Optical characterization of viscosity-dependent residence time distribution in the static micromixer Statmix6

The residence time behaviour of the static chip micro mixer Statmix6 (IPHT Jena) was characterized by a pulse trace experiment applying a micro photometric measurement with two flow-through detectors. The residence time distribution (RTD) shows a characteristic shift with viscosity and flow rate. The change in RTD function can not be explained by reconsidering the Reynolds number exclusively. At lower flow rates, the shift of RTD tailing with flow rate is nearly independent on viscosity. In a transition region, the RTD tailing is reduced strongly, but the characteristic Re number of transition depends on viscosity. The RTD behaviour of the micro mixer was compared with the behaviour of a PTFE tube (1 mm inner diameter) under same experimental conditions and with similar mean residence times (about 0.5 to 40 s). In the tube, a reduction of tailing with increasing flow rate was observed too. But, the change of RTD function with flow rate and their viscosity-dependence dif fers considerably of the functions found in the static micro mixer. The experimental results were interpreted by changes in the flow regime under different local convection mechanism inside the micro device and in the tube. Such changes in mechanisms seem to exist in case of the complex geometry of micro mixer as well as in case of the simple tube. But the characteristic transition regions in the shape of RTD-function are strongly influenced by the structure of device and by the viscosity of the liquid.