非均匀润湿性微纳复合结构强化沸腾换热机理研究

The current heat transfer structures with uniform wettability and single dimension cannot satisfy the multiple requirements of eliminating the boiling hysteresis phenomenon,incresing the heat transfer coefficient,prohibiting the flow instability and increasing the critical heat flux. This project proposes a new scientific concept of coupling the wettability gradient and Micro/Nano structural gradient, which will enhance the heat transfer performance dramatically. Three kinds of new structures based on the gradient synergy criteria will be constructed and the mathematical model for structural characterization will be established. Experimental investigations will be performed to discolse the heat transfer enhancement mechanism with the proposed multi-scale and non-uniform structures. The bubble dynamics, flow pattern transitions, heat transfer enhancement features, instabilities as well as the critical heat fluxes will be focused. Based on the experimental data, a new mathematical model will be proposed. The Lattice Boltzmann method will be coupled with the finite volume analysis to conduct the multi-scale numerical investigations. By the theoretical investigations, a mechanism model will be provided and the optimization criteria for the structural construction will be proposed. Based on the gradient synergy concept, a novel vapor chamber and a new microchannel evaporator will be designed, fabricated and tested, respectively. The novel concept of coupling wettability gradient and Micro/Nano structural gradient for boiling heat transfer enhancement is of scientific and practical values, providing a new perspective for boiling heat transfer investigations.

针对沸腾系统中均匀润湿性表面和单一尺度结构无法同时满足减小沸腾启动过温、增大传热系数、抑制不稳定性及增大临界热流密度的多重需求，本项目提出采用具有非均匀润湿性的微纳复合结构强化沸腾传热的科学构想。围绕"跨尺度结构耦合非均匀润湿条件下的沸腾传热机理"这一核心科学问题，优化制备具有非均匀润湿性的微纳复合新结构并建立结构与性能之间的定量表征；系统开展非均匀润湿性微纳复合新结构强化沸腾传热的实验研究，包括汽泡动力学特性、流型转换特性、不稳定性、传热系数变化特性及临界热流密度条件下传热恶化的发生机理等;采用格子Boltzmann方法和有限容积法耦合进行多尺度数值研究，建立非均匀润湿性微纳复合结构强化传热机理模型和优化设计准则；针对池沸腾和流动沸腾，分别采用该创新强化传热原理优化设计高性能蒸汽腔和微通道蒸发器。本项目提出的"非均匀润湿性微纳复合结构强化沸腾传热"具有较强科学创新性，它即适用于池沸腾也适用于流动沸腾，将为沸腾传热的研究提供新视角。

针对均匀润湿性表面和单一尺度结构无法同时满足减小沸腾启动过温、增大传热系数、抑制不稳定性及增大临界热流密度的多重需求，本项目提出采用具有非均匀润湿性的微纳复合结构强化沸腾传热的科学构想。围绕“跨尺度结构耦合非均匀润湿条件下的沸腾传热机理”这一核心科学问题开展系统的理论、数值模拟以及实验研究，采用电刷镀工艺、高温热氧化法以及MEMS工艺优化制备了具有非均匀润湿性的微纳复合新结构并建立了结构与性能之间的定量表征；系统开展了非均匀润湿性微纳复合新结构强化沸腾传热的实验研究，获得了汽泡动力学特性、流型转换特性、不稳定性、传热系数变化特性及临界热流密度等;采用Fluent软件VOF方法，结合UDF，对不同润湿性微结构表面的气泡动力学特性以及分割式微结构强化两相流换热特性进行了数值模拟，揭示了非均匀润湿性微纳复合结构强化传热机理，本项目制备的非均匀性微纳复合结构与光滑表面相比，最大换热系数提升6.3倍，临界热流提高60%，并发现由加热表面液体补充路径决定的两类气泡生长模式，本项目成果为沸腾传热强化技术的研究提供新视角。