Electrical conductivity of molten binary and ternary mixtures based on the system NaF-AlF3-SiO2 was investigated by means of a tube–cell (made of pyrolytic boron nitride) with stationary electrodes. Viscosity of th...Electrical conductivity of molten binary and ternary mixtures based on the system NaF-AlF3-SiO2 was investigated by means of a tube–cell (made of pyrolytic boron nitride) with stationary electrodes. Viscosity of the binary system Na3AlF6-SiO2 was measured by computerized torsion pendulum method. It was found that conductivity and viscosity varied linearly with temperature in all investigated mixtures. Obtained content dependence of electrical conductivity (isotherms) was divided into two parts. First, one represented the content region up to 10%(mole fraction) of SiO2;second, the region was with a higher content of SiO2 (from 10%up to 40%). While the conductivity considerably decreased with content of SiO2 in the second part; it surprisingly rose in the low content range. A small addition of SiO2 to the molten cryolite (up to 10%) could slightly increase viscosity, but had no influence on the slope of this dependence since it is responsible for a glassy-networks formation in the melt. Further addition of SiO2 to the molten cryolite had a huge effect on the viscosity.展开更多
A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat t...A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below -5℃. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m.s y. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.展开更多
Freeze concentration has great potential in treating wastewaters containing soluble pollutions. It is important for freeze concentration process to produce ice crystals with large size and high purity. In this work ra...Freeze concentration has great potential in treating wastewaters containing soluble pollutions. It is important for freeze concentration process to produce ice crystals with large size and high purity. In this work raw urines of 4660 -7914 mg/L in COD, 512. 71 -872. 41 mg/L in NH3 -N and 22600 -28800 μs/cm in electric conductivity were studied. Urines were frozen by a digital refrigerated circulator bath. Ice crystals were purified by ice-water steep and vacuum filtration. The COD, NH3 - N, and electric conductivity levels of the melted ices were measured to reflect ice crystal purity. Effects of coolant temperature, ice crystal shape, initial solution temperature, solution concentration, ice seeding, re-crystallization process and crystallization time on ice crystal purity were analyzed. The results show that an appropriate coolant temperature, suspended ice crystals, an initial solution temperature of about 6 ℃, introduction of seed ice, addition of re-crystallization process, and crystallization time of less than 30 min axe in favor of producing ice crystals with high purity. Under such conditions, more than 99 percent of inorganic salts, COD and NH3 - N sources in raw urine could he removed.展开更多
Anodic processes on Cu-10 Al electrode in molten KF-AlF3-Al2O3(saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio(CR= x(KF)/x(AlF3)),...Anodic processes on Cu-10 Al electrode in molten KF-AlF3-Al2O3(saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio(CR= x(KF)/x(AlF3)), temperature and particle volume fraction(φ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions(φ=0.12, 0.15) at 750 ℃ with 0.4 A/cm^2 current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions(φ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of φ in the suspension. The results suggest that the Cu-10 Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 ℃.展开更多
The anodic behaviour of pre-oxidised and non-oxidised Cu-Al-based anodes(Cu-10Al and Cu-9.8Al-2Mn)in KF-AlF_(3)-Al_(2)O_(3)melts was studied through galvanostatic and potentiodynamic polarization techniques.The alloy ...The anodic behaviour of pre-oxidised and non-oxidised Cu-Al-based anodes(Cu-10Al and Cu-9.8Al-2Mn)in KF-AlF_(3)-Al_(2)O_(3)melts was studied through galvanostatic and potentiodynamic polarization techniques.The alloy compositions were oxidised for a short-term(8 h)at 700℃,followed by galvanostatic polarization for 1 h at 800℃with an applied current density of 0.4 A/cm^(2).The potentiodynamic curves were recorded with a sweep rate of 0.01 V/s.XRD analysis was conducted on frozen melt samples collected on the surface of the anode,and SEM observation was performed on the anode after the experiment to study the phases of the scales formed on the alloys.All the anode materials had a steady potential between 2.30 and 2.50 V(vs Al/AlF_(3)).The corrosion rates of the anodes were calculated from the data acquired through potentiodynamic polarization.It was seen that pre-oxidised anodes possess a low corrosion rate compared to those without pre-oxidation treatment.展开更多
A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud see...A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.展开更多
Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration.Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microw...Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration.Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microwave assisted freeze drying. The direct observation of the ice crystals formed under microscope reveals that the ice crystal sizes formed from de-ionized water depend on the cooling rate with fast cooling rate giving smaller ice crystals as expected. Once there is a sufficient amount of solute mixed with the de-ionized water, for example the reactive red,the size and its distribution are not very much dependent on either cooling rate or the final temperature provided there is sufficient time of cooling and the final temperature is not too low. The size of ice crystals formed within the solution of reactive red is usually below 100μm with a freezing rate of 1℃·min-1 for a droplet of the size of less than 1 mm. A simplified simulation indicates that such a small ice crystal would not cause a significant non-uniform distribution of temperature for microwave assisted freeze drying. When the ice crystal size is larger than 5 mm, heat conduction from the solute concentrated region to the ice region may need to be considered.展开更多
Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which can measure the dissolution rate of alumina was presented. Effect of factors on dissolution ...Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which can measure the dissolution rate of alumina was presented. Effect of factors on dissolution rate of alumina was studied intuitively and roundly using transparent quartz electrobath and image analysis techniques. Images about dissolution process of alumina were taken at an interval of fixed time from transparent quartz electrobath of double rooms. Gabor wavelet transforms were used for extracting and describing the texture features of each image. After subsampling several times, the dissolution rate of alumina was computed using these texture features in local neighborhood of samples. Regression equation of the dissolution rate of alumina was obtained using these dissolution rates. Experiments show that the regression equation of the dissolution rate of alumina is y=-0.000 5x^3+0.024 0x^2-0.287 3x+ 1.276 7 for Na3AIF6-AIF3-Al2O3-CaF2-LiF- MgF2 system at 920 ℃.展开更多
This paper presents a detailed study on the textural and geochemical characteristics of the proglacial sediments near the edge of modern Nelson Ice Cap, Antarctica. The grain size distributions of the proglacial sedim...This paper presents a detailed study on the textural and geochemical characteristics of the proglacial sediments near the edge of modern Nelson Ice Cap, Antarctica. The grain size distributions of the proglacial sediments are characteristic of glacigenic deposits, but very different from those of aeolian and lacustrine sediments. Moreover, the grain size distributions of the proglacial sediments are fractal with a dimension of about 2.9, and the fractal dimensions can be used as another summary statistical parameter for quantifying the relative amounts of coarse and fine materials. Correlations between the absolute element abundances of the proglacial sediments are very weak due to mineral partitioning and other effects of glacial processes, but correlations between the element/Rb ratios are statistically significant. This finding indicates that element/Rb ratios can be used to reduce or eliminate the effects of glacial processes, evaluate geochemical data and determine the sediment provenance in the foreland of Antarctic glacier. Comparisons on the element concentrations among different environments suggest that the proglacial sediments are derived predominantly from local bedrocks and appear to be natural in origin. Thus these natural sediments can be used to study chemical weathering in the proglacial foreland of modern glacier.展开更多
Aluminum is widely used in transmission lines, and the accumulation of ice on aluminum conductor may inflict serious damage such as tower collapse and power failure. In this study, super-hydrophobic surface (SHS) on...Aluminum is widely used in transmission lines, and the accumulation of ice on aluminum conductor may inflict serious damage such as tower collapse and power failure. In this study, super-hydrophobic surface (SHS) on alurninurn conductor with rnicro-nanostructure was fabricated using the preferential etching principle of crystal defects. The surface rnicrostructure and wettability were investigated by scanning electron microscope and contact angle measurement, respectively. The icing progress was observed with a self-made icing experiment platform at different environment temperature. The results showed that, due to jumping and rolling down of coalesced droplets from SHS of aluminum conductor at low temperature, the formation of icing on SHS could be delayed. Dynamic icing experiment indicated that SHS on aluminum conductor could restrain the formation of icing in certain temperature range, but could not exert influence on the accumulation of icing. This study offers new insight into understanding the anti-icing performance of actual aluminum conductor.展开更多
Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of i...Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of ice-particle mass and radius on hydrometeors,internal energy,and kinetic energy,as well as the primary factors responsible.It was found that the ice content increases notably and the snow content decreases due to the change.This is the consequence of the modulation of cloud microphysical processes.In particular,the Bergeron process and the accretion of snow and cloud ice are markedly influenced.The differences of internal energy and kinetic energy between the two experiments are caused by adjustments to pressure-flux divergence,the coupling of temperature and divergence,and gravitational work,and the reason is that these three factors result in differences of local changes of internal and kinetic energy.展开更多
The effects of surface energy on phase change of water vapor at initial stage of frost growth were studied to find an effective method of restraining frost growth.The mechanism of restraining frost growth by low energ...The effects of surface energy on phase change of water vapor at initial stage of frost growth were studied to find an effective method of restraining frost growth.The mechanism of restraining frost growth by low energy surface(bigger contact angle) was analyzed based on crystal growth theory.Then,the phase change of water vapor and the process of frost growth on the copper and wax energy surfaces were observed using microscope.The results indicate that it is difficult for wax surface(low energy surface),on which there are still water droplets at 100 s,to form critical embryo,so frost growth can be restrained in a way.Water formation,droplet growth,ice formation and dendritic ice growth processes happen on both surfaces,ordinally.But the ice beads,with larger average diameter and sparse distribution on the wax surface,form later(at about 300 s) than that on the copper surface,and the dendritic ice also appears later.All of these support that ice crystal formation and dendritic crystal growth at initial stage of frost growth can be retarded on the low energy surface.展开更多
Uniaxial compression experiments on horizontal and ervoir were conducted at different temperatures and strain rates vertical samples of first-year freshwater ice in a res- with an electronic universal machine equipped...Uniaxial compression experiments on horizontal and ervoir were conducted at different temperatures and strain rates vertical samples of first-year freshwater ice in a res- with an electronic universal machine equipped with low temperature cabinet. The results show that there is no difference between the strengths of two horizontal samples with grain sizes ranging from 1 to 4 mm and 4 to 14 mm, while the strength of the 1--4 mm vertical samples is 1.4 times higher than that of the 4--14 mm vertical samples because of the change of crystal structure. For different load- ing directions, the strengths of the horizontal samples do not differ from those of the vertical samples with the same grain sizes. The relation among the uniaxial compressive strength, strain rate and temperature was established through data analysis in both the ductile and brittle regions.展开更多
基金supported by the Science and Technology Assistance Agency (APVV-0460-10 and SK-CN-0029-12)Slovak Grant Agency (VEGA 2/0116/14 and VEGA 2/0095/12)+2 种基金the National Natural Science Foundation of China (51322406)the Program for New Century Excellent Talents (NCET-13-0107)Ministry of Education of China
文摘Electrical conductivity of molten binary and ternary mixtures based on the system NaF-AlF3-SiO2 was investigated by means of a tube–cell (made of pyrolytic boron nitride) with stationary electrodes. Viscosity of the binary system Na3AlF6-SiO2 was measured by computerized torsion pendulum method. It was found that conductivity and viscosity varied linearly with temperature in all investigated mixtures. Obtained content dependence of electrical conductivity (isotherms) was divided into two parts. First, one represented the content region up to 10%(mole fraction) of SiO2;second, the region was with a higher content of SiO2 (from 10%up to 40%). While the conductivity considerably decreased with content of SiO2 in the second part; it surprisingly rose in the low content range. A small addition of SiO2 to the molten cryolite (up to 10%) could slightly increase viscosity, but had no influence on the slope of this dependence since it is responsible for a glassy-networks formation in the melt. Further addition of SiO2 to the molten cryolite had a huge effect on the viscosity.
