An abnormal fluorescence intensity ratio （FIR） between two green emissions of Er3＋, at room temperature, which is larger than a normal value, emerged in many reported articles. However, up to now detailed work has ...An abnormal fluorescence intensity ratio （FIR） between two green emissions of Er3＋, at room temperature, which is larger than a normal value, emerged in many reported articles. However, up to now detailed work has seldom been done to clarify this abnormal phenomenon. In this paper, green upconversion luminescence of the β-NaLuF4：20%yb3＋,2%Er3＋ powder sample was investigated under 980 um excitation at different circumstances, different pump power densities and different temperatures as well as different air pressures. The corresponding local temperature calculated using FIR technique increased gradually with the enhancement of the pump power density. It was demonstrated that high pump power density of 980 nm laser led to the increase of local temperature of the luminescent material, which further gave the abnormal FIR.展开更多
Nanofluids have attracted many scientists due to their remarkable thermophysical properties.Small percentage of nanoparticles when added to conventional fluid significantly enhances the heat transfer features.Sustaina...Nanofluids have attracted many scientists due to their remarkable thermophysical properties.Small percentage of nanoparticles when added to conventional fluid significantly enhances the heat transfer features.Sustainability and efficiency of nanomaterials have key role in the advancement of nanotechnology.This article analyzes the Hall,Ohmic heating and velocity slip effects on the peristalsis of nanofluid.Convective boundary conditions and heat generation/absorption are considered to facilitate the heat transfer characteristics.Governing equations for the peristaltic flow through a curved channel are derived in curvilinear coordinates.The equations are numerically solved under the assumption of long wavelength and small Reynold number.It has been observed that nanofluid enhances the heat transfer rate and reduces the fluid temperature.Hartman number and Hall parameter show reverse behavior in fluid motion and heat transfer characteristics.In the presence of velocity slip,the pressure gradient rapidly decreases and dominant effect is seen in narrow portion of channel.展开更多
This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion t...This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases. Particular emphasis is placed on the derivation of new analytical expressions of effective specific heats at constant-strain and constant-stress situations, in which a modified Eshelby＇s micromechanics theory is developed and the interaction between inclusions is considered. As an illustrative example, the analytical expression of the effective specific heat for a three-phase thermoelastic composite is presented.展开更多
A comparative optimal design of fluid-saturated prismatic cellular metal honeycombs （PCMHs） having different cell shapes is presented for thermal management applications. Based on the periodic topology of each PCMH,...A comparative optimal design of fluid-saturated prismatic cellular metal honeycombs （PCMHs） having different cell shapes is presented for thermal management applications. Based on the periodic topology of each PCMH, a unit cell （UC） for thermal transport analysis was selected to calculate its effective thermal conductivity. Without introducing any empirical coefficient, we modified and extended the analytical model of parallel-series thermal-electric network to a wider porosity range （0.7 ~ 0.98） by considering the effects of two-dimensional local heat conduction in solid ligaments inside each UC. Good agreement was achieved between analytical predictions and numerical simulations based on the method of finite volume. The concept of ligament heat conduction efficiency （LTCE） was proposed to physically explain the mechanisms underlying the effects of ligament configuration on effective thermal conductivity （ETC）. Based upon the proposed theory, a construct strategy was developed for designing the ETC by altering the equivalent interaction angle with the direction of heat flow： relatively small average interaction angle for thermal conduction and relatively large one for thermal insulation.展开更多
Flow thermomechanics in reactive porous media is of importance in industry including the thermal processing of fossil fuel(coking understood as a slow pyrolysis)involving devolatilisation.On the way to provide a detai...Flow thermomechanics in reactive porous media is of importance in industry including the thermal processing of fossil fuel(coking understood as a slow pyrolysis)involving devolatilisation.On the way to provide a detailed description of the process,a multi-scale approach was chosen to estimate effective transport coefficients.For this case the Lattice Boltzmann method(LBM)was used due to its advantages to accurately model multi-physics and chemistry in a random geometry of granular media.After account for earlier studies,the paper presents description of the model with improved boundary conditions and a benchmark case.Results from meso-scale LBM calculations are presented and discussed regarding the spatial resolution and the choice of relaxation parameter along its influence on the accuracy compared with empirical formulae.Regarding the estimation of effective thermal conductivity coefficient it is shown that occurrence of devolatilization has a crucial effect by reducing heat transfer.Some quantitative results characterise the propagation of thermal front;also presented is the evolution of effective thermal conductivity.The work is a step forward towards a physically sound simulation of thermal processing of fossil fuel.展开更多
Dielectrophoresis(DEP)technology has become important application of microfluidic technology to manipulate particles.By using a local modulating electric field to control the combination of electroosmotic microvortice...Dielectrophoresis(DEP)technology has become important application of microfluidic technology to manipulate particles.By using a local modulating electric field to control the combination of electroosmotic microvortices and DEP,our group proposed a device using a direct current(DC)electric field to achieve continuous particle separation.In this paper,the influence of the Joule heating effect on the continuous separation of particles is analyzed.Results show that the Joule heating effect is caused by the local electric field,and the Joule heating effect caused by adjusting the modulating voltage is more significant than that by driving voltage.Moreover,a non-uniform temperature distribution exists in the channel due to the Joule heating effect,and the temperature is the highest at the midpoint of the modulating electrodes.The channel flux can be enhanced,and the enhancement of both the channel flux and temperature is more obvious for a stronger Joule heating effect.In addition,the ability of the vortices to trap particles is enhanced since a larger DEP force is exerted on the particles with the Joule heating effect;and the ability of the vortex to capture particles is stronger with a stronger Joule heating effect.The separation efficiency can also be increased because perfect separation is achieved at a higher channel flux.Parameter optimization of the separation device,such as the convective heat transfer coefficient of the channel wall,the length of modulating electrode,and the width of the channel,is performed.展开更多
