Thermal modeling of a packed bed thermal energy storage system during charging |
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| Authors: | David MacPhee Ibrahim Dincer |
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| Affiliation: | 1. Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland;2. Airlight Energy Holding SA, 6710 Biasca, Switzerland;3. Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland;1. Université Grenoble Alpes (UGA), CEA-Liten-DTBH, Laboratoire de Stockage Thermique, F-38000 Grenoble, France;2. LOCIE, Univ. Savoie, Campus Scientifique, Savoie Technolac, F-73376 Le Bourget-du-Lac Cedex, France;1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;1. Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy & Power Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China;2. Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027, USA |
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| Abstract: | The process of charging of an encapsulated ice thermal energy storage device (ITES) is thermally modeled here through heat transfer and thermodynamic analyses. In heat transfer analysis, two different temperature profile cases, with negligible radial and/or stream-wise conduction are investigated for comparison, and the temperature profiles for each case are analyzed in an illustrative example. After obtaining temperature profiles through heat transfer analysis, a comprehensive thermodynamic study of the system is conducted. In this regard, energy, thermal exergy and flow exergy efficiencies, internal and external irreversibilities corresponding to flow exergy, as well as charging times are investigated. The energy efficiencies are found to be more than 99%, whereas the thermal exergy efficiencies are found to vary between 40% and 93% for viable charging times. The flow exergy efficiency varies between 48% and 88% for the flows and inlet temperatures selected. For a flow rate of 0.00164 m3/s, the maximum flow exergy efficiency occurs with an inlet temperature of 269.7 K, corresponding to an efficiency of 84.3%. For the case where the flow rate is 0.0033 m3/s, the maximum flow exergy efficiency becomes 87.9% at an inlet temperature of 270.7 K. The results confirm the fact that energy analyses, and even thermal exergy analyses, may lead to some unrealistic efficiency values. This could prove troublesome for designers wishing to optimize performance. For this reason, the flow exergy model provides the most useful information for those wishing to improve performance and reduce losses in such ITES systems. |
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