Effects of hydrophilic-hydrophobic ratios on single-phase forced convection performances with macroscopic hydrophilic-hydrophobic hybrid surfaces

Abstract

Flow drag and heat transfer are important performance metrics in heat exchanger applications, which have profound significance for improving energy utilization efficiency. Hydrophobic surfaces can reduce flow drag but weaken heat transfer due to air cavity thermal resistances. Moreover, existing microscopic hydrophilic-hydrophobic hybrid surfaces have application limitations due to scale effects. In this study, six macroscopic hydrophilic-hydrophobic hybrid surfaces with different hydrophilic-hydrophobic ratios are designed to harmonize flow and heat transfer performances. Based on simplifying the macroscopic hybrid surface model to a single-phase flow model using the flow and experimentally obtained thermal boundary conditions, the performances and influencing mechanisms under different hydrophilic-hydrophobic ratios are investigated using COMSOL software. The results show that hybrid surfaces with hydrophobic substrate have a higher drag reduction rate of up to 27.97% due to the increasing hydrophobic proportion. Conversely, hybrid surfaces with hydrophilic substrate can obtain a higher Nusselt number, with an attenuation rate of less than 10%, which can maintain the heat transfer performance. Hydrophilic substrate hybrid surfaces’ efficiency evaluation criteria are all larger than 1. Among them, the hybrid surface with the hydrophilic-hydrophobic ratio 1:1 has a maximum enhancement rate of 14.76%, effectively harmonizing the flow and heat transfer performances. Through the performance and eddy analyses, the disturbance caused by the backflows and eddies on the hydrophilic/hydrophobic interfaces is also one of the factors influencing performances, except for the hydrophobic proportion. This study is of great significance for designing macroscopic hydrophilic-hydrophobic hybrid surfaces and improving the comprehensive efficiency of heat exchanger equipment.