In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mecha...In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.展开更多
The cyclic oxidation behavior of Fe-9Cr-1Mo steel (9Cr-1Mo) in 10%H2O+90%Ar (volume fraction) atmosphere at 600, 650 and 700 ℃ for various time was studied. The oxidation mechanism of 9Cr-1Mo steel in 10%H2O+90%Ar at...The cyclic oxidation behavior of Fe-9Cr-1Mo steel (9Cr-1Mo) in 10%H2O+90%Ar (volume fraction) atmosphere at 600, 650 and 700 ℃ for various time was studied. The oxidation mechanism of 9Cr-1Mo steel in 10%H2O+90%Ar atmosphere was discussed. The thermal stress was evaluated in two oxide layers to illustrate the spallation of the oxide layer. The experimental results indicate that there exists a duplex oxide scale with an outer layer of Fe2O3 and an inner layer of mixed (Fe, Cr)3O4 formed on 9Cr-1Mo steel during cyclic oxidation. Some cracks generated in both inner and outer oxide layers. Parts of oxide scales spalled from substrate during the cyclic oxidation. A higher tensile stress in the oxide layer is formed at the early oxidation stage than at the later oxidation stage during heating. This tensile stress results in the formation of cracks in the oxide layer.展开更多
A simplified model was developed to describe the water vapor adsorption on activated carbon. The development of the simplified model was started from the original model proposed by DO and his co-workers. Two different...A simplified model was developed to describe the water vapor adsorption on activated carbon. The development of the simplified model was started from the original model proposed by DO and his co-workers. Two different kinds of carbon materials were prepared for water vapor adsorption, and the adsorption experiments were conducted at different temperatures(20-50 °C) and relative humidities(5%-99%) to test the model. It is shown that the amount of adsorbed water vapor in micropore decreases with the temperature increasing, and the water molecules form larger water clusters around the functional group as the temperature is up to a higher value. The simplified model describes reasonably well for all the experimental data. According to the fitted values, the parameters of simplified model were represented by the temperature and then the model was used to calculate the water vapor adsorption amount at 25 °C and 35 °C. The results show that the model can get relatively accurate values to calculate the water vapor adsorption on activated carbon.展开更多
Five different kinds of hydrophilic organic salts were used to modify commercial activated carbon in order to prepare hydrophilic carbon materials. Properties of the samples were analyzed by surface area analyzer and ...Five different kinds of hydrophilic organic salts were used to modify commercial activated carbon in order to prepare hydrophilic carbon materials. Properties of the samples were analyzed by surface area analyzer and SEM-EDX. The hydrophilic organic salts with different properties were introduced into activated carbon and significantly affected the properties of the samples.During adsorption experiments, the water vapor adsorption amount in modified samples increases by 0.57-17.12 times in temperature range from 303 to 323 K and at relative pressure below 0.50. Water molecules combined with surface hydrophilic groups through H-bonding exhibit good thermo stability. The effects of temperature, oxygen content and properties of the hydrophilic organic salts on water vapor adsorption were studied. It is indicated that water vapor adsorption in modified samples is mainly affected by the surface oxygen content. The carboxylate radicals in the hydrophilic organic salts greatly affect the micropore structure of the modified samples, while the metal ions in them exhibit limited influence. Different adsorption capacity of modified samples can be explained with the electronegativity of elements presented by Pauling.展开更多
According to the experimental data, there is an intermediate substance that formed in the initial stage of oxidation reaction when water vapor is absorbed onto the metallic uranium. The minimum energy of UOH 2 wich C ...According to the experimental data, there is an intermediate substance that formed in the initial stage of oxidation reaction when water vapor is absorbed onto the metallic uranium. The minimum energy of UOH 2 wich C 2v configuration is obtained in the state of 5A 1 by B3LYP method of the density function theory (DFT), which is consistent with that by statics of atoms and molecules reaction (AMRS) and group theory. The results from calculations indicate that the adsorption of water vapor on the metallic uranium is an exothermic reaction and that the adsorbed amount decreases with the elevated temperatures. the adsorptive heat at 1 atm is -205.474 7 kJ.mol -1 , which indicates a typical chemical adsorption.展开更多
为探究21世纪10年代以来海河流域年降水量增多的原因,基于实测降水、旱涝等级以及再分析资料等多源数据,利用小波分析、水汽平衡、WRF模型(Weather Research and Forecast Model)数值模拟等方法,分析了海河流域降水丰枯周期特征、外来...为探究21世纪10年代以来海河流域年降水量增多的原因,基于实测降水、旱涝等级以及再分析资料等多源数据,利用小波分析、水汽平衡、WRF模型(Weather Research and Forecast Model)数值模拟等方法,分析了海河流域降水丰枯周期特征、外来水汽收支变化以及外调水对降水的影响。结果表明:海河流域存在33 a的降水周期,最新一轮周期的丰水段从2013年开始,年降水量较上一轮周期枯水段(1997—2012年)增多80.0 mm;2013—2022年较1997—2012年夏季西北通道、东南通道和西南通道水汽输入分别增加0.35、0.29和0.26 kg/(m·s),导致年降水量增加76.7 mm,占降水增量的95.9%;2015—2022年南水北调中线一期工程输入水量导致流域年降水量增加3.3 mm,占降水增量的4.1%。本研究对掌握海河流域降水演变规律、保障流域长期水资源安全具有重要意义。展开更多
基金Projects(51878064, 51378072) supported by the National Natural Science Foundation of ChinaProjects(300102218408, 300102219108) supported by the Fundamental Research Funds for the Central Universities, China。
文摘In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.
