The Experts below are selected from a list of 14973 Experts worldwide ranked by ideXlab platform
Hee Chun Lim - One of the best experts on this subject based on the ideXlab platform.
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consideration of numerical simulation parameters and Heat transfer models for a molten carbonate fuel cell stack
Chemical Engineering Journal, 2002Co-Authors: Joonho Koh, Haikung Seo, Youngsung Yoo, Hee Chun LimAbstract:A fuel cell stack model based on differential Heat balance equations was solved numerically with a computational fluid dynamics code. Theoretical aspects in the simulation of a molten carbonate fuel cell (MCFC) performance model were discussed with regard to numerical accuracy of temperature prediction. The effect of grid setting for gas channel depth was studied to ensure how coarse it can be. A single computational element was sufficient for temperature prediction, while more grid elements are required for calculation of flow field and pressure distribution. The use of Constant velocities is not recommended because it cannot account for the change of linear velocity within fuel cells, indicating the momentum equations have to be solved together with the Heat balance equations. Thermal radiation has little effect on calculation of temperature field from the model. Gas properties vary within fuel cells, but most of them can be treated Constant except for Specific Heat capacity of anode gas. Convection Heat transfer by anode gas can be overestimated when a Constant Specific Heat capacity is used, resulting in prediction of lower temperature curves. Overall, Heat transfer in a co-flow stack is well characterized by two-dimensional model along the axial and vertical coordinates rather than on cell plane.
Paul Cetin - One of the best experts on this subject based on the ideXlab platform.
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thermal storage concept for solar thermal power plants with direct steam generation
Energy Procedia, 2014Co-Authors: Markus Seitz, Paul CetinAbstract:Abstract One possibility to increase the efficiency and thus economic viability of solar thermal power plants is to increase their operating temperature. This approach demands the substitution of the state-of-the-art Heat transfer fluid (HTF) that limits the operating temperature to roughly 400 °C. Promising Heat transfer fluids for future applications are molten salts or water/steam. If water/steam is used as HTF, the feed-water from the power block is fed to the solar field (SF) and directly evaporated and superHeated. This process is called direct steam generation (DSG). A recent study [1] has pointed out that the economic potential of the DSG process is utilized only, if the SF design is simplified and a competitive thermal storage is available. Thus, an R&D project was launched in Germany to develop a complete storage system covering the energy of the evaporation as well as of the pre- and superHeating section. It consists of a phase change material (PCM) storage for evaporation and a molten salt storage for pre- and superHeating. One Specific feature of superHeated steam is its changing Specific Heat capacity with temperature. Using molten salt as storage medium with a nearly Constant Specific Heat and the application of an obvious simple Heat exchange would lead to an inefficient process. A significantly reduced live steam temperature and thus power block efficiency during discharge would be the results. Furthermore, the Specific storage density of the molten salt system would be reduced too. In this paper this effect will be discussed in more detail. The consequences for the storage system will be discussed and solutions of the developed processes for the integration of such storage into a DSG power plant will be presented that reduce or overcome the mentioned restrictions.
Shigeru Koyama - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic analysis of vapor compression Heat pump cycle for tap water Heating and development of co2 Heat pump water Heater for residential use
Applied Thermal Engineering, 2016Co-Authors: Michiyuki Saikawa, Shigeru KoyamaAbstract:Abstract The ideal vapor compression cycle for tap water Heating and its coefficient of performance (COP) have been studied theoretically at first. The ideal cycle is defined as the cycle whose high temperature Heat source varies temperature with Constant Specific Heat and other processes are same as the reverse Carnot cycle. The COP upper limit of single stage compression Heat pump cycle for tap water Heating with various refrigerants such as fluorocarbons and natural refrigerants was calculated. The refrigerant which achieves the highest COP for supplying hot water is CO2. Next, the prototype of CO2 Heat pump water Heater for residential use has been developed. Its outline and experimental results are described. Finally its further possibility of COP improvement has been studied. The COP considered a limit from a technical point of view was estimated about 6.0 at the Japanese shoulder season (spring and autumn) test condition of Heating water from 17 °C to 65 °C at 16 °C Heat source air temperature (dry bulb)/12 °C (wet bulb).
Joonho Koh - One of the best experts on this subject based on the ideXlab platform.
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consideration of numerical simulation parameters and Heat transfer models for a molten carbonate fuel cell stack
Chemical Engineering Journal, 2002Co-Authors: Joonho Koh, Haikung Seo, Youngsung Yoo, Hee Chun LimAbstract:A fuel cell stack model based on differential Heat balance equations was solved numerically with a computational fluid dynamics code. Theoretical aspects in the simulation of a molten carbonate fuel cell (MCFC) performance model were discussed with regard to numerical accuracy of temperature prediction. The effect of grid setting for gas channel depth was studied to ensure how coarse it can be. A single computational element was sufficient for temperature prediction, while more grid elements are required for calculation of flow field and pressure distribution. The use of Constant velocities is not recommended because it cannot account for the change of linear velocity within fuel cells, indicating the momentum equations have to be solved together with the Heat balance equations. Thermal radiation has little effect on calculation of temperature field from the model. Gas properties vary within fuel cells, but most of them can be treated Constant except for Specific Heat capacity of anode gas. Convection Heat transfer by anode gas can be overestimated when a Constant Specific Heat capacity is used, resulting in prediction of lower temperature curves. Overall, Heat transfer in a co-flow stack is well characterized by two-dimensional model along the axial and vertical coordinates rather than on cell plane.
Markus Seitz - One of the best experts on this subject based on the ideXlab platform.
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thermal storage concept for solar thermal power plants with direct steam generation
Energy Procedia, 2014Co-Authors: Markus Seitz, Paul CetinAbstract:Abstract One possibility to increase the efficiency and thus economic viability of solar thermal power plants is to increase their operating temperature. This approach demands the substitution of the state-of-the-art Heat transfer fluid (HTF) that limits the operating temperature to roughly 400 °C. Promising Heat transfer fluids for future applications are molten salts or water/steam. If water/steam is used as HTF, the feed-water from the power block is fed to the solar field (SF) and directly evaporated and superHeated. This process is called direct steam generation (DSG). A recent study [1] has pointed out that the economic potential of the DSG process is utilized only, if the SF design is simplified and a competitive thermal storage is available. Thus, an R&D project was launched in Germany to develop a complete storage system covering the energy of the evaporation as well as of the pre- and superHeating section. It consists of a phase change material (PCM) storage for evaporation and a molten salt storage for pre- and superHeating. One Specific feature of superHeated steam is its changing Specific Heat capacity with temperature. Using molten salt as storage medium with a nearly Constant Specific Heat and the application of an obvious simple Heat exchange would lead to an inefficient process. A significantly reduced live steam temperature and thus power block efficiency during discharge would be the results. Furthermore, the Specific storage density of the molten salt system would be reduced too. In this paper this effect will be discussed in more detail. The consequences for the storage system will be discussed and solutions of the developed processes for the integration of such storage into a DSG power plant will be presented that reduce or overcome the mentioned restrictions.