Heat transfer behaviors of AZ80?1%Y alloy during low frequency electromagnetic casting (LFEC) and direct chilling casting were studied by in-situ temperature measurement. The results demonstrated that the low frequenc...Heat transfer behaviors of AZ80?1%Y alloy during low frequency electromagnetic casting (LFEC) and direct chilling casting were studied by in-situ temperature measurement. The results demonstrated that the low frequency electromagnetic field (EM) caused forced convection in the melt during LFEC. The forced convection led to uniform solidification velocity and temperature field. EM frequency, excitation current intensity and casting temperature could control the heat transfer behavior. The forced convection could improve the microstructure and degrade the difference in microstructure between the edge and center of billet. Appropriate parameters of low frequency EM for casting Mg alloy are 20 Hz of frequency and 60 A of electric current intensity.展开更多
Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been...Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been used or selected as the working fluids in engineering fields such as aerospace,nuclear power,solar energy,refrigeration,geothermal energy,chemical technology,and so on.To better understand the interesting characteristic or abnormal behaviors of supercritical fluids,most valuable research works(including experimental results and numerical studies)from domestic and abroad have been documented.As such,this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications.This review focuses on recently available articles published mainly from 2016 up to the present time.The common problems(i.e.,heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels)in the supercritical field are summarized and some perspectives on future prospects are also included.展开更多
The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting （HPDC） process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the sho...The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting （HPDC） process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the shot sleeve, inverse method has been developed to determine the interfacial heat transfer coefficient in the shot sleeve. Under static condition, Interracial heat transfer coefficient （IHTC） peak values are 11.9, 7,3, 8.33kWm-2K-1 at pouring zone （S2）, middle zone （S5）, and end zone （510）, respectively. During the casting process, the IHTC curve displays a second peak of 6.1 kWm-2 K-1 at middle zone during the casting process at a slow speed of 0.3 ms 1 Subsequently, when the high speed started, the IHTC curve reached a second peal〈 of 12.9 kW m-2K-1 at end zone. Furthermore, under different slow casting speeds, both the calculated initial temperature （TIDs） and the maximum temperature （Tsimax） of shot sleeve surface first decrease from 0.1 ms-1 to 0.3 ms-1, but increase again from 0.3 ms-1 to 0.6 ms-1. This result agrees with the experimental results obtained in a series of ＂plate-shape＂ casting experiments under different slow speeds, which reveals that the amount of ESCs decreases to the minimum values at 0.3 m s-1 and increase again with the increasing casting slow speed.展开更多
This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as th...This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.展开更多
Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),...Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),inverse method was developed to determine the interfacial heat transfer coefficient(IHTC).The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used.It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings.The IHTC could have a higher peak value with increasing the Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.展开更多
High pressure die casting copper is used to produce rotors for induction motors to improve efficiency.Experiments were carried out for a special"step-shape"casting with different step thicknesses.Based on th...High pressure die casting copper is used to produce rotors for induction motors to improve efficiency.Experiments were carried out for a special"step-shape"casting with different step thicknesses.Based on the measured temperature inside the die,the interfacial heat transfer coefficient(IHTC)at the metal/die interface during vacuum die casting was evaluated by solving the inverse problem.The IHTC peak value was 4.5×10^3-11×10^3 W·m^-2·K^-1 under the basic operation condition.The influences of casting pressure,fast shot speed,pouring temperature and initial die surface temperature on the IHTC peak values were investigated.Results show that a greater casting pressure and faster shot speed could only increase the IHTC peak values at the location close to the ingate.An increase of pouring temperature and/or initial die surface temperature significantly increases the IHTC peak values.展开更多
