纳米复合相变材料融化传热特性的格子Boltzmann方法研究

Lattice Boltzmann Simulation of Melting of Composite Phase Change Materials Inserted with Nanoparticle

基于双分布函数模型方法,建立了一个模拟伴随有液相自然对流的纳米复合相变材料融化传热过程的格子Boltzmann方程模型.其中温度分布函数方程的构建采用直接基于焓方程的方法 ,避免传统方法需要迭代处理源项,提高了计算效率.应用该模型对方腔内纳米流体自然对流传热过程进行模拟,模拟结果与文献结果吻合较好;在此基础上对纳米复合相变材料融化过程进行模拟.结果表明,有效黏度系数的变化对纳米复合相变材料融化传热有着至关重要的影响,偏高的黏度系数可能会抑制纳米流体相变换热过程.此外,在给定的纳米粒子体积份额情况下,区域相变材料融化传热性能随Rayleigh数的增大而增强.

A lattice Boltzmann equation model is proposed to characterize the melting processes of composite phase change materials（PCMs） inserted with nanoparticle based on the double-distribution-function approach, where natural convection of melted liquid was considered. The temperature distribution function was adopted directly based on enthalpy equation, which avoided treating source term by iteration steps like traditional method and improved the computational efficiency. The natural convection of nanofluid in a cavity was simulated by the present model and the numerical results were consistent with previous solutions. Based on this, lattice Boltzmann simulations were undertaken for the melting of PCMs filled with nannoparticle in a square enclosure. The results indicated that the effective dynamic viscosity has a strong influence on the melting heat transfer characteristics of composite PCMs. Significant difference in the effective dynamic viscosity enhancement estimated from two adopted formulas leads to contradictory results concerning heat transfer efficacy of the composite PCMs, so that the melting heat transfer across the enclosure can be found to be enhanced or mitigated with respect to the base PCMs. In addition, the melting heat transfer of the composite PCMs becomes much stronger with the increasing of the Rayleigh number at the fixed volumetric fraction of nanoparticle.