Analysis of microdiffuser/nozzles

In this study, an analysis of the performance of micronozzle/diffusers is performed and fabrication of the micronozzle/diffuser is conducted and tested. It is found that the ratio of the loss coefficient of nozzle and diffuser increases with the Reynolds number and with the opening angle. At a given Reynolds number, the pressure loss coefficient for nozzle is higher than that of the diffuser due to considerable difference in the momentum change. At a fixed volumetric flowrate, a ‘minimum’ phenomenon of the pressure loss coefficient versus nozzle/diffuser depth is encountered. This is related to the interactions of velocity change and friction factor. Good agreements of the measured data with the predicted results are found in this study except at a diffuser having an opening angle of 20°. This is because of the presence of flow separation. The departure of this case to the prediction is due to the separation phenomenon in a larger angle of the diffuser. Hence, a more complicated two- and three-dimensional model is adopted to verify this flow separation inside the diffuser. For the simulation of the two-dimensional case, asymmetry flow field is seen for low Reynolds number region, whereas this phenomenon is not seen under three-dimensional simulation due to the confinement of the side wall.