Photothermal catalysis is a widely researched field in which the reaction mechanism is usually investigated based on the photochemical behavior of the catalytic material.Considering that the adsorption of reactants is...Photothermal catalysis is a widely researched field in which the reaction mechanism is usually investigated based on the photochemical behavior of the catalytic material.Considering that the adsorption of reactants is essential for catalytic reactions to occur,in this study,the synergistic effect of photothermal catalysis is innovatively elucidated in terms of the electron transfer behavior of reactant adsorption.For the H_(2)+O2 or CO+H_(2)reaction systems over a ZnO catalyst,UV irradiation at 25°C or heat without UV irradiation did not cause H_(2)oxidation or CO reduction;only photothermal conditions(100 or 150°C+UV light)initiated the two reactions.This result is related to the electron transfer behavior associated with the adsorption of CO or H_(2)on ZnO,in which H_(2)or CO that lost an electron could be oxidized by O2 or hydroxyls.However,the electron‐accepting CO could be reduced by the electron‐donating H_(2)into CH4 under photothermal conditions.Based on the in‐situ characterization and theoretical calculation results,it was established that the synergistic effect of the photothermal conditions acted on the(002)crystal surface of ZnO to stimulate the growth of zinc vacancies,which resulted in the formation of defect energy levels,adsorption sites,and an adjusted Fermi level.As a result,the electron transfer behavior between adsorbed CO or H_(2)and the crystal surface varied,which further affected the photocatalytic behavior.The results show that the effect of photothermal synergy may not only produce the expected kinetic energy,but more importantly,produce energy that can change the activation mode of the reactant gas.This study provides a new understanding of the CO catalytic oxidation and reduction processes over semiconductor materials.展开更多
Tea infusion is the main route of human exposure to pollutants in tea,and it is vital to investigate the transfer rate of pollutants from tea leaves to infusion.Carbendazim is a commonly used systemic fungicide,the tr...Tea infusion is the main route of human exposure to pollutants in tea,and it is vital to investigate the transfer rate of pollutants from tea leaves to infusion.Carbendazim is a commonly used systemic fungicide,the transfer behavior of which in Yingshan Yunwu tea is not clear.Hence,this study firstly established the analytical method for determination of carbendazim with great accuracy and precision via modified QuEChERS method and ultra-performance liquid chromatography-fluorescence detection(UPLC-FLD).Then,the transfer behavior of carbendazim from tea leaves and infusion was systematically investigated.Results indicated that water temperature and proportion of tea to water ration would obviously increase the transfer rate of carbendazim,but times of infusion repetition showed negative correlation with the transfer rate of carbendazim.In addition,brewing time seemed to have lesser impact on the transfer rate.This study will be helpful for the risk assessment of carbendazim residue and provide the guidance for tea brewing.展开更多
In order to analyze the influence of the distance between heat sources(D_(LA))on the welding process,the effects of D_(LA)on the droplet transfer behavior,weld formation characteristics and weld formation mechanism of...In order to analyze the influence of the distance between heat sources(D_(LA))on the welding process,the effects of D_(LA)on the droplet transfer behavior,weld formation characteristics and weld formation mechanism of AH36 in laser and cable-type welding wire gas metal arc welding arc hybrid welding were studied.Real-time photography was conducted using a high-speed camera to determine the droplet transfer and arc behaviors;the surface morphology and macroscopic cross-section of the weld obtained from the experiment were observed and analyzed.The arc height decreases with the increase in the DLA,the arc width shows the opposite change,and the welding current decreases.The allure of the laser to the arc increases with the increase in the D_(LA).The frequency of droplet transfer increases with the increase in the D_(LA),but the growth rate decreases.The continuous increase in the D_(LA)leads to the tendency of the droplet size to decrease first and then increase,and the minimum value is obtained when the D_(LA)is 4 mm.The D_(LA)has obvious influence on the weld formation.The weld penetration and reinforcement change similarly,increasing first and then decreasing as the D_(LA)increases,and the laser area of the weld also increases first and then decreases.展开更多
Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390...Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).展开更多
This work used experimental methods to study heat transfer behavior inside a heat pipe and found that heat transfer behavior inside the heat pipe was changed due to its integration with cooling plates. This change cau...This work used experimental methods to study heat transfer behavior inside a heat pipe and found that heat transfer behavior inside the heat pipe was changed due to its integration with cooling plates. This change caused the heat pipe to have copper-like heat transfer behavior. Experimental performances first built a CPU simulator with maximum heat power 300 W in accordance with the ASTM standard as heat source and measured temperature distribution by using infrared thermography and thermocouple thermometer. Observation of heat transfer behavior inside heat pipe influenced by its integration with cooling plates used color schlieren technique. A commercial CPU heat pipe cooler was also used as reference object in this work. Integration of the heat pipe with cooling plates causes the heat pipe to have the copper-like heat transfer behavior. The results indicate that rebuilding the bare heat pipe’s heat transfer behavior is the best solution for improving cooling efficiency of the heat pipe cooler.展开更多
Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfe...Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfer,contact behavior,and microstructure evolution were investigated using a novel droplet solidification technique.The results revealed that when the hydrogen content increases from 0.0004 to 0.0013 wt.%,the maximum heat flux between the molten steel and cooling substrate decreases from 8.01 to 6.19 MW/m^(2),and the total heat removed in the initial 2 s reduces from 10.30 to 8.27 MJ/m^(2).Moreover,the final contact angle between the molten steel and substrate increases from 103.741°to 113.697°,and the number of pores on the droplet bottom surface increases significantly from 21 to 210 with the increase in hydrogen.The surface roughness of the droplet bottom surface increases from 20.902 to 49.181 pm.In addition,the average grain size of the droplet increases from 14.778 to 33.548 pm with the increase in the hydrogen content.The interfacial contact condition becomes worse due to the escape of hydrogen from the steel matrix during the cooling process,which leads to the reduction in the interfacial heat transfer and the increase in the grain size.展开更多
The microchannel reactor is the most commonly used microreaction technology,an innovative reaction system developed in recent years.This study investigates the mass transfer behavior of a gas-liquid two‐phase Taylor ...The microchannel reactor is the most commonly used microreaction technology,an innovative reaction system developed in recent years.This study investigates the mass transfer behavior of a gas-liquid two‐phase Taylor flow in a microchannel by coupling the volume‐of‐fluid model and the species transport model.The concentration distribution and the volumetric mass transfer coefficient of the gas solute are determined and discussed in detail.The simulation results reveal that the double‐circulation flow influences the concentration distribution in the liquid slug.The highest value is observed at the bubble's surface and decreases rapidly along the vertical direction of the bubble.The increase of bubble velocity leads to a more apparent decreasing trend.The gas-liquid interface renewal rate of the bubble is accelerated with increasing bubble velocity,resulting in an increase in the average mass transfer rate in all regions of the bubble surface with an increase in bubble velocity.The results also indicate that the liquid film area contributes the most to the mass transfer behavior due to the most significant proportion and average mass transfer rate of the liquid film among the bubble.展开更多
Objective Previous work has showed that excess iron accumulation is harrnftd to reproduction and even promotes death; however, whether the multiple biological toxicity of iron （Fe） exposure could be transferred to p...Objective Previous work has showed that excess iron accumulation is harrnftd to reproduction and even promotes death; however, whether the multiple biological toxicity of iron （Fe） exposure could be transferred to progeny remains unknown. The present study used Caenorhabditis elegans to analyze the multiple toxicities of iron exposure and their possible transferable properties. Methods Three concentrations of iron sulfate solution （2.5μmol/L, 75μmol/L, and 200 μmol/L） were used. The endpoints of lifespan, body size, generation time, brood size, head thrash and body bend frequencies, and chemotaxis plasticity were selected to investigate Fe toxicity and its effect on progeny in Caenorhabditis elegans. Results The Fe toxicity could cause multiple biological defects in a dose-dependent manner by affecting different endpoints in nematodes. Most of the multiple biological defects and behavior toxicities could be transferred from Fe-exposed Caenorhabditis elegans to their progeny. Compared to the parents, no recovery phenotypes were observed for some of the defects in the progeny, such as body bend frequency and life span. We further summarized the defects caused by Fe exposure into 2 groups according to their transferable properties. Conclusion Our results suggest that Fe exposure could cause multiple biological defects, and most of these severe defects could be transferred from Fe exposed nematodes to their progeny.展开更多
This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with di...This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is R= 0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800.Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt numbers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant theoretical value for macrochannels. The Reynolds number for the transition from laminar to turbulent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.展开更多
It is important to remove the impurities, such as copper and cadmium, from leaching solution in zinc hydrometallurgy. To improve purification efficiency, a replacement-column purification device was proposed and its m...It is important to remove the impurities, such as copper and cadmium, from leaching solution in zinc hydrometallurgy. To improve purification efficiency, a replacement-column purification device was proposed and its mass transfer characteristics and purification efficiency were experimentally studied. The results show that purification efficiency increases with the decrease of the zinc powder diameter and decreases with the increase of solution velocity. If appropriate structure and operation parameters are used, it is possible to make purification efficiency more than 99%, but the diameter of zinc powder should be larger than 0.45 mm. For the velocity of 0.05-0.7 cm/s, mass transfer coefficient kc is in the range of 3.94×10-7-2.76×10-6 m/s, and increases with the decrease of zinc powder diameter and the increase of solution velocity. Moreover, it can be derived by mass transfer correlations of Sherwood number:Sh=0.1069Re0.5Sc0.33, for 0.3<Re<6.展开更多
