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
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
Mechanical properties of TC17 titanium alloy undergo a significant reduction after linear friction welding(LFW),of which the strength and ductility are hard to be improved simultaneously by traditional aging heat trea...Mechanical properties of TC17 titanium alloy undergo a significant reduction after linear friction welding(LFW),of which the strength and ductility are hard to be improved simultaneously by traditional aging heat treatment(AHT),seriously limiting the application of LFW in the manufacturing of TC17 titanium alloy blisks.To this end,the present work proposes to use electric pulse treatment(EPT)to enhance the strength and ductility of TC17 LFW joints simultaneously by improving its microstructure.The results show that,in comparison to the uneven distribution ofαphases in the welding zone(WZ),heat-affected zone(HAZ),and base metal(BM)zone after AHT,EPT can selectively homogenize theαphase distribution of WZ and HAZ without impacting the BM.The selective effect of EPT is reflected as the synergistic influence of the local Joule heating effect and the electron wind effect,which promotes the diffusion ofβphase stabilizing element Mo and leads to a competitive precipitation ofβphase andαphase in theαphase transition temperature range.The ratio ofαphase toβphase in the WZ and HAZ finally approaches an equilibrium point which is similar to that of BM,leading to a uniform distribution ofαphase and realizing the synergy of strength-ductility of LFW joint:the maximum strength increase observed is 12.9%,accompanied by a corresponding elongation increase of 122%(by AHT&EPT),and the maximum plasticity improvement is 185%,accompanied by a corresponding strength increase of 4.3%(by EPT for 1 h).This study provides essential insights for improving the strength and ductility of LFW TC17 titanium alloy blisks and enhancing the applications of LFW in aeroengine components.展开更多
Recently,application-oriented strain sensor has been intensively investigated in the fields of human motion detection,personalized health management and portable medical diagnosis.Despite significant efforts in improv...Recently,application-oriented strain sensor has been intensively investigated in the fields of human motion detection,personalized health management and portable medical diagnosis.Despite significant efforts in improving its sensitivity and linear sensing range,developing the wearable strain sensor with stable signal remains a challenge.Herein,we proposed an ideal hybrid material with nearly zero temperature coefficient resistance(TCR)for temperature-insensitive strain sensing:the silver nanostructures(AgNTs)were introduced to coat the graphene foam(GrF)conformably by hydrothermal growth.The nanoscaled metal additives(TCR>0)not only endow GrF(TCR<0)with high electrical stability(TCR≈-0.3×10^(-3)℃^(-1)),but also offer the hybrid system additional structural elasticity,potential for next-generation of portable,stretchable and reliable devices.The resultant AgNTs@GrF hybrid material has been processed into a piezoresistive sensor with excellent sensing accuracy(strain error<2.7%),satisfactory gauge factor(GF)of227,wide sensing range up to 90%and good cyclic stability(>3000 cycles).Moreover,our strain sensor can be easily mounted on human skin as an epidermal device for reliable detection of electrophysiological stimuli,thus showing a great promising in practical wearable applications.展开更多
The Regional Climate Model(RegCM)proves valuable for climate analysis and has been applied to a wide range of climate change aspects and other environmental issues at a regional scale.The model also demonstrated succe...The Regional Climate Model(RegCM)proves valuable for climate analysis and has been applied to a wide range of climate change aspects and other environmental issues at a regional scale.The model also demonstrated success in diverse areas of urban research,including urban heat island studies,extreme climate events analysis,assessing urban resilience,and evaluating urbanization impacts on climate and air quality.Recently,more studies have been conducted in utilizing RegCM to address climate change in cities,due to its enhanced ability over the years to capture meteorological phenomena at city scales.However,there are many challenges associated with its implementation in meso-scale research,which are attributed to various shortcomings and thus create room for further improvement in the model.This paper presents a comprehensive overview of the evolution of the RegCM over the years and its customisation across various parameters,demonstrating its versatility in urban climate studies and underscoring the model’s pivotal role in addressing multifaceted challenges in urban environments.By addressing these aspects,the paper offers valuable insights and recommendations for researchers seeking to enhance the accuracy and efficacy of urban climate simulations using the RegCM system,thereby contributing to the advancement of urban climate science and sustainability.展开更多
Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest v...Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest vortex in the warm-sector during a“rain-generated vortex”process and the deep southwest vortex in a“vortex-generated rain”process.The findings were as follows:(1)During the extreme rainstorm on August 11,2020(hereinafter referred to as the“8·11”process),intense surface heating and a high-energy unstable environment were observed.The mesoscale convergence system triggered convection to produce heavy rainfall,and the release of latent condensation heat generated by the rainfall promoted the formation of a southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy preceded the increase(decrease)in vorticity.By contrast,the extreme rainstorm on August 16,2020(hereinafter referred to as the“8·16”process)involved the generation of southwest vortex in a low-energy and highhumidity environment.The dynamic uplift of the southwest vortex triggered rainfall,and the release of condensation latent heat from rainfall further strengthened the development of the southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy exhibited a delayed progression compared to the increase(decrease)in vorticity.(2)The heating effect around the southwest vortex region was non-uniform,and the heating intensity varied in different stages.In the“8·11”process,the heating effect was the strongest in the initial stage,but weakened during the vortex's development.On the contrary,the heating effect was initially weak in the“8·16”process,and intensified during the development stage.(3)The available potential energy of the“8·11”process significantly increased in kinetic energy converted from rotational and divergent winds through baroclinic action,and the divergent wind energy continued to convert into rotational wind energy.By contrast,the“8·16”process involved the conversion of rotational wind energy into divergent wind energy,which in turn converted kinetic energy back into available potential energy,thereby impeding the further development and maintenance of the southwest vortex.展开更多
The accelerating urbanization process and intensifying climate change have exacerbated the urban heat island effect, threatening sustainable urban development. This study investigates the role of green infrastructure ...The accelerating urbanization process and intensifying climate change have exacerbated the urban heat island effect, threatening sustainable urban development. This study investigates the role of green infrastructure in mitigating urban heat island effects, its implementation challenges, and applications. Employing a system dynamics approach, the research models the relationships between green infrastructure, urban microclimate, and human well-being. Findings indicate that large, continuous green spaces, such as urban parks and green corridors, are most effective, potentially reducing surrounding temperatures by 1˚C - 4˚C. Green infrastructure also provides multiple ecosystem services, including improved air quality and increased biodiversity. However, its implementation faces challenges such as land resource limitations and financial constraints. To address these issues, the study proposes a performance-based planning method, emphasizing multifunctional design and cross-sectoral collaboration. Through analysis of international and Chinese urban case studies, best practices and lessons learned are summarized. The research demonstrates that successful strategies must be context-specific, integrating local conditions while emphasizing long-term planning and continuous optimization. This study provides a scientific basis for developing effective heat island mitigation strategies and climate adaptation plans, ultimately achieving sustainable urban development and improved living environments.展开更多
In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest a...In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest access. Urban Heat Island Effects are measurable phenomenon that are being experienced by the world’s most urbanized areas, including increased summer high temperatures and lower evapotranspiration from having impervious surfaces instead of vegetation and trees. Tree canopy cover is our natural mitigation tool that absorbs sunlight for photosynthesis, protects humans from incoming radiation, and releases cooling moisture into the air. Unfortunately, urban areas typically have low levels of vegetation. Vulnerable urban communities are lower-income areas of inner cities with less access to heat protection like air conditioners. This study uses mean evapotranspiration levels to assess the variability of urban heat island effects across the state of Tennessee. Results show that increased developed land surface cover in Tennessee creates measurable changes in atmospheric evapotranspiration. As a result, the mean evapotranspiration levels in areas with less tree vegetation are significantly lower than the surrounding forested areas. Central areas of urban cities in Tennessee had lower mean evapotranspiration recordings than surrounding areas with less development. This work demonstrates the need for increased tree canopy coverage.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
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the National Science Fund for Distinguished Young Scholars(No.52225505)the National Sci-ence and Technology Major Project(No.J2019-VII-0014-0154)+1 种基金the National Natural Science Foundation of China(No.52005412)the Open Research Fund of State Key Laboratory of Precision Man-ufacturing for Extreme Service Performance(No.Kfkt2023-12)for financial supports given to this research.