This paper presents a numerical analysis of Joule heating effect of electroosmo- sis in a finite-length microchannel made of the glass and polydimethylsiloxane （PDMS） polymer. The Poisson-Boltzmann equation of elect...This paper presents a numerical analysis of Joule heating effect of electroosmo- sis in a finite-length microchannel made of the glass and polydimethylsiloxane （PDMS） polymer. The Poisson-Boltzmann equation of electric double layer, the Navier-Stokes equation of liquid flow, and the liquid-solid coupled heat transfer equation are solved to investigate temperature behaviors of electroosmosis in a two-dimensional microchannel. The feedback effect of temperature variation on liquid properties （dielectric constant, vis- cosity, and thermal and electric conductivities） is taken into account. Numerical results indicate that there exists a heat developing length near the channel inlet where the flow velocity, temperature, pressure, and electric field rapidly vary and then approach to a steady state after the heat developing length, which may occupy a considerable portion of the microchannel in cases of thick chip and high electric field. The liquid temperature of steady state increases with the increase of the applied electric field, channel width, and chip thickness. The temperature on a PDMS wall is higher than that on a glass wall due to the difference of heat conductivities of materials. Temperature variations are found in the both longitudinal and transverse directions of the microchannel. The increase of the temperature on the wall decreases the charge density of the electric double layer. The longitudinal temperature variation induces a pressure gradient and changes the behavior of the electric field in the microchannel. The inflow liquid temperature does not change the liquid temperature of steady state and the heat developing length.展开更多
Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27....Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27.12 MHz and power of 60-150 W were investigated.When the power of RCF is lower than 90 W,temperatures of Fe3O4 magnetic nanoparticles(75-150 mg/mL) can be raised and maximal temperatures are all lower than 50 ℃.When the power of RCF is 90-150 W,temperatures of Fe3O4 magnetic nanoparticles can be quickly raised and are all obviously higher than those of normal saline and distilled water under the same conditions.Temperature of Fe3O4 magnetic nanoparticles can even reach 70.2 ℃ under 150 W RCF.Heating effects of Fe3O4 magnetic nanoparticles are related to RCF power,particle size and particle concentration.展开更多
A possible heating effect on the process of high deposition rate microcrystalline silicon has been studied. It includes the discharge time-accumulating heating effect, discharge power, inter-electrode distance, and to...A possible heating effect on the process of high deposition rate microcrystalline silicon has been studied. It includes the discharge time-accumulating heating effect, discharge power, inter-electrode distance, and total gas flow rate induced heating effect. It is found that the heating effects mentioned above are in some ways quite similar to and in other ways very different from each other. However, all of them will directly or indirectly cause the increase of the substrate surface temperature during the process of depositing microcrystalline silicon thin films, which will affect the properties of the materials with increasing time. This phenomenon is very serious for the high deposition rate of microcrystalline silicon thin films because of the high input power and the relatively small inter-electrode distance needed. Through analysis of the heating effects occurring in the process of depositing microcrystalline silicon, it is proposed that the discharge power and the heating temperature should be as low as possible, and the total gas flow rate and the inter-electrode distance should be suitable so that device-grade high quality deposition rate microcrystalline silicon thin films can be fabricated.展开更多
The rotary gas-gas heat exchanger(GGH)is a vital component in waste heat recovery systems,partic-ularly for Selective Catalytic Reduction(SCR)processes employed in cement kiln operations.This study investigates the th...The rotary gas-gas heat exchanger(GGH)is a vital component in waste heat recovery systems,partic-ularly for Selective Catalytic Reduction(SCR)processes employed in cement kiln operations.This study investigates the thermal performance of a rotary GGH in medium-and low-temperature denitrification systems,using a simplified porous medium model based on its actual internal structure.A porous medium representation is developed from the structural characteristics of the most efficient heat transfer element,and a local thermal non-equilibrium(LTNE)model is employed to capture the distinct thermal behaviors of the solid matrix and gas phase.To account for the rotational dynamics of the system,the multiple reference frame(MRF)approach is adopted.Numerical simulation results exhibit an average error of less than 5%,demonstrating the model’s reliability and predictive accuracy.The temperature distributions of both the metallic heat exchange surfaces and the flue gas are systematically analyzed.Results indicate that the solid and gas phases exhibit significant non-equilibrium thermal behavior.Notably,the circumferential temperature fluctuations of both the heat exchange surfaces and flue gas vary markedly with changes in rotational speed.At low rotational speeds,the temperature non-uniformity coefficient reaches 4.296,while at high speeds it decreases to 0.4813-indicating that lower speeds lead to more pronounced temperature fluctuations.The simulated temperature field patterns are consistent with experimental observations,validating the effectiveness of the modeling approach.展开更多
Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization e...Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization effects on premonsoon rainfall using hourly station observations and Weather Research and Forecasting model with the Single Layer Urban Canopy Model(WRF-SLUCM)simulations.Observations show stronger pre-monsoon extreme rainfall in GBA cities than surrounding rural areas,with the urban heat island(UHI)intensifying the urban rainfall intensity and probability.Extreme cases were classified into frontal and shear-line warm-sector types.Enhanced urban rainfall due to UHI was more pronounced under shear-line and warm-sector systems.Four frontal and four shear-line cases were dynamically downscaled using WRF-SLUCM,and four parallel experiments were conducted:“Nourban”(urban areas replaced by cropland),“AH0”,“AH100”,and“AH300”[normal land use,with the diurnal maximum anthropogenic heat(AH)set to 0,100,and 300 W m^(−2)in SLUCM,respectively].In frontal cases,significantly reduced urban rainfall in AH0 is due to decreased(enhanced)surface evaporation(wind divergence)in cities compared to cropland.Strong northerly winds and cold-air intrusion suppress the UHI in AH0 and AH100 during the rainfall process;enhanced urban rainfall occurs only in AH300.In contrast,for shear-line cases,urban friction and UHI promote local convection and wind convergence,increasing urban rainfall significantly in all urban experiments compared to Nourban.Overall,urbanization’s influence on SC’s premonsoon extreme rainfall is highly sensitive to the type of synoptic systems,necessitating further investigation of urban rainfall in this season.展开更多
Based on the observation data of meteorological observation stations in Jining City during 1970-2024,MK mutation test and principal component analysis(PCA)were used to study the evolution characteristics of urban heat...Based on the observation data of meteorological observation stations in Jining City during 1970-2024,MK mutation test and principal component analysis(PCA)were used to study the evolution characteristics of urban heat island intensity(UHII)and the contribution rate of various influencing factors in Jining City over the past 55 years.The results show that from 1970 to 2024,the UHII in Jining City generally rose at a rate of 0.1℃/10 a.On the interannual scale,the correlation between temperature and UHII was most significantly positive.On the seasonal scale,there was a strong negative correlation between wind speed and UHII.PCA reveals that temperature had a significant positive impact on the increase of UHII in Jining City.展开更多
Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ...Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ultrafast electron sources involves irradiating metal tips by ultrashort laser pulses, causing electron beam emission via the photoelectric effect [including photon-driven(quantum) or field-driven(classical) emission]. However, the thermionic electrons emission process due to the heating effect of ultrashort lasers, particularly its dynamic aspects, has rarely been addressed in previous studies. In this paper, we improved the signal-to-noise ratio of a two-pulse correlation measurement on the tip electron emission by nearly two orders of magnitude using a delay time modulation method. This allowed us to obtain information on the temperature evolution of hot electrons and phonons in a non-equilibrium state, and to extract characteristic time scales for electron-phonon and phonon-phonon scattering. Our findings indicate that the thermionic electrons emission, unlike the instantaneous photoelectric effect, causes electron emission to lag behind the laser pulse by tens of picoseconds, thus significantly affecting the detection of ultrafast dynamics of samples. Furthermore, such a lagging effect was found to be sensitive to the local structure of the metal tip, offering new insights into the improved design of ultrafast electron sources.展开更多
Considering the coupled heat transfer effect induced by parallel cross-river road tunnels, the long-term soil temperature variations of shallow sections of cross-river tunnels under the river beach are predicted using...Considering the coupled heat transfer effect induced by parallel cross-river road tunnels, the long-term soil temperature variations of shallow sections of cross-river tunnels under the river beach are predicted using the finite difference method for numerical simulation. The boundary conditions and the initial values are determined by in situ observations and numerical iterations.The simulation results indicate that the ultimate calculated steady heat transfer time is 68 years, and most of the heat transfer is completed in 20 years.The initial constant temperature soil surrounding the tunnels is transformed to an annually variable one.An obvious temperature-varying region of the surrounding soil is discovered within 5 m from the tunnel exterior, as well as within the entire range of soil between the two tunnels.The maximum temperature increase value reaches 7.14 ℃ and the maximum peak-to-valley value of annual temperature increase reaches 10 ℃.The temperature variation of soils surrounding tunnels below 10 m is completely controlled by the heat transfer from the tunnels.The coupled heat transfer effect is confirmed because the ultimate steady temperature of soil between the two tunnels is higher than the ones along other positions.Moreover, the regression model comprising a series of univariate functions is proposed for the annual soil temperature fluctuation estimation for the locations varied distances around the tunnel.This investigation is beneficial to gain an insight into the long-term variation tendencies of local engineering geological conditions of the river beach above shallow sections of the cross-river road tunnels.展开更多
DSOI,bulk Si and SOI MOSFETs are fabricated on the same die successfully using local oxygen implantation process.The thermal properties of the three kinds of devices are described and compared from simulation and mea...DSOI,bulk Si and SOI MOSFETs are fabricated on the same die successfully using local oxygen implantation process.The thermal properties of the three kinds of devices are described and compared from simulation and measurement.Both simulation and measurement prove that DSOI MOSFETs have the advantage of much lower thermal resistance of substrate and suffer less severe self heating effect than their SOI counterparts. At the same time,the electrical advantages of SOI devices can stay.The thermal resistance of DSOI devices is very close to that of bulk devices and DSOI devices can keep this advantage into deep sub micron realm.展开更多
