Functional morphology change of TPMS structures for design and additive manufacturing of compact heat exchangers

Recent advances in additive manufacturing (AM) have driven the development of triply periodic minimal surfaces (TPMSs) for application in heat exchangers (HXs). Although a TPMS structure provides a large area density and thus enhances the heat exchange capability, additional design modifications are required for its use as an industrial HX. First, the flow of hot and cold fluids inside the TPMS channels must be controlled to enhance the heat exchange capability. Secondly, the flow resistance inside the TPMS channels must be reduced. In this study, a mathematical gradation method was proposed to fulfill these requirements by locally changing the TPMS morphology. Three mathematical filters were developed to add functionalities to the TPMS-based HX: (i) a selection filter for the inlet and outlet, (ii) a barrier filter for controlling the flow direction, and (iii) a boundary filter for reducing the flow resistance. Numerical simulations were conducted to investigate the effects of these filters on the flow resistance inside the TPMS channels. Pressure drop tests were performed using the corresponding TPMS HXs fabricated by polymer AM, and it was concluded that the resulting pressure drop decreased by 85% when a boundary filter was applied. Heat exchange tests were then conducted using the optimal HX design fabricated by metal AM, and the resulting heat exchange capability (i.e., the overall heat transfer coefficient) was more than twice that of existing products, showing that the developed functional gradations of TPMS structures are beneficial for enhancing the heat exchange capability of additively manufactured HXs.