【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS...【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS)数据,通过建立OLS模型、面板固定效应模型、中介效应模型进行计量分析,并进一步做出稳健性、内生性检验。【结果】农户分化对农业生产性投资有显著负向影响;农地流转在农户分化与农业生产投资间发挥部分中介作用,农户分化通过影响农地流转进而对农业生产性投资产生影响。【结论】要充分关注农户分化给农业生产造成粗放化、副业化甚至撂荒等潜在危害;积极采取措施发挥农地流转对农业生产投资的刺激作用。展开更多
To predict the heat transfer behavior of A380 alloy in a shot sleeve, a numerical approach(inverse method) is used and validated by high pressure die casting(HPDC) experiment under non-shooting condition. The maximum ...To predict the heat transfer behavior of A380 alloy in a shot sleeve, a numerical approach(inverse method) is used and validated by high pressure die casting(HPDC) experiment under non-shooting condition. The maximum difference between the measured and calculated temperature profiles is smaller than 3 °C, which suggests that the inverse method can be used to predict the heat transfer behavior of alloys in a shot sleeve. Furthermore, the results indicate an increase in maximum interfacial heat flux density(q_(max)) and heat transfer coefficient(h_(max)) with an increase in sleeve filling ratio, especially at the pouring zone(S2 zone). In addition, the values of initial temperature(T_(IDS)) and maximum shot sleeve surface temperature(T_(simax)) at the two end zones(S2 and S10) are higher than those at the middle zone(S5). Moreover, in comparison with fluctuations in heat transfer coefficient(h) with time at the two end zones(S2 and S10), 2.4-6.5 kW ·m^(-2)·K^(-1), 3.5-12.5 kW ·m^(-2)·K^(-1), respectively, more fluctuations are found at S5 zone, 2.1-14.7 kW ·m^(-2)·K^(-1). These differences could theoretically explain the formation of the three zones: smooth pouring zone, un-smooth middle zone and smooth zone, with different morphologies in the metal log under the non-shot casting condition. Finally, our calculations also reveal that the values of q_(max) and h_(max) cast at 680 °C are smaller than those cast at 660 °C and at 700 °C.展开更多
The thermal properties of a nanostructured semiconductor are affected by multi-physical fields,such as stress and electromagnetic fields,causing changes in temperature and strain distributions.In this work,the influen...The thermal properties of a nanostructured semiconductor are affected by multi-physical fields,such as stress and electromagnetic fields,causing changes in temperature and strain distributions.In this work,the influence of stress-dependent thermal conductivity on the heat transfer behavior of a GaN-based nanofilm is investigated.The finite element method is adopted to simulate the temperature distribution in a prestressed nanofilm under heat pulses.Numerical results demonstrate the effect of stress field on the thermal conductivity of GaN-based nanofilm,namely,the prestress and the thermal stress lead to a change in the heat transfer behavior in the nanofilm.Under the same heat source,the peak temperature of the film with stress-dependent thermal conductivity is significantly lower than that of the film with a constant thermal conductivity and the maximum temperature difference can reach 8.2 K.These results could be useful for designing GaN-based semiconductor devices with higher reliability under multi-physical fields.展开更多
基金Project(2013CB632203)supported by the National Basic Research and Development Program of ChinaProject(2014028027)supported by the Liaoning Provincial Natural Science Foundation,China
文摘Heat transfer behaviors of AZ80?1%Y alloy during low frequency electromagnetic casting (LFEC) and direct chilling casting were studied by in-situ temperature measurement. The results demonstrated that the low frequency electromagnetic field (EM) caused forced convection in the melt during LFEC. The forced convection led to uniform solidification velocity and temperature field. EM frequency, excitation current intensity and casting temperature could control the heat transfer behavior. The forced convection could improve the microstructure and degrade the difference in microstructure between the edge and center of billet. Appropriate parameters of low frequency EM for casting Mg alloy are 20 Hz of frequency and 60 A of electric current intensity.
基金sponsored by the National Natural Science Foundation of China(Nos.51676163,51976161,U1867218)the National 111 Project,China(No.B18041)+1 种基金the Fundamental Research Funds of Shenzhen City,China(No.JCYJ20170306155153048)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX202029).
文摘Supercritical fluids(e.g.,hydrocarbon fuels,water,carbon dioxide,and organic working medium,etc)have been recognized as working media to improve thermal efficiencies in power cycles and energy conversion,and have been used or selected as the working fluids in engineering fields such as aerospace,nuclear power,solar energy,refrigeration,geothermal energy,chemical technology,and so on.To better understand the interesting characteristic or abnormal behaviors of supercritical fluids,most valuable research works(including experimental results and numerical studies)from domestic and abroad have been documented.As such,this paper presents a comprehensive review on heat transfer behaviors of some supercritical fluids in engineering applications.This review focuses on recently available articles published mainly from 2016 up to the present time.The common problems(i.e.,heat transfer enhancement and heat transfer deterioration particularly for the supercritical hydrocarbon fuels)in the supercritical field are summarized and some perspectives on future prospects are also included.
