| Microfluidics is a rapidly emerging field with numerous applications in electronics, instrumentation, bioengineering, medicine, communications, and advanced energy systems. However, while there are many functioning microfluidic systems currently in use, microscale flow characteristics are often not well understood, reliable microfluidic design data are limited, and the parameters and computational methods used to model microsystems are not well established. This study numerically substantiates, and adds to previous microfluidic results and numerical methods utilized to predict the flow and heat transfer characteristics for a few common microfluidic configurations. An existing continuum based, three-dimensional, unsteady, compressible numerical algorithm capable of modeling fluid-structure-interaction is modified to include a number of effects common in microscale fluid systems, namely first- and second-order accurate slip boundary conditions, creep flow, and viscous dissipation. The resulting algorithm is then utilized to complete the following studies. First, convective heat transfer rates and frictional losses of rarified, steady state, laminar, constant wall temperature and constant wall heat flux rectangular microchannel flows are investigated. Effects of aspect ratio, rarefaction, creep flow, viscous dissipation, axial conduction, and thermally/hydrodynamically developing flow are considered. The effect of these parameters on the frictional losses and the convective heat transfer rates are given through the Poiseuille number and Nusselt numbers, respectively. Second, the momentum and thermal energy exchange models of the original fluid-structure-interaction algorithm are modified, such that the equivalent of first-order slip velocity and temperature jump boundary conditions are achieved at fluid-solid surfaces which may move and deform with time. The resulting algorithm is evaluated with comparison to analytical models, and previously established numerical and experimental data for (1) velocity profiles of a rarified gas between parallel plates; (2) temperature profiles of a rarified gas between parallel plates; (3) drag coefficients and Nusselt numbers for rarified gas flow around a infinite cylinder; and, (4) the transient thermal/structural response of a damped-oscillatory three-dimensional cylinder subject to an impulsively started rarified flow. |