[Objective] The aim was to analyse the variation characteristics of temperature in Anqing City and urban heat island effect.[Method] Based on the observation data of temperature from Anqing Station,other surrounding m...[Objective] The aim was to analyse the variation characteristics of temperature in Anqing City and urban heat island effect.[Method] Based on the observation data of temperature from Anqing Station,other surrounding meteorological stations and local automatic meteorological stations in suburbs,the annual variation of temperature and regional consistency was analysed,then the abrupt change of annual average temperature was tested by Mann-Kendall test,finally the influences of urban heat island effect on temperature variation in Anqing Station were studied.[Result] Affected by station migration and urban construction,the annual average temperature increased significantly in Anqing Station from 1977 to 2009,and the rising was more prominent after the middle of the 1990s.Mann-Kendall test showed that the change of temperature in Anqing Station was obviously abrupt around 1993;because of the development of urbanization,average temperature in Anqing Station was 0.8 ℃ higher than that in suburbs,and the minimum temperature rose more remarkably.In addition,urban heat island effect was the strongest in spring,followed by summer and autumn,while it was the weakest in winter.[Conclusion] The effects of urbanization development on the temperature in Anqing City were understood through this research.展开更多
Considering the main thermal forcing factor, which is critical for the development of synoptic systems, the concept of the moist ageostrophic vector Q is introduced. A formula of the moist ageostrophic Q and the ageos...Considering the main thermal forcing factor, which is critical for the development of synoptic systems, the concept of the moist ageostrophic vector Q is introduced. A formula of the moist ageostrophic Q and the ageostrophic diabatic equation, in which the divergence of the moist ageostrophic Q is taken as a single forcing term, is derived. Meanwhile, the moist ageostrophic Q is applied to diagnose a torrential rain process in North China. The results suggest that the moist ageostrophic Q can clearly reveal the system development during the torrential rain process; the corresponding relationship between the divergence of the moist ageostrophic Q and the rainfall area is better than that of the vertical velocity (w) and the divergence of the dry Q; the 6-h rainfall region can be correctly drawn according to the negative area of the divergence of the moist ageostrophic Q, and its precipitation is positively correlated to the magnitude of the divergence of the moist ageostrophic Q. The research provides valuable information for improving short-term weather forecast.展开更多
We study the quantization of mesoscopic inductance coupling circuit and discuss its time evolution. Bymeans of the thermal field dynamics theory we study the quantum fluctuation of the system at finite temperature.
Aim To prepare and characterize ferromagnetic fluids for hyperthermia of tumor. Methods Ferromagnetic fluids （FFs） of magnetite （Fe3O4） was prepared in the presence of polyethylene glycol （PEG-6000） by chemical ...Aim To prepare and characterize ferromagnetic fluids for hyperthermia of tumor. Methods Ferromagnetic fluids （FFs） of magnetite （Fe3O4） was prepared in the presence of polyethylene glycol （PEG-6000） by chemical precipitation method. The iron content of the FFs was determined by spectrophotometric method using o-phenanthroline. The FFs/PEG-6000 was characterized by transmission electron microscopy （TEM）, X-ray diffraction （XRD）, infrared spectrometry （IR）, and vibrating sample magnetometer （VSM）. Heating effects of the FFs was measured in an alternating magnetic field in vitro. The hyperthermia of FFs in a rabbit was performed. Results The FFs/PEG-6000 was proved to be composed of Fe3O4 by XRD and IR. TEM showed that the ferromagnetic particles appeared to be almost spherical and dispersed well The average particle size was 13.3 ± 3.8 nm by XRD. The saturation magnetization and residual magnetization of the FFs were 23.39 A/m （1.556 emu/g） and 0.56 A/m （0.02604 emu/g）, respectively. The coercive force was 12 Oe. The specific absorption rate （SAR） of FFs was 69 ± 10W/g [Fe]. After direct injection of FFs to hepatic VX2 carcinoma of a rabbit, the temperature in the core of the tumor was between 41 - 46 ℃ in an alternating magnetic field. Conclusion FFs/PEG-6000 was expected to be useful in hyperthermia of tumor.展开更多
To meet the needs of preventing information leakage in space engineering and military industry,an efficient method was introduced to obtain layered electromagnetic shielding sealing rubber.The carbon fiber,Ni-Fe coati...To meet the needs of preventing information leakage in space engineering and military industry,an efficient method was introduced to obtain layered electromagnetic shielding sealing rubber.The carbon fiber,Ni-Fe coating,and Carbon Nano Tube(CNT)were combined by chemical plating and in-situ polymerization to obtain a lightweight(0.14 g/cm^(2))and thin(1 mm thick)Carbon fiber Fabric(CF)/Ni-Fe/CNT/silicone layered electromagnetic shielding composites.The layered material obtained by adjusting the electroless plating time exhibited a high Shielding Efficiency(SE)of 60.2–85.5 d B in the range of 0–4800 MHz,which can be used for aviation electromagnetic shielding.Carbon fibers and carbon nanotubes mainly attenuated electromagnetic waves through absorption loss,while the nickel-iron alloy coating through reflection loss interacted with the magnetic vector of incident Electro Magnetic(EM)radiation and magnetic dipoles,therefore,the EM Interference(EMI)shielding composite attenuated EM waves with the“absorptionreflection-absorption”cooperative interaction.Moreover,the flexible fabric substrate adhered with silicone rubber possessed a breaking elongation of 52.3%,which can be utilized as a good sealing material.Simultaneously,the outstanding exothermicity(67.2℃ under the applied voltage of 5 V)makes it possible to be applied in electric heating area.The electromagnetic shielding composites prepared in this paper have good potential in the fields of precision electronic equipment and aviation systems.展开更多
基金Project supported by the National Natural Science Foundation of China(11374291,11274299 and 11204292)
文摘An abnormal fluorescence intensity ratio （FIR） between two green emissions of Er3＋, at room temperature, which is larger than a normal value, emerged in many reported articles. However, up to now detailed work has seldom been done to clarify this abnormal phenomenon. In this paper, green upconversion luminescence of the β-NaLuF4：20%yb3＋,2%Er3＋ powder sample was investigated under 980 um excitation at different circumstances, different pump power densities and different temperatures as well as different air pressures. The corresponding local temperature calculated using FIR technique increased gradually with the enhancement of the pump power density. It was demonstrated that high pump power density of 980 nm laser led to the increase of local temperature of the luminescent material, which further gave the abnormal FIR.