基金financially supported by the National Major Science and Technology Program of China(No.2012ZX04012011)the National Natural Science Foundation of China(No.51275269)
文摘The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting （HPDC） process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the shot sleeve, inverse method has been developed to determine the interfacial heat transfer coefficient in the shot sleeve. Under static condition, Interracial heat transfer coefficient （IHTC） peak values are 11.9, 7,3, 8.33kWm-2K-1 at pouring zone （S2）, middle zone （S5）, and end zone （510）, respectively. During the casting process, the IHTC curve displays a second peak of 6.1 kWm-2 K-1 at middle zone during the casting process at a slow speed of 0.3 ms 1 Subsequently, when the high speed started, the IHTC curve reached a second peal〈 of 12.9 kW m-2K-1 at end zone. Furthermore, under different slow casting speeds, both the calculated initial temperature （TIDs） and the maximum temperature （Tsimax） of shot sleeve surface first decrease from 0.1 ms-1 to 0.3 ms-1, but increase again from 0.3 ms-1 to 0.6 ms-1. This result agrees with the experimental results obtained in a series of ＂plate-shape＂ casting experiments under different slow speeds, which reveals that the amount of ESCs decreases to the minimum values at 0.3 m s-1 and increase again with the increasing casting slow speed.
基金supported by National Natural Science Foundation of China(Grant No.51265029)
文摘This paper deals with a novel dual shield TIG welding method named gas pool coupled activating TIG( GPCA-TIG)welding. The welding method divides the shielding gas into two layers. Inert gas such as Ar is adopted as the inner layer gas to protect the tungsten electrode and the molten pool metal. Pure O_2,N_2 or mixture of them are used as the outer layer gas to increase the weld penetration and improve the low temperature toughness of weld metal. Through analyzing the interaction between outer gas and arc and the distributions and existing forms of oxygen and nitrogen elements,the transfer behaviors of nitrogen and oxygen from arc to pool were investigated. The results show that,the interaction between the outer gas and arc plasma makes the arc slightly constrict. The incoming oxygen enriches on the molten pool surface and exists in the form of iron oxide,chromium oxide,manganese oxide and silicon oxygen compounds. The incoming nitrogen evenly distributes in the molten pool and exists in the form of nitrogen atom.
基金Project (2016YFB0301001) supported by the National Key Research and Development Program of ChinaProject (2015M580093) supported by the General Financial Grant from the China Postdoctoral Science Foundation of China
文摘Vacuum die casting can reduce the'air entrapment'phenomenon during casting process.Based on the temperature measurements at metal-die interface with different processing parameters,such as slow shot speed(VL),high shot speed(VH),pouring temperature(Tp)and initial die temperature(Tm),inverse method was developed to determine the interfacial heat transfer coefficient(IHTC).The results indicate that a closer contact between the casting and die could be achieved when the vacuum system is used.It is found that the vacuum could strongly increase the values of IHTC and decrease the grain size in castings.The IHTC could have a higher peak value with increasing the Tp from680to720℃or the VL from0.1to0.4m/s.In addition,the influence of the VH and Tm on IHTC could be negligible.
文摘High pressure die casting copper is used to produce rotors for induction motors to improve efficiency.Experiments were carried out for a special"step-shape"casting with different step thicknesses.Based on the measured temperature inside the die,the interfacial heat transfer coefficient(IHTC)at the metal/die interface during vacuum die casting was evaluated by solving the inverse problem.The IHTC peak value was 4.5×10^3-11×10^3 W·m^-2·K^-1 under the basic operation condition.The influences of casting pressure,fast shot speed,pouring temperature and initial die surface temperature on the IHTC peak values were investigated.Results show that a greater casting pressure and faster shot speed could only increase the IHTC peak values at the location close to the ingate.An increase of pouring temperature and/or initial die surface temperature significantly increases the IHTC peak values.
文摘Photothermal catalysis is a widely researched field in which the reaction mechanism is usually investigated based on the photochemical behavior of the catalytic material.Considering that the adsorption of reactants is essential for catalytic reactions to occur,in this study,the synergistic effect of photothermal catalysis is innovatively elucidated in terms of the electron transfer behavior of reactant adsorption.For the H_(2)+O2 or CO+H_(2)reaction systems over a ZnO catalyst,UV irradiation at 25°C or heat without UV irradiation did not cause H_(2)oxidation or CO reduction;only photothermal conditions(100 or 150°C+UV light)initiated the two reactions.This result is related to the electron transfer behavior associated with the adsorption of CO or H_(2)on ZnO,in which H_(2)or CO that lost an electron could be oxidized by O2 or hydroxyls.However,the electron‐accepting CO could be reduced by the electron‐donating H_(2)into CH4 under photothermal conditions.Based on the in‐situ characterization and theoretical calculation results,it was established that the synergistic effect of the photothermal conditions acted on the(002)crystal surface of ZnO to stimulate the growth of zinc vacancies,which resulted in the formation of defect energy levels,adsorption sites,and an adjusted Fermi level.As a result,the electron transfer behavior between adsorbed CO or H_(2)and the crystal surface varied,which further affected the photocatalytic behavior.The results show that the effect of photothermal synergy may not only produce the expected kinetic energy,but more importantly,produce energy that can change the activation mode of the reactant gas.This study provides a new understanding of the CO catalytic oxidation and reduction processes over semiconductor materials.
