. Simulation results indicate that the altitude and free stream incoming Mach number have a significant effect on the whole micro-channel flow field, whereas the angle of attack mainly affects the entrance part of micro-channel flow field. The fundamental mechanism behind the simulation results is also presented. With the increase of altitude, thr free stream would be partly prevented from entering into micro-channel.Meanwhile, the gas flow in micro-channel is decelerated, and the increase in the angle of attack also decelerates the gas flow. In contrast, gas flow in micro-channel is accelerated as free stream incoming Mach number increases. A noteworthy finding is that the rarefaction effects can become very dominant when the free stream incoming Mach number is low. In other words, a free stream with a larger incoming velocity is able to reduce the influence of the rarefaction effects on gas flow in the micro-channel.展开更多
Currently,the increasing demands for portable,implantable,and wearable electronics have triggered the interest in miniaturized energy storage devices.Different from conventional energy storage devices,interdigital mic...Currently,the increasing demands for portable,implantable,and wearable electronics have triggered the interest in miniaturized energy storage devices.Different from conventional energy storage devices,interdigital microbatteries(IMBs) are free of separators and prepared on a single substrate,potentially achieving a short ionic diffusion path and better performance.Meanwhile,they can be easily fabricated and integrated into on-chip miniaturized electronics,holding the promise to provide long-lasting power for advanced microelectronic devices.To date,while many seminal works have been reviewed the topic of microbatteries,there is no work that systematically summarizes the development of IMBs of high energy density and stable voltage platforms from fabrication,functionalization to integration.The current review focuses on the most recent progress in IMBs,discussing advanced micromachining techniques with compatible features to construct high-performance IMBs with smart functions and intelligent integrated systems.The future opportunities and challenges of IMBs are also highlighted,calling for more efforts in this dynamic and fast-growing research field.展开更多
In this work the applicability of the micro-channel reactor technique to the production of promising platform chemical 5-hydroxymethyl furan(HMF) from fructose in aqueous solution is systemically investigated by perfo...In this work the applicability of the micro-channel reactor technique to the production of promising platform chemical 5-hydroxymethyl furan(HMF) from fructose in aqueous solution is systemically investigated by performing CFD simulations.Influential factors including solvents,residence time distribution of reaction mixtures,heat transfer conditions and micro-channel configurations are evaluated in terms of the reaction performance indices,i.e.,conversion of fructose,HMF selectivity and yield.A scale-up method from a single channel to a multiple channel reactor is also proposed.It is demonstrated that:1) at the single channel scale,controlling residence times and temperature distribution of the reaction mixture within the channel is crucial for enhancing the reaction performance,while different channel configurations lead to marginal improvements;2) for the scaling-up of the reaction process,a reactor module containing 15 circular parallel channels could be used as module blocks,which can be stacked one by one to meet the required reactor performance and production capacity.The present results show that micro-reactors are quite suitable for HMF production.展开更多
In the micro-molding of component with a micro-sized channel, the ability for polymer melt to flowing into the micro-channel in a macro-sized part is a big challenge. The multidimensional flow behaviors are included i...In the micro-molding of component with a micro-sized channel, the ability for polymer melt to flowing into the micro-channel in a macro-sized part is a big challenge. The multidimensional flow behaviors are included in the injection molding the macro-component with a micro-channel. In this case, a simplified model is used to analyze the flow behaviors of the macro-sized part within a micro-channel. The flow behaviors in the macro-cavity are estimated by using the finite element and finite difference methods. The influence of the injection rate, micro-channel size, heat transfer coefficient, and mold temperature on the flowing distance is investigated based on the non-isothermal analytic method. The results show that an increase in the radius of the micro-channel and mold temperature can improve effectively the flowing distance in the micro-channel.展开更多
