Temporally resolved temperature and pressure drop, and flow visualization at G = 300 kg/m² · s. (a) Midpoint backside surface temperature T₃ and pressure drop across a smooth surface microchannel and a structured surface microchannel S4 at q″ = 430 W/cm². Insets are optical images of a smooth bottom channel surface and a structured bottom channel surface (S4). Midpoint backside surface temperature T₃ and pressure drop of a smooth surface microchannel and a structured surface microchannel S4 at (b) q″ = 520 W/cm² and (c) q″ = 615 W/cm². The uncertainties of the temperature and pressure drop measurement were approximately ±2 °C and ±300 Pa.