Future aircraft power electronics requires careful management of the heat generated by the resistors. This involves designing and optimising more efficient compact heat exchanges (HEX). In this paper, a cold plate HEX will be defined in detail such that other researchers can make use of it for their future comparative and validation studies. High-fidelity simulation results for the traditional, namely serpentine cooling passages will be provided and compared to different topology optimised shapes. In particular, a class of triply periodic minimal Surfaces (TPMS) namely Gyroids and Diamonds are used as initial shapes for the fluid passages. The design space is made of the TPMS periods in three x, y & z directions, and their relative thickness variations. The objective functions defined as the peak surface temperature, gradient of the temperature and total pressure, all of which are aimed to be minimised. The coolant fluid is a mixture of water and ethylene-glycol mixture. The performance of the HEX is assessed using a high-fidelity CFD model making use of conjugate heat transfer by solving the RANS equations with k-ω SST model in Ansys Fluent. Different fluid and solid meshes have been generated using ICEM and an in-house version of the Boxer, a cut-cell Cartesian meshing tool. A grid-independent solution was sought, aiming for a y+ of 1 on all viscous surfaces.