Heat sinks are components usually present in electronic devices to keep the temperature below critical values- set by constructors to guarantee proper functioning. Moreover, the widespread trend toward electronics miniaturisation results in power per volume unit increase. This translates to higher temperatures that could damage the device. Innovative solutions are required to improve the cooling of miniaturized electronics. One option is to use triply periodic minimal surfaces (TPMS), which are porous structures with zero mean surface curvature and a high surface-to-volume ratio (s/V)—a feature that enhances cooling, leading to advantages in heat dissipation. However, despite these benefits, the complexity of TPMS structures introduces tortuosity in the liquid cooling flow, resulting in a pressure drop that could make the cooling process costly. Since the improvement in cooling and the pressure drop are correlated, it is essential to design TPMS structures that balance these two effects to achieve optimal performance. This research simulates the outcomes of TPMS-gyroid structures in a liquid-cooled heat sink-like demonstrator with a U-shaped channel, using Computational Fluid Dynamics (CFD) software. The demonstrator consists of a modular aluminum box 336x180x44 mm^3 with a liquid circuit of 66x10 mm^2 cross section, inlet and outlet connectors with inlet volume flow 8 l/min at 23 °C, 18 resistances on top to generate heat sources for a total of 400 W, and AlSi10Mg gyroid inserts inside the cavity. Temperatures on the box top and the pressure drop at the circuit outlet were recorded and compared for each simulation. Different scenarios were simulated to investigate the effect of gyroid structure features (unit cell size 10x10x10 mm^3). Four wall thicknesses were considered: 0.5, 1.0, 1.5 and 2.5 mm. Width effect was investigated comparing two scenarios: three structures positioned underneath the heat sources and a single structure, occupying respectively the 68.2% and the 100% of the channel width. The simulations demonstrate that the best compromise between minimizing pressure drop and maximizing cooling efficiency is achieved with a gyroid insert having a width equal to the circuit channel and a wall thickness of 1.0 mm.