Chaotic flow in a closed-loop pulsating heat pipe

The wall temperature pulsating of pulsating heat pipes using ultrapure water and phase change microcapsule fluids is tested by experiments and the temperature signals are processed by numerical calculation methods. The chaotic characteristics of vapor-liquid two-phase pulsating are analyzed through chaotic attractors, delay time, embedding dimension, and correlation dimension. It is found that The increasing of concentration of phase change microcapsule fluid weakens the periodicity of temperature pulsating, and the randomness of temperature pulsating can reflect the chaotic characteristics. The distribution of attractors is related to temperature pulsating and can reflect the running of PHPs. The temperature stability of the evaporation section and distribution concentration of attractors gradually increases with the heating power increasing, which shows the better heat transfer performance. The attractor distribution shows a divergent state with larger amplitude and lower frequency because of the less heating power, and the attractors present compact cluster distribution with different delay times because of the higher heating power, indicating that the time series cannot be fully expanded with the lower embedding dimension, and it is necessary to describe the running of working fluid with the higher dimensional space. The delay time roughly shows a decreasing trend with increasing of heating power. The embedding dimension of PHP using phase change microcapsules as working fluid has a higher value than that of ultrapure water during the running, which may be due to the disturbance effect of phase change microcapsule particles. The saturation correlation dimension of the PHP is slightly greater with heating power increasing. The higher the correlation dimension, the more factors that affect the heat transfer of PHPs, which indicate that the more complex running, the stronger sustainability and the better heat transfer.