Dynamic Chaotic Evolution Law and Flow Characteristics of Pulsating Heat Pipes

Heating, ventilation and air conditioning (HVAC) accounts for an overwhelmingly large proportion of building energy consumption. Mass low-grade cold and heat energy dissipates during system operation, endowing pulsating heat pipes (PHPs) with promising application prospects in building energy systems. Combining experimental tests and the phase-space reconstruction method, this paper investigates the intrinsic correlation between the flow behavior of working fluids and chaotic characteristics under varied working fluids, heating powers and liquid filling ratios. The working fluid type dominates the oscillation characteristics of pulsating heat pipes. When distilled water serves as the working fluid, the attractor presents a scattered distribution. In contrast, the PHP charged with HFE-7100 achieves stable unidirectional circulation with high-frequency, small-amplitude pulsation, forming a densely distributed attractor. Increasing the flow velocity of the working fluid drives the attractor distribution to evolve from scattered to concentrated. Intermittent flow of the working fluid induces a multi-temperature-zone distribution on the tube wall, and the attractor takes on a multi-region spiral morphology. A low liquid filling ratio triggers working fluid dry-out, and the attractor trajectory maintains a continuous unidirectional upward trend; by comparison, the attractor shows a multi-region spiral distribution under high filling ratio conditions. Research on chaotic dynamic characteristic identification, evolutionary law analysis and stable domain regulation of pulsating heat pipes can lay a theoretical foundation for structural optimization and operating condition adjustment of high-performance pulsating heat pipe devices for building waste heat recovery.