基金Supported by Hubei Key Laboratory of Economic Forest Germplasm Improvement and Resources Comprehensive Utilization,Hubei Collaborative Innovation Center for the Characteristic Resources Exploitation of Dabie Mountains Fund(2021CX06)Teaching and Research Project of Huanggang Normal University(2021CE20).
文摘Tea infusion is the main route of human exposure to pollutants in tea,and it is vital to investigate the transfer rate of pollutants from tea leaves to infusion.Carbendazim is a commonly used systemic fungicide,the transfer behavior of which in Yingshan Yunwu tea is not clear.Hence,this study firstly established the analytical method for determination of carbendazim with great accuracy and precision via modified QuEChERS method and ultra-performance liquid chromatography-fluorescence detection(UPLC-FLD).Then,the transfer behavior of carbendazim from tea leaves and infusion was systematically investigated.Results indicated that water temperature and proportion of tea to water ration would obviously increase the transfer rate of carbendazim,but times of infusion repetition showed negative correlation with the transfer rate of carbendazim.In addition,brewing time seemed to have lesser impact on the transfer rate.This study will be helpful for the risk assessment of carbendazim residue and provide the guidance for tea brewing.
基金This work is supported by the National Natural Science Foundation of China(Grant No.51905231)China Postdoctoral Science Foundation(Grant No.2020M670943)Graduate Student Scientific Research Innovation Projects in Jiangsu Province(Grant No.KYCX22_3788).
文摘In order to analyze the influence of the distance between heat sources(D_(LA))on the welding process,the effects of D_(LA)on the droplet transfer behavior,weld formation characteristics and weld formation mechanism of AH36 in laser and cable-type welding wire gas metal arc welding arc hybrid welding were studied.Real-time photography was conducted using a high-speed camera to determine the droplet transfer and arc behaviors;the surface morphology and macroscopic cross-section of the weld obtained from the experiment were observed and analyzed.The arc height decreases with the increase in the DLA,the arc width shows the opposite change,and the welding current decreases.The allure of the laser to the arc increases with the increase in the D_(LA).The frequency of droplet transfer increases with the increase in the D_(LA),but the growth rate decreases.The continuous increase in the D_(LA)leads to the tendency of the droplet size to decrease first and then increase,and the minimum value is obtained when the D_(LA)is 4 mm.The D_(LA)has obvious influence on the weld formation.The weld penetration and reinforcement change similarly,increasing first and then decreasing as the D_(LA)increases,and the laser area of the weld also increases first and then decreases.
基金financially supported by the class General Financial Grant from the China Postdoctoral Science Foundation(No.2015M580093)the National Nature Science Foundation of China(No.20151301587)the National Major Science and Technology Program of China(No.2012ZX04012011)
文摘Heat transfer at the metal-die interface has a great influence on the solidification process and casting structure. As thin-wall components are extensively produced by high pressure die casting process(HPDC), the B390 alloy finger-plate casting was cast against an H13 steel die on a cold-chamber HPDC machine. The interfacial heat transfer behavior at different positions of the die was carefully studied using an inverse approach based on the temperature measurements inside the die. Furthermore, the filling process and the solidification rate in different finger-plates were also given to explain the distribution of interfacial heat flux(q) and interfacial heat transfer coefficient(h). Measurement results at the side of sprue indicates that qmax and hmax could reach 9.2 MW·m^(-2) and 64.3 kW ·m^(-2)·K^(-1), respectively. The simulation of melt flow in the die reveals that the thinnest(T_1) finger plate could accelerate the melt flow from 50 m·s^(-1) to 110 m·s^(-1). Due to this high velocity, the interfacial heat flux at the end of T_1 could firstly reach a highest value 7.92 MW·m^(-2) among the ends of T_n(n=2,3,4,5). In addition, the q_(max) and h_(max) values of T_2, T_4 and T_5 finger-plates increase with the increasing thickness of the finger plate. Finally, at the rapid decreasing stage of interfacial heat transfer coefficient(h), the decreasing rate of h has an exponential relationship with the increasing rate of solid fraction(f).
文摘This work used experimental methods to study heat transfer behavior inside a heat pipe and found that heat transfer behavior inside the heat pipe was changed due to its integration with cooling plates. This change caused the heat pipe to have copper-like heat transfer behavior. Experimental performances first built a CPU simulator with maximum heat power 300 W in accordance with the ASTM standard as heat source and measured temperature distribution by using infrared thermography and thermocouple thermometer. Observation of heat transfer behavior inside heat pipe influenced by its integration with cooling plates used color schlieren technique. A commercial CPU heat pipe cooler was also used as reference object in this work. Integration of the heat pipe with cooling plates causes the heat pipe to have the copper-like heat transfer behavior. The results indicate that rebuilding the bare heat pipe’s heat transfer behavior is the best solution for improving cooling efficiency of the heat pipe cooler.
