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Convective heat transfer on flat and concave surfaces subjected to an impinging jet form lobed nozzle

Science China(Technological Sciences) 2020年第1期63卷 116-127页

作者： LYU YuanWei ZHANG JingZhou WANG BoYan TAN XiaoMing College of Energy and Power Engineering Nanjing University of Aeronautics and Astronautics

A tri-dimensional lobed nozzle is concerned in the jet impingement on a flat target and a concave target in the current study. The jet impingement heat transfer experiments are conducted under two jet Reynolds numbers(Re=10000 and 20000) and four nozzle-to-surface distances(H/d=2, 4, 6 and 8). Simultaneously, to characterize the flow dynamics of lobed jet impingement onto different target surfaces, some computations are conducted under a specific jet Reynolds number. The results show that the lobed jet is capable of achieving an increase of stagnation Nusselt number about 25% in relative to the round jet at small nozzle-tosurface distances. However, at large nozzle-to-surface distances, the lobed jet otherwise weakens the convective heat transfer in the vicinity of jet stagnation, especially under high jet Reynolds number. When compared to the flat target, approximately a20%–30% reduction of stagnation Nusselt number is produced on a concave target, which is attributed to the combined effect of destabilization and confinement due to the concave curvature.

关键词： jet impingement enhanced heat transfer lobed nozzle flat surface concave surface

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High-quality micro-shape fabrication of monocrystalline diamond by nanosecond pulsed laser and acid cleaning

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International Journal of Extreme Manufacturing 2022年第2期4卷 173-183页

作者： Yasuhiro Okamoto Tubasa Okubo Atsuya Kajitani Akira Okada Graduate School of Natural Science and Technology Okayama UniversityOkayamaJapan

The flat plane of small surface roughness below 0.1μm average roughness was obtained for monocrystalline diamond by nanosecond pulsed laser irradiation of 1060 nm and post-process acid cleaning,at a laser fluence around the material removal threshold *** glossy and flat plane at the bottom of the micro-groove was parallel to the top surface of the specimen,although the round beam of Gaussian mode was irradiated in the direction perpendicular to the top surface of *** square beam of top-hat mode produced a shallower micro-groove with a wider,flatter bottom compared with the round beam in Gaussian *** creation method of the flat plane with small surface roughness was discussed in the arrangement strategy of linear micro-grooving by the square beam of top-hat *** side-by-side repetition of linear micro-grooving did not create a flat plane with constant ***,a two-step scanning method was proposed in order to overcome the problem in the normal side-by-side repetition of liner ***-removal areas were partly retained between the processing lines in the first step,and the laser scanning was conducted on the retained area in the second *** newly proposed two-step scanning method was practical and useful to create a widely flat plane with small surface roughness,and the two-step scanning method provided superior control over the micro-groove *** proposed method can reduce the surface roughness in addition to the shape creation of monocrystalline diamond,and it can be used as a high-quality micro-shape fabrication method of monocrystalline diamond.

关键词： monocrystalline diamond nanosecond pulsed laser flat surface smooth surface micro-grooving

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