Effect of wettability and surface roughness on flow and heat transfer characteristics in nanochannels

The flow and heat transfer processes of liquid argon within nanochannels with random roughness are investigated using the molecular dynamics method. This study explores the effects of surface roughness and wettability on flow and heat transfer performance. The results indicate that both surface roughness and wettability significantly influence temperature jumps, velocity slip, flow resistance, and temperature distribution. Specifically, hydrophilic surfaces can reduce temperature jumps and velocity slip due to their enhanced ability to adsorb liquid atoms, which effectively improves heat transfer while simultaneously increasing flow resistance. The fractal dimension D characterizes the surface roughness, which decreases as D increases. Additionally, both the Nusselt number and drag coefficient decrease with increasing D. In this study, we investigate cases where D ranges from 2.5 to 2.9, with D = 2.5 representing the highest roughness, and the smooth channel corresponding to the lowest roughness. For hydrophilic nanochannels at D = 2.5, the Nusselt number and drag coefficient increased by factor of 2.2 times and 5.2 times compared to smooth channels, respectively. For hydrophobic nanochannels at D = 2.5, the Nusselt number and drag coefficient increased by a factor of 4.5 times and 29.1 times compared to smooth surface channels, respectively. Considering both flow and heat transfer performances, the best comprehensive performance is achieved with D = 2.8 for channels with hydrophilic surfaces and D = 2.6 for channels with hydrophobic surfaces. This work systematically investigates the coupled effects of random roughness and wettability on the flow and heat transfer characteristics in nanochannels, providing new theoretical insights for optimizing nanochannel design.