In this study, a parametric investigation on mixing of two fluids in a modified Tesla microchannel, has been preformed. Modified Tesla micromixer applies both flow separation and vortices string principles to enhance the mixing. The fluid stream splits into two sub-streams and one of them mixes with the other again at the exit of the Tesla unit. Analyses of mixing and flow field have been carried out for a wide range of Reynolds number from 0.05 to 40. Mixing performance and pressure drop characteristics with two geometrical parameters, i.e, ratio of the diffuser gap to channel width ( h/w ) and ratio of the curved gap to the channel width ( s/w ), have been analyzed at six different Reynolds numbers. The vortical structure of the flow has been analyzed to explain mixing performance. The sensitivity analysis reveals that mixing is more sensitive s/w , than the h/w .

A valve-less micro-pump was realized with just one diffuser/nozzle element. The pressure-loss in a nozzle is lower than that in a diffuser, and therefore one-way flow may be realized in the nozzle direction. The frequency characteristics and the pump characteristics are measured. Dimensionless numbers are introduced to rearrange the measured data and to understand the physical mechanisms of the micro-pump. Simplified analysis was done for unsteady operation of the pump by considering the channel geometries and pressure-loss coefficients based on Bernoulli’s theorem. The calculated pump characteristics agreed with the measured ones. Numerical calculations were made using the commercial CFD (computational fluid dynamics) code CFX. The calculated flow patterns showed differences between the diffuser and nozzle directions.

This study presents a diffuser micropump and characterizes its output flow rates, like the parabola shape on the frequency domain and the effecting factors. First, equivalent circuit using fluid-electric analogy was built up; then, the flow rate analysis results were compared to experiment results to verify the applicability of the circuit simulation. The operation frequency was 800 Hz for both cases and the maximum flow rates were 0.078 and 0.075 μl/s for simulation and experiment result, respectively. The maximum flow rate difference was 3.7%. The circuit then was used to analyze the inertial effects of transferred fluid as well as system components to the output flow rates. This work also explains why the flow rate spectrum has the shape of parabola. The analysis results showed that without inertial effects, the micropump flow rates are linearly proportional to the operation frequency; otherwise it has parabola shape. The natural frequency of the actuator-membrane structure was recognized using finite element method to verify if this parameter affects the characteristics of the flow rates. The experiment and simulation results demonstrated 800 Hz and 91.4 kHz for the frequency of the maximum pumping flow rate and the first mode natural frequency of actuator-membrane structure, respectively. It indicates that the structure natural frequencies of the actuator-membrane structure do not play any role to operate the micropumps.

A thermopneumatic valveless micropump with a PDMS-based nozzle/diffuser structure was firstly designed and realized herein by stacking three layers of PDMS on a glass slide. Unlike the conventional peristaltic pumping configuration, the new structure of the micropump consists of only one set of heater on the glass slide, a thermopneumatic actuation chamber, and an actuation diaphragm. Additionally, it includes a flowing channel with nozzle/diffuser structure and inlet/outlet ports. In this valveless microchannel, fluid is driven by asymmetric flow resistance produced from the nozzle and diffuser configuration. The actuation diaphragm between the gas-pneumatic chamber and the flowing channel can bend up and down due to the gas expansion as well as the thermal buckling of the PDMS diaphragm imposed from the heating in the gas-pneumatic actuation chamber.

Referring to regulation of ISO 9300, the discharge coefficients of 2mm, 5mm and 10mm nozzles with 2.5°, 4.0° and 6.0° diffuser angle were measured, respectively. Through comparisons among experimental results, simulation results and prediction results of empirical equations, it was clear that the discharge coefficients were the same for the nozzles with the same throat diameter and were in good agreement with the results of the empirical equations for 10mm nozzles, while that changed with different diffuser angle for other two sets of nozzles. The influence of throat diameter, surface roughness and entrance contour on discharge coefficient was analyzed one by one. The results showed the large out-of-roundness of entrance contour might be the most important reason resulted in the experimental results.