Study on thermal cycle in oscillating heat pipes by numerical analysis

This paper discusses the thermal cycle found within oscillating heat pipes (OHPs). An OHP is a two-phase heat transfer device using self-exited oscillation. Over the past few decades, a considerable number of studies have been conducted to understand the physics of OHP phenomena. However, little is known about the thermal cycle in OHPs. In this study, we developed a one-dimensional slug flow model to reproduce thermal and hydrodynamic phenomena in OHPs. Fast Fourier transform (FFT) and cross-correlation analysis were used to process oscillation waveform data. A multi-branch OHP consisting of a stainless steel pipe wall and R134a working fluid was simulated. The numerical results revealed pressure propagation within the OHP. Moreover, the results indicated that the vapor volume oscillated with the same frequency as the pressure. Additionally, the vapor plug obtained energy or performed work depending on the direction of pressure propagation. As a result, the propagation of energy was identified as a reason for pressure propagation within the OHP.