文摘Nanofluids have attracted many scientists due to their remarkable thermophysical properties.Small percentage of nanoparticles when added to conventional fluid significantly enhances the heat transfer features.Sustainability and efficiency of nanomaterials have key role in the advancement of nanotechnology.This article analyzes the Hall,Ohmic heating and velocity slip effects on the peristalsis of nanofluid.Convective boundary conditions and heat generation/absorption are considered to facilitate the heat transfer characteristics.Governing equations for the peristaltic flow through a curved channel are derived in curvilinear coordinates.The equations are numerically solved under the assumption of long wavelength and small Reynold number.It has been observed that nanofluid enhances the heat transfer rate and reduces the fluid temperature.Hartman number and Hall parameter show reverse behavior in fluid motion and heat transfer characteristics.In the presence of velocity slip,the pressure gradient rapidly decreases and dominant effect is seen in narrow portion of channel.
基金Project supported by the National Natural Science Foundation of China (Nos. 10602002 and 10932001)the Major State Basic Research Development Program (No. 2010CB731503)
文摘This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases. Particular emphasis is placed on the derivation of new analytical expressions of effective specific heats at constant-strain and constant-stress situations, in which a modified Eshelby＇s micromechanics theory is developed and the interaction between inclusions is considered. As an illustrative example, the analytical expression of the effective specific heat for a three-phase thermoelastic composite is presented.
基金supported by the National Natural Science Foundation of China(51506160,11472208,11472209)China Post-Doctoral Science Foundation Project(2015M580845)+1 种基金the Fundamental Research Funds for Xi’an Jiaotong University(xjj2015102)the Beijing Key Lab of Heating,Gas Supply,Ventilating and Air Conditioning Engineering(NR2016K01)
文摘A comparative optimal design of fluid-saturated prismatic cellular metal honeycombs （PCMHs） having different cell shapes is presented for thermal management applications. Based on the periodic topology of each PCMH, a unit cell （UC） for thermal transport analysis was selected to calculate its effective thermal conductivity. Without introducing any empirical coefficient, we modified and extended the analytical model of parallel-series thermal-electric network to a wider porosity range （0.7 ~ 0.98） by considering the effects of two-dimensional local heat conduction in solid ligaments inside each UC. Good agreement was achieved between analytical predictions and numerical simulations based on the method of finite volume. The concept of ligament heat conduction efficiency （LTCE） was proposed to physically explain the mechanisms underlying the effects of ligament configuration on effective thermal conductivity （ETC）. Based upon the proposed theory, a construct strategy was developed for designing the ETC by altering the equivalent interaction angle with the direction of heat flow： relatively small average interaction angle for thermal conduction and relatively large one for thermal insulation.
文摘Flow thermomechanics in reactive porous media is of importance in industry including the thermal processing of fossil fuel(coking understood as a slow pyrolysis)involving devolatilisation.On the way to provide a detailed description of the process,a multi-scale approach was chosen to estimate effective transport coefficients.For this case the Lattice Boltzmann method(LBM)was used due to its advantages to accurately model multi-physics and chemistry in a random geometry of granular media.After account for earlier studies,the paper presents description of the model with improved boundary conditions and a benchmark case.Results from meso-scale LBM calculations are presented and discussed regarding the spatial resolution and the choice of relaxation parameter along its influence on the accuracy compared with empirical formulae.Regarding the estimation of effective thermal conductivity coefficient it is shown that occurrence of devolatilization has a crucial effect by reducing heat transfer.Some quantitative results characterise the propagation of thermal front;also presented is the evolution of effective thermal conductivity.The work is a step forward towards a physically sound simulation of thermal processing of fossil fuel.
基金Project supported by the National Natural Science Foundation of China(Grant No.11572139).
文摘Dielectrophoresis(DEP)technology has become important application of microfluidic technology to manipulate particles.By using a local modulating electric field to control the combination of electroosmotic microvortices and DEP,our group proposed a device using a direct current(DC)electric field to achieve continuous particle separation.In this paper,the influence of the Joule heating effect on the continuous separation of particles is analyzed.Results show that the Joule heating effect is caused by the local electric field,and the Joule heating effect caused by adjusting the modulating voltage is more significant than that by driving voltage.Moreover,a non-uniform temperature distribution exists in the channel due to the Joule heating effect,and the temperature is the highest at the midpoint of the modulating electrodes.The channel flux can be enhanced,and the enhancement of both the channel flux and temperature is more obvious for a stronger Joule heating effect.In addition,the ability of the vortices to trap particles is enhanced since a larger DEP force is exerted on the particles with the Joule heating effect;and the ability of the vortex to capture particles is stronger with a stronger Joule heating effect.The separation efficiency can also be increased because perfect separation is achieved at a higher channel flux.Parameter optimization of the separation device,such as the convective heat transfer coefficient of the channel wall,the length of modulating electrode,and the width of the channel,is performed.
