水基氧化铝纳米流体液滴蒸发过程特性仿真研究
Simulation study on evaporation process characteristics of aqueous alumina nanofluid droplets
摘要：
纳米流体作为一种新型高效的能量输运工质,可以显著提高空调换热器的传热性能。对纳米流体液滴蒸发特性的研究可为其在蒸发器中的强化传热应用提供理论支撑。仿真研究纳米流体液滴的蒸发可以节约实验资源,快速分析各因素对液滴蒸发的影响规律。综合考虑液滴蒸发过程中的恒接触半径(CCR)和恒接触角(CCA)2种蒸发模式,建立了基于动态接触角的纳米流体液滴蒸发模型。仿真研究了水基氧化铝纳米流体液滴蒸发过程中纳米颗粒初始质量分数、基板类型和基板温度对液滴蒸发特性的影响。研究表明,纳米颗粒初始质量分数越大,沉积在三相线处的纳米颗粒越多,接触半径的变化范围越小,液滴的导热性能越强,蒸发速率越快。PDMS基板上纳米流体液滴的蒸发过程包括CCR和CCA 2种模式,而Al基板上仅存在CCR模式;Al基板上纳米流体液滴的平均蒸发速率是PDMS基板上的2.3倍。相比纳米颗粒初始质量分数,基板温度对蒸发速率的影响更为显著,基板温度从室温每升高5 ℃,PDMS基板和Al基板液滴平均蒸发速率分别升高33%和43%。
Abstract：
As a new and efficient energy transport fluid,nanofluids can significantly improve the heat transfer performance of air conditioning heat exchangers.The study on the evaporation characteristics of nanofluid droplets can provide theoretical support for its enhanced heat transfer application in evaporators.The simulation study on the evaporation of nanofluid droplets can save experimental resources and quickly analyse the influence laws of various factors on droplet evaporation.Considering the two evaporation modes of constant contact radius (CCR) and constant contact angle (CCA) in the process of droplet evaporation comprehensively,an evaporation model of nanofluid droplets based on dynamic contact angle is established.The effects of the initial mass fraction of nanoparticles,substrate type and substrate temperature on the evaporation characteristics of droplets during the evaporation process of aqueous alumina nanofluid droplets are simulated.The results show that the larger the nanoparticle initial mass fraction,the more nanoparticles depositing at the three-phase line,the smaller the range of contact radius,the stronger the thermal conductivity of the droplets,and the faster the evaporation rate.The evaporation process of nanofluid droplets on the PDMS substrate includes two modes of CCR and CCA,while only CCR mode exists on the Al substrate.The average evaporation rate of nanofluid droplets on the Al substrate is 2.3 times that of the PDMS substrate.Compared with the initial mass fraction of nanoparticles,the substrate temperature has a more significant effect on the evaporation rate.When the substrate temperature increases by 5 ℃ from room temperature,the average evaporation rates of droplets on the PDMS substrate and Al substrate increase by 33% and 43%,respectively.
Keywords:aqueous alumina; nanofluid droplet; evaporation characteristic; enhanced heat transfer; constant contact radius(CCR); constant contact angle(CCA); dynamic contact angle; heated substrate