换热器微细通道纳米流体沸腾混沌特征与强化传热的关系  

Relationship between chaotic characteristics of nanofluid boiling and heat transfer enhancement in microchannels of heat exchanger

作　　者：罗小平[1] 郭峰[1] 王文 廖政标 

机构地区：[1]华南理工大学机械与汽车工程学院,广州510640

出　　处：《农业工程学报》2018年第3期210-218,共9页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金资助项目(21776096)

摘　　要：为探究微细通道内纳米流体流动沸腾系统的传热性能、非线性特性及其相互关系,分别以质量分数为0.05%、0.10%、0.15%、0.20%和0.30%的Al2O3/R141b纳米流体和R141b纯制冷剂为试验工质,在2 mm×2 mm的矩形微细通道内进行流动沸腾试验,计算得到了不同浓度纳米流体的沸腾传热系数,建立了试验段进出口压差时间序列,运用Hurst指数分析、关联维数、最大Lyapunov数和Kolmogorov熵研究了该时间序列的非线性特征,并比较其与传热系数之间的关系,结果表明:相比纯制冷剂,纳米流体流动沸腾系统的混沌程度更强,传热性能也更好;纳米流体的混沌程度随着浓度的升高先增强后减弱,其沸腾传热系数也随着浓度的升高先增加后减小,试验工况下质量分数为0.1%的纳米流体的各项非线性特征量均达到最大值,混沌程度最强,相应的沸腾传热系数也为最大,其平均沸腾传热系数可达4.25 k W/(m^2·K),而纯制冷剂仅为2.42 k W/(m^2·K)。该文采用非线性分析与试验相结合的方法,更能准确描述微细通道沸腾系统的动力学特征,可为进一步研究微细通道纳米流体相变强化传热机理提供参考。Micro channel heat exchanger has become the focus of scholars as a kind of highly efficient heat transfer equipment, and the nanofluid flow boiling heat transfer in microchannels is a hot topic at present. The flow boiling as a vapor-liquid two-phase flow, including a series of sub-processes of generation, growth, detachment and interaction of many boiling bubbles, is complex nonlinear system, and their nonlinear characteristics have an important influence on the boiling heat transfer performance of the entire microchannels. The simple experimental analysis method adopted by scholars does not accurately describe the dynamic characteristics of the flow boiling system in microchannel. Therefore, in order to investigate the heat transfer characteristics, non-linear characteristics and their interrelationships of nanofluid flow boiling system in microchannels, uniform and stable 0.05-0.30 wt% Al_2O_3/R141 b nanofluids were prepared as the experimental working fluid and the experimental platform was built, and the flow boiling test was carried out in the microchannels of 2 mm × 2 mm under the heat flux of 14-46 kW/m^2, mass flow rate of 310.5 kg/（m2·s）, and system pressure of 165 k Pa. The boiling heat transfer coefficient is calculated through the heat transfer model and the univariate time series is established by importing and exporting pressure data through the experimental section. The nonlinear characteristics of the time series are studied by Hurst exponential analysis, correlation dimension, maximum Lyapunov number and Kolmogorov entropy. The relationship between the nonlinear characteristics and the heat transfer performance is also compared. The results show that the boiling heat transfer coefficient of nanofluids first increases and then decreases with the increase of heat flux density under the experimental conditions, and the heat transfer coefficient reaches the maximum at 38 kW/m^2 heat flux density. The flow boiling of the nanofluid Al_2O_3/R141 b and pure refrigerant R141 b in the microchannels

关 键 词：传热 非线性分析 换热器 纳米流体 流动沸腾 微细通道 混沌 

分 类 号：TK124[动力工程及工程热物理—工程热物理]