Publications (3)3.47 Total impact
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Article: An optical flow MTV based technique for measuring microfluidic flow in the presence of diffusion and Taylor dispersion
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ABSTRACT: A novel technique is presented for accurately measuring flow fields in microfluidic flows from molecular tagging velocimetry (MTV). Limited optical access is frequently encountered in microfluidic systems. Therefore, in this contribution we analyze the special case of tagging a line across the thin dimension of a microchannel and subsequent imaging along this line. This represents a set-up that is applicable to a wide range of microfluidic applications. A volume illumination has to be used, resulting in an integration of the visualized dye across the flow profile. This leads to the well-known effect of Taylor dispersion. Our novel technique consists of measuring motion from digital image sequences in a gradient-based approach. A motion model is developed which explicitly deals with brightness changes due to Taylor dispersion and additional molecular diffusion of dyes. The presented approach is specific to the case of a parabolic velocity profile. In the presence of these effects, an accurate computation of motion is only possible by applying this novel motion model. Our technique is tested on simulated sequences corrupted with varying levels of noise and on actual measurements. Measurements were conducted in a microfluidic mixer of precisely known flow properties. In the same mixer, a comparative study of our MTV technique toμPIV was performed. Also, the results were compared to bulk measurements of the fluid flow velocity. The novel algorithm compared favorably and also, measurements were conducted on inhomogeneous flow configurations.Experiments in Fluids 04/2012; 44(3):439-450. · 1.74 Impact Factor -
Chapter: 2D-Measurement Technique for Simultaneous Quantitative Determination of Mixing Ratio and Velocity Field in Microfluidic Applications
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ABSTRACT: Two-dimensional Molecular-Tagging-Velocimetry (2D-MTV) has been used to investigate velocity fields of liquid flow in a micro mixer. Optical tagging was realized by using caged dye. For the first time patterns were generated by structured laser illumination using optical masks. This allows the generation of nearly any imaginable pattern. The flow induced deformation of the optically written pattern is tracked by imaging of laser induced fluorescence. Quantitative analysis of raw image series is carried out by novel “optical flow” based techniques. A comparison to the standard technique of μPIV has also been conducted. Additionally Planar Spontaneous Raman Scattering (PSRS) was applied in order to determine concentration fields for mixtures of ethanol and water.04/2009: pages 155-164; -
Article: Micro-flow analysis by molecular tagging velocimetry and planar Raman-scattering
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ABSTRACT: The two dimensional molecular tagging velocimetry (2D-MTV) has been used to measure velocity fields of the flow in a micro mixer. Instead of commonly used micro particles an optical tagging of the flow has been performed by using a caged dye. The pattern generation is done by imaging a mask for the first time. This allows to generate nearly any imaginable pattern. The flow induces a deformation of the optically written pattern that can be tracked by laser induced fluorescence. The series of raw images acquired in this way were analyzed quantitatively with a novel optical flow based technique. The reference measurements have been carried out allowing to draw conclusions about the accuracy of this procedure. A comparison to the standard technique ofμPIV has also been conducted. Apart from measuring flow velocities in microfluidic mixing processes, the spatial distribution of concentration fields for different species has also been measured. To this end, a new technique has been developed that allows spatial measurements from Planar Spontaneous Raman Scattering (PSRS). The Raman stray light of the relevant species has been spectrally selected by a narrow bandpass filter and thus detected unaffectedly by the Raman stray light of other species. The successful operation of this measurement procedure in micro flows will be demonstrated exemplary for a mixing process of water and ethanol.Experiments in Fluids 02/2008; 44(3):419-430. · 1.74 Impact Factor
