Additive Manufacturing of Capillary-Driven Two-Phase Cold Plates

An additively manufactured capillary-driven two-phase cold plate was fabricated for use in a hybrid two-phase cooling system (HTPCS). The pumped two-phase loop continuously supplies the cold plate with a liquid refrigerant (R245fa), which is transported by capillary action through a wick structure to the heat source. High heat flux cooling is then provided by evaporation at the menisci formed within the wick. The cold plate includes eight heaters that are located at the top and bottom surface of the cold plate. The main significance of the HTPCS lies within cold plate, or evaporator, which prevents flooding of the evaporator wick by balancing pressure drop between the liquid supply manifold and wick, while separating the liquid supply region from the vapor generation region with a non-permeable barrier (NPB). This separation allows for heat transfer by evaporation rather than boiling and enables high heat flux transport. The cold plate, integrated with wick structures and the NPB, is made of an aluminum alloy (AlSi10Mg) through one single direct metal laser sintering process. The present study is performed as a proof-of-concept to evaluate the cooling performance of the additively manufactured cold plate in a recently developed HTPCS developed by the authors. The motivation of this work is to reduce the current multiple labor-intensive fabrication processes related to previous versions of this cold plate into only one single process. The cold plate removes ~ 210 W/cm2 from the heaters; however, the inconsistent trends of thermal resistances, as well as different thermal resistances among heaters, indicate that there are effects caused by external parameter(s) that adversely affect the wicking performance of the evaporation region. Although further detailed research is required to address discrepancies among thermal resistances, current limitations in the fabrication process, such as using internal supports inside the cold plate as well as limitations to decrease the pore size below a threshold value, are identified as possible reasons for inconsistency in thermal resistances. Such limitations need to be addressed through further research into the additive manufacturing processes.