Numerical Simulation Of Natural Convection Over Microscale Heated Surface

The study of natural convection heat transfer in microscale has become more and more important with the development of microelectronic machinery and device nowadays. Meanwhile, nanofluid, a novel heat transfer fluid prepared by dilute suspension of nanoparticles in a base fluid, exihibits the special flow and heat transfer characteristics and can promisingly be applied in the industries such as energy, chemistry, and electronics. Hence the study of microscale natural convection with nanofluids also becomes one of the hot topics in heat transfer researches.In this study, we used the commercial CFD software packet FLUENT to simulate the natural convenction over microscale heated wires with diameters of20,40,60,80, and100μm, respectively. The results show that the distributions of velocity and temperature are related to the setting of the boundaries, and to the wire diameters, e.g., the size effect. The calculated Nusselt numbers approach to constants near the heated surfaces or when the diameters of the heated wires decrease. This result can reasonably be explained by the dominant heat conduction in the vicinity of the heated wire when the size of which decreases. We also simulated the natural convection over a wire with diameter of20um in a confined space.The results show that the velocity changes rapidly along the negative y direction in the confined space, while it changes slowly in the positive y direction in the infinite space. The calculated Nusselt numbers also show enhanced heat transfer in the infinite space. We then simulate the natural convection of a typical nanofluid in the confined space, using the one-phase model and two-phase model in the FLUENT, respectively. The results indicate that the setting of the one-phase model in the FLUENT only changes the physical properties of the medium, so that the velocity and temperature do not increase obviously. For the two-phase flow model in the FLUENT, however, the velocity and the temperature increase greatly, probably because that the setting of the two-phase model takes into account of the interaction between the solid particles and base liquid, leading to the abnormal flow and heat transfer characteristrics of nanofluid.The discussion on the microscale natural convection of traditional fluid and nanofluid can theoretically be benifitial to, e.g., the miniaturization of devices, and will be useful to the pratical application of nanofluid in the industry. Although there exists the limitation of simulation, the results are expected to be validated through corresponding experimental studies.