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近年来,微尺度条件下功能性流体换热与流动已经成为极具潜力和挑战性的课题,在化工、医药、传热与能源利用等系统中获得广泛应用。超临界CO_2流体作为一种天然替代性环保工质,在相关细微尺度下已证明具有良好的热力学性能。本研究采用了数值计算的方法对近临界CO_2流体在微通道内流动稳定性和换热特性进行了系列的探索。研究发现,在靠近临界点的相对较宽泛的区域内,流体具有强膨胀特性和低热扩散特性,从而在微尺度条件下产生局部旋涡流动,大大促进了微尺度的混合和对流换热效率。进一步,研究针对这种微尺度局部涡动进行了机理分析,获得了微通道内近临界流体瞬态换热和超临界热膨胀效应特性。
In recent years, functional fluid heat exchange and flow at the micro-scale have become a highly potential and challenging subject and are widely used in chemical, pharmaceutical, heat transfer and energy utilization systems. Supercritical CO 2 fluid, as a naturally-occurring alternative environmentally friendly working fluid, has proved to have good thermodynamic properties at the relevant microscale. In this study, a numerical method was used to explore the flow stability and heat transfer characteristics of near-critical CO_2 in microchannels. The results show that the fluid has strong swell property and low thermal diffusivity in a relatively wide area close to the critical point, resulting in local vortex flow at the micro-scale, greatly promoting the micro-scale mixing and convection heat transfer efficiency. Further, the mechanism of this micro-scale local vortex was studied and the characteristics of transient heat transfer and supercritical thermal expansion of near-critical fluid in microchannels were obtained.