Impact of the Phase Change Governing Factors on the Nonlinear Dynamics of a Pulsating Heat Pipe

Abstract

Abstract. Pulsating heat pipes have demonstrated great potential in advanced thermal management owing to their ability to passively transfer heat through self-sustained oscillations of the working fluid. These oscillations, primarily driven by phase-change phenomena at the evaporator, are inherently nonlinear and depend on the dynamic coupling between heat transfer, wall temperature distribution, and fluid motion. Unlike earlier simplified approaches that modeled phase change phenomena using an overall coefficient, the present study develops a nonlinear mathematical model that explicitly accounts for three dominant factors governing phase change, namely, phase-change limit, wall temperature gradient, and evaporation rate. By analyzing the steady-state behavior and temporal evolution of the meniscus position, the system is shown to undergo Hopf bifurcations for each contributing factor, indicating the onset of oscillatory motion. Through numerical continuation and time-series analysis, the combined variation of two factors revealed well-defined stability boundaries separating stable, unstable, and constant-amplitude oscillatory regimes. The results demonstrate that any combination involving the wall temperature gradient and phase-change limit promotes growing, self-sustained oscillations, whereas the evaporation rate alone fails to sustain periodic motion near the instability boundary. This systematic analysis provides a new theoretical framework to identify the operational regions required for continuous and thermally stable performance of PHPs. The study highlights that proper control of wall thickness and heat input is crucial for maintaining the phase-change limit and wall temperature gradient within the oscillatory domain, thereby ensuring safe, efficient, and self-sustained operation under transient conditions.