The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6....The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.展开更多
Direct chemical vapor deposition(CVD)growth of graphene on dielectric/insulating materials promises transfer-free applications of graphene.However,growing graphene on non-catalytic substrates faces significant challen...Direct chemical vapor deposition(CVD)growth of graphene on dielectric/insulating materials promises transfer-free applications of graphene.However,growing graphene on non-catalytic substrates faces significant challenges,particularly due to its limited growth rate,restricting large-scale production and potential applications.Here,we develop graphene-skinned glass fiber fabric(GGFF)by growing graphene CVD on commercial glass fiber fabric(GFF).This study utilizes propane as a carbon source to prepare GGFF rapidly.The active carbon source(C2H)derived from propane plays a significant role in facilitating the rapid growth of graphene films.It accelerated growth rates(~50 times faster),and reduced growth temperature(~100℃ lower)compared to the conventional carbon source methane.Additionally,propane consistently maintains a higher graphene growth rate than methane at equivalent growth temperatures.The lightweight flexibility,excellent thermal radiation properties,and energy efficiency of GGFF make it an outstanding material for infrared radiation drying.展开更多
Direct growth of graphene on dielectric or insulating materials via chemical vapor deposition(CVD)offers a novel,transfer-free approach for various applications.However,challenges remain in growing graphene on non-cat...Direct growth of graphene on dielectric or insulating materials via chemical vapor deposition(CVD)offers a novel,transfer-free approach for various applications.However,challenges remain in growing graphene on non-catalytic substrates.In particular,the low growth rate of graphene remains a significant barrier to its large-scale production.In this study,propane(C_(3)H_(8))was used as the carbon source to prepare graphene on commercial alumina fiber fabric(AFF)via CVD,resulting in the synthesis of a novel material:graphene-skinned alumina fiber fabric(GAFF).Through comparative analysis of the graphene growth behaviors using C3H8 and traditional carbon sources(CH_(4)and C_(2)H_(4))on AFF,the growth mechanism of C_(3)H_(8)was elucidated.The pyrolysis of C_(3)H_(8) generates the unique carbon species C_(3)H,which exhibits distinct advantages in terms of migration,nucleation,and growth on AFF.Graphene nucleation density using C_(3)H_(8)was found to be 160 times higher than that of CH_(4)and 50 times higher than C_(2)H_(4).The resulting GAFF exhibits a wide tunable electrical conductivity range(1 to 7000Ω·sq^(−1)),high tensile strength(>170 MPa),lightweight properties,flexibility,and a hierarchical macrostructure.These characteristics make GAFF a promising candidate for various applications,including electromagnetic interference(EMI)shielding.展开更多
Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene.However,the stable mass production o...Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene.However,the stable mass production of graphene with a favorable growth rate and quality remains a grand challenge.Herein,graphene glass fiber fabric (GGFF) was successfully developed through the controllable growth of graphene on non-catalytic glass fiber fabric,employing a synergistic binary-precursor CVD strategy to alleviate the dilemma between growth rate and quality.The binary precursors consisted of acetylene and acetone,where acetylene with high decomposition efficiency fed rapid graphene growth while oxygencontaining acetone was adopted for improving the layer uniformity and quality.Notably,the bifurcating introducing-confluent premixing (BI-CP) system was self-built for the controllable introduction of gas and liquid precursors,enabling the stable production of GGFF.GGFF features solar absorption and infrared emission properties,based on which the self-adaptive dual-mode thermal management film was developed.This film can automatically switch between heating and cooling modes by spontaneously perceiving the temperature,achieving excellent thermal management performances with heating and cooling power of~501.2 and~108.6 W m-2,respectively.These findings unlock a new strategy for the large-scale batch production of graphene materials and inspire advanced possibilities for further applications.展开更多
