Molecular dynamics simulation on evaporation of a suspending difluoromethane nanodroplet
Molecular dynamics simulation on evaporation of a suspending difluoromethane nanodroplet
复制标题
悬浮二氟甲烷纳米液滴蒸发的分子动力学模拟
DOI：
10.1016/j.ijheatmasstransfer.2020.120024
复制
发表时间：
2020
影响因子：
5.2
通讯作者：
Yuanyuan Duan
中科院分区：
文献类型：
--
作者：
xinghui Wu;Zhen Yang;Yuanyuan Duan
纳米液滴蒸发是广泛存在于自然界和工业应用中的基本过程。二氟甲烷（CH2F2，又称“R32”）以其优异的热物理特性在制冷、热泵、有机朗肯循环等领域受到越来越多的关注。采用分子动力学模拟方法研究了R32纳米液滴在大空间中的蒸发过程。研究了蒸发过程中不同条件（液滴尺寸、初始温度和环境温度）下液滴的动态蒸发特性，定量分析了不同参数对蒸发速率的影响。将模拟结果与基于扩散模型和动力学模型的计算结果进行了比较。根据蒸发过程的密度、温度场和速度分布等动态规律，对各模型的计算精度进行了评价，并对模型预测与模拟结果偏差的原因进行了分析。结果表明，环境温度和初始饱和温度的升高可导致液滴蒸发速率显著增加，缩短液滴达到准稳态蒸发阶段所需的预热时间。液滴尺寸的增加也会增加预热时间，但对蒸发速率没有显著影响。对于本文研究的蒸发情景（Knudsen数（Kn）近似为1），现有的动力学模型修正方法可以提高R32液滴准稳态蒸发阶段蒸发速率的预测精度。直接应用基于扩散的模型预测偏差较大，考虑尺度效应对导热系数进行修正可以显著提高预测精度。(C)2020爱思唯尔有限公司保留所有权利。
Nanodroplet evaporation is a basic process widely existing in nature and industrial applications. Difluoromethane (CH2F2, also called "R32") has attracted more and more attention in refrigeration, heat pump, Organic Rankine Cycle and other fields because of its excellent thermophysical characteristics. In this work, the evaporation process of R32 nanodroplet in large space is studied by means of molecular dynamics simulation. This work focuses on the dynamic evaporation characteristics of droplets under different conditions (droplet size, initial temperature, and ambient temperature) in the evaporation process, and quantitatively analyzes the effects of different parameters on the evaporation rate. The simulation results were compared with the results calculated from the diffusion-based model and the kinetic model. Based on the dynamic law of evaporation process, such as density, temperature field and velocity distribution, the calculation accuracy of each model is evaluated, the reasons for the deviation between model prediction and simulation results are also discussed. The results show that the increase of ambient temperature and initial saturation temperature can lead to a significant increase of droplet evaporation rate, and shorten the pre-heating time needed for droplet to reach quasi-steady evaporation stage. The increase of droplet size also increases pre-heating time, but has no significant effect on evaporation rate. For the evaporation scenario studied in this paper (Knudsen number (Kn) similar to 1), the existing modification methods of the kinetic model can enhance the prediction accuracy of the evaporation rate of R32 droplets in the quasi-steady evaporation stage. The prediction deviation of diffusion-based model applied directly is large, the accuracy of prediction can be significantly improved by correcting the thermal conductivity considering the scale effect. (C) 2020 Elsevier Ltd. All rights reserved.