Abstract
The increasing implementation of mini and microchannels in industrial or biomedical applications is a source of novel challenges for pressure drop. Pressure loss due to surface roughness for flows in microchannels is reported to deviate from conventional macroscale theory in both the laminar and turbulent regime even for small relative roughness (less than 5% of the hydraulic diameter).
This work aims to characterize the influence of the geometry parameters of Q-type structured surface roughness on the hydraulic performance in two-dimensional rectangular channels under steady laminar flow. The surface roughness is modeled as spatially periodic rectangular elements, which is commonly used for micro heat exchangers. Computational Fluid Dynamics (CFD) is used to solve the governing continuity and momentum equations. The selected roughness parameters are typical for industrial microdevices (e.g. micro heat exchangers) and biomedical systems.
It is shown that the pressure drop is larger in both mini and microchannels when compared to conventional channels for relative roughness less than 5%. Different flow regimes are identified. A novel correlation between pressure drop and roughness characteristics is developed. Predictions are compared to the available literature for similar roughness configuration and results show good agreement. Although the proposed correlation is defined for Q-type structured roughness, the predictions are of acceptable accuracy for other roughness geometries.
The results led to the proposal of a simplified approach for modeling the influence of distributed surface roughness on bulk flow parameters through a prescription of boundary condition on the rough wall for laminar and steady duct flows. This approach promises to predict the averaged velocity profile above the roughness amplitude without detailing flow behavior near the rough wall.
