Experimental investigation of a scaled-up passive micromixer with uneven interdigital inlet and teardrop obstruction elements

Abstract

Micromixers are vital components in micro total analysis systems. It is desirable to develop micromixers which are capable of rapidly mixing two or more fluids in a small footprint area, while minimizing mechanical losses. A novel planar scaled-up passive micromixer is experimentally investigated in this study. The design incorporates a 7-substream uneven interdigital inlet which supplies two liquid species in a parallel arrangement and promotes diffusion along the side walls. Forty-eight staggered teardrop-shaped obstruction elements located along the channel length combined with 32 side walls protrusions increase the two-fluid interfacial area while converging the flow due to periodic reductions in crosssectional area. The scaled-up micromixer has a mixing channel length of 110 mm with a mixing channel height and width of 2 and 5 mm, respectively. Experimental investigations are carried out at four locations along the channel length and at Reynolds numbers equal to 1, 5, 10, 25, 50, and 100, where the Reynolds number is calculated based on total two-fluid flow and the mixing channel hydraulic diameter. Flow visualization is employed to study flow patterns, while induced fluorescence (IF), using de-ionized water and low concentration Rhodamine 6G solutions, provides mixing efficiency data. Results show a change in dominant mixing mechanism from mass diffusion to mass advection, with a critical Reynolds number of 25. At high Reynolds numbers, the formation of additional lamellae is observed, as is the formation of Dean vortices in the vicinity of the teardrop obstructions. Of the tested cases, the highest outlet mixing efficiency, 68.5%, is achieved at a Reynolds number of 1, where mass diffusion dominates. At low Reynolds numbers, superior mixing efficiency is due primarily to the implementation of the uneven interdigital inlet. A comparable mixing length is proposed to allow for reasonable comparison with published studies. List of symbolsC Concentration (lg/L) D Diffusion coefficient (m 2 s -1 ) D H Hydraulic diameter (mm) H Channel height (mm) I Fluorescence intensity j diff Flux of diffusion (kg m -2 s -1 ) L Length (mm) M Mixing efficiency N Total number of samples U Average velocity (m s -1 ) W Width (mm) w p Width of pin (mm)Greek l Dynamic viscosity (N s m -2 ) q Density (kg m -3 )

Design and Mixing Performance of Passive Micromixers: A Critical Review

“…98.2%, at Re = 0.1). Cook et al (2012) designed a planar scaled-up micromixer consisting of an uneven interdigital inlet, staggered teardrop-shaped obstructions, and wall protrusions. The experimental Investigation at Re = 1˗100 showed that the proposed design achieved the maximum efficiency of 68.5% at Re = 1 because of multi-lamination caused by the uneven interdigital inlet.…”

A hybrid micromixer with planar mixing units

“…Kristina J. Cook et al in her study employed uneven interdigital inlets to investigate her proposed micromixer for the Re ranging between 1 and 100. 32 A series of obstacles in the shape of a teardrop were used to increase the mixing efficiency. Fig.…”

Flow Configurations in a Y Splitting-Junction Microchannel

“…Considering the effects due to change in geometry in micro-channel flow, a very effective and simple geometry to increase diffusion is to add a Y splitting section and then recombine the two branches in an inverse Y junction [6][7][8][9]. This configuration is rather simple to be manufactured and can be also used for flow measurements (flow rate) and control.…”