The Experts below are selected from a list of 3762 Experts worldwide ranked by ideXlab platform
Kelly Homan - One of the best experts on this subject based on the ideXlab platform.
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on simplified models for the rate and time dependent performance of stratified Thermal Storage
Journal of Energy Resources Technology-transactions of The Asme, 2007Co-Authors: Kelly HomanAbstract:In direct Sensible Thermal Storage systems, both the energy discharging and charging processes are inherently time-dependent as well as rate-dependent. Simplified models which depict the characteristics of this transient process are therefore crucial to the sizing and rating of the Storage devices. In this paper, existing models which represent three distinct classes of models for Thermal Storage behavior are recast into a common formulation and used to predict the variations of discharge volume fraction, Thermal mixing factor, and entropy generation. For each of the models considered, the parametric dependence of key performance measures is shown to be expressible in terms of a Peclet number and a Froude number or temperature difference ratio. The Thermal mixing factor for each of the models is reasonably well described by a power law fit with Fr2Pe for the convection-dominated portion of the operating range. For the uniform and nonuniform diffusivity models examined, there is shown to be a Peclet number which maximizes the discharge volume fraction. In addition, the cumulative entropy generation from the simplified models is compared with the ideally-stratified and the fully-mixed limits. Of the models considered, only the nonuniform diffusivity model exhibits an optimal Peclet number at which the cumulative entropy generation is minimized. For each of the other models examined, the cumulative entropy generation varies monotonically with Peclet number.
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internal entropy generation limits for direct Sensible Thermal Storage
Journal of Energy Resources Technology-transactions of The Asme, 2003Co-Authors: Kelly HomanAbstract:This paper presents results for the entropy generated internally during the charging and discharging processes of a direct, Sensible Thermal energy store. The two processes correspond to the inflow of either a low or high temperature liquid stream into an enclosure initially filled with a uniformly high or low temperature liquid, respectively. The level of internal entropy generation due to Thermal mixing between the inflow and the initial liquid volume corresponds to losses in the usable fraction of the stored volume and therefore decreased efficiency. Empirically, the observed behavior of direct Sensible Storage devices spans the range of nearly mixed to highly stratified. In the present work, analytical models for the fully-mixed and ideally-stratified limits are used to bound these behaviors and to analytically determine the corresponding entropy generation levels. The ratio of total entropy generation for the ideally-stratified limit relative to that of the fully-mixed limit is shown to vary as √8/(πPe). The limiting behaviors therefore define a continuum of entropy generation levels separated by up to several orders of magnitude for typical Peclet numbers. A published numerical model which accounts for aspects of the observed Thermal mixing is then examined in relation to these limits. The model predicts entropy generation levels midway between the limiting behaviors which suggests significant potential for improvements in the efficiency of direct Sensible Storage devices.
Ellen Stechel - One of the best experts on this subject based on the ideXlab platform.
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performance assessment of fischer tropsch liquid fuels production by solar hybridized dual fluidized bed gasification of lignite
Energy & Fuels, 2015Co-Authors: Peijun Guo, Peter J. Ashman, Graham J. Nathan, Philip J Van Eyk, Woei L Saw, Ellen StechelAbstract:A novel solar hybridized dual fluidized bed (DFB) gasification process for Fischer–Tropsch liquid (FTL) fuels production is proposed and investigated here for the case with lignite as the fuel, although it is also applicable to biomass. The concept offers Sensible Thermal Storage of bed material, the use of inert particles in the solar receiver to avoid the need for sealing, and a process that delivers a constant production rate and quality of syngas despite solar variability. This solar hybridized coal-to-liquids (SCTL) process is simulated using a pseudodynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. The annual energetic and environmental performance of this SCTL process is investigated as a function of the solar multiple (i.e., the heliostat field area relative to that required to meet the demand of the DFB gasifier at the point of peak solar Thermal output), bed material Storage capacity, the assumed char conversion in...
