Mikrokanallarda yüzey pürüzlüğünün ısı transferine etkisi.

In this study, effect of surface roughness on convective heat transfer and fluid flow in two dimensional parallel plate microchannels is analyzed by numerically. For this purpose, single-phase, developing, laminar fluid flow at steady state and in the slip flow regime is considered. The continuity, momentum, and energy equations for Newtonian fluids are solved numerically for constant wall temperature boundary condition. Slip velocity and temperature jump at wall boundaries are imposed to observe the rarefaction effect. Effect of axial conduction inside the fluid and viscous dissipation also considered separately. Roughness elements on the surfaces are simulated by triangular geometrical obstructions. Then, the effect of these roughness elements on the velocity field and Nusselt number are compared to the results obtained from the analyses of flows in microchannels with smooth surfaces. It is found that increasing surface roughness reduces the heat transfer at continuum conditions. However in slip flow regime, increase in Nusselt number with increasing roughness height is observed. Moreover, this increase is found to be more obvious at low rarefied flows. It is also found that presence of axial conduction and viscous dissipation has increasing effect on heat transfer in smooth and rough channels.M.S. - Master of Scienc

Çeşitli mikrokanallardaki akışkan akışı ve ısı transferinin 3 boyutlu sayısal simülasyonu.

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.Ph.D. - Doctoral Progra

Numerical simulation of fluid flow and heat transfer in a trapezoidal microchannel with COMSOL multiphysics: A case study

In this study, fluid flow and heat transfer in a trapezoidal microchannel are numerically investigated. For this purpose, a reference study with experimental and numerical solutions is adopted from the literature and solved with COMSOL multiphysics. Good agreement with the results of the reference work is obtained. In addition, effects of stabilization methods and element discretization options that are offered by the program on the results are investigated and discussed with examples. In addition, two different versions of the same program are compared on the effect of stabilization methods on results. Last, some comments on the level of relative tolerance are provided