Characterization of a Sub-Atmospheric Pressure-Inducing Micropump Based on Flow Rate and Gauge Pressure Measurements

The pumping mechanism in multi-inlet microfluidic channels usually requires multiple micropumps to be separately attached to each inlet. Unfortunately, this may create fluid leakage resulting from a considerably high internal pressure. To address this, a passive sub-atmospheric pressure-inducing micropump is proposed and its performance is characterized as a function of the flow rate and the gauge pressure. With this pump, a sufficiently high flow rate is generated, comparable to some active-piezoelectric micropumps. The gauge pressure is exponentially descending with time and can be crudely classified into three regions of high, moderate, and slow pressure-release times. Overall, the stabilized pressure is identified within 70 s < t £ 300 s for slow rate mixing while rapid mixing is applicable at t £ 70 s

Fatigue life cycle prediction equation based on grain angles and stress levels for Acacia Mangium

This study aims to investigate and understand the nature of Acacia mangium axial fatigue strengths under repeated stress. Acacia mangium trees, which were cut to produce oven-dried dog bone shaped specimens, were tested in repeated axial-tensile loading with sinusoidal waveform. Findings of this study had shown that Acacia mangium has a significant difference in the strengths parallel and perpendicular to the grain line. Extreme reduction in tensile strength for 0° and 90° grain angles saw a shift from 143.87 MPa to 6.32 MPa (a 95.6% reduction of the Ultimate Tensile Strength). It was observed that the Acacia mangium N-S (Wöhler) plots showed an exponential correlation, in which the N – intercept of the vertical axis was at five (5) million cycles, while the intercept of the horizontal S – axis, was at 143.87 MPa. It was also observed that Acacia mangium has a fatigue endurance limit at 10% of the ultimate tensile strength. From static testing, the Osgood’s coefficient of species for Acacia mangium, (a), was identified algebraically to be 0.49. The finding showed that life cycles predicted by the Fatigue Life Prediction Equation as having almost similar magnitudes with the results defined by the verification test for each stress level. The comparison between the verification test results and the predictions by the equation indicated an impressive fit between them at 30° grain angle

Enhanced Fluid Mixing Using a Reversed Multistage Tesla Micromixer

A two-dimensonal Tesla micromixer is experimentally characterized at varying Reynolds numbers (Re) and valve stages with the aim to acquire sufficiently high mixing performance. To ease fabrication, a simplified Tesla valve design is adopted. Results show two distinctive regimes of low and high Re. In the low-Re regime, a steady incremental mixing was observed as the fluid passes by each valve, whereas an enhanced mixing was identified right in the first valve in the high-Re regime. This is predominantly due to the amplified opposing flow from the helix branch which promotes stronger chaotic advection in the main microchannel. Interestingly, the measured mixing performance was found comparable to that of three-dimensional passive micromixers reported in the literature