The residence time distribution of LTCC microreactors was investigated depending on flow rates and fluid viscosities. A pulse trace experiment was used for monitoring the tracer signals before and behind the microreactors. The tracer signals were measured by use of micro flow-through photometers without disturbing the liquid flow. Therefore, the micro photometers were mounted directly onto FEP tubings. The residence time distribution (RTD) was determined by calculation of the dispersion model using the inlet and outlet tracer profiles. The RTD of a LTCC micro mixer and a LTCC plain meandered channel mixer were determined in the flow rate range between 50 μL/min and 3 000 μL/min using water and aqueous glycerol mixtures up to a glycerol content of 50%. Received data were compared with a PTFE tube (1 mm internal diameter) as reference. A complex relation of determined RTDs between the Reynolds number (Re) and the fluid viscosities was found. A significant non-monotonous effect of the fluid viscosity was observed. The RTD as well as the tailing behavior indicates clearly viscosity-dependent changes in the fluid regime and transport mechanisms.

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