The active layer thickness (ALT) is a key parameter for permafrost studies. Changes in the ALT are affected mainly by air and ground temperatures, physical and thermal properties of the surface and ...subsurface materials, soil moisture, vegetation, and the duration and thickness of snow cover. Ground penetrating radar (GPR) and electrical resistivity tomography (ERT) were employed across a snow fence during the thawing season to delineate and monitor the active layer of permafrost in Cambridge Bay, Nunavut, Canada. The variation of the ALT is well captured by the high-resolution time-lapse radargram. At the position of the fence, the active layer thickens over the thawing period from 0.5 m depth at the beginning to 1.0 m depth at the end. The active layer is thicker in the pre-fence area (C zone) than in the post-fence area (H zone). As the air temperature increases with time, the difference in thickness between the two zones decreases, eventually becoming almost equal. Changes in the ALT are represented in the ERT by low resistivities (< 200 Ωm), which decrease gradually with time. This occurs most significantly in the H zone due to the rapidly increasing temperature in the absence of snow cover. The electrical resistivity structure of the active layer is well correlated with the vegetation activity, as measured by the normalized difference vegetation index, air/ground temperatures, soil moisture, snow cover, and snow accumulation controlled by the fence. Geophysical data interpretation and correlation schemes with vegetation and meteorological data explored in this paper can be applied to monitor the active layer, which is expected to thin during the freezing season.
One-dimensional packed bed reactor model accounting for interfacial and intra-particle gradients was developed and based on it numerical analyses were performed to investigate the dynamic behavior of ...a commercial scale methanation reactor. Methanation reaction was almost complete near the reactor inlet and gases with equilibrated composition were discharged from the reactor. Both the intra-particle temperature gradient and differential surface temperature rise were found to be severe near the reactor inlet. To reduce the possible degradation or fracture of catalyst particles and prevent local overheating on the catalyst, addition of inert material can be an effective way.
고온수소 전환 반응기에 관한 수치해석적 연구 서동균(Dong-kyun Seo); 이진향(Jin-hyang Lee); 지준화(Jun-hwa Chi) ...
한국수소 및 신에너지학회 논문집,
2018, Letnik:
29, Številka:
4
Journal Article
Odprti dostop
In this study a numerical study was conducted to show flow, temperature and gas distributions in a high temperature CO shift reactor which was designed specially for energy saving and then evaluated ...with the related experiment. Mole fractions of syngas at the end of the catalyst bed were predicted with various assumed pre-exponential factors, were compared with the corresponding experimental results and $10^8$ was finally selected as the value. With the selection, a base case was examined. It was calculated that the inlet duct attached asymmetrically to the CO shift reactor affects on the distribution of the upward momentum (+z directional). In addition, CO conversion ratio is achieved up to 90% in the catalyst bed and especially it reached up to 70% at the initial part of catalyst bed.
저탄장에서의 석탄 자연발화에 관한 수치 해석적 연구 홍진표(Jinpyo Hong); 김재관(Jaekwan Kim); 지준화(Junhwa Chi) ...
한국수소 및 신에너지학회 논문집,
2017, Letnik:
28, Številka:
6
Journal Article
Odprti dostop
In this work, an one-dimensional analysis on spontaneous combustion in a coal stockpile was conducted using a commercial software $gPROMS^{(R)}$ based on assumption suggested by Arioy and Akgun. ...According to them, it is assumed that there is temperature difference between the surface of coal particle and the gas surrounded around the particle, and it is also assumed that the velocity of the gas is constant and thus oxygen is fed to the stockpile with same velocity. The higher temperature zone is formed to the surface of the coal stockpile at the initial phase and it became deepen as time is taken. Finally it was found that the temperature difference between coal particle and the gas was calculated as $57^{\circ}C$ and spontaneous combustion have not been occurred during 6 months since coal was piled in the stock.
Simulation studies on catalytic methanation reaction in externally cooled tubular reactor filled with monolithic catalysts were carried out using a general purpose modelling tool $gPROMS^{(R)}$. We ...investigated the effects of operating parameters such as gas space velocity, temperature and pressure of feeding gas on temperature distribution inside the reactor, overall CO conversion, and chemical composition of product gas. In general, performance of methanation reaction is favored under low temperature and high pressure for a wide range of their values. However, methane production becomes negligible at temperatures below 573K when the reactor temperature is not high enough to ignite methanation reaction. Capacity enhancement of the reactor by increasing gas space velocity and/or gas inlet pressure resulted no significant reduction in reactor performance and heat transfer property of catalyst.
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