A design of a rotating condenser is suggested. The maximum radius under the effect of rotation is estimated analytically .It is found that it decreases with the angular velocity. This in turn increases the rate of swe...A design of a rotating condenser is suggested. The maximum radius under the effect of rotation is estimated analytically .It is found that it decreases with the angular velocity. This in turn increases the rate of sweeping the surface by departing droplets. The appearance of droplets with smaller radii will be predominant. These small droplets offer small thermal resistances, thus enhancing heat transfer through the condenser surface. It is found also that the maximum radius is a function of the distance from the axis of the rotating condenser. Thus the value of the maximum radius under rotation is not unique. This in turn makes the heat flux through the condenser surface not to be uniform.展开更多
Six surfaces were prepared with defferent surface division patterns for the experimental investigationof steam condensation heat transfer characteristics for dropwise and filmwise coexisting(DFC)condensationsurfaces u...Six surfaces were prepared with defferent surface division patterns for the experimental investigationof steam condensation heat transfer characteristics for dropwise and filmwise coexisting(DFC)condensationsurfaces under atmospheric pressure Dropwise condensation(DWC)was promoted with an ultrathin polytetrafluoroethylene(PTFE)film,which was prepared by the dynamic ion-beam mixed implantation(DIMI)method.The results showed that the condensation phenomena at the intersection between the dropwise andfilmwise condensation regios were quite different for different relative positions of the dropwise and filmwisecondensation regions.The experimental results revealed that the condensation heat transfer characteristics werehighly influenced by the surface division number and the relative area ratio of the dropwise and filmwise conden-sation regions.The impact of thesc findings on heat transfer enhancement mechanism for condensation heattransfer is discussed in detail.展开更多
Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two diffe...Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two different modes including filmwise (FWC) and dropwise (DWC) condensation.DWC occurring on hydrophobic and superhydrophobic surfaces has a much higher heat transfer capacity than FWC.Therefore,wide investigations have been done to produce DWC in recent years.Superhydrophobic surfaces have micro/nano structures with low surface energy.In this study,a two-step electrodeposition process is used to produce micro/nano structures on copper specimens.The surface energy of specimens is reduced by a self-assembled monolayer using ethanol and 1-octadecanethiol solution.The results show that there is an optimum condition for electrodeposition parameters.For example,a surface prepared by 2000 s step time has 5 times greater heat transfer than FWC while a surface with 4000 s step time has nearly the same heat transfer as FWC.The surfaces of the fabricated specimens are examined using XRD and SEM analyses.The SEM analyses of the surfaces show that there are some micro-structures on the surfaces and the surface porosities are reduced by increasing the second step electrodeposition time.展开更多
The plasma polymerization method and dynamic ion-beam mixed implantation method were employed to coat ultra-thin polymer films on copper plates. Experiments indicated that steady dropwise condensation of steam at atmo...The plasma polymerization method and dynamic ion-beam mixed implantation method were employed to coat ultra-thin polymer films on copper plates. Experiments indicated that steady dropwise condensation of steam at atmospheric pressure occurred. The condensation heat transfer coefficients increased by approximately 3 and 5－7 times for the polytrimethylvinylsilane film and polytetrafluoroethylene film respectively, compared with the value for film condensation under the same experimental conditions. The temperatures on the condensing surface and inside the test block were found to be rapidly and randomly fluctuated. The properties of the coated films and advantages of the methods used in this investigation were discussed briefly.展开更多
Herein,self-assembled superhydrophobic composite coatings were successfully prepared using a one-step dip-coating method on different irregular parts.The fluorinated nano-SiO_(2) particles spread into a uniform layer ...Herein,self-assembled superhydrophobic composite coatings were successfully prepared using a one-step dip-coating method on different irregular parts.The fluorinated nano-SiO_(2) particles spread into a uniform layer owing to the viscosity of the composite resin.After the optimization of the process,the fabricated nanoporous-structured coating has low adhesion properties with chemical and high thermal stabilities.After baking at 250℃ for 2 h or soaking in a solution of pH=1 or pH=13 for 10 days,the coating could maintain its good superhydrophobicity.The self-ejecting effects of the condensed dewdrops and droplet bounce phenomenon indicate that the coatings can be well-distributed on components of different structures,and they have significant application prospects in irregular parts and industrial production in the near future.展开更多
