As an effective heat transfer medium, Nanofluid is used widely in heat transfer field. However, due to the contra-diction between the heat conductivity coefficient of nanofluid and the cost of nanoparticles, a new mixed nanofluid is developed. In order to investigate the natural convection heat transfer characteristics and the interaction mechanism between nanoparticles, the lattice Boltzmann equations of nanofluid flow and temperature fields are deduced by multi-scale technique based on considering the interaction forces between nanoparticles, and the lattice Boltzmann model of Cu/Al2O3-water mixed nanofluid is established by coupling the evolution equations of flow with temperature fields. Nanoparticles distribution in enclosure and interaction forces between nanoparticles are investigated, it is found that Brownian motion force is far bigger than any other forces, and the effects of temperature difference driving force and Brownian motion force on nanoparticles distribution are biggest. In addition, the effects of nanoparticles fractions and Rayleigh number on natural convection are investigated, and the natural convection heat transfer characteristics of mixed nanofluid (Cu/Al2O3-water) are compared with those of single metal nanoparticle nanofluid (Al2O3-water). It is found that the mixed nanofluid has a higher heat transfer characteristic than other common nanofluid.%纳米流体作为一种较高的导热介质，广泛应用于各个传热领域。鉴于纳米颗粒导热系数和成本之间的矛盾，本文提出了一种混合纳米流体。为了研究混合纳米流体颗粒间相互作用机理和自然对流换热特性，在考虑颗粒间相互作用力的基础上，利用多尺度技术推导了纳米流体流场和温度场的格子Boltzmann方程，通过耦合流动和温度场的演化方程，建立了Cu/Al2 O3水混合纳米流体的格子Boltzmann模型，研究了混合纳米流体颗粒间的相互作用机理和纳米颗粒在腔体内的分布。发现在颗粒间相互作用力中，布朗力远远大于其他作用力，温差驱动力和布朗力对纳米颗粒的分布影响最大。分析了纳米颗粒组分、瑞利数对自然对流换热的影响，对比了混合纳米流体(Cu/Al2 O3-水)与单一金属颗粒纳米流体(Al2 O3-水)的自然对流换热特性，发现混合纳米流体具有更强的换热特性。
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