Thermal Transport in Nanoporous Yttria-Stabilized Zirconia by Molecular Dynamics Simulation

Yttria-stabilized zirconia (YSZ) is widely used as thermal barrier coatings (TBCs) to reduce heat transfer between hot gases and metallic components in gas-turbine engines. Porous structure can generally reduce the lattice thermal conductivity of bulk material, so porous YSZ can be potentially used as TBCs with better thermal performance. In this work, we investigate the thermal conductivity of nanoporous YSZ using the nonequilibrium molecular dynamics (NEMD) simulation, and comprehensively discuss the effects of cross-sectional area, pore size, structure length, porosity, Y₂O₃ concentration and temperature on the thermal conductivity. To compare with the results of the NEMD simulation, we solve the heat diffusion equation and the gray Boltzmann transport equation (BTE) to calculate the thermal conductivity of the same porous structure. From the results, we find that the thermal conductivity of YSZ has a weak dependence on the structure length at the length range from 10 to 26 nm, which indicates that the majority of heat carriers have very short mean free path (MFP) but there exists small percentage (about 3%) of phonons with longer MFP (larger than 10 nm) contributing to the thermal conductivity. The thermal conductivity predicted by NEMD simulation is smaller than that of solving heat diffusion equation (diffusive limit) with the same porous structure. It shows that the presence of pores affects phonon scattering and further affects the thermal conductivity of nanoporous YSZ. The results agree well with the solution of gray BTE with a average MFP of 0.6 nm. The thermal conductivity of nanoporous YSZ weakly depends on the Y₂O₃ concentration and temperature, which shows the phonons with very short MFP play the major contribution to the thermal conductivity. The results help to better understand the heat transfer in porous YSZ structure and develop better TBCs.     

基于锂电池模组的风冷方式研究

风冷技术虽已广泛应用于动力锂电池系统,但目前锂电池系统风冷的研究主要集中在如何利用电芯间隙冷却,电芯排布方式和模组进出风口形式的设计上,然而这些方法在实际应用中具有一定的限制。针对以上问题,本文在模组底部加装导热垫及散热片,同时利用计算流体力学的方法对该技术方案进行数值模拟,并分析对比加装不同形式的散热片,电池模组内电芯温度的差异。结果表明,模组底部加装散热片能够快速的将电芯的热量传递给冷却气流,并有效降低电芯间的温差;交错翅片型散热片的散热性能优于平直翅片型散热片;翅片数量及厚度在一定程度上影响了散热片的散热性能。