混合工质具有组分优势互补、可按需主动设计的优点，在热力系统中具有十分光明的应用前景。认清混合工质的汽化传热特性和机理是提升其热力系统综合性能的关键。目前对混合工质汽化传热的研究较为欠缺，精细和深入的机理认识缺失，且纯工质的相关结论无法直接推广至混合工质。从纳米尺度、分子微观层面上开展研究能够有效揭示混合工质汽化传热机理。本文以R32/R1234yf混合工质纳米尺度汽化传热过程为主要对象，采用分子动力学模拟与理论研究相结合的方法，分别对加热表面液滴蒸发、悬浮液滴蒸发、加热表面液膜沸腾和气泡生长四个关键过程开展研究，从微观分子层面上深入认识混合工质汽化传热机理。对于加热表面纳米液滴蒸发过程，发现混合工质非均匀蒸发形成液滴内部浓度梯度，驱动内部流动导致三相接触线失稳振荡，振荡幅度与易挥发组分R32的摩尔分数正相关；考虑界面浓度梯度导致的传质阻力影响，发展了半理论模型，对混合工质液滴蒸发速率预测的平均偏差从传统模型的59%减少至26%。对于Kn接近1的纳米悬浮液滴蒸发过程，分子动理论模型和宏观扩散模型对模拟结果的预测偏差较大。考虑气相分子扩散效应修正分子动理论模型，对纯工质液滴蒸发速率预测的精度从67%提升至34%。考虑尺度对导热系数的影响修正宏观扩散模型，对纯工质和混合工质液滴蒸发速率预测精度分别从92%、90%提升至10%和40%。进一步考虑蒸发过程中界面处组分动态变化和浓度梯度作用，提出了更高精度的混合物纳米液滴蒸发理论模型，精度达到11%。针对加热表面上纳米液膜汽化过程，验证了Hertz-Knudsen-Schrage关联式对纯工质和混合工质纳米尺度薄液膜汽化速率预测的适用性；由于R32相较于R1234yf更容易被固体表面吸附，增加易挥发组分R32浓度会使起沸点显著提前，导致混合工质薄液膜更易沸腾。沸腾初期为惯性控制阶段，并出现传热恶化现象，相关机理主要为：各组分扩散速率差异导致界面饱和压力低于名义组分下饱和压力而造成界面传质速率下降。针对加热表面纳米气泡生长过程，增加R1234yf浓度会推迟气泡起沸点、抑制气泡核化和生长，且由于不同工质扩散速率间存在差异，混合工质气泡生长过程更接近纯R1234yf工质。气泡生长速率随壁面亲液特性增强先增后减。随着R1234yf摩尔分数上升，气泡生长速率对润湿性的敏感性增强。通过与液相中气泡生长类比，提出了加热表面气泡惯性控制阶段生长模型，对模拟数据预测的平均偏差低于10%。

Mixture working fluids have the advantages of complementary components and active design, therefore it has a promising future in the application of thermal system. The key to improve the comprehensive performance of the thermal system is to understand the mechanism of vaporization heat transfer of mixture working fluids. At present, there are few studies on the nanoscale vaporization heat transfer of mixture working fluids, the detailed and in-depth understanding of the mechanism is missing, and the relevant conclusions on the vaporization of pure working fluids cannot be directly generalized to mixture working fluids. Researches on nanoscale and molecular level can effectively reveal the mechanism of vaporization heat transfer of mixture working fluids. In this work, R32/R1234yf was taken as the main research object, by combining molecular dynamics simulation and theoretical research, the evaporation of sessile droplet on the heating surface, suspended droplet evaporation, liquid film vaporization and bubble growth were studied respectively, the mechanism of vaporization heat transfer of mixture working fluids was studied at the molecular level.For the evaporation of sessile droplet on a smooth heated surface, it was found that the concentration gradient inside the droplet generated by the non-uniform evaporation of the mixture drove the internal flow and made the contact line oscillate and unstable. The oscillation amplitude of the contact line is positively correlated with the mole fraction of volatile components. Considering the effect of mass transfer resistance caused by interfacial concentration gradient, a semi-theoretical model was developed, and the average prediction deviation of droplet evaporation of mixture working fluids is reduced from 59% of the traditional model to 26%.For the evaporation process of nanoscale suspended droplets with Kn close to 1, the prediction deviations of the kinetic theory model and the macroscopic diffusion-based model are large. The prediction accuracy of droplet evaporation rate of pure working fluids was improved from 67% to 34% by modifying the kinetic theory model considering the molecular diffusion effect in vapor phase. Considering the scale effect, the thermal conductivity in the macroscopic diffusion-based model is modified, the prediction accuracy of droplet evaporation rate of pure working fluids and mixture working fluids is improved from 92% and 90% to 10% and 40%, respectively. Further considering the dynamic change of components at the interface during the evaporation, a more accurate theoretical model for the evaporation of mixture nanodroplet was proposed, with an accuracy of 11%.The vaporization process of nanoscale liquid film on heating surface was studied. The applicability of Hertz-Knudsen-Schrage equation for predicting the vaporization rate of pure and mixture nanoscale liquid film was verified. Since R32 is more easily adsorbed by the solid surface than R1234yf, increasing the concentration of volatile component R32 will significantly advance the boiling point, resulting in easier boiling of the mixture liquid film. The initial boiling stage is inertial controlled stage, and heat transfer deteriorates. The main mechanism is that the interfacial saturation pressure is lower than that under nominal component due to the difference of diffusion rate for each component, and the interfacial mass transfer rate decreases.The nanobubble growth on heated surface was studied. Increasing the concentration of R1234yf can delay the bubble inception time, inhibit the nucleation and growth of bubbles, and the dynamic process of bubble growth of the mixture is closer to that of pure R1234yf due to the difference of diffusion rate for different components. The bubble growth rate increases first and then decreases with the increase of wall lyophilic characteristics. As the mole fraction of R1234yf increases, the sensitivity of bubble growth rate to wetting characteristics becomes stronger. Compared with the bubble growth model in bulk liquid phase, a bubble growth model in the inertial-controlled stage on the heated surface is proposed, and the average prediction deviation is less than 10%.