Purely organic room-temperature phosphors,which have received extensive attention as emerging stateof-the-art luminescent materials in various fields,have a longer lifetime than fluorophores.The energy gap law and El-...Purely organic room-temperature phosphors,which have received extensive attention as emerging stateof-the-art luminescent materials in various fields,have a longer lifetime than fluorophores.The energy gap law and El-Sayed’s rule provide clear design principles for the development of organic room-temperature phosphorescence.Therefore,the incorporation of heteroatoms(such as sulfur and phosphorus)usually promotes the intersystem crossing rate and increases the 3(π,π*)configuration to realize long lifetimes.Furthermore,boron-containing phosphors not only display excellent phosphorescence properties but also expand El-Sayed’s rule without(n,π*)transitions.This review summarizes recent work on organic phosphorescence of heterocycles with boron,sulfur,and phosphorus heteroatoms and highlights the significance of the guidelines for constructing efficient phosphorescence molecules.This work is instrumental in further diversifying the pool of phosphorescent molecules and developing new and effective design strategies.展开更多
With the continuous advancements in electronics towards downsizing and integration,efficient thermal dissipation from chips has emerged as a critical factor affecting their lifespan and operational efficiency.The fan-...With the continuous advancements in electronics towards downsizing and integration,efficient thermal dissipation from chips has emerged as a critical factor affecting their lifespan and operational efficiency.The fan-less chip cooling system has two critical interfaces for thermal transport,which are the contact interface between the base and the chip dominated by thermal conduction,and the surface of the fins dominated by thermal radiation.The different thermal transfer modes of these two critical interfaces pose different requirements for thermal management materials.In the study,a novel approach was proposed by developing graphene thermal transport functional material whose morphology could be intentionally designed via reformed plasmaenhanced chemical vapor deposition(PECVD)methods to meet the diverse requirements of heat transfer properties.Specifically,graphene with multilevel branching structure of vertical graphene(BVG)was fabricated through the hydrogenassisted PECVD(H_(2)-PECVD)strategy,which contributed a high emissivity of~0.98.BVG was deposited on the fins’surface and functioned as the radiation enhanced layer to facilitate the rapid radiation of heat from the heat sinks into the surrounding air.Meanwhile,the well-oriented vertical graphene(OVG)was successfully prepared through the vertical electric field-assisted PECVD process(EF-PECVD),which showed a high directional thermal conductivity of~53.5 W·m^(-1)·K^(-1).OVG was deposited on the contact interface and functioned as the thermal conduction enhanced layer,allowing for the quick transmission of heat from the chip to the heat sink.Utilizing this design concept,the two critical interfaces in the chip cooling system can be jointly enhanced,resulting in a remarkable cooling efficiency enhancement of~30.7%,demonstrating that this novel material possessed enormous potential for enhancing the performance of cooling systems.Therefore,this research not only provided new design concepts for the cooling system of electronic devices but also opened up new avenues for the application of graphene materials in thermal management.展开更多
Chemical vapor deposition(CVD)-grown graphene films on Cu foils,exhibiting fine scalability and high quality,are still suffering from the adverse impact of surface contamination,i.e.,amorphous carbon.Despite the recen...Chemical vapor deposition(CVD)-grown graphene films on Cu foils,exhibiting fine scalability and high quality,are still suffering from the adverse impact of surface contamination,i.e.,amorphous carbon.Despite the recent successful preparation of superclean graphene through Cu-vapor-assisted reactions,the formation mechanism of amorphous carbon remains unclear,especially with regard to the functions of substrates.Herein,we have found that the crystallographic orientations of underlying metal substrates would determine the cleanness of graphene in such a way that slower diffusion of active carbon species on asformed graphene-Cu(100)surface is the key factor that suppresses the formation of contamination.The facile synthesis of clean graphene is achieved on the meter-sized Cu(100)that is transformed from the polycrystalline Cu foils.Furthermore,a clean surface of graphene on Cu(100)ensures the reduction of transfer-related polymer residues,and enhanced optical and electrical performance,which allows for versatile applications of graphene in biosensors,functioning as flexible transparent electrodes.This work would offer a promising material platform for the fundamental investigation and create new opportunities for the advanced applications of high-quality graphene films.展开更多
基金This work was supported by the Guangdong Basic and Applied Basic Research Foundation(2019A1515111116)Key R&D Program of Shandong Province(Nos.2019GSF109051,2019GGX101030)+1 种基金Shandong Provincial Postdoctoral Innovation Project(No.201902002)Foundation of Shandong University for Young Scholar’s Future Plans.