A model is proposed to predict and evaluate the heat transfer characteristics of dropwise-filmwise hybrid surface.This is approached by modifying the original drop-size distribution,which is defined for fully dropwise...A model is proposed to predict and evaluate the heat transfer characteristics of dropwise-filmwise hybrid surface.This is approached by modifying the original drop-size distribution,which is defined for fully dropwise condensation(DWC)and making it applicable for dropwise-filmwise condensation(DFC).The modification is achieved by simulation work to determine two parameters:the area fraction occupied by large drops f and the ratio of the maximum radius of newly formed drops to that of larger drops γ.Simulation results show a good agreement with the literature for fully DWC and provide a correlation for each parameter with respect to DWC region width in the DFC hybrid surface.The present model evaluates the heat transfer performance of DFC by utilizing these correlations.A comparison is made between the proposed model with experimental work from the literature and results show a good agreement.While changing filmwise condensation(FWC)region width significantly affects the overall heat transfer performance,utilizing smaller width to that of DWC region has the advantage over fully DWC.Furthermore,surface renewal within the hydrophobic region is controlled by adjusting the DWC region width.When the ratio of drop maximum diameter to DWC region width is unity,surface renewal is achieved by drops merging to adjacent FWC regions only.When the ratio is less than unity,surface renewal is achieved by sweeping of departing drops within the hydrophobic region and by merging.For each case,an optimum DWC region width which corresponds to the maximum DFC heat flux is defined.展开更多
Here we presented a novel technology to achieve a Super-hydrophobic coating with microscopic roughness on copper surface. First, make a layer of verdigris grow on the fresh pure copper surface. Gain it by exposing the...Here we presented a novel technology to achieve a Super-hydrophobic coating with microscopic roughness on copper surface. First, make a layer of verdigris grow on the fresh pure copper surface. Gain it by exposing the copper to air and the mist of acetic acid solution. The green coating is a mixture of basic copper（II） carbonate and copper（II） acetate. Second heat the coating and make it decompose to CuO. Lastly, form an n-octadecanethiol self-assembled monolayers coating on the outermost surface. Contact angle test, scanning electron microscope analysis and electrochemical testing were carded out to characterize the surface, and a heat transfer experiment for dropwise condensation of steam was performed also. Results show that the modified surface bears a few Super-hydrophobic features, the static contact angle is higher than that in literatures, reaching 153.1±1.7°. The microscopic roughness can be seen in SEM images, differing much from H2O2 etched surface and bare copper surface. The condensation of steam on the surface is a typical form of dropwise condensation, in the measured range of temperature difference, under 0.1 MPa, the average convection heat transfer coefficients of the vertical surface are 1.7-2.1 times for those of film condensation. At the same time, the inhibition efficiency of surface is improved to some extent comparing with the same kind of SAMs, which suggests that the lifetime of maintenance dropwise condensation would have the possibility to surpass the existing record.展开更多
Excellent dropwise condensation of steam was observed on a polytethefluoroethylene (PTFE) coated plate. The experimental results indicated that the condensation heat transfer performance was increased by 30 to 47 time...Excellent dropwise condensation of steam was observed on a polytethefluoroethylene (PTFE) coated plate. The experimental results indicated that the condensation heat transfer performance was increased by 30 to 47 times when compared with film condensation values at the same surface subcooling degrees. The random fluctuation of the surface temperature was resulted from the high thermal conductivity of the copper substrate and the ultra thin coated polymer film with lower surface free energy. The effect of the steam temperature for pressures near atmospheric pressure on the dropwise condensation heat transfer characteristics was investigated as well.展开更多
Condensation is critical for a wide range of applications such as electrical power generation,distillation,natural gas processing,dehumidification and water harvest,and thermal management.Compared with‘‘filmwise&quo...Condensation is critical for a wide range of applications such as electrical power generation,distillation,natural gas processing,dehumidification and water harvest,and thermal management.Compared with‘‘filmwise"mode of condensation(FWC)prevailing in industrial-scale systems,dropwise condensation(DWC)can provide an order of magnitude higher heat transfer rate owing to drastically reduced thermal resistance from the formation of discrete and mobile droplets.In the past,promoting DWC by controlling surface wetting has attracted wide attention,but DWC highly relies on non-wetting surfaces and only lasts days under practical conditions due to the poor reliability of coatings.Here,we developed nanostructured graphene coatings on nickel(Ni)substrates that we can control and enhance the nucleation of water droplets on graphene grain boundaries.Surprisingly,this enables DWC even under normal‘‘wetting"conditions.This is contradictory to the widely accepted DWC mechanism.Moreover,the Nigraphene surface enables exceptional long-term condensation from days to more than 3 years under practical or even more aggressive testing environments.展开更多
