Nonlinear Dynamic Analysis of Temperature Characteristics in Oscillating Heat Pipes Under Radial Rotations

Radial rotating oscillating heat pipes (R-OHPs) have excellent thermal performance and great potential for application in the thermal management of rotatory machinery. However, the heat transport behavior and temperature characteristics of R-OHPs are complex, and their understanding is still limited, hence necessitating further research. In this study, thanks to an experimental investigation involving a copper R-OHP running with acetone and water, its thermal performance is evaluated, and then the temperature characteristics are analyzed by nonlinear dynamic analysis. The study reveals that the effective heat transfer coefficient of R-OHPs undergoes a notable increase with rising rotational speed, exhibiting a peak at a threshold speed value. Such a peak is present irrespectively of the working fluid, and, after exceeding the threshold, higher rotational speeds lead to a lower thermal performance. Based on nonlinear dynamic analysis, the power spectrum density of the evaporator temperature indicates a lack of dominant frequency in temperature signals, suggesting a complex behavior characterized by random oscillations of vapor slugs and liquid plugs. In order to better understand how strong the chaotic behavior is, an autocorrelation analysis was carried out, the OHP at static state has a stronger chaos than R-OHPs. The correlation dimension analysis of the evaporator temperature provides values ranging from 1.2 to 1.6, which together with the Lyapunov exponent calculations, further support an evident chaotic nature of R-OHPs.