Topology optimization for the CFD design of heat sinks coupled with phase change materials

This work addresses the design of a passive PCM-based heat sink (HS) via topology optimization (TO) by using the commercial code COMSOL Multiphysics (R) as CFD tool and optimization engine. The thermal management problem involves the design of alternatives solid structures to be embedded in the PCM, i.e., paraffin wax, in place of foams or periodic cellular structures (BCC, body-centered cubic). By doing this, the bottleneck of PCMs low thermal conductivity can be solved through TO-based structures able to spread heat at a faster rate, and so that PCMs can store/release large amounts of energy at more or less uniform and constant temperature. In detail, this study applies TO to optimize the design of such a structure, assuming a heat flux equal to 1 W/cm 2, coming from a Ni-Cr conductor. In this regard, the CFD model of the heat sink is developed by implementing the enthalpy-porosity method and calibrated against experimental data. The TO problem is formulated and solved by using the adjoint method for sensitivity analysis, the global convergent method of moving asymptotes (GCMMA) as optimization algorithm, and the solid isotropic material with penalization (SIMP) as the interpolation scheme. By assuming the same solid volume of traditional solutions, the material distribution - topology - is optimized. The objective function to be minimized is the average temperature of the domain in order to limit the maximum temperature of the hot surface to be cooled (heater).