The syntheses of nanosized carbonated hydroxyapatite （CHA） were performed by comparing dropwise and direct pouring of acetone solution of Ca（NO3）2·4H2O into mixture of （NH4）2HPO4 and NH4HCO3 at room tempera...The syntheses of nanosized carbonated hydroxyapatite （CHA） were performed by comparing dropwise and direct pouring of acetone solution of Ca（NO3）2·4H2O into mixture of （NH4）2HPO4 and NH4HCO3 at room temperature controlled at pH 11. Direct pouring method was later applied to study the increment of carbonate content in syntheses. The as-synthesized powders were characterized by various characterization techniques. The crystallographic results of the produced powders were obtained from X-ray diffraction analysis, whilst the carbonate content in the produced powders was determined by the CHNS/O elemental analyzer. Fourier transform infrared analysis confirmed that the CHA powders formed were B-type. Field emission scanning electron microscopy revealed that the powders were highly agglomerated in nanosized range and hence energy filtered transmission electron microscopy was employed to show elongated particles which decreased with increasing carbonate content.展开更多
TO develop an excellent heat transfer element under the vacuum condition, experiments about the heat transfer performance of horizontal tube bundles of different materials under various vacuum conditions were carried ...TO develop an excellent heat transfer element under the vacuum condition, experiments about the heat transfer performance of horizontal tube bundles of different materials under various vacuum conditions were carried out, including the stainless steel tube, the brass tube, the Ni-based implanted steel tube and the ion implanted brass tube. The relative trends show that the condensation heat transfer coefficient and the overall heat transfer coefficient of bundles of four materials all increase with the vacuum degree, especially, those of the Ni-based implanted steel tube and the ion implanted brass tube. Under a high vacuum condition （0.07 MPa）, the condensation heat transfer coefficient of the Ni-based implanted steel tube bundle is about 1.4 times of that of the stainless steel tube bundle, the condensation heat transfer coefficient of the ion implanted brass tube bundle is found to be about 1.3 times of that of the common brass tube bundle. Therefore, according to the condensation heat transfer characteristics studied under high vacuum conditions, it is believed that a dropwise condensation is partly achieved on the surface of these two implanted tube bundles, and the ion implantation is shown to be an effective method to achieve the dropwise condensation. Based on this study, it is believed that the Ni-based steel tube may replace the brass tube, which is more expensive as a heat transfer component.展开更多
The demand for lithium has been steadily growing in recent years due to the boom of electric cars.High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte.Sulfate residuals originat...The demand for lithium has been steadily growing in recent years due to the boom of electric cars.High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte.Sulfate residuals originating from acid leaching of lithium ores must be limited to below 20 mg·L^(−1) during refining.There are methods to remove sulfate such as membrane processing and chemical precipitation using barium salts.However,membrane separation is unable to achieve the required purity while chemical precipitation often causes secondary contamination with barium and requires extra filtration processes that lead to increased processing costs.In this study,we developed a polymeric matrix entrapped with barium ions as a novel adsorbent to selectively adsorb sulfate in aqueous solutions.The adsorbent was prepared by dropwise injection method where alginate droplets were crosslinked with barium to form hydrogel microcapsules.In a typical scenario,the microcapsules had a diameter of 3 mm and contained 5 wt-%alginate.The microcapsules could successfully reduce sulfate concentration in a solution from 100 to 16 mg·L^(−1),exceeding the removal target.However,the microcapsules were mechanically unstable in the presence of an excess amount of sulfate.Hence,calcium ions were added as a secondary crosslinking agent to improve the integrity of the microcapsules.The two-step Ca/Ba@alginate microcapsules showed an exceptional adsorption performance,reducing the sulfate concentration to as low as 0.02 mg·L^(−1).Since the sulfate selective microcapsules can be easily removed from the aqueous system and do not result in secondary barium contamination,these Ca/Ba@alginate adsorbents will find applications in ultra-refining of lithium in industry.展开更多
文摘A design of a rotating condenser is suggested. The maximum radius under the effect of rotation is estimated analytically .It is found that it decreases with the angular velocity. This in turn increases the rate of sweeping the surface by departing droplets. The appearance of droplets with smaller radii will be predominant. These small droplets offer small thermal resistances, thus enhancing heat transfer through the condenser surface. It is found also that the maximum radius is a function of the distance from the axis of the rotating condenser. Thus the value of the maximum radius under rotation is not unique. This in turn makes the heat flux through the condenser surface not to be uniform.