基金supported by the National Natural Science Foundation of China (Nos.10872076 and 50805059)
文摘This paper presents a numerical analysis of Joule heating effect of electroosmo- sis in a finite-length microchannel made of the glass and polydimethylsiloxane （PDMS） polymer. The Poisson-Boltzmann equation of electric double layer, the Navier-Stokes equation of liquid flow, and the liquid-solid coupled heat transfer equation are solved to investigate temperature behaviors of electroosmosis in a two-dimensional microchannel. The feedback effect of temperature variation on liquid properties （dielectric constant, vis- cosity, and thermal and electric conductivities） is taken into account. Numerical results indicate that there exists a heat developing length near the channel inlet where the flow velocity, temperature, pressure, and electric field rapidly vary and then approach to a steady state after the heat developing length, which may occupy a considerable portion of the microchannel in cases of thick chip and high electric field. The liquid temperature of steady state increases with the increase of the applied electric field, channel width, and chip thickness. The temperature on a PDMS wall is higher than that on a glass wall due to the difference of heat conductivities of materials. Temperature variations are found in the both longitudinal and transverse directions of the microchannel. The increase of the temperature on the wall decreases the charge density of the electric double layer. The longitudinal temperature variation induces a pressure gradient and changes the behavior of the electric field in the microchannel. The inflow liquid temperature does not change the liquid temperature of steady state and the heat developing length.
基金Projects(30571779,10775085) supported by the National Natural Science Foundation of ChinaProject(Z07000200540704) supported by Beijing Municipal Science and Technology Commission,China
文摘Fe3O4 magnetic nanoparticles with diameters varying from 10 to 426 nm were synthesized and characterized.Heating effects of Fe3O4 magnetic nanoparticles under radiofrequency capacitive field(RCF) with frequency of 27.12 MHz and power of 60-150 W were investigated.When the power of RCF is lower than 90 W,temperatures of Fe3O4 magnetic nanoparticles(75-150 mg/mL) can be raised and maximal temperatures are all lower than 50 ℃.When the power of RCF is 90-150 W,temperatures of Fe3O4 magnetic nanoparticles can be quickly raised and are all obviously higher than those of normal saline and distilled water under the same conditions.Temperature of Fe3O4 magnetic nanoparticles can even reach 70.2 ℃ under 150 W RCF.Heating effects of Fe3O4 magnetic nanoparticles are related to RCF power,particle size and particle concentration.
基金Project supported by Hi-Tech Research and Development Program of China (Grant Nos. 2007AA05Z436 and 2009AA050602)Science and Technology Support Project of Tianjin (Grant No. 08ZCKFGX03500)+3 种基金National Basic Research Program of China(Grant Nos. 2006CB202602 and 2006CB202603)National Natural Science Foundation of China (Grant No. 60976051)International Cooperation Project between China-Greece Government (Grant Nos. 2006DFA62390 and 2009DFA62580)Program for New Century Excellent Talents in University of China (Grant No. NCET-08-0295)
文摘A possible heating effect on the process of high deposition rate microcrystalline silicon has been studied. It includes the discharge time-accumulating heating effect, discharge power, inter-electrode distance, and total gas flow rate induced heating effect. It is found that the heating effects mentioned above are in some ways quite similar to and in other ways very different from each other. However, all of them will directly or indirectly cause the increase of the substrate surface temperature during the process of depositing microcrystalline silicon thin films, which will affect the properties of the materials with increasing time. This phenomenon is very serious for the high deposition rate of microcrystalline silicon thin films because of the high input power and the relatively small inter-electrode distance needed. Through analysis of the heating effects occurring in the process of depositing microcrystalline silicon, it is proposed that the discharge power and the heating temperature should be as low as possible, and the total gas flow rate and the inter-electrode distance should be suitable so that device-grade high quality deposition rate microcrystalline silicon thin films can be fabricated.
基金supported the Eco-Environment Project of the Key Research and Development Program of Anhui Province(No.202104i07020016).
文摘The rotary gas-gas heat exchanger(GGH)is a vital component in waste heat recovery systems,partic-ularly for Selective Catalytic Reduction(SCR)processes employed in cement kiln operations.This study investigates the thermal performance of a rotary GGH in medium-and low-temperature denitrification systems,using a simplified porous medium model based on its actual internal structure.A porous medium representation is developed from the structural characteristics of the most efficient heat transfer element,and a local thermal non-equilibrium(LTNE)model is employed to capture the distinct thermal behaviors of the solid matrix and gas phase.To account for the rotational dynamics of the system,the multiple reference frame(MRF)approach is adopted.Numerical simulation results exhibit an average error of less than 5%,demonstrating the model’s reliability and predictive accuracy.The temperature distributions of both the metallic heat exchange surfaces and the flue gas are systematically analyzed.Results indicate that the solid and gas phases exhibit significant non-equilibrium thermal behavior.Notably,the circumferential temperature fluctuations of both the heat exchange surfaces and flue gas vary markedly with changes in rotational speed.At low rotational speeds,the temperature non-uniformity coefficient reaches 4.296,while at high speeds it decreases to 0.4813-indicating that lower speeds lead to more pronounced temperature fluctuations.The simulated temperature field patterns are consistent with experimental observations,validating the effectiveness of the modeling approach.
基金supported by CUHK Strategic Impact Enhancement Fund(project no.3135536)Guangdong Basic and Applied Basic Research Foundation(2023B1515020029).
