Nanoscale Thin-Film Boiling Processes on Heterogeneous Surfaces

Abstract

Acquiring rapid and efficient boiling processes has been the focus of industry as they have the potential to improve the energy efficiency and reduce the carbon emissions of production processes. Here, we report nanoscale thin-film boiling on different heterogeneous surfaces. Through nonequilibrium molecular dynamics simulation, we captured the triple-phase interface details, visualized the bubble nucleation, and recorded the internal fluid flow and thermal characteristics. It is found that nanoscale thin-film boiling without the occurrence of bubble nucleation shows excellent heat and mass transfer performance, which differs from macroscale boiling. In general, rough structures advance the onset time of stable boiling and improve the efficiency. The heat transfer coefficient and heat flux on a rough hydrophilic surface respectively reach to 7.43 × 104 kW/(m2·K) and 1.3 × 106 kW/m2 at a surface temperature of 500 K, which are 100-fold higher than those of micrometer-scale thin-film boiling. However, due to the resultant vapor film trapped between the liquid and the surface, the rough hydrophobic surface leads to heat transfer deterioration instead. It is revealed that the underlying mechanism of regulatory effects resulting from surface physicochemical properties is originated from the variation of interfacial thermal resistance. It is available to reduce the overall interfacial resistance and further improve the heat and mass transfer efficiency through increasing surface roughness, enhancing surface wettability, and increasing the area proportion of the hydrophilic region. This work provides guidelines to achieve rapid and efficient thin-liquid-film boiling and serves as a reference for the optimized design of surfaces utilized for high-heat flux removal through vaporization processes.

Sequential Self-Propelled Morphology Transitions of Nanoscale Condensates Diversify the Jumping-Droplet Condensation

“…To delve deeper into the morphological evolutions of nanoscale condensates during condensation, particularly the incipient behaviors of nucleating embryos, largescale MD simulations were conducted as depicted in Figure 1. In the model system with the dimensions of 54.3 nm  54.3 nm  54.3 nm, the nanopillar surfaces with various topologies and wettability (see Table S1 in Supplementary Material (SM) for detailed geometric dimensions, including the width 𝑊 , spacing 𝑆 and height 𝐻 of the nanopillars, the roughness and the solid fraction of surface) were initially submerged in the saturated water vapor, and the bottom substrate is divided into the fixed layer, the phantom layer and the conduction layer [44]. For convenience, all geometric dimensions are normalized by 𝑊 (3.1 nm), and the dimensionless parameters are presented with an asterisk, e.g., 𝑆 * = 𝑆/𝑊 , 𝐻 * = 𝐻/𝑊 .…”