文摘Mechanical properties of TC17 titanium alloy undergo a significant reduction after linear friction welding(LFW),of which the strength and ductility are hard to be improved simultaneously by traditional aging heat treatment(AHT),seriously limiting the application of LFW in the manufacturing of TC17 titanium alloy blisks.To this end,the present work proposes to use electric pulse treatment(EPT)to enhance the strength and ductility of TC17 LFW joints simultaneously by improving its microstructure.The results show that,in comparison to the uneven distribution ofαphases in the welding zone(WZ),heat-affected zone(HAZ),and base metal(BM)zone after AHT,EPT can selectively homogenize theαphase distribution of WZ and HAZ without impacting the BM.The selective effect of EPT is reflected as the synergistic influence of the local Joule heating effect and the electron wind effect,which promotes the diffusion ofβphase stabilizing element Mo and leads to a competitive precipitation ofβphase andαphase in theαphase transition temperature range.The ratio ofαphase toβphase in the WZ and HAZ finally approaches an equilibrium point which is similar to that of BM,leading to a uniform distribution ofαphase and realizing the synergy of strength-ductility of LFW joint:the maximum strength increase observed is 12.9%,accompanied by a corresponding elongation increase of 122%(by AHT&EPT),and the maximum plasticity improvement is 185%,accompanied by a corresponding strength increase of 4.3%(by EPT for 1 h).This study provides essential insights for improving the strength and ductility of LFW TC17 titanium alloy blisks and enhancing the applications of LFW in aeroengine components.
基金financially supported by Zhejiang Provincial Natural Science Foundation of China(Nos.LQ20E020007,LQ19E020004 and LQ19E020005)the National Nature Science Foundation of China(Nos.51872069,52102230,52102165 and Y21E030023)+1 种基金the Teacher Professional Development Project for Domestic Visiting Scholars(No.FX2023015)the Fundamental Research Funds for the Provincial Universities of Zhejiang。
文摘Recently,application-oriented strain sensor has been intensively investigated in the fields of human motion detection,personalized health management and portable medical diagnosis.Despite significant efforts in improving its sensitivity and linear sensing range,developing the wearable strain sensor with stable signal remains a challenge.Herein,we proposed an ideal hybrid material with nearly zero temperature coefficient resistance(TCR)for temperature-insensitive strain sensing:the silver nanostructures(AgNTs)were introduced to coat the graphene foam(GrF)conformably by hydrothermal growth.The nanoscaled metal additives(TCR>0)not only endow GrF(TCR<0)with high electrical stability(TCR≈-0.3×10^(-3)℃^(-1)),but also offer the hybrid system additional structural elasticity,potential for next-generation of portable,stretchable and reliable devices.The resultant AgNTs@GrF hybrid material has been processed into a piezoresistive sensor with excellent sensing accuracy(strain error<2.7%),satisfactory gauge factor(GF)of227,wide sensing range up to 90%and good cyclic stability(>3000 cycles).Moreover,our strain sensor can be easily mounted on human skin as an epidermal device for reliable detection of electrophysiological stimuli,thus showing a great promising in practical wearable applications.
文摘The Regional Climate Model(RegCM)proves valuable for climate analysis and has been applied to a wide range of climate change aspects and other environmental issues at a regional scale.The model also demonstrated success in diverse areas of urban research,including urban heat island studies,extreme climate events analysis,assessing urban resilience,and evaluating urbanization impacts on climate and air quality.Recently,more studies have been conducted in utilizing RegCM to address climate change in cities,due to its enhanced ability over the years to capture meteorological phenomena at city scales.However,there are many challenges associated with its implementation in meso-scale research,which are attributed to various shortcomings and thus create room for further improvement in the model.This paper presents a comprehensive overview of the evolution of the RegCM over the years and its customisation across various parameters,demonstrating its versatility in urban climate studies and underscoring the model’s pivotal role in addressing multifaceted challenges in urban environments.By addressing these aspects,the paper offers valuable insights and recommendations for researchers seeking to enhance the accuracy and efficacy of urban climate simulations using the RegCM system,thereby contributing to the advancement of urban climate science and sustainability.
