纳米颗粒添加对熔融盐传热特性的影响

Effects of Nanoparticles Addition on Heat Transfer Characteristics of Molten Salt

熔融盐由于其蒸汽压力低、工作温度高、热稳定性良好等特点,在集中式太阳能热发电系统中作为传热和蓄热工质应用较多。但熔融盐热导率较低,导致发电系统效率降低、能耗增加,发电系统成本升高。向熔融盐中加入纳米颗粒形成熔盐基纳米流体是能够改善熔盐热物性,文章以添加SiO_(2)纳米颗粒的Hitec盐基纳米流体为研究对象,利用平衡分子动力学方法模拟计算热导率,从多角度分析以揭示物理机理。结果表明纳米颗粒质量分数为2%、4%和6%时,纳米流体热导率分别提高了5.75%、6.47%和0.05%。扩散系数结果表明,纳米颗粒添加不会强化基液微对流。分析径向分布函数发现,纳米颗粒添加导致了Na原子和NO_(3)^(-)中N原子间的配位数增加,粒子间作用力增强,引发纳米流体热导率提升。此外,随着温度升高,熔盐纳米流体热导率减小;颗粒质量分数/粒径变大,热导率出现非单调变化。

Molten salt has the advantages of low vapor pressure,high working temperature and good thermal stability,and can be used as heat transfer and heat storage working medium in centralized solar thermal power generation system.However,its thermal conductivity is low,resulting in lower efficiency power generation system,more energy consumption and higher cost.It is an effective way to improve the thermophysical properties of molten salt to form molten salt-based nanofluid by adding nanoparticles into molten salt,so in this paper,the Hitec salt-based nanofluid with SiO_(2) nanoparticles is used as the research object.The thermal conductivity is simulated by the equilibrium molecular dynamics method.Moreover,the physical mechanisms is revealed through analysis from multiple perspectives.The results show that,when the mass fraction of nanoparticles is 2%,4%and 6%,the thermal conductivity of the nanofluid is increased by 5.75%,6.47%and 0.05%respectively.The diffusion coefficient results show that the addition of nanoparticles does not enhance the microconvection in the base liquid.By analyzing the radial distribution function,it is found that the addition of nanoparticles leads to the increase of coordination number between Na atom and N atom in NO_(3)^(-),and the strengthening of the force between particles,which results in the increase of the thermal conductivity of the nanofluid.In addition,with the increase of temperature,the thermal conductivity of molten salt nanofluids decreases,the particle mass fraction/particle size increases and the thermal conductivity changes nonmonotonically.