Thermal-hydraulic performance of ammonia in manifold microchannel heat sink

•Ammonia is used as working fluid in manifold microchannel heat sink for the first time.•The influence of operating conditions on the thermal–hydraulic performance was explored extensively.•The heat sink has outstanding heat dissipation capacity for a hot spot of 1542 W/cm2 and 1 mm × 6 mm with the heating surface temperature of 68.05 ℃ and a pressure drop of 10.6 kPa. With the increasing miniaturisation of electronic devices, the demand for cooling technologies with high efficiency has increased. Therefore, in this study, a manifold microchannel heat sink was designed and fabricated to enhance the dissipating capability of high-heat-flux hotspots. Owing to its excellent thermophysical properties, ammonia was selected as the working fluid, and its thermal–hydraulic characteristics were evaluated. In addition, the effects of flow rate, heat flux, saturation temperature, and inlet conditions were investigated through experiments. High-subcooled inlet experiments revealed that the thermal resistance decreased and pressure drop increased with increasing flow rate. Moreover, localised subcooled boiling was observed near the heated region. In near-saturated inlet experiments, jet impingement and microchannel cooling were identified as the dominant heat transfer mechanisms over different flow ranges. Notably, the higher heat flux, lower saturation temperature, and two-phase inlet condition reduced the thermal resistance under the operating conditions of the study. The proposed heat sink dissipated the heat flux (up to 1542 W/cm2) from the heat source (1 mm × 6 mm) with a pressure drop of 10.6 kPa, and the corresponding heating surface temperature and thermal resistance were 68.05 ℃ and 0.450 K/W, respectively.