中低负荷下脉动热管壁温信号的分形特性分析

Fractal characteristics of temperature oscillation in pulsating heat pipe under medium-low load

运用功率谱、小波分解、相空间重构、关联维数计算等非线性分析方法对脉动热管壁面温度波动信号分析。表明：功率谱呈现连续谱线,时间序列存在自相似性,展现温度波动信号的混沌行为;小波分解表现出温度波动的分形特性;重构吸引子展现出4种不同的空间分形结构,说明温度信号波动属于分形下的混沌行为。计算分形维数与传热性能的关系,发现系统存在3～6个分形维;随嵌入维数的增加,分形速度关系为R134a大于丙酮大于去离子水,基本表现为分形维数越大,传热性能越好。并发现关联维和热阻成负相关关系。

Various method, including analyses of power spectrum, wavelet decomposition, pseudo-phase-plane trajectories and correlation dimension, were used to analyze the non-linear dynamics characteristics of temperature oscillation signal of pulsating heat pipes（PHPs）. A continuous line, self-similarity were identified under different sampling frequency, and the chaotic behavior of temperature oscillation signal was shown by power spectrum diagram. Wavelet decomposition indicated fractal characteristics of temperature oscillation. Four types of attractors were identified under different power inputs, which showed different space fractal structure. It was found that the temperature fluctuations belong to fractal chaotic behavior. All of the calculated fractal dimension showed that the system existed 3—6 fractal dimension. With the increase of embedding dimension, the fractal speed relations as R134 a was greater than acetone, and acetone was higher than deionized water. For most runs, the large correlation dimensions were corresponded to better thermal performance.