文摘The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.
基金financially supported by the National Natural Science Foundation of China(Nos.T2188101,52272032,12302236,and 52021006).
文摘Direct chemical vapor deposition(CVD)growth of graphene on dielectric/insulating materials promises transfer-free applications of graphene.However,growing graphene on non-catalytic substrates faces significant challenges,particularly due to its limited growth rate,restricting large-scale production and potential applications.Here,we develop graphene-skinned glass fiber fabric(GGFF)by growing graphene CVD on commercial glass fiber fabric(GFF).This study utilizes propane as a carbon source to prepare GGFF rapidly.The active carbon source(C2H)derived from propane plays a significant role in facilitating the rapid growth of graphene films.It accelerated growth rates(~50 times faster),and reduced growth temperature(~100℃ lower)compared to the conventional carbon source methane.Additionally,propane consistently maintains a higher graphene growth rate than methane at equivalent growth temperatures.The lightweight flexibility,excellent thermal radiation properties,and energy efficiency of GGFF make it an outstanding material for infrared radiation drying.
基金supported by the National Natural Science Foundation of China(Nos.T2188101,52272032,12302236,and 52021006).
文摘Direct growth of graphene on dielectric or insulating materials via chemical vapor deposition(CVD)offers a novel,transfer-free approach for various applications.However,challenges remain in growing graphene on non-catalytic substrates.In particular,the low growth rate of graphene remains a significant barrier to its large-scale production.In this study,propane(C_(3)H_(8))was used as the carbon source to prepare graphene on commercial alumina fiber fabric(AFF)via CVD,resulting in the synthesis of a novel material:graphene-skinned alumina fiber fabric(GAFF).Through comparative analysis of the graphene growth behaviors using C3H8 and traditional carbon sources(CH_(4)and C_(2)H_(4))on AFF,the growth mechanism of C_(3)H_(8)was elucidated.The pyrolysis of C_(3)H_(8) generates the unique carbon species C_(3)H,which exhibits distinct advantages in terms of migration,nucleation,and growth on AFF.Graphene nucleation density using C_(3)H_(8)was found to be 160 times higher than that of CH_(4)and 50 times higher than C_(2)H_(4).The resulting GAFF exhibits a wide tunable electrical conductivity range(1 to 7000Ω·sq^(−1)),high tensile strength(>170 MPa),lightweight properties,flexibility,and a hierarchical macrostructure.These characteristics make GAFF a promising candidate for various applications,including electromagnetic interference(EMI)shielding.
基金National Natural Science Foundation of China (52272032, T2188101, and 52021006)Beijing Nova Program of Science and Technology (20220484079)。
文摘Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene.However,the stable mass production of graphene with a favorable growth rate and quality remains a grand challenge.Herein,graphene glass fiber fabric (GGFF) was successfully developed through the controllable growth of graphene on non-catalytic glass fiber fabric,employing a synergistic binary-precursor CVD strategy to alleviate the dilemma between growth rate and quality.The binary precursors consisted of acetylene and acetone,where acetylene with high decomposition efficiency fed rapid graphene growth while oxygencontaining acetone was adopted for improving the layer uniformity and quality.Notably,the bifurcating introducing-confluent premixing (BI-CP) system was self-built for the controllable introduction of gas and liquid precursors,enabling the stable production of GGFF.GGFF features solar absorption and infrared emission properties,based on which the self-adaptive dual-mode thermal management film was developed.This film can automatically switch between heating and cooling modes by spontaneously perceiving the temperature,achieving excellent thermal management performances with heating and cooling power of~501.2 and~108.6 W m-2,respectively.These findings unlock a new strategy for the large-scale batch production of graphene materials and inspire advanced possibilities for further applications.
基金the Ministry of Education and Synergetic Innovation Center for Organic Electronics and Information Displays,LiaoNing Revitalization Talents Program(grant no.XLYC1902111)and the Key Projects of the Department of Education,Liaoning Province(grant no.LZD202005)for their financial support of this research.