A fully developed steady immiscible flow of nanofluid in a two-layer microchannel is studied in the presence of electro-kinetic effects.Buongiorno’s model is employed for describing the behavior of nanofluids.Differe...A fully developed steady immiscible flow of nanofluid in a two-layer microchannel is studied in the presence of electro-kinetic effects.Buongiorno’s model is employed for describing the behavior of nanofluids.Different from the previous studies on two-layer channel flow of a nanofluid,the present paper introduces the flux conservation conditions for the nanoparticle volume fraction field,which makes this work new and unique,and it is in coincidence with practical observations.The governing equations are reduced into a group of ordinary differential equations via appropriate similarity transformations.The highly accurate analytical approximations are obtained.Important physical quantities and total entropy generation are analyzed and discussed.A comparison is made to determine the significance of electrical double layer(EDL)effects in the presence of an external electric field.It is found that the Brownian diffusion,the thermophoresis diffusion,and the viscosity have significant effects on altering the flow behaviors.展开更多
基金Project supported by the Chinese Ministry of Science and Technology Projects(Grant Nos.2012AA050304 and Y0GZ124S01)the National Natural Science Foundation of China(Grant Nos.11104319,11274346,51202285,51402347,and 51172268)the Fund of the Solar Energy Action Plan from the Chinese Academy of Sciences(Grant Nos.Y3ZR044001 and Y2YF014001)
文摘The n-type silicon integrated-back contact（IBC） solar cell has attracted much attention due to its high efficiency,whereas its performance is very sensitive to the wafer of low quality or the contamination during high temperature fabrication processing, which leads to low bulk lifetime τbulk. In order to clarify the influence of bulk lifetime on cell characteristics, two-dimensional（2D） TCAD simulation, combined with our experimental data, is used to simulate the cell performances, with the wafer thickness scaled down under various τbulk conditions. The modeling results show that for the IBC solar cell with high τbulk,（such as 1 ms-2 ms）, its open-circuit voltage V oc almost remains unchanged, and the short-circuit current density J sc monotonically decreases as the wafer thickness scales down. In comparison, for the solar cell with low τbulk（for instance, 〈 500 μs） wafer or the wafer contaminated during device processing, the V oc increases monotonically but the J sc first increases to a maximum value and then drops off as the wafer＇s thickness decreases. A model combing the light absorption and the minority carrier diffusion is used to explain this phenomenon. The research results show that for the wafer with thinner thickness and high bulk lifetime, the good light trapping technology must be developed to offset the decrease in J sc.
文摘The Cl2-sensitive heteropolysiloxanes(HPS) film was formed on the interdigital capacitor based on silicon dioxide by means of sol-gel process and spin-on technique.Measurements of interdigital capacitance were performed at room temperature for frequencies 100 Hz,1 kHz and 10 kHz.It is shown that there is a linear relationship between the capacitance and the concentration of chlorine gas.Influences of the measurement frequency and film thickness of silicate on the sensitivity of the sensor to C12 gas were discussed.And organically modified N,N-diethylaminopropyl-trimethoxysilane (APMS) had a much higher sensitivity.
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)The APC was covered by the Special Innovation Project Fund of the the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01).
文摘This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.
基金Project(51005053)supported by the National Science Foundation for Young Scientists of China
文摘Liquid metal filling flow process in the microscale during the centrifugal casting process was studied by means of similar physical simulation. The research was focused on derived similarity criterion. Based on the traditional flow equations, the flow equation and the Bernoulli＇s equation for liquid metal flows in micro-scale space were derived, which provides a mathematical model for numerical simulation of micro-scale flow. In the meanwhile, according to the micro-flow equation and the similarity theory, the similarity criterion for the physical simulation of the mold filling behaviors was presented under centrifugal force field, so as to achieve the visual observation and quantitative analysis of micro-flow process.
基金Project(51146010)supported by the National Natural Science Foundation of ChinaProject(S2011040003189)supported by the Doctoral Research Fund of Guangdong Natural Science Foundation,ChinaProject supported by the Fundation of Key Laboratory of Surface Functional Structure Manufacturing of Guangdong Higher Education Institutes,South China University of Technology
文摘A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.
基金Project (51005053) supported by the National Science Foundation for Young Scientists of China
文摘By means of similar physical simulation, liquid metal filling flow pattern in the microscale during the centrifugal casting process was studied. It was found that, in microscale, the flow channel with the maximum cross-sectional area was filled first, and the micro flow channels with 0.1 mm in diameter were filled when the rotational speed was increased to 964 r/min. The total fluid energy remained constant during the mould filling, and the changes of cross-sectional area only occurred in the microflow channels with 0.3 mm in diameter. Filling velocity increased with processing time, and a peak value was achieved rapidly, followed by a gentle increase as the process proceeded further. The time required to achieve the peak filling rate decreased dramatically with increase of rotational speed.
