The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of material...The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of materials.This study aims at investigating in more detail the soil-water interaction during the test,exposing its mechanism.For that,a model soil named Hamburg Sand was coated with a hydrophobic fluoropolymer and then a WDPT test was performed while computed tomography(CT)images were taken.Tomography experiments were performed at the P07 high-energy materials science(HEMS)beamline,operated by Helmholtz–Zentrum Hereon,at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron(DESY)in Hamburg.Using synchrotron radiation,a tomogram can be obtained in about 10 min,way less time than regular laboratory X-ray sources usually owned by universities.The faster imaging enables the observation of the drop penetration during time and thus provides insight into the dynamics of the process.After that,digital discrete image correlation is performed to track the displacement of the grains throughout time.From the results one can observe that,as the drop is absorbed at the material's surface,the grains directly around the droplet base are dragged to the liquid-air interface around the drop,revealing grain kinematics during capillary interactions of the penetrating liquid and sand grains.展开更多
The temperature drop of molten metal flowing in open channels is numerically determined. Rectangular, trapezoidal and triangular geometries are considered. The overall heat transfer coefficients for the bottom, side w...The temperature drop of molten metal flowing in open channels is numerically determined. Rectangular, trapezoidal and triangular geometries are considered. The overall heat transfer coefficients for the bottom, side walls and free surface of the channel have been taken from the literature. For each geometry, the volumetric flow rate, mean residence time and temperature drop as a function of the channel inclination angle were determined. The rectangular and trapezoidal geometries present the smallest temperature drops, while the triangular geometry presents the greatest temperature drop. The factors that most affect this drop are the value of the free surface area of the channel, and the average residence time of the molten metal in the channel.展开更多
The wettability of coarse-grained soils has been studied previously.However,soil drying in arid regions due to limited precipitation or irrigation has resulted in soil water repellency to some extent in fine-grained s...The wettability of coarse-grained soils has been studied previously.However,soil drying in arid regions due to limited precipitation or irrigation has resulted in soil water repellency to some extent in fine-grained soils.In this study,laboratory experiments were conducted to investigate the effects of plane(Platanus orientalis L.)leaf biochar with fine(<0.1 mm)and coarse grains(0.1-0.5 mm)on the wettability of a silty clay soil irrigated with saline and non-saline water.Eleven rates of each biochar,ranging from 0 to 10%with 1%intervals,were investigated along with five ionic strengths of water,including 0,0.2,0.4,0.6,and 0.8 mol L^(-1),prepared using sodium and calcium chloride,which are two dominant salts in arid regions.The results showed that application of 5%-10%fine-grained biochar changed the soil hydrophobicity class from strongly to slightly water-repellent,while only 4%coarse-grained biochar was sufficient for the same change in soil wettability.Furthermore,the use of 10%coarse-grained biochar made the soil hydrophilic.The positive effect of plane leaf biochar on soil water repellency reduction was limited by water salinity.The sodium chloride solution was more effective in decreasing the soil wettability than calcium chloride solution and increased the demand for biochar for soil water repellency reduction.In conclusion,plane leaf biochar could be beneficial in managing the hydrophobicity of fine-grained soils.However,water quality as well as biochar particle size determined the quantity of biochar required for improving soil wettability.展开更多
基金funding of this research by the German Research Foundation(Deutsche Forschungsgemeinschaft,DFG)in the framework of Research Training Group GRK 2462:Processes in natural and technical Particle-Fluid-Systems at Hamburg University of Technology(TUHH).
文摘The water drop penetration time(WDPT)test consists of placing water drops on a material's surface in order to evaluate how long it takes to penetrate the pores.It is used to evaluate the hydrophobicity of materials.This study aims at investigating in more detail the soil-water interaction during the test,exposing its mechanism.For that,a model soil named Hamburg Sand was coated with a hydrophobic fluoropolymer and then a WDPT test was performed while computed tomography(CT)images were taken.Tomography experiments were performed at the P07 high-energy materials science(HEMS)beamline,operated by Helmholtz–Zentrum Hereon,at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron(DESY)in Hamburg.Using synchrotron radiation,a tomogram can be obtained in about 10 min,way less time than regular laboratory X-ray sources usually owned by universities.The faster imaging enables the observation of the drop penetration during time and thus provides insight into the dynamics of the process.After that,digital discrete image correlation is performed to track the displacement of the grains throughout time.From the results one can observe that,as the drop is absorbed at the material's surface,the grains directly around the droplet base are dragged to the liquid-air interface around the drop,revealing grain kinematics during capillary interactions of the penetrating liquid and sand grains.
文摘The temperature drop of molten metal flowing in open channels is numerically determined. Rectangular, trapezoidal and triangular geometries are considered. The overall heat transfer coefficients for the bottom, side walls and free surface of the channel have been taken from the literature. For each geometry, the volumetric flow rate, mean residence time and temperature drop as a function of the channel inclination angle were determined. The rectangular and trapezoidal geometries present the smallest temperature drops, while the triangular geometry presents the greatest temperature drop. The factors that most affect this drop are the value of the free surface area of the channel, and the average residence time of the molten metal in the channel.
文摘The wettability of coarse-grained soils has been studied previously.However,soil drying in arid regions due to limited precipitation or irrigation has resulted in soil water repellency to some extent in fine-grained soils.In this study,laboratory experiments were conducted to investigate the effects of plane(Platanus orientalis L.)leaf biochar with fine(<0.1 mm)and coarse grains(0.1-0.5 mm)on the wettability of a silty clay soil irrigated with saline and non-saline water.Eleven rates of each biochar,ranging from 0 to 10%with 1%intervals,were investigated along with five ionic strengths of water,including 0,0.2,0.4,0.6,and 0.8 mol L^(-1),prepared using sodium and calcium chloride,which are two dominant salts in arid regions.The results showed that application of 5%-10%fine-grained biochar changed the soil hydrophobicity class from strongly to slightly water-repellent,while only 4%coarse-grained biochar was sufficient for the same change in soil wettability.Furthermore,the use of 10%coarse-grained biochar made the soil hydrophilic.The positive effect of plane leaf biochar on soil water repellency reduction was limited by water salinity.The sodium chloride solution was more effective in decreasing the soil wettability than calcium chloride solution and increased the demand for biochar for soil water repellency reduction.In conclusion,plane leaf biochar could be beneficial in managing the hydrophobicity of fine-grained soils.However,water quality as well as biochar particle size determined the quantity of biochar required for improving soil wettability.
