查看更多>>摘要：The drag reduction equipment (DRE) suffers dual environmental stress of high-speed spin and rapid depressurization during the launching process, disturbing the projectile intensely. To research the effect of this extreme process on heat and mass transfer, flow field development, as well as drag reduction performance of the DRE, a numerical model was established based on the MT-based pyrotechnics combustion mechanism and the H2-CO combustion mechanism. Simulation on the unsteady reacting flow was conducted to investigate the effect of high-speed spin on the performance of the DRE under depressurization. The results indicate that the wake flow field of the DRE transforms from a supersonic under-expanded jet into a subsonic swirling flow, and two recirculation zones with low-pressure appear at the base of the DRE. The transition region between propellant gas and igniter gas in the combustion chamber displays the Kelvin-Helmholtz instability, in which a vortex core forms with a high tangential velocity gradient. The igniter gas burns in the combustion chamber, resulting in an axial high-temperature region. And then the combustion products of igniter gas are mixed with propellant gas and inject outwards, reacting with the air near the jet boundary to be an intense post-combustion. High-speed spin improves the nozzle mass flow rate, enhancing the post-combustion. Eventually, compared with the nonspin case, the mass flow rate and base temperature in the case of 20,000 rpm are improved by 67.6% and 21.56%, respectively. And the base drag is reduced by 10.14%.
查看更多>>摘要：This paper proposes a novel stand-alone liquid air energy storage (LAES) system to enhance round-trip efficiency (RTE) using a thermal energy storage system. Thermal energy storage comprises sensible heat storage with quartz and latent heat storage with cryogenic phase change material (PCM) for recycling cold energy from the LAES discharge process. The liquid air in the pressurized tank was released during the discharge cycle and used to store energy using PCM and quartz. The cryogenic phase change material melts at 110 K based on experimental result, making it possible to provide cold heat of fusion 61.62 kJ/kg at a constant temperature for air liquefaction. Thus, proposed system can effectively increase the cold energy recycle. In addition, the two-dimension numerical model allowed us to estimate the outlet temperature of sensible heat store without isothermal assumption by Biot Number. The proposed process is modified from Linde-Hampson, and a sensitivity analysis is performed using ASPEN HYSYS. The analysis shows that the implementation of energy recycling from the compressor and thermal store leads to a high round-trip efficiency (60.6%) higher than base case (34.4%) of LAES system. Therefore, the proposed system is a promising process in terms of simplification and high efficiency, cognizant of the integration of waste heat from industrial plants.
查看更多>>摘要：The safety analysis of flow blockage accident is significant for plate-type fuel reactor, especially swelling of cladding, which is resulted from irradiation damage in high burnup condition and needs to be paid more attention. In this study, experimental and numerical researches have been conducted to study the convective heat transfer and flow structure within narrow rectangular channel, where exists different numbers and arrangements of spherical crown protrusions. Compared with the experimental data of single protrusion condition, the overall heat transfer capacity even deteriorates more than 20% when protrusions are aligned in streamwise direction. In contrast, the global Nu is nearly 10% higher when three protrusions are located in spanwise direction. Conclusions can be drawn that existence of protrusion can also significantly change convective flow condition in narrow channel, and the laminar flow is altered to transitional/quasi-turbulent even though Re is only nearly 1600. Besides, the local information, such as flow boundary layer separation, low-speed recirculation and vortex evolution etc., can also be acquired by the Computational Fluid Dynamics (CFD) method comprehensively. Combined with experimental data and numerical results, the distinct heat transfer behaviors and flow structures for different flow blockage conditions can be explained in detail. In summary, conclusions about the flow and thermal processes influenced by protrusions in narrow rectangular channel are fundamental to safety analysis and design criteria of plate-type fuel assembly for flow blockage condition. Besides, it also can be applied in other industry scene during convective laminar flow within narrow rectangular channel.
NSTL
Elsevier