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Droplet-based high heat flux dissipation technique under multi-gravitational environments has gained increasing research attention due to the increased requirements of heat dissipation in advanced air-/space-borne electronics. In this paper, a three-dimensional model was developed to investigate the impact of continuous droplets on liquid film under various Weber numbers and gravity loads. In other words, the effects of Weber number and gravity load on the flow and heat transfer characteristics were investigated. The results demonstrated that the dissipated heat flux was positively correlated with both Weber number and gravity load. A large Weber number indicated larger kinetic energy of a droplet, leading to a greater disturbance on the impacted film area. When the Weber number was doubled, the average wall heat flux could be enhanced by 36.3%. In addition, the heat flux could be boosted by 5.4% when the gravity load ranged from 0 to 1g. Moreover, a weightless condition suppressed the vapor escape rates on the heating wall where the volume fraction of the vapor on the wall could increase by 20% under 0g, leading to deteriorated heat transfer performance. The novelty in this paper lies in the accurate three-dimensional modeling of an aerospace-oriented droplet impacting two-phase heat transfer and fluid dynamics, associating macro-scale thermal performance to microscale thermophysics mechanisms. The findings of this study could guide the development of aerospace-borne spray cooling facilities for advanced aerospace thermal management. © 2023, Science China Press.

Advancements in spacecraft formation and space solar power plant technologies promote wireless energy transmission among satellites and the Earth. Although microwave-based, laser-based, and sunlight-based wireless energy transmission technologies have been reported previously, none of them have been practically deployed because of major limitations. In this paper, a concentrated sunlight energy wireless transmission system (CSEWTS) using single plano-convex lenses to harvest space sunlight and a single corresponding optical fibre bundle (OFB) to realize flexible energy transmission is schematically developed and its prototype is established experimentally. This system utilizes sunlight as the transmission media to avoid intermediate energy conversion and where energy efficiency can be enhanced compared to microwave-based or laser-based energy wireless transmission. Furthermore, the OFB-based CSEWTS can lighten the mirror-based system, which was developed previously. Various effects of optical coupling, condenser outline in the energy receiver, smog, distance, and bending were experimentally or theoretically investigated. An optimized coupling incident angle into OFB of 18° was attained theoretically and validated experimentally where an improvement of 19.9% in system efficiency was acquired from a wrong angle to an optimal one. Besides, aspheric lenses were experimentally proved to be more appropriate to condense sunlight where a 16.5% − 19.5% enhancement was obtained. In addition, lens coating, condenser outline in the energy receiver, smog, and distance effects were also analyzed. Smog harms energy transmission which casts shadows on its space-Earth application. Energy transmission to a no-cloud area is the only probable option. The developed technologies can also be used in solar sail spacecraft, contributing to global carbon neutrality and clean aerospace flight.

There is an impulsion to introduce machine-learning algorithms into the thermo-fluids areas. Machine learning modeling, especially in high-precision regression problems, relies on large amounts of randomly-selected training data. Such randomness has little effect on final results because a big database (millions or billions of data points) can swallow such randomness. However, training data in the heat transfer area is not so huge and in fact it should be kept as small as possible because data acquisition is not convenient. Therefore, training data need to be shrunk without sacrificing prediction accuracy. Based on our previous work, we herein detail the selection process for a smart-sized training dataset. The smart-sized training dataset was slimmed by 50% with improved prediction accuracy. The prediction accuracy for the worst condition was still above 90%, an increase of 3.5% on previous results. This is a great improvement on our previous work because the training data scale was substantially reduced, demonstrating better results with half of the effort. The developed small-sample modeling using the deep learning algorithm provides a powerful information-processing tool to augment the understanding of the nonlinear systems in thermo-fluids mechanics, and to even transform current lines of thermo-fluids-related and more extensive applications. © 2022 American Medical Association. All rights reserved.

Advancements in spacecraft formation and space solar power plant technologies promote wireless energy transmission among satellites and the Earth. Although microwave-based, laser-based, and sunlight-based wireless energy transmission technologies have been reported previously, none of them have been practically deployed because of major limitations. In this paper, a concentrated sunlight energy wireless transmission system (CSEWTS) using single plano-convex lenses to harvest space sunlight and a single corresponding optical fibre bundle (OFB) to realize flexible energy transmission is schematically developed and its prototype is established experimentally. This system utilizes sunlight as the transmission media to avoid intermediate energy conversion and where energy efficiency can be enhanced compared to microwave-based or laser-based energy wireless transmission. Furthermore, the OFB-based CSEWTS can lighten the mirror-based system, which was developed previously. Various effects of optical coupling, condenser outline in the energy receiver, smog, distance, and bending were experimentally or theoretically investigated. An optimized coupling incident angle into OFB of 18° was attained theoretically and validated experimentally where an improvement of 19.9% in system efficiency was acquired from a wrong angle to an optimal one. Besides, aspheric lenses were experimentally proved to be more appropriate to condense sunlight where a 16.5% − 19.5% enhancement was obtained. In addition, lens coating, condenser outline in the energy receiver, smog, and distance effects were also analyzed. Smog harms energy transmission which casts shadows on its space-Earth application. Energy transmission to a no-cloud area is the only probable option. The developed technologies can also be used in solar sail spacecraft, contributing to global carbon neutrality and clean aerospace flight.