Fabrication and capillary characterization of multi-scale microgroove wicks for ultrathin phase-change heat transfer devices

Multi-scale microgroove wicks (MWs) with the features of micro fins, micropillars, and reentrant cavities were fabricated for the application in ultrathin phase-change heat transfer devices. Wire electrical discharge machining (WEDM), electrical discharge shape machining (EDSM), micro-milling, and grinding were used to fabricate MWs with the same design parameters. The structural features of the MWs were characterized by SEM and their capillary performances were evaluated through the capillary rise test. The machining methods affected the structure characteristics of MWs greatly, i.e., MW fabricated by the combination of WEDM and EDSM (MW-WE) maintained the best forming shape, while MW fabricated by micro-milling deformed severely and some micropillars even disappeared. The capillary rise tests were conducted with ethanol and acetone as the working fluid, respectively. MWs showed similar capillary performances under both working liquids. MW-WE maintained the best capillary performance while MW fabricated by micro-milling performed worst. The wicking height and capillary parameter of MW-WE achieved 60.4 mm and 1.57 μm, respectively, which were about twice and 4.62 times that of MW fabricated by micro-milling. The superior capillary performance of MW-WE was attributed to the fluent microgrooves, capillary value effect induced by reentrant cavities, and rough surfaces.