This paper presents the performance of a passive planar rhombic micromixer with diamond-shapedobstacles and a rectangular contraction between the rhombi. The device was experimentally optimizedusing water for high mixing efficiency and a low pressure drop over a wide range of Reynolds numbers(Re ¼ 0.1–117.6) by varying geometrical parameters such as the number of rhombi, the distancebetween obstacles and the contraction width. Due to the large amount of data generated, statisticalmethods were used to facilitate and improve the results of the analysis. The results revealed a rank offactors influencing mixing efficiency: Reynolds number > number of rhombi > contraction width > interobstaclesdistance. The pressure drop measured after three rhombi depends mainly on Re and interobstacledistance. The resulting optimum geometry for the low Re regime has a contraction width of101 mm and inter-obstacles distance of 93 mm, while for the high Re regime a contraction width of400 mm and inter-obstacle distance of 121 mm are more appropriate. These mixers enabled 80% mixingefficiency creating a pressure drop of 6.0 Pa at Re ¼ 0.1 and 5.1 104 Pa at Re ¼ 117.6, with a mixerlength of 2.5 mm. To the authors' knowledge, the developed mixer is one of the shortest planar passivemicromixers reported to date.
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