A cold vent is an area where methane-rich fluid seepage occurs. This seepage may alter the local temperature, salinity, and subsequent accumulation of the gas hydrate. Using a kinetic gas hydrate formation model and i...A cold vent is an area where methane-rich fluid seepage occurs. This seepage may alter the local temperature, salinity, and subsequent accumulation of the gas hydrate. Using a kinetic gas hydrate formation model and in situ measurement of tempera- ture, salinity and fluid flux at the southern summit of Hydrate Ridge, we simuIate the gas hydrate accumulation at three distinct fluid sites： clam, bacterial mat, and gas discharge sites. At the clam sites （pore water flux 〈 20 kg m-2 yr-1）, pore water advec- tion has little influence on temperature and salinity. However, the salinity and temperature are increased （peak salinity 〉 0.8 tool kg-1） by the formation of gas hydrate causing the base of the hydrate stability zone to move gradually from -115 to -70 meters below seafloor （mbsf）. The gas hydrate saturation at the clam sites is relatively high. The water flux at the bacterial mat sites ranges from 100 to 2500 kg m-2 yr-1. The water flow suppresses the increase in salinity resulting in a salinity close to or slightly higher than that of seawater （〈 0.65 mol kg-l）. Heat advection by water flow increases temperature significantly, shifting the base of the hydrate stability zone to above 50 or even 3 mbsf. The gas hydrate saturation is relatively low at the bacterial mat site. At the gas discharge sites, the pore water flux could reach 10^10 kg m-2 yr-1, and the temperature could reach that of the source area in 9 min. There is no gas hydrate formation at the gas discharge sites. Our simulative analysis therefore reveals that a lower pore water flux would result in lower salinity, higher temperature, and a shallower base of the hydrate sta- bility zone. This in turn induces a lower gas hydrate formation rate, lower hydrate saturation, and eventually less gas hydrate resources.展开更多
The drag reduction effect of super-hydrophobic surface induced by the entrapped gas is unstable due to the gradual disappearance of the trapped gas.In this paper,a hydrophobic transverse grooved surface was designed t...The drag reduction effect of super-hydrophobic surface induced by the entrapped gas is unstable due to the gradual disappearance of the trapped gas.In this paper,a hydrophobic transverse grooved surface was designed to sustain gas in valleys.A detail numerical simulation was presented to investigate the flow field near the proposed surface.When water flowed over this surface,the entrapped gas was blocked by the ridges and the solid-liquid interface was replaced by the liquid-gas interface due to the entrapped gas,furthermore the micro-vortex formed in the groove.Because there was an effective slippage between water and solid induced by the entrapped gas,the velocity gradient of boundary layer decreased,which contributed to a remarkable drag reduction effect.Additionally,considering the extra undesired pressure drag reduction which negatively impacted the drag reduction effect of this method,the total drag coefficient including the viscous drag coefficient and the pressure coefficient was analyzed.An effective drag reduction rate of about 15%was achieved and the effect of this method was confirmed by experiments conducted in a high-speed water tunnel when grooves were optimized.展开更多
基金supported by National Basic Research Program of China (Grant No.2009CB219508)Chinese Academy of Sciences (Grant No.KZCX2-YW-GJ03)+2 种基金National Natural Science Foundation of China (GrantNos. 91228206 & 40725011)GIGCAS 135 Program (Grant No.Y234021001)Scientific and Technological Program of Guangdong Province (Grant No. 2011A080403021)
文摘A cold vent is an area where methane-rich fluid seepage occurs. This seepage may alter the local temperature, salinity, and subsequent accumulation of the gas hydrate. Using a kinetic gas hydrate formation model and in situ measurement of tempera- ture, salinity and fluid flux at the southern summit of Hydrate Ridge, we simuIate the gas hydrate accumulation at three distinct fluid sites： clam, bacterial mat, and gas discharge sites. At the clam sites （pore water flux 〈 20 kg m-2 yr-1）, pore water advec- tion has little influence on temperature and salinity. However, the salinity and temperature are increased （peak salinity 〉 0.8 tool kg-1） by the formation of gas hydrate causing the base of the hydrate stability zone to move gradually from -115 to -70 meters below seafloor （mbsf）. The gas hydrate saturation at the clam sites is relatively high. The water flux at the bacterial mat sites ranges from 100 to 2500 kg m-2 yr-1. The water flow suppresses the increase in salinity resulting in a salinity close to or slightly higher than that of seawater （〈 0.65 mol kg-l）. Heat advection by water flow increases temperature significantly, shifting the base of the hydrate stability zone to above 50 or even 3 mbsf. The gas hydrate saturation is relatively low at the bacterial mat site. At the gas discharge sites, the pore water flux could reach 10^10 kg m-2 yr-1, and the temperature could reach that of the source area in 9 min. There is no gas hydrate formation at the gas discharge sites. Our simulative analysis therefore reveals that a lower pore water flux would result in lower salinity, higher temperature, and a shallower base of the hydrate sta- bility zone. This in turn induces a lower gas hydrate formation rate, lower hydrate saturation, and eventually less gas hydrate resources.
基金supported by the National Natural Science Foundation of China(Grant Nos.51075228 and 51021064)
文摘The drag reduction effect of super-hydrophobic surface induced by the entrapped gas is unstable due to the gradual disappearance of the trapped gas.In this paper,a hydrophobic transverse grooved surface was designed to sustain gas in valleys.A detail numerical simulation was presented to investigate the flow field near the proposed surface.When water flowed over this surface,the entrapped gas was blocked by the ridges and the solid-liquid interface was replaced by the liquid-gas interface due to the entrapped gas,furthermore the micro-vortex formed in the groove.Because there was an effective slippage between water and solid induced by the entrapped gas,the velocity gradient of boundary layer decreased,which contributed to a remarkable drag reduction effect.Additionally,considering the extra undesired pressure drag reduction which negatively impacted the drag reduction effect of this method,the total drag coefficient including the viscous drag coefficient and the pressure coefficient was analyzed.An effective drag reduction rate of about 15%was achieved and the effect of this method was confirmed by experiments conducted in a high-speed water tunnel when grooves were optimized.
