PCHE is one of compact heat exchanger which can sustain high pressure and high temperature conditions due to the structural rigidity. They are widely chosen as a heat source and sink for a compact supercritical Brayton cycle power conversion system. The densely-stacked structure allows high compactness, and the diffusion-bounded junctions enable high rigidity. However, the optimized channel designs for PCHE is not yet determined. Therefore, we are actively working on understanding what phenomena happen in PCHE and find out the best channel designs for energy system applications.