基金Supported by the National-Natural Science Foundation of China （20821004, 20806004） and the National High Technology Research and Development Program of China （2007AA030207, 2006AA030202, 2006AA030203）.
文摘Micromixing efficiency of viscous media in Y-type micro-channel reactor was studied by using iodide-iodate test reaction as working system.Experiments were carried out in water-glycerin mixtures with 7 different viscosities.The experimental results showed that segregation index of the micro-channel reactor increases with the decrease of volumetric flow rate and the increase of solution viscosity.Based on the incorporation model,the micromixing time tm of the micro-channel reactor was estimated in the range of 10-4-10-3s at different viscosities,which indicated that the micro-channel reactor possesses a much better micromixing performance compared to the stirred tank(tm=0.02-0.2s).
基金This project is supported by National Natural Science Foundation of China (No. 60404017)Municipal Natural Science Foundation of Beijing, China (No.4052008)Plan of Excellent People Cultivation of Beijing, China (No. 20051D0501506)
文摘Lamb waves are used to detect fouling in food vessels. The propagation of the Lamb waves in plates exhibits many modes and dispersion characteristics, which have great influence on fouling detection. The relative distribution of the in-plane and out-of-plane displacement of the mode across the thickness of the plate will determine the sensitivity of the mode to a particular loading condition. By considering the dispersion and multi-mode characteristics of guided waves, an interdigital polyvi- nylidene fluoride （PVDF） transducer is designed to realize the mode selection of gnided waves, and a single a0 mode is used for guided wave detection. Fouling detection experiments are conducted in the laboratory using epoxy adhesive on a thin plate. Using the interdigital PVDF transducer, three fouled areas are detected. Using one of the time-frequency analysis methods, the waveforms are further processed. This also demonstrates the validity of this method of fouling detection.
基金supported by the National Natural Science Foundation of China(No.21176137) and Petro China
文摘Milliseconds process to produce hydrogen by steam methane reforming （SMR） reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon （SIC） was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.
文摘The algorithm of gaseous flow in bi-dimensional micro-channels is set up andthe corresponding program based on micro-flow theory is presented. Gaseous flow in micro-channels isnumerically analyzed and the pressure drop along the duct as well .as the velocity profile in themicro-channels is obtained. The numerical results agreed well with the experimental results in thereferences. Moreover, the effects of Kn, sigma_v and Re on the velocity profiles are analyzed. It isfound that for Kn>0.001, with increasing Kn number, the slip velocity on the wall boundaryincreases; the tangential momentum coefficient sigma_v affects the slip velocity greatly. The slipvelocity increases with decreasing a, In the slip flow regime and for low Re numbers, the slipvelocity is little influenced by the Re number.
基金Project supported by the National Natural Science Foundation of China (No.20299030)
文摘Numerical simulation using the finite differential method was carried out to analyze the diffusion of an impulse sample in the micro-channel driven by electroosmosis. The results show that the electrical field strength applied externally and the concentration of buffer solution play a significant role in the diffusion of sample, however, hydraulic diameter and aspect ratio of height to width of channel play a small role in it. Weakening the electrical field strength applied externally and the concentration of buffer solution properly can prevent the sample band from broadening effectively, and promote the efficiency of testing and separation as well as keep a faster speed of transport. The conclusions are helpful to the optimal design for micro-channel.
基金supported in part by the National Natural Science Foundation of China(Grant No.62104056)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LQ21F010010)+4 种基金the National Natural Science Foundation of China(Grant Nos.62141409 and 62204204)the National Key R&D Program of China(Grant No.2022ZD0208602)the Zhejiang Provincial Key Research&Development Fund(Grant Nos.2019C04003 and 2021C01041)the Shanghai Sailing Program(Grant No.21YF1451000)the Key Research and Development Program of Shaanxi(Grant No.2022GY-001).