文摘Urbanization’s impact on pre-monsoon extreme rainfall in the Greater Bay Area(GBA),coastal South China(SC),and its relation to different synoptic systems remains understudied.This research investigates urbanization effects on premonsoon rainfall using hourly station observations and Weather Research and Forecasting model with the Single Layer Urban Canopy Model(WRF-SLUCM)simulations.Observations show stronger pre-monsoon extreme rainfall in GBA cities than surrounding rural areas,with the urban heat island(UHI)intensifying the urban rainfall intensity and probability.Extreme cases were classified into frontal and shear-line warm-sector types.Enhanced urban rainfall due to UHI was more pronounced under shear-line and warm-sector systems.Four frontal and four shear-line cases were dynamically downscaled using WRF-SLUCM,and four parallel experiments were conducted:“Nourban”(urban areas replaced by cropland),“AH0”,“AH100”,and“AH300”[normal land use,with the diurnal maximum anthropogenic heat(AH)set to 0,100,and 300 W m^(−2)in SLUCM,respectively].In frontal cases,significantly reduced urban rainfall in AH0 is due to decreased(enhanced)surface evaporation(wind divergence)in cities compared to cropland.Strong northerly winds and cold-air intrusion suppress the UHI in AH0 and AH100 during the rainfall process;enhanced urban rainfall occurs only in AH300.In contrast,for shear-line cases,urban friction and UHI promote local convection and wind convergence,increasing urban rainfall significantly in all urban experiments compared to Nourban.Overall,urbanization’s influence on SC’s premonsoon extreme rainfall is highly sensitive to the type of synoptic systems,necessitating further investigation of urban rainfall in this season.
基金Supported by the Project of Jining Meteorological Bureau(2024JNZL08).
文摘Based on the observation data of meteorological observation stations in Jining City during 1970-2024,MK mutation test and principal component analysis(PCA)were used to study the evolution characteristics of urban heat island intensity(UHII)and the contribution rate of various influencing factors in Jining City over the past 55 years.The results show that from 1970 to 2024,the UHII in Jining City generally rose at a rate of 0.1℃/10 a.On the interannual scale,the correlation between temperature and UHII was most significantly positive.On the seasonal scale,there was a strong negative correlation between wind speed and UHII.PCA reveals that temperature had a significant positive impact on the increase of UHII in Jining City.
基金supported by the National Key R&D Program under Grant No.2021YFA1400500the National Natural Science Foundation of China under Grant No.22273029+1 种基金the New Cornerstone Science Foundation through the New Cornerstone Investigator Program under Grant No.NCI202303 and the XPLORER PRIZEthe Beijing Outstanding Young Scientist Program under Grant No.JWZQ20240101002。
文摘Ultrafast electron sources, which enable high spatiotemporal resolution in time-resolved electron microscopy and scanning probe microscopy, are receiving increased attention. The most widely used method for achieving ultrafast electron sources involves irradiating metal tips by ultrashort laser pulses, causing electron beam emission via the photoelectric effect [including photon-driven(quantum) or field-driven(classical) emission]. However, the thermionic electrons emission process due to the heating effect of ultrashort lasers, particularly its dynamic aspects, has rarely been addressed in previous studies. In this paper, we improved the signal-to-noise ratio of a two-pulse correlation measurement on the tip electron emission by nearly two orders of magnitude using a delay time modulation method. This allowed us to obtain information on the temperature evolution of hot electrons and phonons in a non-equilibrium state, and to extract characteristic time scales for electron-phonon and phonon-phonon scattering. Our findings indicate that the thermionic electrons emission, unlike the instantaneous photoelectric effect, causes electron emission to lag behind the laser pulse by tens of picoseconds, thus significantly affecting the detection of ultrafast dynamics of samples. Furthermore, such a lagging effect was found to be sensitive to the local structure of the metal tip, offering new insights into the improved design of ultrafast electron sources.
基金The National Natural Science Foundation of China(No.40902076)the Natural Science Foundation of Jiangsu Province(No.BK20141224)
文摘Considering the coupled heat transfer effect induced by parallel cross-river road tunnels, the long-term soil temperature variations of shallow sections of cross-river tunnels under the river beach are predicted using the finite difference method for numerical simulation. The boundary conditions and the initial values are determined by in situ observations and numerical iterations.The simulation results indicate that the ultimate calculated steady heat transfer time is 68 years, and most of the heat transfer is completed in 20 years.The initial constant temperature soil surrounding the tunnels is transformed to an annually variable one.An obvious temperature-varying region of the surrounding soil is discovered within 5 m from the tunnel exterior, as well as within the entire range of soil between the two tunnels.The maximum temperature increase value reaches 7.14 ℃ and the maximum peak-to-valley value of annual temperature increase reaches 10 ℃.The temperature variation of soils surrounding tunnels below 10 m is completely controlled by the heat transfer from the tunnels.The coupled heat transfer effect is confirmed because the ultimate steady temperature of soil between the two tunnels is higher than the ones along other positions.Moreover, the regression model comprising a series of univariate functions is proposed for the annual soil temperature fluctuation estimation for the locations varied distances around the tunnel.This investigation is beneficial to gain an insight into the long-term variation tendencies of local engineering geological conditions of the river beach above shallow sections of the cross-river road tunnels.
文摘DSOI,bulk Si and SOI MOSFETs are fabricated on the same die successfully using local oxygen implantation process.The thermal properties of the three kinds of devices are described and compared from simulation and measurement.Both simulation and measurement prove that DSOI MOSFETs have the advantage of much lower thermal resistance of substrate and suffer less severe self heating effect than their SOI counterparts. At the same time,the electrical advantages of SOI devices can stay.The thermal resistance of DSOI devices is very close to that of bulk devices and DSOI devices can keep this advantage into deep sub micron realm.
