3-D numerical simulations of fluid flow and heat transfer in various micro conduits

Turgay, Metin Bilgehan
In this work, it is aimed to investigate the effect of roughness geometrical properties and configurations on laminar flow and heat transfer characteristics in microchannels, numerically. For this purpose, two-dimensional parallel plate, and three-dimensional trapezoidal microchannels with different roughness properties are modeled along with the smooth ones. Fluid flow and heat transfer simulations are conducted with COMSOL Multiphysics. Roughness is modeled as triangular obstructions on one of the plates in two-dimensions, and conical obstructions in three-dimensions on the base of the trapezoidal channel, to mimic the natural roughness in silicon microchannels and microstructures on lotus leaves. Numerically obtained results, for smooth and rough channels, are compared with each other, and with the results that exist in the literature. It is found that, both in 2D and 3D tested geometries, local Nusselt number increases through the tip of the roughness elements due to increased velocity of the subjected flow. However, near the base of the roughness elements and between them, reduction in local Nusselt number is observed due to reduced velocity fields reduced convective heat flux in the fluid, and increased thermal conductivity of the fluid through the exit of the channels. Frictional characteristics of the tested rough geometries showed nonlinear behavior with the complexity of the surface parameters. It is shown that widely used relative roughness height concept is not enough to define the roughness effect in microchannels. Additionally, effects of stabilization methods, element discretization order, and relative tolerance level on the results of microfluidic simulations with COMSOL are investigated.