For the first time, the enhanced recovery of confined methane (CH4) with carbon dioxide (CO2) is investigated through molecular dynamics simulations. The adsorption energy and configuration of CH4 and CO2 on the carbon surface were compared, which shows that CO2 is a good candidate in displacing confined CH4. The energy barrier required for displacing CH4 by CO2 injection was found to depend on the displacement angle. When CO2 approached vertically to the carbon surface, the displacement of CH4 occurred most easily. The curvature and size effects of the carbon nanopores on CH4 recovery were revealed and indicated that there exists an optimum pore size making the displacement occur most efficiently. The underlying mechanisms of these phenomena were uncovered. Our findings and related analyses may help to understand CO2 enhanced gas recovery from the atomic level and assist the future design in engineering.

Adsorption is an important issue both in the estimation of natural gas reserves and efficient storage of methane. In this study, we focus on the mechanisms of methane adsorption in carbon nanopores and endeavor to establish the equation of state for the adsorbed phase through molecular dynamics simulations and theoretical analyses. Here, the nanopores were modeled by carbon nanotubes (CNTs). The higher storage capacity of the CNT compared to the bulk phase was attributed to the additional pressure exerted by the CNT wall on the adsorbed phase, considering which, the equation of state for the adsorbed phase was established. As the CNT diameter increases, the adsorption structure transforms from a single-file chain to two adsorption layers. Moreover, it was found that there exists an optimal CNT diameter that maximizes the adsorption, which is due to the competition between the curvature effect and the size effect. In the explanation of this phenomenon, the nanostructure of the CNT wall plays an important role, without considering which, the adsorption density would monotonically decrease as the CNT diameter rises. Our findings and related analyses may help reveal the underlying mechanisms behind the adsorption phenomena, which is not only of theoretical importance, but may also help estimate the natural gas reserves and design nanoporous materials with higher storage capacity.

The ability of FLake, WRF‐Lake, and CoLM‐Lake models in simulating the thermal features of Lake Nam Co in Central Tibetan Plateau has been evaluated in this study. All the three models with default settings exhibited distinct errors in the simulated vertical temperature profile. Then model calibration was conducted by adjusting three (four) key parameters within FLake and CoLM‐Lake (WRF‐Lake) in a series of sensitive experiments. Results showed that each model's performance is sensitive to the key parameters and becomes much better when adjusting all the key parameters relative to tuning single parameter. Overall, setting the temperature of maximum water density to 1.1 °C instead of 4 °C in the three models consistently leads to improved vertical thermal structure simulation during cold seasons; reducing the light extinction coefficient in FLake results in much deeper mixed layer and warmer thermocline during warm seasons in better agreement with the observation. The vertical thermal structure can be clearly improved by decreasing the light extinction coefficient and increasing the turbulent mixing in WRF‐Lake and CoLM‐Lake during warm seasons. Meanwhile, the modeled water temperature profile in warm seasons can be significantly improved by further replacing the constant surface roughness lengths by a parameterized scheme in WRF‐Lake. Further intercomparison indicates that among the three calibrated models, FLake (WRF‐Lake) performs the best to simulate the temporal evolution and intensity of temperature in the layers shallower (deeper) than 10 m, while WRF‐Lake is the best at simulating the amplitude and pattern of the temperature variability at all depths.