基金the Specialized Research Fund for the Doctoral Program of Higher Education of China(20060286034)
文摘A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below -5℃. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m.s y. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.
基金Sponsored by the High Technology Research and Development Programm of China(Grant No.2002AA743022).
文摘Freeze concentration has great potential in treating wastewaters containing soluble pollutions. It is important for freeze concentration process to produce ice crystals with large size and high purity. In this work raw urines of 4660 -7914 mg/L in COD, 512. 71 -872. 41 mg/L in NH3 -N and 22600 -28800 μs/cm in electric conductivity were studied. Urines were frozen by a digital refrigerated circulator bath. Ice crystals were purified by ice-water steep and vacuum filtration. The COD, NH3 - N, and electric conductivity levels of the melted ices were measured to reflect ice crystal purity. Effects of coolant temperature, ice crystal shape, initial solution temperature, solution concentration, ice seeding, re-crystallization process and crystallization time on ice crystal purity were analyzed. The results show that an appropriate coolant temperature, suspended ice crystals, an initial solution temperature of about 6 ℃, introduction of seed ice, addition of re-crystallization process, and crystallization time of less than 30 min axe in favor of producing ice crystals with high purity. Under such conditions, more than 99 percent of inorganic salts, COD and NH3 - N sources in raw urine could he removed.
文摘Anodic processes on Cu-10 Al electrode in molten KF-AlF3-Al2O3(saturated) and suspensions were characterized using chronopotentiometric and cyclic voltammetric techniques. Effects of cryolite ratio(CR= x(KF)/x(AlF3)), temperature and particle volume fraction(φ) on the electrochemical behaviour of the anode were demonstrated. Initially, the anode was polarised in the galvanostatic mode in melt and suspensions(φ=0.12, 0.15) at 750 ℃ with 0.4 A/cm^2 current density. The anode potential in melt varied between 2.5 and 3.2 V and in suspensions(φ= 0.12) between 3.3 and 3.4 V. XRD analysis was conducted to study the oxide phases on the anode surface. Anode limiting current densities and mass transfer coefficients drastically decreased with the increase of φ in the suspension. The results suggest that the Cu-10 Al electrode works better in suspensions with CR of 1.4 and particle volume fraction of 0.09 at 800 ℃.
文摘The anodic behaviour of pre-oxidised and non-oxidised Cu-Al-based anodes(Cu-10Al and Cu-9.8Al-2Mn)in KF-AlF_(3)-Al_(2)O_(3)melts was studied through galvanostatic and potentiodynamic polarization techniques.The alloy compositions were oxidised for a short-term(8 h)at 700℃,followed by galvanostatic polarization for 1 h at 800℃with an applied current density of 0.4 A/cm^(2).The potentiodynamic curves were recorded with a sweep rate of 0.01 V/s.XRD analysis was conducted on frozen melt samples collected on the surface of the anode,and SEM observation was performed on the anode after the experiment to study the phases of the scales formed on the alloys.All the anode materials had a steady potential between 2.30 and 2.50 V(vs Al/AlF_(3)).The corrosion rates of the anodes were calculated from the data acquired through potentiodynamic polarization.It was seen that pre-oxidised anodes possess a low corrosion rate compared to those without pre-oxidation treatment.
基金This study was jointly supported by the National Key Research and Development Program of China[grant number 2018YFC1507900]the National Natural Science Foundation of China[grant numbers 41875172 and 42075192].
