Residence time distributions in microchannels: Comparison between channels with herringbone structures and a rectangular channel

Residence time distributions (RTD) have been determined numerically and experimentally for channels with and without herringbone structures. Computational fluid dynamics (CFD) and particle tracking with random walk diffusion were employed for the numerical calculation of the RTD. The axial dispersion exchanging mass with a stagnant zone model was shown to fit the particle tracking data for the channels with staggered herringbone structures. This model provides a simpler method for RTD characterisation. Experimental RTD measurements were performed by monitoring the concentration of a tracer dye by means of a LED-photodiode system. For all cases, the calculations agreed well with experiments. The results show that for low Peclet numbers (Pe < 102) the use of herringbone structures does not have an impact on the RTD, however at high Peclet numbers (Pe > 102), channels with herringbone structures exhibit a narrower RTD than a plain channel of the same dimensions. Thus, at high Pe, inclusion of herringbones to the bottom floor of rectangular channels allows the increase in channel dimensions without adverse effect on the RTD behaviour or reaction performance.