接触模式对球床堆有效导热系数影响的数值分析

Effects of Particle Contact Modifications on Effective Thermal Conductivity of a Pebble Bed

为了分析相邻颗粒的接触模式对有效导热系数的影响,数值分析了 3种不同的接触模式下有序堆积球床堆的有效导热系数。首先采用间隙模型分析了不考虑接触导热下的球床堆有效导热系数,然后采用面接触和短圆柱模型分析了考虑接触导热下的球床堆有效导热系数,最后分析了不同温度下接触模式对球床堆有效导热系数的影响。计算结果表明,在不考虑接触导热时,间隙模型下的球床堆计算结果与ZS关联式吻合很好。当考虑接触导热时,由于受网格质量限制,面接触计算模型的接触半径较大,因此计算的球床堆有效导热系数与ZSK关联式的结果相比误差较大;采用短圆柱接触模式计算发现,接触半径越小,计算得到的结果与ZSK关联式的结果吻合越好,因此在网格生成质量允许的情况下,推荐使用较小接触半径的短圆柱接触计算模型。同时发现随着温度的升高,接触模式对球床堆有效导热系数的影响减弱。

To analyze the effects of particle contact treatment on the effective thermal conductivity,three different contact models (gap,overlap and bridge treatment) are adopted to analyze the effective thermal conductivity of several orderly packed pebble beds.The gap treatment is adopted to predict the effective thermal conductivity of a pebble bed without considering the thermal contact conduction,and then overlap and bridge methods are used to calculate the effective thermal conductivity in consideration of thermal contact conduction.Finally,the effects of particle contact modifications on the effective thermal conductivity under different temperatures are analyzed.The results show that without considering the thermal contact conduction,the effective thermal conductivity of a pebble bed can be well predicted with the gap treatment when compared with the ZS correlation.When the thermal contact conduction is considered,the contact radius for the overlap model is relatively large due to the limit of mesh quality,which causes large error compared with the ZSK correlation.The bridge treatment with smaller contact radius would fit better with the ZSK correlation.Therefore,the bridge treatment with small contact radius is recommended if the mesh quality is satisfied.It is also found that the effects of particle contact modifications on the effective thermal conductivity would obviously weaken as the temperature increases.