颗粒团聚对太阳盐纳米流体导热性能的影响特性研究

doi:10.12096/j.2096-4528.pgt.23046

摘要/Abstract

摘要：

目的纳米流体技术是提升太阳能光热电站熔盐储热材料导热性能的重要手段。然而实际熔盐基纳米流体中纳米粒子通常会自发聚集并沉降，进而显著影响储能介质的热导率。为了深入探究熔盐基纳米流体热物性的调控规律，在太阳盐相变介质中分别构建了具有不同分散形态的二氧化硅纳米颗粒。方法基于分子动力学和格子玻尔兹曼方法，重点探讨了体系温度、纳米颗粒的质量分数以及聚集体微观形貌对太阳盐-二氧化硅纳米流体热导率的影响特性。结果添加纳米颗粒能有效提升基液的导热性能。相较于均匀分散的纳米流体，聚集型纳米流体的热导率更高，并且随着团聚颗粒分形维数的增加而降低。此外，纳米流体的热导率与温度、团聚尺寸呈负相关，而与纳米粒子的质量分数、聚集体主链的粒子数量以及其团聚程度呈正相关。结论研究成果揭示了纳米颗粒聚集对相变材料内热输运的作用机制，并为熔盐基纳米流体热物性的设计提供了参考。

关键词: 太阳能热发电, 储热, 纳米流体, 熔盐, 分子动力学, 格子玻尔兹曼方法

Abstract:

Objectives Nanofluid technology is an important means to improve the thermal conductivity of energy storage materials in solar thermal power plants. However, the nanoparticles in actual molten salt based nanofluid usually aggregate and settle down, which significantly affects the thermal performance of the composites. To gain a deeper insight into the variation of thermophysical properties of molten salt based nanofluids, the silica nanoparticles with different aggregation morphologies were constructed in solar salt. Methods The effects of system temperature, mass fraction of nanoparticles, and micromorphology of aggregates were investigated based on the molecular dynamics simulation and lattice Boltzmann method. Results It is found that the inclusion of nanoparticles can effectively enhance the thermal conductivity of the base fluid. Compared with the uniformly dispersed nanofluid, the heat conduction performance of the aggregated nanofluid is better, and it decreases with the increase of fractal dimension of agglomerates. Moreover, the thermal conductivity of nanofluid is negatively correlated with temperature and aggregate size, and positively correlated with mass fraction of nanoparticles, backbone length of each aggregate and degree of agglomeration. Conclusions The research results reveal the mechanism of nanoparticle aggregation on the heat transport within phase change materials and provide critical reference on the design of thermophysical properties of molten salt based nanofluids.

Key words: solar thermal power generation, heat storage, nanofluids, molten salt, molecular dynamics, lattice Boltzmann method

中图分类号:

TK 11

邱立翔, 黄超, 魏高升, 崔柳, 杜小泽. 颗粒团聚对太阳盐纳米流体导热性能的影响特性研究[J]. 发电技术, 2024, 45(5): 878-887.

Lixiang QIU, Chao HUANG, Gaosheng WEI, Liu CUI, Xiaoze DU. Effect of Particle Agglomeration on Thermal Conductivity of Solar Salt Nanofluids[J]. Power Generation Technology, 2024, 45(5): 878-887.

图/表 15

图1 纳米流体的分子动力学模型

Fig. 1 Molecular dynamics model of nanofluids

表1 Buckingham势函数的相关势参数

Tab. 1 Related potential parameters of Buckingham potential function

原子	A_ii / (×4 184 J/mol)	ρ_ii /nm	C_ii /(×10^-60m×4 184 J/mol)	q_i /eV
Na	9 778.06	0.031 7	24.18	1
K	35 833.47	0.033 7	349.9	1
N	33 652.75	0.026 46	259.1	0.95
NO₃^-中O	62 142.9	0.023 92	259.4	-0.65
Si	72 460.64	0.035 1	14 415.29	1.910 241 8
SiO₂中O	15 170.70	0.038 6	617.24	-0.955 209

表2 NO3-中原子相互作用的势能参数

Tab. 2 Potential energy parameters of atomic interactions in NO3-

K_r /(eV⋅10^-20m)	r₀ /nm	K_θ /eV	θ /(°)	K_UB /eV	r_UB/nm
17.534 4	0.126	2.712 2	120	4.960 8	0.219 55

图2 LBM的计算域及边界条件

Fig. 2 Calculation domain and boundary conditions in LBM

图3 纯熔盐弛豫过程的温度波动

Fig. 3 Temperature fluctuation in the relaxation process of pure molten salt

图4 纯熔盐密度实验值与模拟值对比

Fig. 4 Comparison of experimental and simulated values of pure molten salt density

图5 双组分体系串联模型

Fig. 5 Series model for two-component system

图6 λ1∶λ2=1∶5时的温度分布模拟值与解析值对比

Fig. 6 Comparison of simulated and analytical values of temperature distribution when λ1∶λ2=1∶5

图7 不同结构模型的热导率

Fig. 7 Thermal conductivity of different structural models

图8 质量分数对纳米流体热导率的影响

Fig. 8 Effect of mass fraction on thermal conductivity of nanofluid

图9 温度对纳米流体热导率的影响

Fig. 9 Effect of temperature on thermal conductivity of nanofluid

图10 2种模拟方法所得不同体积分数下的热导率

Fig. 10 Thermal conductivity at different volume fractions obtained by two simulation methods

图11 不同聚集程度的纳米流体热导率

Fig. 11 Thermal conductivity of nanofluid with different aggregation degrees

图12 不同主链长度的聚集纳米流体热导率

Fig. 12 Thermal conductivity of aggregated nanofluids with different backbone lengths

图13 不同聚集体尺寸的纳米流体热导率

Fig. 13 Thermal conductivity of nanofluids with different aggregate sizes

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