Pirouz Kavehpour - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic performance and cost optimization of a novel hybrid Thermal compressed air energy Storage system design
Journal of energy storage, 2018Co-Authors: Sammy Houssainy, Mohammad Janbozorgi, Pirouz KavehpourAbstract:Abstract Compressed Air Energy Storage (CAES) can potentially allow renewable energy sources to meet electricity demands as reliably as coal-fired power plants. However, conventional CAES systems rely on the combustion of natural gas, require large Storage volumes, and operate at high pressures, which possess inherent problems such as high costs, strict geological locations, and the production of greenhouse gas emissions. A novel and patented hybrid Thermal-compressed air energy Storage (HT-CAES) design is presented which allows a portion of the available energy, from the grid or renewable sources, to operate a compressor and the remainder to be converted and stored in the form of heat, through joule heating in a Sensible Thermal Storage medium. The HT-CAES design incudes a turbocharger unit that provides supplementary mass flow rate alongside the air Storage. The hybrid design and the addition of a turbocharger have the beneficial effect of mitigating the shortcomings of conventional CAES systems and its derivatives by eliminating combustion emissions and reducing Storage volumes, operating pressures, and costs. Storage efficiency and cost are the two key factors, which upon integration with renewable energies would allow the sources to operate as independent forms of sustainable energy. The potential of the HT-CAES design is illustrated through a thermodynamic optimization study, which outlines key variables that have a major impact on the performance and economics of the Storage system. The optimization analysis quantifies the required distribution of energy between Thermal and compressed air energy Storage, for maximum efficiency, and for minimum cost. This study provides a roundtrip energy and exergy efficiency map of the Storage system and illustrates a trade off that exists between its capital cost and performance.
Peijun Guo - One of the best experts on this subject based on the ideXlab platform.
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performance assessment of fischer tropsch liquid fuels production by solar hybridized dual fluidized bed gasification of lignite
Energy & Fuels, 2015Co-Authors: Peijun Guo, Peter J. Ashman, Graham J. Nathan, Philip J Van Eyk, Woei L Saw, Ellen StechelAbstract:A novel solar hybridized dual fluidized bed (DFB) gasification process for Fischer–Tropsch liquid (FTL) fuels production is proposed and investigated here for the case with lignite as the fuel, although it is also applicable to biomass. The concept offers Sensible Thermal Storage of bed material, the use of inert particles in the solar receiver to avoid the need for sealing, and a process that delivers a constant production rate and quality of syngas despite solar variability. This solar hybridized coal-to-liquids (SCTL) process is simulated using a pseudodynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. The annual energetic and environmental performance of this SCTL process is investigated as a function of the solar multiple (i.e., the heliostat field area relative to that required to meet the demand of the DFB gasifier at the point of peak solar Thermal output), bed material Storage capacity, the assumed char conversion in...
Sammy Houssainy - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic performance and cost optimization of a novel hybrid Thermal compressed air energy Storage system design
Journal of energy storage, 2018Co-Authors: Sammy Houssainy, Mohammad Janbozorgi, Pirouz KavehpourAbstract:Abstract Compressed Air Energy Storage (CAES) can potentially allow renewable energy sources to meet electricity demands as reliably as coal-fired power plants. However, conventional CAES systems rely on the combustion of natural gas, require large Storage volumes, and operate at high pressures, which possess inherent problems such as high costs, strict geological locations, and the production of greenhouse gas emissions. A novel and patented hybrid Thermal-compressed air energy Storage (HT-CAES) design is presented which allows a portion of the available energy, from the grid or renewable sources, to operate a compressor and the remainder to be converted and stored in the form of heat, through joule heating in a Sensible Thermal Storage medium. The HT-CAES design incudes a turbocharger unit that provides supplementary mass flow rate alongside the air Storage. The hybrid design and the addition of a turbocharger have the beneficial effect of mitigating the shortcomings of conventional CAES systems and its derivatives by eliminating combustion emissions and reducing Storage volumes, operating pressures, and costs. Storage efficiency and cost are the two key factors, which upon integration with renewable energies would allow the sources to operate as independent forms of sustainable energy. The potential of the HT-CAES design is illustrated through a thermodynamic optimization study, which outlines key variables that have a major impact on the performance and economics of the Storage system. The optimization analysis quantifies the required distribution of energy between Thermal and compressed air energy Storage, for maximum efficiency, and for minimum cost. This study provides a roundtrip energy and exergy efficiency map of the Storage system and illustrates a trade off that exists between its capital cost and performance.
