Modeling of convection enhancement mechanisms

Most compact heat exchangers and heat dissipating components rely on convection enhancement mechanisms that reduce the continuous growth of boundary layers. Usually surface irregularities, in the form of interruptions and/or vortex generators, are introduced in the flow passages. The resulting geometric configurations are periodic in space and, after a short distance from the entrance, induce velocity and thermal fields that repeat themselves from module to module. The numerical models presented here consider the space-periodicity and allow flows that are stationary at sub-critical values of the Reynolds number, but become time-periodic, or quasi periodic, above the critical value of the Reynolds number. Space discretizations are achieved by an equal order finite element procedure based on a projection algorithm. Two-dimensional schematizations are employed to analyze the effects of surface interruptions and transverse vortex generators, while three-dimensional schematizations are employed for longitudinal vortex generators.