## 3 Results and Discussion
### Influence of Heat Sink Geometry in Flow Distribution  
Three sets of geometries were investigated and characterized by the orientation of the flow, the type of collector and the number of parallel channels. The numerical study performed in the commercial _COMSOL Multiphysics 5.6\({}^{\text{\text{\textregistered}}}\)_ software allowed the determination of the flow rate through each section, and the analysis of the quadratic deviations enabled the quantification of the FDU through the FDU coefficient, S. It can already be stated that the rectangular-shaped support manifold is the one that provides the lowest values of flow distribution uniformity coefficient (S) when compared with the circular and triangular shapes. As such, the rectangular shape is the one causing the greater uniformity in the distribution of the heat transfer in the microchannels, as was clearly outlined in the abstract, and because of this fact the rectangular shape is the only one to be considered in the further analysis undertaken in this work. The orientation of the flowing the rectangular-shaped manifold was imposed by the positioning of the inlet and outlet, as presented in Figure 10. After the numerical simulation, the FDU coefficient was determined for the different geometries. The results are compiled in Figure 11. The coefficient increases exponentially with the increase in the flow rate. The vertical placement of the inlet and outlet allowed the development of a more uniform flow. Regarding the horizontal flow, a small difference was noticed when placing the inlet and outlet on the same or opposite faces. Finally, the greatest flow maldistribution was observed with the injection of the fluid frontally. Figure 9: Comparison of the difference in temperature generated in the experimental tests and in the numerical simulation. The observed distributions can be better explained by analyzing particular cases. In the case of the frontal configuration, a jet is formed in the center while two recirculation regions form laterally, as observed in Figure 12a. Figure 12b shows that the maximum value of the standardized flow rate occurs in the central channels, 3 and 4. The path passing through the central channels has low resistance to flow, which explains why this configuration presents the highest coefficient. Figure 11: Coefficient of the uniformity distribution of the flow for different heat sink configurations. Figure 10: Different configurations for the microchannel device: (**a**) horizontal frontal; (**b**) horizontal parallel; (**c**) horizontal parallel inverted; (**d**) vertical. Both horizontal configurations presented a similar distribution, only diverging in the exit collector, which also affected the coefficient. The inverted horizontal configuration was slightly more uniform than the parallel horizontal configuration. Figure 13 shows that the fluid flows preferentially via channel 6, which is placed in the opposite side to one of the inlets, this flow pattern being caused by the inertia of the fluid. The vertical configuration presented the best results, since the placement of the inlet vertically allows it to be perpendicular to the smallest dimension of the collector (height of 1 mm). In this way, the jet is immediately broken and spread radially. This phenomenon is known as jet impingement [31], and is shown in Figure 14. It is responsible for the uniformity in this configuration, where no preferential flow path is noted. Figure 12: Flow distribution uniformity (FDU) study for the frontal configuration. (**a**) Schematic view of the velocity profile for a 100 mL/min flow and at a scale of 2. (**b**) The standardized flow in each channel of the heat sink. Figure 13: FDU study for the inverted horizontal configuration. (**a**) Schematic view of the velocity profile for a 100 mL/min flow and at a scale of 2. (**b**) The standardized flow in each channel of the heat sink.