超临界CO2在螺旋管式冷却器内的传热特性研究

螺旋管结构紧凑、换热效率高,在CO₂气体冷却器中应用广泛. 超临界CO₂热物性变化剧烈,其在螺旋管内的传热特性异常复杂. 通过对不同冷却热流密度和质量流速工况下的数值模拟发现,螺旋管内超临界CO₂传热系数沿流动方向呈近似抛物线分布; 冷却热流密度越大,传热系数峰值越高,出现峰值的流动转角越小; 质量流速越大,传热系数峰值越高,出现峰值的流动转角越大; 不同热流密度与质量流速的比值决定整个流动方向传热系数的涨落,基于此提出了一个适用于均匀冷却螺旋管内超临界CO₂传热计算的关联式,可为螺旋管式气体冷却器的优化与设计提供参考.

Study on the Heat Transfer Characteristics of Supercritical CO2in Helical Tube Gas Cooler

With compact structure and high heat exchange efficiency,helical tube is widely used in CO₂ gas cooler. The thermophysical properties of supercritical CO₂ change dramatically which makes the heat transfer characteristics of supercritical CO₂ in helical tubes more complicated. Through the numerical simulation of different conditions of cooling heat flux and mass flux,it is found that the distribution of heat transfer coefficient of supercritical CO₂ in the helical tube is approximately parabolic along the flow direction. The peak value of heat transfer coefficient(PV-HTC)increases with the increase of cooling heat flux,while where the PV-HTC appeared,the flow swirl angle shows the opposite tendency. The PV-HTC increases with the increase of mass flux,and where PV-HTC appeared,the flow swirl angle shows the same tendency. Since the ratio of heat flux to mass flux determines the distribution of heat transfer coefficient along the flow direction,a correlation suitable for supercritical CO₂ heat transfer calculation in uniformly cooled helical tube is proposed,which can provide a reference for optimization and design of helical tube gas cooler.