基金Project(2006-8) supported by the Huadian International Corporation Limited
文摘The cyclic oxidation behavior of Fe-9Cr-1Mo steel (9Cr-1Mo) in 10%H2O+90%Ar (volume fraction) atmosphere at 600, 650 and 700 ℃ for various time was studied. The oxidation mechanism of 9Cr-1Mo steel in 10%H2O+90%Ar atmosphere was discussed. The thermal stress was evaluated in two oxide layers to illustrate the spallation of the oxide layer. The experimental results indicate that there exists a duplex oxide scale with an outer layer of Fe2O3 and an inner layer of mixed (Fe, Cr)3O4 formed on 9Cr-1Mo steel during cyclic oxidation. Some cracks generated in both inner and outer oxide layers. Parts of oxide scales spalled from substrate during the cyclic oxidation. A higher tensile stress in the oxide layer is formed at the early oxidation stage than at the later oxidation stage during heating. This tensile stress results in the formation of cracks in the oxide layer.
基金Projects(21376274,51206192)supported by the National Natural Science Foundation of China
文摘A simplified model was developed to describe the water vapor adsorption on activated carbon. The development of the simplified model was started from the original model proposed by DO and his co-workers. Two different kinds of carbon materials were prepared for water vapor adsorption, and the adsorption experiments were conducted at different temperatures(20-50 °C) and relative humidities(5%-99%) to test the model. It is shown that the amount of adsorbed water vapor in micropore decreases with the temperature increasing, and the water molecules form larger water clusters around the functional group as the temperature is up to a higher value. The simplified model describes reasonably well for all the experimental data. According to the fitted values, the parameters of simplified model were represented by the temperature and then the model was used to calculate the water vapor adsorption amount at 25 °C and 35 °C. The results show that the model can get relatively accurate values to calculate the water vapor adsorption on activated carbon.
基金Projects(21376274,51206192)supported by the National Natural Science Foundation of China
文摘Five different kinds of hydrophilic organic salts were used to modify commercial activated carbon in order to prepare hydrophilic carbon materials. Properties of the samples were analyzed by surface area analyzer and SEM-EDX. The hydrophilic organic salts with different properties were introduced into activated carbon and significantly affected the properties of the samples.During adsorption experiments, the water vapor adsorption amount in modified samples increases by 0.57-17.12 times in temperature range from 303 to 323 K and at relative pressure below 0.50. Water molecules combined with surface hydrophilic groups through H-bonding exhibit good thermo stability. The effects of temperature, oxygen content and properties of the hydrophilic organic salts on water vapor adsorption were studied. It is indicated that water vapor adsorption in modified samples is mainly affected by the surface oxygen content. The carboxylate radicals in the hydrophilic organic salts greatly affect the micropore structure of the modified samples, while the metal ions in them exhibit limited influence. Different adsorption capacity of modified samples can be explained with the electronegativity of elements presented by Pauling.
文摘According to the experimental data, there is an intermediate substance that formed in the initial stage of oxidation reaction when water vapor is absorbed onto the metallic uranium. The minimum energy of UOH 2 wich C 2v configuration is obtained in the state of 5A 1 by B3LYP method of the density function theory (DFT), which is consistent with that by statics of atoms and molecules reaction (AMRS) and group theory. The results from calculations indicate that the adsorption of water vapor on the metallic uranium is an exothermic reaction and that the adsorbed amount decreases with the elevated temperatures. the adsorptive heat at 1 atm is -205.474 7 kJ.mol -1 , which indicates a typical chemical adsorption.
文摘为探究21世纪10年代以来海河流域年降水量增多的原因,基于实测降水、旱涝等级以及再分析资料等多源数据,利用小波分析、水汽平衡、WRF模型(Weather Research and Forecast Model)数值模拟等方法,分析了海河流域降水丰枯周期特征、外来水汽收支变化以及外调水对降水的影响。结果表明:海河流域存在33 a的降水周期,最新一轮周期的丰水段从2013年开始,年降水量较上一轮周期枯水段(1997—2012年)增多80.0 mm;2013—2022年较1997—2012年夏季西北通道、东南通道和西南通道水汽输入分别增加0.35、0.29和0.26 kg/(m·s),导致年降水量增加76.7 mm,占降水增量的95.9%;2015—2022年南水北调中线一期工程输入水量导致流域年降水量增加3.3 mm,占降水增量的4.1%。本研究对掌握海河流域降水演变规律、保障流域长期水资源安全具有重要意义。