文摘Six surfaces were prepared with defferent surface division patterns for the experimental investigationof steam condensation heat transfer characteristics for dropwise and filmwise coexisting(DFC)condensationsurfaces under atmospheric pressure Dropwise condensation(DWC)was promoted with an ultrathin polytetrafluoroethylene(PTFE)film,which was prepared by the dynamic ion-beam mixed implantation(DIMI)method.The results showed that the condensation phenomena at the intersection between the dropwise andfilmwise condensation regios were quite different for different relative positions of the dropwise and filmwisecondensation regions.The experimental results revealed that the condensation heat transfer characteristics werehighly influenced by the surface division number and the relative area ratio of the dropwise and filmwise conden-sation regions.The impact of thesc findings on heat transfer enhancement mechanism for condensation heattransfer is discussed in detail.
文摘Condensation is an important regime of heat transfer which has wide applications in different industries such as power plants,heating,ventilating and air conditioning,and refrigeration.Condensation occurs in two different modes including filmwise (FWC) and dropwise (DWC) condensation.DWC occurring on hydrophobic and superhydrophobic surfaces has a much higher heat transfer capacity than FWC.Therefore,wide investigations have been done to produce DWC in recent years.Superhydrophobic surfaces have micro/nano structures with low surface energy.In this study,a two-step electrodeposition process is used to produce micro/nano structures on copper specimens.The surface energy of specimens is reduced by a self-assembled monolayer using ethanol and 1-octadecanethiol solution.The results show that there is an optimum condition for electrodeposition parameters.For example,a surface prepared by 2000 s step time has 5 times greater heat transfer than FWC while a surface with 4000 s step time has nearly the same heat transfer as FWC.The surfaces of the fabricated specimens are examined using XRD and SEM analyses.The SEM analyses of the surfaces show that there are some micro-structures on the surfaces and the surface porosities are reduced by increasing the second step electrodeposition time.
基金the National Natural Science Foundation of China (No. 59906002) and the Foundation for Young Teachers of Dalian University of Technology.
文摘The plasma polymerization method and dynamic ion-beam mixed implantation method were employed to coat ultra-thin polymer films on copper plates. Experiments indicated that steady dropwise condensation of steam at atmospheric pressure occurred. The condensation heat transfer coefficients increased by approximately 3 and 5－7 times for the polytrimethylvinylsilane film and polytetrafluoroethylene film respectively, compared with the value for film condensation under the same experimental conditions. The temperatures on the condensing surface and inside the test block were found to be rapidly and randomly fluctuated. The properties of the coated films and advantages of the methods used in this investigation were discussed briefly.
基金We are grateful for the supports received from the National Natural Science Foundation of China(Grant No.52071076)Scientific Research Foundation of Graduate School of Southeast University(YBPY1875).
文摘Herein,self-assembled superhydrophobic composite coatings were successfully prepared using a one-step dip-coating method on different irregular parts.The fluorinated nano-SiO_(2) particles spread into a uniform layer owing to the viscosity of the composite resin.After the optimization of the process,the fabricated nanoporous-structured coating has low adhesion properties with chemical and high thermal stabilities.After baking at 250℃ for 2 h or soaking in a solution of pH=1 or pH=13 for 10 days,the coating could maintain its good superhydrophobicity.The self-ejecting effects of the condensed dewdrops and droplet bounce phenomenon indicate that the coatings can be well-distributed on components of different structures,and they have significant application prospects in irregular parts and industrial production in the near future.
