Topology optimization design of nanofluid-cooled microchannel heat sink with temperature-dependent fluid properties

The geometric structure of a two-dimensional (2-D) nanofluid-cooled microchannel heat sink (NMHS) is optimized using a topology optimization method. We describe the flow and heat transfer in the NMHS as a singlephase nanofluid-based convective heat transfer model. Since the thermophysical properties of the nanofluid strongly depend on temperature, the temperature-dependent fluid properties are considered in the model. A heat transfer maximization problem is studied under a constant pressure difference using a density based topology optimization method to optimize configurations of NMHS. In the optimization, the material density is adopted as the design variable to control the variation of the fluid domain. An adjoint-based sensitivity analysis method is applied to obtain the gradient information used for updating the design variable. In numerical examples, the effects of temperature-dependent fluid properties on the optimal configurations of the NMHS are first investigated. Additionally, the effects of the characteristics of the nanofluid, such as the base fluid, nanoparticle volume fraction and diameter, on optimized designs are assessed. The numerical results reveal that the temperature-dependent fluid properties can significantly affect the optimal results; more branched flow channels are produced in the optimal configurations as the pressure difference or heat generation coefficient increases; and more complex optimal configuration can be obtained by reducing the nanoparticle volume fraction. From an engineering standpoint, this study provides an applicable optimization method for the design of a well-performing NMHS.