In industrial processes, the microtechnology concept refers to the operation of small devices that integrate the elements of operational and reaction units to save energy and space. The advancement of knowledge in the field of microfluidics has resulted in fabricating devices with different applications in micro and nanoscales. Micro- and nano-devices can provide energy-efficient systems due to their high thermal performance. Fluid flow in microchannels and microstructures has been widely considered by researchers in the last two decades. In this paper, a review study on fluid flow within microstructures is performed. The present study aims to present the results obtained in previous studies on this type of system. First, different types of flows in microchannels are examined. The present article will then review previous articles and present a general summary in each section. Then, the multi-phase flows inside the microchannels are discussed, and the flows inside the micropumps, microturbines, and micromixers are evaluated. According to the literature review, it is found that the use of microstructures enhances energy efficiency. The results of previous investigations revealed that the use of nanofluids as a working fluid in microstructures improves energy efficiency. Previous studies have demonstrated special attention to the design aspects of microchannels and micro-devices compared to other design strategies to improve their performance. Finally, general concluding remarks are presented, and the existing challenges in the use of these devices and suggestions for future investigations are presented.

中文翻译：

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不同微通道形状内多相流建模方法综述及其应用

在工业过程中，微技术概念是指将操作和反应单元的元素集成在一起以节省能源和空间的小型设备的操作。微流体领域知识的进步导致制造在微米和纳米尺度上具有不同应用的设备。由于其高热性能，微型和纳米器件可以提供节能系统。在过去的二十年中，研究人员广泛考虑了微通道和微结构中的流体流动。在本文中，对微观结构内的流体流动进行了回顾性研究。本研究旨在展示先前对此类系统的研究所获得的结果。首先，检查了微通道中不同类型的流动。然后，本文将回顾以前的文章，并在每个部分中进行概括总结。然后，讨论了微通道内的多相流动，并评估了微型泵、微型涡轮机和微型混合器内的流动。根据文献综述，发现微结构的使用提高了能量效率。先前的研究结果表明，在微观结构中使用纳米流体作为工作流体可以提高能源效率。先前的研究表明，与其他设计策略相比，对微通道和微器件的设计方面的特别关注以提高其性能。最后，提出了一般性结论，并提出了使用这些设备的现有挑战和对未来调查的建议。