A Novel Approach for Flow Analysis in Pulsating Heat Pipes: Cross-Correlation of Local Heat Flux

Pulsating heat pipe is a promising two-phase heat transfer device that has many advantages such as a simple wickless structure and high thermal performance. Its thermal behavior is inherently time-dependent, and it can also be characterized by substantial spatial variations. However, there are few studies investigating the interaction or similarity of the local physical quantities, such as heat fluxes exchanged between the working fluid and the device wall in adjacent branches. In the present work, a new approach based on the application of cross-correlation analysis to local heat fluxes is proposed to deepen the understanding of the flow characteristics in pulsating heat pipes. The temperature distribution in the condenser of a seven-turn pulsating heat pipe was measured with an infrared camera, changing the power input. The local heat flux distributions were estimated by solving the inverse heat conduction problem in the tube wall. The cross-correlation of the heat fluxes at different positions of central and edge tubes in the condenser was analyzed. The result revealed the different trends in the cross-correlation depending on the power input: there were no clear cross-correlations in 0.5 W, while it was shown more clearly on the diagonal line with increasing power input to 2 W and 3.5 W because of the more activated flow throughout the heat pipe than that of the low power input. Moreover, the results of 3.5 W indicated a synchronized flow. It is suggested that the original approach presented in this work would lead to a deeper understanding of the chaotic fluid oscillation in pulsating heat pipes.