基金Key Project of Joint Meteorological Fund of the National Natural Science Foundation of China (U2242202)Key Project of the National Natural Science Foundation of China (42030611)+1 种基金Innovative Development Special Project of China Meteorological Administration (CXFZ2023J016)Innovation Team Fund of Sichuan Provincial Meteorological Service (SCQXCX7D-202201)。
文摘Based on ERA5 reanalysis data,the present study analyzed the thermal energy development mechanism and kinetic energy conversion characteristics of two extreme rainstorm processes in relation to the shallow southwest vortex in the warm-sector during a“rain-generated vortex”process and the deep southwest vortex in a“vortex-generated rain”process.The findings were as follows:(1)During the extreme rainstorm on August 11,2020(hereinafter referred to as the“8·11”process),intense surface heating and a high-energy unstable environment were observed.The mesoscale convergence system triggered convection to produce heavy rainfall,and the release of latent condensation heat generated by the rainfall promoted the formation of a southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy preceded the increase(decrease)in vorticity.By contrast,the extreme rainstorm on August 16,2020(hereinafter referred to as the“8·16”process)involved the generation of southwest vortex in a low-energy and highhumidity environment.The dynamic uplift of the southwest vortex triggered rainfall,and the release of condensation latent heat from rainfall further strengthened the development of the southwest vortex.The significant increase(decrease)in atmospheric diabatic heating and kinetic energy exhibited a delayed progression compared to the increase(decrease)in vorticity.(2)The heating effect around the southwest vortex region was non-uniform,and the heating intensity varied in different stages.In the“8·11”process,the heating effect was the strongest in the initial stage,but weakened during the vortex's development.On the contrary,the heating effect was initially weak in the“8·16”process,and intensified during the development stage.(3)The available potential energy of the“8·11”process significantly increased in kinetic energy converted from rotational and divergent winds through baroclinic action,and the divergent wind energy continued to convert into rotational wind energy.By contrast,the“8·16”process involved the conversion of rotational wind energy into divergent wind energy,which in turn converted kinetic energy back into available potential energy,thereby impeding the further development and maintenance of the southwest vortex.
文摘The accelerating urbanization process and intensifying climate change have exacerbated the urban heat island effect, threatening sustainable urban development. This study investigates the role of green infrastructure in mitigating urban heat island effects, its implementation challenges, and applications. Employing a system dynamics approach, the research models the relationships between green infrastructure, urban microclimate, and human well-being. Findings indicate that large, continuous green spaces, such as urban parks and green corridors, are most effective, potentially reducing surrounding temperatures by 1˚C - 4˚C. Green infrastructure also provides multiple ecosystem services, including improved air quality and increased biodiversity. However, its implementation faces challenges such as land resource limitations and financial constraints. To address these issues, the study proposes a performance-based planning method, emphasizing multifunctional design and cross-sectoral collaboration. Through analysis of international and Chinese urban case studies, best practices and lessons learned are summarized. The research demonstrates that successful strategies must be context-specific, integrating local conditions while emphasizing long-term planning and continuous optimization. This study provides a scientific basis for developing effective heat island mitigation strategies and climate adaptation plans, ultimately achieving sustainable urban development and improved living environments.
文摘In recent decades, Urban Heat Island Effects have become more pronounced and more widely examined. Despite great technological advances, our current societies still experience great spatial disparity in urban forest access. Urban Heat Island Effects are measurable phenomenon that are being experienced by the world’s most urbanized areas, including increased summer high temperatures and lower evapotranspiration from having impervious surfaces instead of vegetation and trees. Tree canopy cover is our natural mitigation tool that absorbs sunlight for photosynthesis, protects humans from incoming radiation, and releases cooling moisture into the air. Unfortunately, urban areas typically have low levels of vegetation. Vulnerable urban communities are lower-income areas of inner cities with less access to heat protection like air conditioners. This study uses mean evapotranspiration levels to assess the variability of urban heat island effects across the state of Tennessee. Results show that increased developed land surface cover in Tennessee creates measurable changes in atmospheric evapotranspiration. As a result, the mean evapotranspiration levels in areas with less tree vegetation are significantly lower than the surrounding forested areas. Central areas of urban cities in Tennessee had lower mean evapotranspiration recordings than surrounding areas with less development. This work demonstrates the need for increased tree canopy coverage.
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.