基金The financial support for this work from the National Natural Science Foundation of China(52274342,52130408)the Hunan Scientific Technology Projects(Grant No.2020WK2003)+1 种基金the Natural Science Foundation of Hunan Province(2021JJ40731)the Postgraduate Scientific Research Innovation Project of Hunan Province(CX20220099)is gratefully acknowledged.
文摘Typical Q235 low-carbon steel samples with different hydrogen contents(0.0004,0.0008,and 0.0013 wt.%)were prepared by adjusting the environment humidity and moisture.The effects of hydrogen on interfacial heat transfer,contact behavior,and microstructure evolution were investigated using a novel droplet solidification technique.The results revealed that when the hydrogen content increases from 0.0004 to 0.0013 wt.%,the maximum heat flux between the molten steel and cooling substrate decreases from 8.01 to 6.19 MW/m^(2),and the total heat removed in the initial 2 s reduces from 10.30 to 8.27 MJ/m^(2).Moreover,the final contact angle between the molten steel and substrate increases from 103.741°to 113.697°,and the number of pores on the droplet bottom surface increases significantly from 21 to 210 with the increase in hydrogen.The surface roughness of the droplet bottom surface increases from 20.902 to 49.181 pm.In addition,the average grain size of the droplet increases from 14.778 to 33.548 pm with the increase in the hydrogen content.The interfacial contact condition becomes worse due to the escape of hydrogen from the steel matrix during the cooling process,which leads to the reduction in the interfacial heat transfer and the increase in the grain size.
基金National Natural Science Foundation of China(NSFC),Grant/Award Numbers:61821002,92163213Applied Basic Research Program of Suzhou,Grant/Award Number:SYG202026+1 种基金Collaborative Innovation Center of Suzhou Nano Science and TechnologyPriority Academic Program Development of Jiangsu Higher Education Institutions。
文摘The microchannel reactor is the most commonly used microreaction technology,an innovative reaction system developed in recent years.This study investigates the mass transfer behavior of a gas-liquid two‐phase Taylor flow in a microchannel by coupling the volume‐of‐fluid model and the species transport model.The concentration distribution and the volumetric mass transfer coefficient of the gas solute are determined and discussed in detail.The simulation results reveal that the double‐circulation flow influences the concentration distribution in the liquid slug.The highest value is observed at the bubble's surface and decreases rapidly along the vertical direction of the bubble.The increase of bubble velocity leads to a more apparent decreasing trend.The gas-liquid interface renewal rate of the bubble is accelerated with increasing bubble velocity,resulting in an increase in the average mass transfer rate in all regions of the bubble surface with an increase in bubble velocity.The results also indicate that the liquid film area contributes the most to the mass transfer behavior due to the most significant proportion and average mass transfer rate of the liquid film among the bubble.
基金supported by the Southeast University Foundation for Excellent Young Scholars (No. 4023001013).
文摘Objective Previous work has showed that excess iron accumulation is harrnftd to reproduction and even promotes death; however, whether the multiple biological toxicity of iron （Fe） exposure could be transferred to progeny remains unknown. The present study used Caenorhabditis elegans to analyze the multiple toxicities of iron exposure and their possible transferable properties. Methods Three concentrations of iron sulfate solution （2.5μmol/L, 75μmol/L, and 200 μmol/L） were used. The endpoints of lifespan, body size, generation time, brood size, head thrash and body bend frequencies, and chemotaxis plasticity were selected to investigate Fe toxicity and its effect on progeny in Caenorhabditis elegans. Results The Fe toxicity could cause multiple biological defects in a dose-dependent manner by affecting different endpoints in nematodes. Most of the multiple biological defects and behavior toxicities could be transferred from Fe-exposed Caenorhabditis elegans to their progeny. Compared to the parents, no recovery phenotypes were observed for some of the defects in the progeny, such as body bend frequency and life span. We further summarized the defects caused by Fe exposure into 2 groups according to their transferable properties. Conclusion Our results suggest that Fe exposure could cause multiple biological defects, and most of these severe defects could be transferred from Fe exposed nematodes to their progeny.
