Analysis of Wall Shear Stress and Velocity Gradient from Fluid Flow on a Microreactor System

Microreactors are quickly finding their place in breath analysis for the detection of endogenous biomarkers from lipid peroxidation. Previous research from our group has shown that the current design of a 21(L) x7(W) mm triangular pillar array microreactor can capture carbonyl compounds in exhaled breath. The purpose of the current work was to establish a modeling approach using Ansys to microreactor design to understand if a correlation exists between Wall Shear Stress (WSS) at the pillar walls, the velocity profile and carbonyl compound capture. The pillar shapes used in this simulation were triangle, circle, and diamond shapes of various sizes ranging from 20 to 50um. For the sake of computational efficiency, the length of the micropillar array was scaled from 21mm to approximately 700 um which corresponds to around 1/30^th of the total length. Pressure loss across the pillar array was compared to estimated values using the Ergun equation to establish confidence in the model. The pressure loss across the pillar section was 1.19E-4, 1.06E-4, and 1.48E-4 psi for triangle, circle, and diamond pillars respectively. When compared to the Ergun equation, each shape was found to be within similar order of magnitude however the correlation seems to decrease as the pillar array void fraction increases. The WSS for the triangle pillar array was 2.18E-7 psi, several orders of magnitude higher compared to circle and diamond pillars. Since, based on previous work, Triangle pillars have higher capture efficiency, increased WSS may be an indicator for increased microreactor performance in future design simulations. Further design iterations of array width and pillar size were simulated under the same conditions. It was found that reducing the array width from 7mm to 3.5 mm or 4.5 mm along with a decrease in pillar size, increased the velocity gradient approaching the wall giving increased WSS.