文摘A 2D axisymmetric bin model is used to conduct idealized numerical experiments of cloud seeding.The simulations are performed for two clouds that differ in their initial wind shear.Results show that,although cloud seeding with an ice concentration of 1000 Lin a regime that has relatively high supercooled liquid water can obtain a positive effect,the rainfall enhancement seems more pronounced when the cloud develops in a wind shear environment.In no-shear environment,the change in the microphysical thermodynamic field after seeding shows that,although more graupel is produced via riming and this can increase the surface rainfall intensity,the larger drag force and cooling of melting graupel is unfavorable for the development of cloud.On the contrary,when the cloud develops in a wind shear environment,since the main downdraft is behind the direction of movement of the cloud,its negative effect on precipitation is much weaker.
文摘Freeze drying of an aqueous solution would result in the non-uniform distribution of solute concentration.Because ice is almost transparent to microwave, therefore such a non-uniform distribution may affect the microwave assisted freeze drying. The direct observation of the ice crystals formed under microscope reveals that the ice crystal sizes formed from de-ionized water depend on the cooling rate with fast cooling rate giving smaller ice crystals as expected. Once there is a sufficient amount of solute mixed with the de-ionized water, for example the reactive red,the size and its distribution are not very much dependent on either cooling rate or the final temperature provided there is sufficient time of cooling and the final temperature is not too low. The size of ice crystals formed within the solution of reactive red is usually below 100μm with a freezing rate of 1℃·min-1 for a droplet of the size of less than 1 mm. A simplified simulation indicates that such a small ice crystal would not cause a significant non-uniform distribution of temperature for microwave assisted freeze drying. When the ice crystal size is larger than 5 mm, heat conduction from the solute concentrated region to the ice region may need to be considered.
基金Projects(51101104,51072121) supported by the National Natural Science Foundation of ChinaProject(LS2010109) supported by the Key Laboratory Foundation of Liaoning Province,China
文摘Determination of dissolution rate of alumina is one of the classical problems in aluminum electrolysis. A novel method which can measure the dissolution rate of alumina was presented. Effect of factors on dissolution rate of alumina was studied intuitively and roundly using transparent quartz electrobath and image analysis techniques. Images about dissolution process of alumina were taken at an interval of fixed time from transparent quartz electrobath of double rooms. Gabor wavelet transforms were used for extracting and describing the texture features of each image. After subsampling several times, the dissolution rate of alumina was computed using these texture features in local neighborhood of samples. Regression equation of the dissolution rate of alumina was obtained using these dissolution rates. Experiments show that the regression equation of the dissolution rate of alumina is y=-0.000 5x^3+0.024 0x^2-0.287 3x+ 1.276 7 for Na3AIF6-AIF3-Al2O3-CaF2-LiF- MgF2 system at 920 ℃.
基金The work was supported by the Nationa1 Natural ScienceFoundation of China(Grant No.40231002 and 40076032)the project of Chinese Academy of Sciences(Grant No.KZCX2-303)
文摘This paper presents a detailed study on the textural and geochemical characteristics of the proglacial sediments near the edge of modern Nelson Ice Cap, Antarctica. The grain size distributions of the proglacial sediments are characteristic of glacigenic deposits, but very different from those of aeolian and lacustrine sediments. Moreover, the grain size distributions of the proglacial sediments are fractal with a dimension of about 2.9, and the fractal dimensions can be used as another summary statistical parameter for quantifying the relative amounts of coarse and fine materials. Correlations between the absolute element abundances of the proglacial sediments are very weak due to mineral partitioning and other effects of glacial processes, but correlations between the element/Rb ratios are statistically significant. This finding indicates that element/Rb ratios can be used to reduce or eliminate the effects of glacial processes, evaluate geochemical data and determine the sediment provenance in the foreland of Antarctic glacier. Comparisons on the element concentrations among different environments suggest that the proglacial sediments are derived predominantly from local bedrocks and appear to be natural in origin. Thus these natural sediments can be used to study chemical weathering in the proglacial foreland of modern glacier.
