非能动传热球床堆有效导热系数的壁面效应分析

本文针对非能动传热机制下简单立方球床堆有效导热系数进行了数值研究,根据有效导热系数的空间分布特性,对球床堆的近壁面区域和主体区域作了划分;分析了不同非能动传热机制下的有效导热系数的壁面效应;最后分析了导热、辐射和自然对流对近壁面和主体区域有效导热系数的贡献。结果发现,近壁面区域是在壁面附近一个球径范围内的区域;由于辐射和自然对流的影响,相同温度下近壁面有效导热系数比主体区域的有效导热系数小了近15%。当温度分别超过950 K和1080 K时,辐射成为球床堆主体区域和近壁面区域的主导传热机制;自然对流对有效导热系数的贡献并不大,当温度超过600 K时,自然对流可以忽略。研究结果可以为高温球床堆的设计与优化提供理论基础。

Wall Effect Analysis for Effective Thermal Conductivity of Pebble Beds Under Passive Heat Transfer Mechanism

In the present study,the effective thermal conductivity in a simple cubic pebble bed under passive heat transfer mechanism is numerically studied.Near-wall regions and bulk regions are defined according to effective thermal conductivity distributions.The wall effect for effective thermal conductivity under different heat transfer mechanism is studied.At last,the contributions of the conduction,radiation and natural convection to effective thermal conductivity in near-wall regions and bulk regions are analyzed.It is found that near-wall regions can be defined as within one pebble diameter distance from walls.Because of the radiation and natural convection,the effective thermal conductivity in near-wall regions is about 15%lower than that in bulk regions at the same temperature.The radiation is the dominant heat transfer mechanism in the bulk regions or near-wall regions when the temperature is over 950 K or 1080 K.The contribution of natural convection is relatively small and the natural convection could be ignored when the temperature is over 600 K.The results could provide the theoretical basis for the design and optimism of high-temperature pebble beds.