文摘Flexible pressure sensors have many potential applications in the monitoring of physiological signals because of their good biocompatibil-ity and wearability.However,their relatively low sensitivity,linearity,and stability have hindered their large-scale commercial application.Herein,aflexible capacitive pressure sensor based on an interdigital electrode structure with two porous microneedle arrays(MNAs)is pro-posed.The porous substrate that constitutes the MNA is a mixed product of polydimethylsiloxane and NaHCO3.Due to its porous and interdigital structure,the maximum sensitivity(0.07 kPa-1)of a porous MNA-based pressure sensor was found to be seven times higher than that of an imporous MNA pressure sensor,and it was much greater than that of aflat pressure sensor without a porous MNA structure.Finite-element analysis showed that the interdigital MNA structure can greatly increase the strain and improve the sensitivity of the sen-sor.In addition,the porous MNA-based pressure sensor was found to have good stability over 1500 loading cycles as a result of its bilayer parylene-enhanced conductive electrode structure.Most importantly,it was found that the sensor could accurately monitor the motion of afinger,wrist joint,arm,face,abdomen,eye,and Adam’s apple.Furthermore,preliminary semantic recognition was achieved by monitoring the movement of the Adam’s apple.Finally,multiple pressure sensors were integrated into a 33 array to detect a spatial pressure distribu-×tion.Compared to the sensors reported in previous works,the interdigital electrode structure presented in this work improves sensitivity and stability by modifying the electrode layer rather than the dielectric layer.
基金financially supported by the China Scholarship Council and the Wisconsin Institute for Discovery(WID),that enabled the authors to perform this research at the University of Wisconsin-Madison,the National Natural Science Foundation of China(No.51303027)the Scientific Research Staring Foundation,Fujian University of Technology,China(No.GY-Z13028)
文摘A novel highly porous 3-D poly（e-caprolactone） （PCL） scaffold with micro-channels was fabricated by injection molding and diluent acetic acids leaching technologies. In this study, the chitosan fiber was employed to form the microchannel in PCL matrix. The morphology, porosity and mechanical properties of the scaffolds were studied and calculated. It was found that the larger the content of chitosan fiber is, the higher the porosity would be, due to the volumetric expansion of chitosan fiber in PCL matrix during it being leached. In addition, the less the content of chitosan fiber is, the higher the compressive modulus would be.
基金Supported by the National Natural Science Foundation of China(Grant Nos.51975135 and 52005422)Guangzhou Science and Technology Project(Grant No.201707010429)Special Innovation Projects of Universities in Guangdong Province(Grant No.2018GKTSCX085).
文摘With the advent of the 5G era,the design of electronic equipment is developing towards thinness,intelligence and multi-function,which requires higher cooling performance of the equipment.Micro-channel heat sink is promising for the heat dissipation of super-thin electronic equipment.In this study,thermal resistance theoretical model of the micro-channel heat sink was first established.Then,fabrication process of the micro-channel heat sink was introduced.Subsequently,heat transfer performance of the fabricated micro-channel heat sink was tested through the developed testing platform.Results show that the developed micro-channel heat sink has more superior heat dissipation performance over conventional metal solid heat sink and it is well suited for high power LEDs application.Moreover,the micro-channel structures in the heat sink were optimized by orthogonal test.Based on the orthogonal optimization,heat dissipation performance of the micro-channel radiator was further improved.
基金Project supported by the National Natural Science Foundation of China(Grant No.11802264)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20180896)
文摘Gas flow in a micro-channel usually has a high Knudsen number. The predominant predictive tool for such a microflow is the direct simulation Monte Carlo(DSMC) method, which is used in this paper to investigate primary flow properties of supersonic gas in a circular micro-channel for different inflow conditions, such as free stream at different altitudes, with different incoming Mach numbers, and with different angles of attack. Simulation results indicate that the altitude and free stream incoming Mach number have a significant effect on the whole micro-channel flow field, whereas the angle of attack mainly affects the entrance part of micro-channel flow field. The fundamental mechanism behind the simulation results is also presented. With the increase of altitude, thr free stream would be partly prevented from entering into micro-channel.Meanwhile, the gas flow in micro-channel is decelerated, and the increase in the angle of attack also decelerates the gas flow. In contrast, gas flow in micro-channel is accelerated as free stream incoming Mach number increases. A noteworthy finding is that the rarefaction effects can become very dominant when the free stream incoming Mach number is low. In other words, a free stream with a larger incoming velocity is able to reduce the influence of the rarefaction effects on gas flow in the micro-channel.
