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Liquid air energy storage (LAES) technology is a promising large-scale energy storage solution due to its high capacity, scalability, and lack of geographical constraints, making it effective for integrating renewable energy sources. The core unit of the LAES system is the cold energy storage (CES) unit, which significantly influences its overall efficiency. However, the current mainstream liquid-phase and solid-phase CES methods have inherent drawbacks, including safety, environmental issues, and the dynamic effect of the thermocline. Moreover, previous research has often over-idealized the CES unit and neglected the actual heat transfer processes during the CES and cold energy release (CER) processes. In the innovative study, a gravity-driven moving packed bed (MPB) based LAES system (MPB-LAES) adopting quartz sand as the CES medium is proposed. A thermodynamic model for the LAES system is constructed, and the gas-solid counterflow coupling heat transfer model for the MPB is developed based on the continuous solid-phase model and finite difference method. The accuracy of the model is validated through experimentation using the constructed test apparatus. The research findings reveal the gas-solid coupling heat transfer characteristics in the low-temperature region of −180 ° C to 30 ° C , particularly the asymmetry during the CES and CER processes. The cold energy transfer mechanism within the CES unit is also uncovered, and the analysis of exergy destruction within various components is carried on. Through design parameter analysis and optimization of the MPB-LAES system, an impressive round-trip efficiency of 57.0% is achieved. This marks a significant breakthrough as it is the first report that a LAES system based on solid-phase CES has attained a round-trip efficiency (RTE) of over 55.0% while considering the actual heat transfer processes. • The LAES system utilizing moving packed beds is proposed. • The gas-solid coupling heat transfer model is established and verified. • The cold energy transfer mechanism in the CES is uncovered. • Irreversible analyses are performed in the CES and CER processes. • An RTE of 57.0% is achieved considering actual heat transfer for the first time. [ABSTRACT FROM AUTHOR]

• The length ratio of the TPCT can significantly affect its heat transfer efficiency. • There exists the best length ratio for the TPCT with specific inclination angle. • The best length ratio changes with the inclination angle and inner diameter. Two-phase closed thermosyphons (TPCTs) have been widely used in solar energy utilization. The work presents an optimization of the TPCT used in cooling foundation in permafrost regions. A series of experiments under negative temperature conditions were conducted to investigate the effect of length ratios (LRs, length ratio of the evaporator section to the condenser section) on the cooling performance of the TPCT. Experimental results show that there exists a best LR for each angle, and it varies with the inclination angle. As an example, for the TPCT with 5.0-cm inner diameter, the maximum efficiency can be decreased by 17.3% for the TPCT with the LR of 1.00 compared with the TPCT with the best LR of 1.65. Under the best LR, the efficiency can be raised by 30.2% for the TPCT with the inclination angle of 20° compared with that of 90°. Besides, the best LR also changes with the pipe inner diameter, e.g. the best LR varies from 1.65 to 1.27 when the inner diameter changed from 5.0 cm to 8.1 cm. The results suggest that the equivalent length of the evaporator section should be appropriately lengthened to enhance the cooling performance of TPCTs in permafrost engineering. [ABSTRACT FROM AUTHOR]

Heat pipe cooled reactors with closed Brayton cycle (CBC) have the potential of achieving both high efficiency and high safety. However, the coupled characteristics and performance of CBC coupled with heat pipe reactors have not been well studied. Few works consider both the neutron dynamics in heat pipe cooled reactors and the dynamic heat and mass transfer in CBC. In this paper, a novel nuclear power system configuration, heat pipe cooled reactor with CBC, is proposed and comprehensively analyzed. A dynamic model is built based on the modular modeling idea, and verified using a Brayton cycle test bench. The proposed system has load following capability within certain motor speed, and its maximum thermal-electric energy conversion efficiency exceeds 20%. The dynamic charge amount control strategy is further proposed to improve efficiency. The maximum efficiency improvement is about 5% at 2kWe. The self-power-regulation and inherent passive safety of the reactor are verified through dynamic simulation. The power and temperature overshoots of the dynamic responses are selected as quantitative indicators of system dynamic performance. MAPs of the temperature and power overshoots for unit changes in output power are obtained, and can be used to evaluate the system safety during dynamic operations. • Coupled dynamic model of heat pipe cooled reactor and closed Brayton cycle. • Considering both the neutron dynamics and dynamic heat and mass transfer. • Dynamic charge amount control strategy for higher energy conversion efficiency. • MAPs for evaluating the efficiency and safety of the system. [ABSTRACT FROM AUTHOR]