轴向非均匀热流条件下超临界二氧化碳垂直管内换热特性

Heat transfer characteristics of supercritical carbon dioxide in vertical tube under axial non-uniform heat flux

针对超临界二氧化碳(S-CO_(2))燃煤锅炉冷却壁热边界条件的实际分布,采用SST k-ω低雷诺数湍流模型,数值模拟研究了半周加热轴向非均匀热流作用下S-CO_(2)在垂直圆管内的传热特性,分析了不同热流分布、质量流速对换热性能以及圆管内壁温度分布的影响。研究结果表明:轴向非均匀热流分布对S-CO_(2)传热具有显著影响,在平均热流相同的条件下,相较于均匀热流分布,轴向非均匀热流分布下总传热系数最大提高了约8%;轴向非均匀热流分布对传热恶化有抑制作用,有效降低了壁温峰值点;非均匀热流条件下,S-CO_(2)传热主要受类气膜厚度、类气膜导热系数及近壁区定压比热容的影响较大。研究结果可为燃煤S-CO_(2)锅炉设计提供理论指导。

In view of the actual distribution of heat boundary conditions on the cooling wall of supercritical carbon dioxide(S-CO_(2))coal-fired boiler,the heat transfer characteristics of supercritical CO_(2) in a vertical circular tube under axial non-uniform heat flux were numerically studied by using SST k-ωlow Reynolds number turbulence model.The influence of different heat flux distribution,mass flux on heat transfer performance and wall temperature distribution was analyzed.The results show that the axial non-uniform heat flux distribution has a significant effect on the heat transfer of S-CO_(2).Compared with the uniform heat flux,the total heat transfer coefficient under the axial non-uniform heat flux increases by about 8%.The non-uniform distribution of axial heat flux can inhibit the heat transfer deterioration and effectively reduce the peak wall temperature.Under the condition of non-uniform heat flux,the heat transfer of S-CO_(2) is mainly affected by the thickness of the gas-like film,the thermal conductivity of the gas-like film and the specific heat near the wall.The results provide theoretical guidance for the design of supercritical CO_(2) boiler.