Enhancing Liquid–Vapor Phase-Change Heat Transfer with Micro/Nano-Structured Surfaces

Abstract

Liquid–vapor phase-change heat transfer plays an important role in many industrial systems, ranging from power generation and air conditioning to water desalination, food processing, and thermal management of electronics and data centers. Recent advances in micro/nanofabrication have enabled desirable manipulation of multiscale dynamics governing droplet/bubble motion and capillary liquid flows for highly efficient phase-change heat transfer. However, there lacks a comprehensive review on the design and fabrication of micro/nanostructured surfaces with controlled morphology and wettability, to enhance the diverse phase-change heat transfer processes. Here, we review the advances in micro/nanostructuring for phase-change heat transfer applications. While traditional mechanical machining and sintering have commonly been used to manufacture structures down to sub-millimeter or micron scales, advanced micro/nanostructure fabrication methods such as laser texturing, oxidation, lithography-based etching, and spray coating are being utilized to manufacture surfaces with hierarchical structures or heterogeneous wettability. Droplets, bubbles, and liquid films generally experience a multiscale life cycle from nanometer scale to millimeter scale in the phase-change processes, including condensation, pool boiling, capillary-driven evaporation, and liquid film boiling. Micro/nanostructured surfaces need to be designed to coordinate different requirements of the surface wettability and morphology for the multiscale dynamics of droplets, bubbles, and films including increased nucleation, facilitated growth, accelerated transport, and departure. For active phase-change processes with pump-driven flow, including flow condensation, flow boiling, jet impingement boiling, and spray cooling, the enhancement strategies using functionalized micro/nanostructures focus on sustaining thin liquid films, strengthening thin film evaporation, promoting nucleate boiling, and regulating bubble departure within the convective liquid film. We conclude this review by a short discussion on the practical aspects of micro/nanoenabled phase-change heat transfer including reliability and scalability.