不同长径比的分形肋片强化PCM熔化传热数值分析

Numerical analysis of fractal fins with different aspect ratios to enhance phase change material melting heat transfer

为了探究分形肋片强化相变传热的规律,基于相变传热理论和分形理论,建立了分形相变换热器模型,采用热焓-孔隙率法,模拟了分形肋片换热器中PCM熔化传热过程。分析了分形肋片径向长度与换热管道管径及其比值对PCM熔化传热的影响。结果表明,在Fo<0.02时,PCM熔化速率随着长径比的增大而减小;在Fo>0.02时,PCM熔化速率随着长径比的增大而增大并最终趋于平稳。在相同无量纲时刻,随着长径比增加,PCM温度分布的均匀性越好。初始时刻,热流密度随着长径比的增加而减小;熔化后期,热流密度随着长径比增加而增加,并且随着时间的推移维持在较高的稳定水平。在PCM熔化过程中,分形肋片径向长度与换热器换热管径之间存在的最佳比值为12,即在换热管径为10 mm时,分形肋片最佳径向长度为120 mm。这为分形相变换热器的结构设计提供了理论依据。

A fractal phase change heat exchanger model was established to study the law of enhanced phase change heat transfer by fractal fins on the basis of phase change heat transfer theory and fractal theory,and the enthalpy-porosity method was used to simulate phase change material(PCM)melting and heat transfer in the fractal fin heat exchanger.The influence of the radial length of the fractal fins,the diameter of the heat exchange pipe,and their ratio on the melting heat transfer of PCM is analyzed.The results show that when Fo<0.02,the PCM melting rate decreases with the increase in the aspect ratio;when Fo>0.02,the PCM melting rate increases with the aspect ratio and finally stabilizes.At the same dimensionless time,the uniformity of the PCM temperature distribution increases as the aspect ratio increases.At the initial moment,the heat flux decreases with the increase in the aspect ratio;in the late melting stage,the heat flux increases with the increase in the aspect ratio and maintains a relatively high and stable level over time.During PCM melting,the best ratio between the radial length of the fractal fins and the heat exchanger tube diameter is 12;that is,when the heat exchange tube diameter is 10 mm,the best radial length of the fractal fins is 120 mm.This provides a theoretical basis for the structural design of fractal phase change energy storage.