| 1. |
- Gkoutzamanis, Vasilis G., et al.
(author)
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Conceptual Design and Energy Storage Positioning Aspects for a Hybrid-Electric Light Aircraft
- 2021
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In: Journal of engineering for gas turbines and power. - : ASME International. - 0742-4795 .- 1528-8919. ; 143:9
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Journal article (peer-reviewed)abstract
- This work is a feasibility study of a 19-passenger hybrid-electric aircraft, to serve the short-haul segment within the 200-600 nautical miles. Its ambition is to answer some dominating research questions, during the evaluation and design of aircraft based on alternative propulsion architectures. The potential entry into service (EIS) is foreseen beyond 2030. A literature review is performed to identify similar concepts under research and development. After the requirements' definition, the first level of conceptual design is employed. The objective of design selections is driven by the need to reduce CO2 emissions and accommodate aircraft electrification with boundary layer ingestion engines. Based on a set of assumptions, a methodology for the sizing of the hybrid-electric aircraft is described to explore the basis of the design space, incorporating a parametric analysis for the consideration of boundary layer ingestion effects. Additionally, a methodology for the energy storage positioning is provided to highlight the multidisciplinary aspects between the sizing of an aircraft, the selected architecture (series/ parallel partial hybrid), and the storage characteristics. The results show that it is not possible to fulfill the initial design requirements (600 nmi) with a fully-electric aircraft configuration, due to the farfetched battery necessities. It is also highlighted that compliance with airworthiness standards is favored by switching to hybrid-electric aircraft configurations and relaxing the design requirements (targeted range, payload, battery technology). Finally, the lower degree of hybridization (40%) is observed to have a higher energy efficiency (-12% energy consumption) compared to the higher degree of hybridization (50%) and greater CO2 reduction, with respect to the conventional configuration.
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| 2. |
- Xu, Tianhao, et al.
(author)
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Design Aspects of a Latent Heat Storage Unit for Heat Production Shifting at a Cogeneration Plant
- 2019
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In: SWC2019 Proceedings.
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Conference paper (peer-reviewed)abstract
- In the present study, a latent heat thermal energy storage (LHTES) unit with two different configurations (a shell-and-tube design using spiral coils as tubes and an encapsulation design using commercial capsules) are investigated and compared over their thermal performance for providing heat storage and recovery. The designed latent heat storage unit is to be implemented at an existing cogeneration plant for heat production shifting purposes. The design procedure involves several aspects of theoretical investigations: the determination of suitable melting point of the employed phase-change material (PCM); the selection of heat exchanger configuration; and the prediction of the units’ transient charging/discharging thermal behavior under operating conditions set by the cogeneration plant. Numerical approaches are used in this study to estimate the heat transfer conditions in PCMs as well as the transient charging/discharging thermal power of the entire unit. The accumulative stored/released energy throughout a charging process of three hours and a discharging process of one hour is also calculated. With the cylindrical containment tank in the same geometry, the spiral coil design exhibits a 52%-higher total heat storage capacity than the encapsulation design, and the simulation results show that it can store a higher amount of heat by 20% after first three hours of charging. For discharging, however, the encapsulation design exhibits a higher completion rate of 96% than the spiral coil design (53%) after first hour of discharging. Besides, the heat recovery capacity with the encapsulation design is 26% higher. The spiral coil design therefore shows advantage in the charging mode in terms of higher storage capacity while the encapsulation design outperforms when discharging due to is higher discharge rate within the given discharge operating duration of one hour.
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| 3. |
- Xu, Tianhao, et al.
(author)
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Performance evaluation of three latent heat storage designs for cogeneration applications
- 2021
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In: Solar Energy. - : Elsevier BV. - 0038-092X .- 1471-1257. ; 225, s. 444-462
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Journal article (peer-reviewed)abstract
- Well-integrated thermal energy storage units can enhance flexibility and profitability for a cogeneration system by enabling its decoupling of electricity and heat production. In the present study, novel latent heat thermal energy storage technologies are numerically investigated on their thermal and economic performance to evaluate their implementation at an existing combined cycle power plant. Three commercially available storage designs are analyzed: one shell-and-tube heat exchanger design based on planar spiral coils, and two types of advanced macro-encapsulated designs with capsules resembling ellipsoid and slab in shape, respectively. For the spiral coil design, three-dimensional flow velocity and temperature fields are simulated with finite volume method to predict the transient storage heat transfer process, including the effect of secondary flow induced by centrifugal forces. For the macro-encapsulated designs, effective heat transfer coefficients between heat transfer fluid (HTF) and phase change material (PCM) are inferred from scaled-down storage prototyping and testing. A onedimensional two-phase packed bed model was developed based on the apparent heat capacity-based enthalpy method to numerically study the heat transfer in macro-encapsulated PCM. With an operating temperature range of 46-72 degrees C and a HTF supplying flowrate range of 4.2-8.4 m3/h defined by the cogeneration strategy, thermal power and accumulated storage capacity are calculated and compared for the first three hours of charge and the first hour of discharge for the three designs. The effect from increasing the HTF flowrate to accelerate charging/ discharging processes is indicated by the simulation results. Performance comparison among the three designs shows that the slab capsule design exhibits the highest accumulated storage capacity (710 kWh) and state of charge (40%) after three hours of charge, though it has a lower theoretical total storage capacity (1760 kWh) than the spiral coil design (1830 kWh). The ellipsoid capsule design shows a slightly lower accumulated storage capacity (700 kWh) than the slab design for 3-hr charge and an equivalent accumulated storage capacity/depth of discharge (250 kWh/14%) as the latter. Furthermore, the storage power cost of the slab capsule design is the lowest, by 6-12% lower than the spiral coil design and by 2-3% lower than the ellipsoid capsule design. However, with the highest design flowrate of 8.4 m3/h, the low state of charge (below 40%) after three hours and the low depth of discharge (below 14%) after one hour indicate that redesigning the heat transfer boundary conditions and the configurations of the three units are necessary to meet desirable storage performance in cogeneration applications.
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