文摘This paper experimentally investigates the effect of surface roughness on flow and heat transfer characteristics in circular microchannels. All test pieces include 44 identical, parallel circular microchannels with diameters of 0.4 mm and 10 mm in length. The surface roughness of the microchannels is R= 0.86, 0.92, 1.02 lm, and the Reynolds number ranges from 150 to 2800.Results show that the surface roughness of the circular microchannels has remarkable effects on the performance of flow behavior and heat transfer. It is found that the Poiseuille and Nusselt numbers are higher when the relative surface roughness is larger. For flow behavior, the friction factor increases consistently with the increasing Reynolds number, and it is larger than the constant theoretical value for macrochannels. The Reynolds number for the transition from laminar to turbulent flow is about 1500, which is lower than the value for macrochannels. For the heat transfer property, Nusselt number also increases with increasing Reynolds number, and larger roughness contributes to higher Nusselt number.
基金Project(Y2010-1-005)supported by the Collaborative Fund of Hunan Nonferrous Metals Holding Group-Central South University,China
文摘It is important to remove the impurities, such as copper and cadmium, from leaching solution in zinc hydrometallurgy. To improve purification efficiency, a replacement-column purification device was proposed and its mass transfer characteristics and purification efficiency were experimentally studied. The results show that purification efficiency increases with the decrease of the zinc powder diameter and decreases with the increase of solution velocity. If appropriate structure and operation parameters are used, it is possible to make purification efficiency more than 99%, but the diameter of zinc powder should be larger than 0.45 mm. For the velocity of 0.05-0.7 cm/s, mass transfer coefficient kc is in the range of 3.94×10-7-2.76×10-6 m/s, and increases with the decrease of zinc powder diameter and the increase of solution velocity. Moreover, it can be derived by mass transfer correlations of Sherwood number:Sh=0.1069Re0.5Sc0.33, for 0.3<Re<6.
文摘【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS)数据,通过建立OLS模型、面板固定效应模型、中介效应模型进行计量分析,并进一步做出稳健性、内生性检验。【结果】农户分化对农业生产性投资有显著负向影响;农地流转在农户分化与农业生产投资间发挥部分中介作用,农户分化通过影响农地流转进而对农业生产性投资产生影响。【结论】要充分关注农户分化给农业生产造成粗放化、副业化甚至撂荒等潜在危害;积极采取措施发挥农地流转对农业生产投资的刺激作用。
基金supported by the National Major Science and Technology Program of China(2012ZX04012011)the National Nature Science Foundation of China(51275269)
文摘To predict the heat transfer behavior of A380 alloy in a shot sleeve, a numerical approach(inverse method) is used and validated by high pressure die casting(HPDC) experiment under non-shooting condition. The maximum difference between the measured and calculated temperature profiles is smaller than 3 °C, which suggests that the inverse method can be used to predict the heat transfer behavior of alloys in a shot sleeve. Furthermore, the results indicate an increase in maximum interfacial heat flux density(q_(max)) and heat transfer coefficient(h_(max)) with an increase in sleeve filling ratio, especially at the pouring zone(S2 zone). In addition, the values of initial temperature(T_(IDS)) and maximum shot sleeve surface temperature(T_(simax)) at the two end zones(S2 and S10) are higher than those at the middle zone(S5). Moreover, in comparison with fluctuations in heat transfer coefficient(h) with time at the two end zones(S2 and S10), 2.4-6.5 kW ·m^(-2)·K^(-1), 3.5-12.5 kW ·m^(-2)·K^(-1), respectively, more fluctuations are found at S5 zone, 2.1-14.7 kW ·m^(-2)·K^(-1). These differences could theoretically explain the formation of the three zones: smooth pouring zone, un-smooth middle zone and smooth zone, with different morphologies in the metal log under the non-shot casting condition. Finally, our calculations also reveal that the values of q_(max) and h_(max) cast at 680 °C are smaller than those cast at 660 °C and at 700 °C.
基金This research is supported by the National Natural Science Foundation of China(Grant Nos.11772294,11621062)the Fundamental Research Funds for the Central Universities(Grant No.2017QNA4031).
文摘The thermal properties of a nanostructured semiconductor are affected by multi-physical fields,such as stress and electromagnetic fields,causing changes in temperature and strain distributions.In this work,the influence of stress-dependent thermal conductivity on the heat transfer behavior of a GaN-based nanofilm is investigated.The finite element method is adopted to simulate the temperature distribution in a prestressed nanofilm under heat pulses.Numerical results demonstrate the effect of stress field on the thermal conductivity of GaN-based nanofilm,namely,the prestress and the thermal stress lead to a change in the heat transfer behavior in the nanofilm.Under the same heat source,the peak temperature of the film with stress-dependent thermal conductivity is significantly lower than that of the film with a constant thermal conductivity and the maximum temperature difference can reach 8.2 K.These results could be useful for designing GaN-based semiconductor devices with higher reliability under multi-physical fields.