文摘Purely organic room-temperature phosphors,which have received extensive attention as emerging stateof-the-art luminescent materials in various fields,have a longer lifetime than fluorophores.The energy gap law and El-Sayed’s rule provide clear design principles for the development of organic room-temperature phosphorescence.Therefore,the incorporation of heteroatoms(such as sulfur and phosphorus)usually promotes the intersystem crossing rate and increases the 3(π,π*)configuration to realize long lifetimes.Furthermore,boron-containing phosphors not only display excellent phosphorescence properties but also expand El-Sayed’s rule without(n,π*)transitions.This review summarizes recent work on organic phosphorescence of heterocycles with boron,sulfur,and phosphorus heteroatoms and highlights the significance of the guidelines for constructing efficient phosphorescence molecules.This work is instrumental in further diversifying the pool of phosphorescent molecules and developing new and effective design strategies.
基金financially supported by the National Natural Science Foundation of China(Nos.52272032,T2188101,and 52021006)the Beijing Nova Program of Science and Technology(No.20220484079).
文摘With the continuous advancements in electronics towards downsizing and integration,efficient thermal dissipation from chips has emerged as a critical factor affecting their lifespan and operational efficiency.The fan-less chip cooling system has two critical interfaces for thermal transport,which are the contact interface between the base and the chip dominated by thermal conduction,and the surface of the fins dominated by thermal radiation.The different thermal transfer modes of these two critical interfaces pose different requirements for thermal management materials.In the study,a novel approach was proposed by developing graphene thermal transport functional material whose morphology could be intentionally designed via reformed plasmaenhanced chemical vapor deposition(PECVD)methods to meet the diverse requirements of heat transfer properties.Specifically,graphene with multilevel branching structure of vertical graphene(BVG)was fabricated through the hydrogenassisted PECVD(H_(2)-PECVD)strategy,which contributed a high emissivity of~0.98.BVG was deposited on the fins’surface and functioned as the radiation enhanced layer to facilitate the rapid radiation of heat from the heat sinks into the surrounding air.Meanwhile,the well-oriented vertical graphene(OVG)was successfully prepared through the vertical electric field-assisted PECVD process(EF-PECVD),which showed a high directional thermal conductivity of~53.5 W·m^(-1)·K^(-1).OVG was deposited on the contact interface and functioned as the thermal conduction enhanced layer,allowing for the quick transmission of heat from the chip to the heat sink.Utilizing this design concept,the two critical interfaces in the chip cooling system can be jointly enhanced,resulting in a remarkable cooling efficiency enhancement of~30.7%,demonstrating that this novel material possessed enormous potential for enhancing the performance of cooling systems.Therefore,this research not only provided new design concepts for the cooling system of electronic devices but also opened up new avenues for the application of graphene materials in thermal management.
基金The authors thank Beijing National Laboratory for Molecular ScienceThis work was supported by Beijing National Laboratory for Molecular Sciences(No.BNLMS-CXTD-202001)+2 种基金This work was financially supported by the Beijing Municipal Science&Technology Commission(Nos.Z181100004818001 and Z201100008720005)the National Basic Research Program of China(No.2016YFA0200101)the National Natural Science Foundation of China(No.52072042).
文摘Chemical vapor deposition(CVD)-grown graphene films on Cu foils,exhibiting fine scalability and high quality,are still suffering from the adverse impact of surface contamination,i.e.,amorphous carbon.Despite the recent successful preparation of superclean graphene through Cu-vapor-assisted reactions,the formation mechanism of amorphous carbon remains unclear,especially with regard to the functions of substrates.Herein,we have found that the crystallographic orientations of underlying metal substrates would determine the cleanness of graphene in such a way that slower diffusion of active carbon species on asformed graphene-Cu(100)surface is the key factor that suppresses the formation of contamination.The facile synthesis of clean graphene is achieved on the meter-sized Cu(100)that is transformed from the polycrystalline Cu foils.Furthermore,a clean surface of graphene on Cu(100)ensures the reduction of transfer-related polymer residues,and enhanced optical and electrical performance,which allows for versatile applications of graphene in biosensors,functioning as flexible transparent electrodes.This work would offer a promising material platform for the fundamental investigation and create new opportunities for the advanced applications of high-quality graphene films.