文摘[Objective] The aim was to analyse the variation characteristics of temperature in Anqing City and urban heat island effect.[Method] Based on the observation data of temperature from Anqing Station,other surrounding meteorological stations and local automatic meteorological stations in suburbs,the annual variation of temperature and regional consistency was analysed,then the abrupt change of annual average temperature was tested by Mann-Kendall test,finally the influences of urban heat island effect on temperature variation in Anqing Station were studied.[Result] Affected by station migration and urban construction,the annual average temperature increased significantly in Anqing Station from 1977 to 2009,and the rising was more prominent after the middle of the 1990s.Mann-Kendall test showed that the change of temperature in Anqing Station was obviously abrupt around 1993;because of the development of urbanization,average temperature in Anqing Station was 0.8 ℃ higher than that in suburbs,and the minimum temperature rose more remarkably.In addition,urban heat island effect was the strongest in spring,followed by summer and autumn,while it was the weakest in winter.[Conclusion] The effects of urbanization development on the temperature in Anqing City were understood through this research.
基金supported by the National Natural Science Foundation of China under Grant Nos.40205008 and 401350201.
文摘Considering the main thermal forcing factor, which is critical for the development of synoptic systems, the concept of the moist ageostrophic vector Q is introduced. A formula of the moist ageostrophic Q and the ageostrophic diabatic equation, in which the divergence of the moist ageostrophic Q is taken as a single forcing term, is derived. Meanwhile, the moist ageostrophic Q is applied to diagnose a torrential rain process in North China. The results suggest that the moist ageostrophic Q can clearly reveal the system development during the torrential rain process; the corresponding relationship between the divergence of the moist ageostrophic Q and the rainfall area is better than that of the vertical velocity (w) and the divergence of the dry Q; the 6-h rainfall region can be correctly drawn according to the negative area of the divergence of the moist ageostrophic Q, and its precipitation is positively correlated to the magnitude of the divergence of the moist ageostrophic Q. The research provides valuable information for improving short-term weather forecast.
文摘We study the quantization of mesoscopic inductance coupling circuit and discuss its time evolution. Bymeans of the thermal field dynamics theory we study the quantum fluctuation of the system at finite temperature.
文摘Aim To prepare and characterize ferromagnetic fluids for hyperthermia of tumor. Methods Ferromagnetic fluids （FFs） of magnetite （Fe3O4） was prepared in the presence of polyethylene glycol （PEG-6000） by chemical precipitation method. The iron content of the FFs was determined by spectrophotometric method using o-phenanthroline. The FFs/PEG-6000 was characterized by transmission electron microscopy （TEM）, X-ray diffraction （XRD）, infrared spectrometry （IR）, and vibrating sample magnetometer （VSM）. Heating effects of the FFs was measured in an alternating magnetic field in vitro. The hyperthermia of FFs in a rabbit was performed. Results The FFs/PEG-6000 was proved to be composed of Fe3O4 by XRD and IR. TEM showed that the ferromagnetic particles appeared to be almost spherical and dispersed well The average particle size was 13.3 ± 3.8 nm by XRD. The saturation magnetization and residual magnetization of the FFs were 23.39 A/m （1.556 emu/g） and 0.56 A/m （0.02604 emu/g）, respectively. The coercive force was 12 Oe. The specific absorption rate （SAR） of FFs was 69 ± 10W/g [Fe]. After direct injection of FFs to hepatic VX2 carcinoma of a rabbit, the temperature in the core of the tumor was between 41 - 46 ℃ in an alternating magnetic field. Conclusion FFs/PEG-6000 was expected to be useful in hyperthermia of tumor.
基金supported by the National Natural Science Foundation of China(No.U1830108)the Innovation Foundation of Shanghai Aerospace Science and Technology,China(No.SAST2018-061)the Exploratory Research Project of “Yanchang Petroleum(Group)-Fudan University”,China。
文摘To meet the needs of preventing information leakage in space engineering and military industry,an efficient method was introduced to obtain layered electromagnetic shielding sealing rubber.The carbon fiber,Ni-Fe coating,and Carbon Nano Tube(CNT)were combined by chemical plating and in-situ polymerization to obtain a lightweight(0.14 g/cm^(2))and thin(1 mm thick)Carbon fiber Fabric(CF)/Ni-Fe/CNT/silicone layered electromagnetic shielding composites.The layered material obtained by adjusting the electroless plating time exhibited a high Shielding Efficiency(SE)of 60.2–85.5 d B in the range of 0–4800 MHz,which can be used for aviation electromagnetic shielding.Carbon fibers and carbon nanotubes mainly attenuated electromagnetic waves through absorption loss,while the nickel-iron alloy coating through reflection loss interacted with the magnetic vector of incident Electro Magnetic(EM)radiation and magnetic dipoles,therefore,the EM Interference(EMI)shielding composite attenuated EM waves with the“absorptionreflection-absorption”cooperative interaction.Moreover,the flexible fabric substrate adhered with silicone rubber possessed a breaking elongation of 52.3%,which can be utilized as a good sealing material.Simultaneously,the outstanding exothermicity(67.2℃ under the applied voltage of 5 V)makes it possible to be applied in electric heating area.The electromagnetic shielding composites prepared in this paper have good potential in the fields of precision electronic equipment and aviation systems.