基金financial support from the National Natural Science Foundation of China(NSFC)(22109009)the China Postdoctoral Science Foundation(2020M680376)+2 种基金the National Key R&D Program of China(2017YFB1104300)the NSFC(21975027,22035005,52073159)the NSFC-STINT(21911530143)。
文摘Currently,the increasing demands for portable,implantable,and wearable electronics have triggered the interest in miniaturized energy storage devices.Different from conventional energy storage devices,interdigital microbatteries(IMBs) are free of separators and prepared on a single substrate,potentially achieving a short ionic diffusion path and better performance.Meanwhile,they can be easily fabricated and integrated into on-chip miniaturized electronics,holding the promise to provide long-lasting power for advanced microelectronic devices.To date,while many seminal works have been reviewed the topic of microbatteries,there is no work that systematically summarizes the development of IMBs of high energy density and stable voltage platforms from fabrication,functionalization to integration.The current review focuses on the most recent progress in IMBs,discussing advanced micromachining techniques with compatible features to construct high-performance IMBs with smart functions and intelligent integrated systems.The future opportunities and challenges of IMBs are also highlighted,calling for more efforts in this dynamic and fast-growing research field.
文摘In this work the applicability of the micro-channel reactor technique to the production of promising platform chemical 5-hydroxymethyl furan(HMF) from fructose in aqueous solution is systemically investigated by performing CFD simulations.Influential factors including solvents,residence time distribution of reaction mixtures,heat transfer conditions and micro-channel configurations are evaluated in terms of the reaction performance indices,i.e.,conversion of fructose,HMF selectivity and yield.A scale-up method from a single channel to a multiple channel reactor is also proposed.It is demonstrated that:1) at the single channel scale,controlling residence times and temperature distribution of the reaction mixture within the channel is crucial for enhancing the reaction performance,while different channel configurations lead to marginal improvements;2) for the scaling-up of the reaction process,a reactor module containing 15 circular parallel channels could be used as module blocks,which can be stacked one by one to meet the required reactor performance and production capacity.The present results show that micro-reactors are quite suitable for HMF production.
基金Project supported by the National Natural Science Foundation of China(Nos.51303027 and 11172271)the Scientific Research Staring Foundation,Fujian University of Technology of China(No.GY-Z13028)+1 种基金the Research Fund of Fujian Education Department(No.JA11189)the Research Fund for Enterprise Technology Innovation(No.2011-702-04)
文摘In the micro-molding of component with a micro-sized channel, the ability for polymer melt to flowing into the micro-channel in a macro-sized part is a big challenge. The multidimensional flow behaviors are included in the injection molding the macro-component with a micro-channel. In this case, a simplified model is used to analyze the flow behaviors of the macro-sized part within a micro-channel. The flow behaviors in the macro-cavity are estimated by using the finite element and finite difference methods. The influence of the injection rate, micro-channel size, heat transfer coefficient, and mold temperature on the flowing distance is investigated based on the non-isothermal analytic method. The results show that an increase in the radius of the micro-channel and mold temperature can improve effectively the flowing distance in the micro-channel.
基金Project supported by the National Natural Science Foundation of China(No.11872241)
文摘A fully developed steady immiscible flow of nanofluid in a two-layer microchannel is studied in the presence of electro-kinetic effects.Buongiorno’s model is employed for describing the behavior of nanofluids.Different from the previous studies on two-layer channel flow of a nanofluid,the present paper introduces the flux conservation conditions for the nanoparticle volume fraction field,which makes this work new and unique,and it is in coincidence with practical observations.The governing equations are reduced into a group of ordinary differential equations via appropriate similarity transformations.The highly accurate analytical approximations are obtained.Important physical quantities and total entropy generation are analyzed and discussed.A comparison is made to determine the significance of electrical double layer(EDL)effects in the presence of an external electric field.It is found that the Brownian diffusion,the thermophoresis diffusion,and the viscosity have significant effects on altering the flow behaviors.
