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This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers.

This study presents a two and three-dimensional numerical simulations of a flow-through a sudden expansion and contraction microchannels. The finite element method was used to discretize the equations governing the physical model. By carrying out the numerical simulations, results indicate the apparition of a separate vortex, situated in the corner after the sudden expansion of the microchannel for low Reynolds numbers. For high values of Reynolds number and expansion ratios, the vortex separation length increases. Also, the three-dimensional character of the flow is more pronounced for higher Reynolds numbers. [ABSTRACT FROM AUTHOR]

This article involves computational and experimental investigations into the flow of a Newtonian fluid through a sudden expansion microchannel consisting of a rectangular block. The results elucidate that the Reynolds number and aspect ratio has a significant impact on the sequence of vortex growth downstream of the expansion channel. The experimental flow visualization results are found to be in good agreement with the numerical predictions of the local fluid dynamics. The simulation results also draw the Re-γ (Reynolds number-aspect ratio) flow pattern map to classify how the flow structures vary with Reynolds number, for example, the resulting flow structures can be classified as five types progressively. The findings in this study provide designers with valuable guidelines for improving the design and operation of the proposed microfluidic rectifier. [ABSTRACT FROM AUTHOR]

This paper deals with computational and experimental investigations into pressure-driven flow in sudden expansion microfluidic channels. Improving the design and operation of microfluidic systems requires that the capabilities and limitations of 2-dimensional (2-D) and 3-dimensional (3-D) numerical methods in simulating the flow field in a sudden expansion microchannel be well understood. The present 2-D simulation results indicate that a flow separation vortex forms in the corner behind the sudden expansion microchannel when the Reynolds number is very low ( Re∼0.1). However, the experimental results indicate that this prediction is valid only in the case of a sudden expansion microchannel with a high aspect ratio (aspect ratio >> 1). 3-D computational fluid dynamics simulations are performed to predict the critical value of Re at which the flow separation vortex phenomenon is induced in sudden expansion microchannels of different aspect ratios. The experimental flow visualization results are found to be in good agreement with the 3-D numerical predictions. The present results provide designers with a valuable guideline when choosing between 2-D or 3-D numerical simulations as a means of improving the design and operation of microfluidic devices. [ABSTRACT FROM AUTHOR]