Saline aquifers are chosen for geological storage of greenhouse gas CO_2 because of their storage potential.In almost all cases of practical interest,CO_2 is present on top of the liquid and CO_2 dissolution leads to ...Saline aquifers are chosen for geological storage of greenhouse gas CO_2 because of their storage potential.In almost all cases of practical interest,CO_2 is present on top of the liquid and CO_2 dissolution leads to a small increase in the density of the aqueous phase.This situation results in the creation of negative buoyancy force for downward density-driven natural convection and consequently enhances CO_2 sequestration.In order to study CO_2 injection at pore-level,an isothermal Lattice Boltzmann Model(LBM) with two distribution functions is adopted to simulate density-driven natural convection in porous media with irregular geometry obtained by image treatment.The present analysis showed that after the onset of natural convection instability,the brine with a high CO_2 concentration infringed into the underlying unaffected brine,in favor of the migration of CO_2 into the pore structure.With low Rayleigh numbers,the instantaneous mass flux and total dissolved CO_2 mass are very close to that derived from penetration theory(diffusion only),but the fluxes are significantly enhanced with high Ra number.The simulated results show that as the time increases,some chaotic and recirculation zones in the flow appear obviously,which promotes the renewal of interfacial liquid,and hence enhances dissolution of CO_2 into brine.This study is focused on the scale of a few pores,but shows implications in enhanced oil/gas recovery with CO_2 sequestration in aquifers.展开更多
Heat dissipation of electronic devices keeps as a tough issue for decades. As the most classical coolant in a convective heat transfer process, water has been widely adopted which however inherits with limited thermal...Heat dissipation of electronic devices keeps as a tough issue for decades. As the most classical coolant in a convective heat transfer process, water has been widely adopted which however inherits with limited thermal conductivity and relies heavily on mechanical pump. As an alternative, the room temperature liquid metal was increasingly emerging as an important coolant to realize much stronger enhanced heat transfer. However, its thermal capacity is somewhat lower than that of water, which may restrict the overall cooling performance. In addition, the high cost by taking too much amount of liquid metal into the device also turns out to be a big concern for practical purpose. Here, through combining the individual merits from both the liquid metal with high conductivity and water with large heat capacity, we proposed and demonstrated a new conceptual cooling de- vice that integrated hybrid coolants, radiator and annular channel together for chip thermal management. Particularly, the elec- trically induced actuation effect of liquid metal was introduced as the only flow driving strategy, which significantly simplified the whole system design. This enables the liquid metal sphere and its surrounding aqueous solution to be quickly accelerated to a large speed under only a very low electric voltage. Further experiments demonstrated that the cooling device could effective- ly maintain the temperature of a hotpot （3.15 W/cm2） below 55℃ with an extremely small power consumption rate （0.8 W）. Sev- eral situations to simulate the practical working of the device were experimentally explored and a theoretical thermal resistance model was established to evaluate its heat transfer performance. The present work suggests an important way to make highly compact chip cooling device, which can be flexibly extended into a wide variety of engineering areas.展开更多
文摘Saline aquifers are chosen for geological storage of greenhouse gas CO_2 because of their storage potential.In almost all cases of practical interest,CO_2 is present on top of the liquid and CO_2 dissolution leads to a small increase in the density of the aqueous phase.This situation results in the creation of negative buoyancy force for downward density-driven natural convection and consequently enhances CO_2 sequestration.In order to study CO_2 injection at pore-level,an isothermal Lattice Boltzmann Model(LBM) with two distribution functions is adopted to simulate density-driven natural convection in porous media with irregular geometry obtained by image treatment.The present analysis showed that after the onset of natural convection instability,the brine with a high CO_2 concentration infringed into the underlying unaffected brine,in favor of the migration of CO_2 into the pore structure.With low Rayleigh numbers,the instantaneous mass flux and total dissolved CO_2 mass are very close to that derived from penetration theory(diffusion only),but the fluxes are significantly enhanced with high Ra number.The simulated results show that as the time increases,some chaotic and recirculation zones in the flow appear obviously,which promotes the renewal of interfacial liquid,and hence enhances dissolution of CO_2 into brine.This study is focused on the scale of a few pores,but shows implications in enhanced oil/gas recovery with CO_2 sequestration in aquifers.
基金supported by the Research Funding from the Technical Institute of Physics and ChemistryChinese Academy of Sciences
文摘Heat dissipation of electronic devices keeps as a tough issue for decades. As the most classical coolant in a convective heat transfer process, water has been widely adopted which however inherits with limited thermal conductivity and relies heavily on mechanical pump. As an alternative, the room temperature liquid metal was increasingly emerging as an important coolant to realize much stronger enhanced heat transfer. However, its thermal capacity is somewhat lower than that of water, which may restrict the overall cooling performance. In addition, the high cost by taking too much amount of liquid metal into the device also turns out to be a big concern for practical purpose. Here, through combining the individual merits from both the liquid metal with high conductivity and water with large heat capacity, we proposed and demonstrated a new conceptual cooling de- vice that integrated hybrid coolants, radiator and annular channel together for chip thermal management. Particularly, the elec- trically induced actuation effect of liquid metal was introduced as the only flow driving strategy, which significantly simplified the whole system design. This enables the liquid metal sphere and its surrounding aqueous solution to be quickly accelerated to a large speed under only a very low electric voltage. Further experiments demonstrated that the cooling device could effective- ly maintain the temperature of a hotpot （3.15 W/cm2） below 55℃ with an extremely small power consumption rate （0.8 W）. Sev- eral situations to simulate the practical working of the device were experimentally explored and a theoretical thermal resistance model was established to evaluate its heat transfer performance. The present work suggests an important way to make highly compact chip cooling device, which can be flexibly extended into a wide variety of engineering areas.