基金supported by the National Natural Science Foundation of China (No.51272208)
文摘Aluminum is widely used in transmission lines, and the accumulation of ice on aluminum conductor may inflict serious damage such as tower collapse and power failure. In this study, super-hydrophobic surface (SHS) on alurninurn conductor with rnicro-nanostructure was fabricated using the preferential etching principle of crystal defects. The surface rnicrostructure and wettability were investigated by scanning electron microscope and contact angle measurement, respectively. The icing progress was observed with a self-made icing experiment platform at different environment temperature. The results showed that, due to jumping and rolling down of coalesced droplets from SHS of aluminum conductor at low temperature, the formation of icing on SHS could be delayed. Dynamic icing experiment indicated that SHS on aluminum conductor could restrain the formation of icing in certain temperature range, but could not exert influence on the accumulation of icing. This study offers new insight into understanding the anti-icing performance of actual aluminum conductor.
基金supported by the National Basic Research Program of China (Grant No.2013CB430105)the Key Program of the Chinese Academy of Sciences (Grant No.KZZD-EW-05)+2 种基金the Project of Chinese Academy of Meteorological Sciences (Grant No.2011LASW-B15)the Special Scientific Research Fund of Meteorological Public Welfare of the Ministry of Sciences and Technology (Grant No.GYHY200906004)and the National Natural Science Foundation of China (Grant Nos.41175060,41075098,and 41005005)
文摘Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of ice-particle mass and radius on hydrometeors,internal energy,and kinetic energy,as well as the primary factors responsible.It was found that the ice content increases notably and the snow content decreases due to the change.This is the consequence of the modulation of cloud microphysical processes.In particular,the Bergeron process and the accretion of snow and cloud ice are markedly influenced.The differences of internal energy and kinetic energy between the two experiments are caused by adjustments to pressure-flux divergence,the coupling of temperature and divergence,and gravitational work,and the reason is that these three factors result in differences of local changes of internal and kinetic energy.
基金Project(50376052) supported by the National Natural Science Foundation of ChinaProject(307013) supported by the Key Project of Chinese Ministry of EducationProject(2008BAJ12B02) supported by the National Science and Technology Pillar Program in the 11th Five-Year Plan Period
文摘The effects of surface energy on phase change of water vapor at initial stage of frost growth were studied to find an effective method of restraining frost growth.The mechanism of restraining frost growth by low energy surface(bigger contact angle) was analyzed based on crystal growth theory.Then,the phase change of water vapor and the process of frost growth on the copper and wax energy surfaces were observed using microscope.The results indicate that it is difficult for wax surface(low energy surface),on which there are still water droplets at 100 s,to form critical embryo,so frost growth can be restrained in a way.Water formation,droplet growth,ice formation and dendritic ice growth processes happen on both surfaces,ordinally.But the ice beads,with larger average diameter and sparse distribution on the wax surface,form later(at about 300 s) than that on the copper surface,and the dendritic ice also appears later.All of these support that ice crystal formation and dendritic crystal growth at initial stage of frost growth can be retarded on the low energy surface.
基金Supported by National Natural Science Foundation of China (No. 50879008 and No. 51079021)
文摘Uniaxial compression experiments on horizontal and ervoir were conducted at different temperatures and strain rates vertical samples of first-year freshwater ice in a res- with an electronic universal machine equipped with low temperature cabinet. The results show that there is no difference between the strengths of two horizontal samples with grain sizes ranging from 1 to 4 mm and 4 to 14 mm, while the strength of the 1--4 mm vertical samples is 1.4 times higher than that of the 4--14 mm vertical samples because of the change of crystal structure. For different load- ing directions, the strengths of the horizontal samples do not differ from those of the vertical samples with the same grain sizes. The relation among the uniaxial compressive strength, strain rate and temperature was established through data analysis in both the ductile and brittle regions.