文摘A model is proposed to predict and evaluate the heat transfer characteristics of dropwise-filmwise hybrid surface.This is approached by modifying the original drop-size distribution,which is defined for fully dropwise condensation(DWC)and making it applicable for dropwise-filmwise condensation(DFC).The modification is achieved by simulation work to determine two parameters:the area fraction occupied by large drops f and the ratio of the maximum radius of newly formed drops to that of larger drops γ.Simulation results show a good agreement with the literature for fully DWC and provide a correlation for each parameter with respect to DWC region width in the DFC hybrid surface.The present model evaluates the heat transfer performance of DFC by utilizing these correlations.A comparison is made between the proposed model with experimental work from the literature and results show a good agreement.While changing filmwise condensation(FWC)region width significantly affects the overall heat transfer performance,utilizing smaller width to that of DWC region has the advantage over fully DWC.Furthermore,surface renewal within the hydrophobic region is controlled by adjusting the DWC region width.When the ratio of drop maximum diameter to DWC region width is unity,surface renewal is achieved by drops merging to adjacent FWC regions only.When the ratio is less than unity,surface renewal is achieved by sweeping of departing drops within the hydrophobic region and by merging.For each case,an optimum DWC region width which corresponds to the maximum DFC heat flux is defined.
基金supports of the National Natural Seience Foundation of China (Grant No.50706053)the National High Teelmology Research and Development Program of China(863 Prograrn,Grant No.2007AA052259) are gratefully acknowledged.
文摘Here we presented a novel technology to achieve a Super-hydrophobic coating with microscopic roughness on copper surface. First, make a layer of verdigris grow on the fresh pure copper surface. Gain it by exposing the copper to air and the mist of acetic acid solution. The green coating is a mixture of basic copper（II） carbonate and copper（II） acetate. Second heat the coating and make it decompose to CuO. Lastly, form an n-octadecanethiol self-assembled monolayers coating on the outermost surface. Contact angle test, scanning electron microscope analysis and electrochemical testing were carded out to characterize the surface, and a heat transfer experiment for dropwise condensation of steam was performed also. Results show that the modified surface bears a few Super-hydrophobic features, the static contact angle is higher than that in literatures, reaching 153.1±1.7°. The microscopic roughness can be seen in SEM images, differing much from H2O2 etched surface and bare copper surface. The condensation of steam on the surface is a typical form of dropwise condensation, in the measured range of temperature difference, under 0.1 MPa, the average convection heat transfer coefficients of the vertical surface are 1.7-2.1 times for those of film condensation. At the same time, the inhibition efficiency of surface is improved to some extent comparing with the same kind of SAMs, which suggests that the lifetime of maintenance dropwise condensation would have the possibility to surpass the existing record.
基金the Nahonal NaedScience Foundation of China (No.599060()2) and the Scienhficresereh FOundahon for the Retwed Oversea Chinese
文摘Excellent dropwise condensation of steam was observed on a polytethefluoroethylene (PTFE) coated plate. The experimental results indicated that the condensation heat transfer performance was increased by 30 to 47 times when compared with film condensation values at the same surface subcooling degrees. The random fluctuation of the surface temperature was resulted from the high thermal conductivity of the copper substrate and the ultra thin coated polymer film with lower surface free energy. The effect of the steam temperature for pressures near atmospheric pressure on the dropwise condensation heat transfer characteristics was investigated as well.
基金supported by the National Science Foundation(NSF)Program of thermal transport processes under Grant No.1336443。
文摘Condensation is critical for a wide range of applications such as electrical power generation,distillation,natural gas processing,dehumidification and water harvest,and thermal management.Compared with‘‘filmwise"mode of condensation(FWC)prevailing in industrial-scale systems,dropwise condensation(DWC)can provide an order of magnitude higher heat transfer rate owing to drastically reduced thermal resistance from the formation of discrete and mobile droplets.In the past,promoting DWC by controlling surface wetting has attracted wide attention,but DWC highly relies on non-wetting surfaces and only lasts days under practical conditions due to the poor reliability of coatings.Here,we developed nanostructured graphene coatings on nickel(Ni)substrates that we can control and enhance the nucleation of water droplets on graphene grain boundaries.Surprisingly,this enables DWC even under normal‘‘wetting"conditions.This is contradictory to the widely accepted DWC mechanism.Moreover,the Nigraphene surface enables exceptional long-term condensation from days to more than 3 years under practical or even more aggressive testing environments.
