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Gas recognition based on the physicochemical parameters determined by monitoring diffusion rates in microfluidic channels
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Monitoring the diffusion progress rates of different gases in a microfluidic channel affords their
discrimination by the comparison of their temporal profiles in a high-dimensional feature space. Here, we
demonstrate gas recognition by determination of their three important physicochemical parameters via a
model-based examination of the experimentally determined diffusion rates in two different cross-section
channels. The system utilized comprises two channels with respective cross-sectional diameters of 1000 μm
and 50 μm. The open end of both channels are simultaneously exposed to the analyte, and the temporal
profiles of the diffusion rates are recorded by continuous resistance measurements on the chemoresistive
sensors spliced to the channels at their other ends. Fitting the solutions of the diffusion equation to the
experimental profiles obtained from the large cross-section channel results in the diffusivity of the analyte.
The results of small cross-section channel, however, fit the solutions of a modified diffusion equation which
accounts for the adsorption of the analyte molecules to the channel walls, as well. The latter fitting process
results in the adsorption parameter for the analyte-channel wall interactions and the population of the
effective adsorption sites on the unit area of the walls. The allocation of these three meaningful parameters to
an unknown gaseous analyte affords its recognition
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