On the interaction between liquid slug and vapor bubble in the chaotic operation of pulsating heat pipe

Abstract

A pulsating heat pipe has shown promising results in heat transfer enhancement for several industrial applications. Despite having multiple advantages in the design and physics-based parameters, its applications are still limited due to the lack of understanding of the dynamics of the chaotic interaction of the liquid slug and vapor bubble. The randomly distributed liquid slug and vapor bubble start oscillating upon applying the heat at the evaporator section. A transition from the self-sustained oscillatory to chaotic operation in the pulsating heat pipe has been observed in various experimental studies. However, there are only a few works explaining the chaotic interaction of liquid slugs and vapor bubbles. We present the analysis of the oscillatory behavior of the position of the liquid slug in the pulsating heat pipe using a nonlinear mathematical model. The identification of various operating regions in the parameter space using the bifurcation analysis reveals the presence of a route to chaos by the period-doubling bifurcation. The fast Fourier transform of the temporal evolutions confirms the presence of the period doubling phenomena. Furthermore, the Lyapunov exponent and the correlation dimension are used to detect chaos and quantify the dimension of the chaotic attractor, respectively. Moreover, the Hurst exponent is used to determine the persistency of the oscillations, which indicates that the oscillations are weakly persistent in the chaotic regime. The transition to the chaotic regime is analyzed by period doubling, and a change in the frequency beyond period-doubling shows a gradual shift to the chaotic operation.