基金Universiti Sains Malaysia for the USM FellowshipUSM-RU-PGRS(8033006)for the financial support
文摘The syntheses of nanosized carbonated hydroxyapatite （CHA） were performed by comparing dropwise and direct pouring of acetone solution of Ca（NO3）2·4H2O into mixture of （NH4）2HPO4 and NH4HCO3 at room temperature controlled at pH 11. Direct pouring method was later applied to study the increment of carbonate content in syntheses. The as-synthesized powders were characterized by various characterization techniques. The crystallographic results of the produced powders were obtained from X-ray diffraction analysis, whilst the carbonate content in the produced powders was determined by the CHNS/O elemental analyzer. Fourier transform infrared analysis confirmed that the CHA powders formed were B-type. Field emission scanning electron microscopy revealed that the powders were highly agglomerated in nanosized range and hence energy filtered transmission electron microscopy was employed to show elongated particles which decreased with increasing carbonate content.
基金the National Key Basic ResearchProgram of China (973 Program, Grant No. 2011CB710702)
文摘TO develop an excellent heat transfer element under the vacuum condition, experiments about the heat transfer performance of horizontal tube bundles of different materials under various vacuum conditions were carried out, including the stainless steel tube, the brass tube, the Ni-based implanted steel tube and the ion implanted brass tube. The relative trends show that the condensation heat transfer coefficient and the overall heat transfer coefficient of bundles of four materials all increase with the vacuum degree, especially, those of the Ni-based implanted steel tube and the ion implanted brass tube. Under a high vacuum condition （0.07 MPa）, the condensation heat transfer coefficient of the Ni-based implanted steel tube bundle is about 1.4 times of that of the stainless steel tube bundle, the condensation heat transfer coefficient of the ion implanted brass tube bundle is found to be about 1.3 times of that of the common brass tube bundle. Therefore, according to the condensation heat transfer characteristics studied under high vacuum conditions, it is believed that a dropwise condensation is partly achieved on the surface of these two implanted tube bundles, and the ion implantation is shown to be an effective method to achieve the dropwise condensation. Based on this study, it is believed that the Ni-based steel tube may replace the brass tube, which is more expensive as a heat transfer component.
基金This work was supported by the Department of Chemical Engineering at The University of Melbourne.
文摘The demand for lithium has been steadily growing in recent years due to the boom of electric cars.High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte.Sulfate residuals originating from acid leaching of lithium ores must be limited to below 20 mg·L^(−1) during refining.There are methods to remove sulfate such as membrane processing and chemical precipitation using barium salts.However,membrane separation is unable to achieve the required purity while chemical precipitation often causes secondary contamination with barium and requires extra filtration processes that lead to increased processing costs.In this study,we developed a polymeric matrix entrapped with barium ions as a novel adsorbent to selectively adsorb sulfate in aqueous solutions.The adsorbent was prepared by dropwise injection method where alginate droplets were crosslinked with barium to form hydrogel microcapsules.In a typical scenario,the microcapsules had a diameter of 3 mm and contained 5 wt-%alginate.The microcapsules could successfully reduce sulfate concentration in a solution from 100 to 16 mg·L^(−1),exceeding the removal target.However,the microcapsules were mechanically unstable in the presence of an excess amount of sulfate.Hence,calcium ions were added as a secondary crosslinking agent to improve the integrity of the microcapsules.The two-step Ca/Ba@alginate microcapsules showed an exceptional adsorption performance,reducing the sulfate concentration to as low as 0.02 mg·L^(−1).Since the sulfate selective microcapsules can be easily removed from the aqueous system and do not result in secondary barium contamination,these Ca/Ba@alginate adsorbents will find applications in ultra-refining of lithium in industry.
