Chaos in pulsating heat pipes

The oscillating or pulsating heat pipe (OPH or PHP) is a very promising heat transfer device. In addition to its excellent heat transfer performance, it has a simple structure. Due to essential applications of pulsating heat pipes in several areas of industry, study of its mechanism, behavior and performance is crucial. Several theoretical, numerical and experimental investigations have been carried out to get better understanding and solving of the issues in pulsating heat pipes. Despite simple structure of PHPs, it has a complicated behavior. Existence of chaos in the system is one of the significant reasons for such complicated behavior. In this chapter, numerical study of the chaotic behavior in pulsating heat pipes has been implemented using quantitative approaches such as spectral analysis of time series, correlation dimension, autocorrelation function (ACF), Lyapunov exponent, and phase space reconstruction. In addition, volume fraction of liquid and vapor has been simulated and studied under different operating conditions. Constant temperature and heat flux have been employed to investigate thermal performance such as thermal resistance and axial mean temperature for several boundary conditions. Volume of Fluid (VoF) method was used for liquid-vapor two-phase flow simulation. Water and ethanol have been used as working fluids in pulsating heat pipe. This chapter is divided into three major parts depending on the PHP's geometry and dimension. First part studies a simple two dimensional geometry. Second part studies a multi-turn two dimensional geometry and third part investigates a three dimensional geometry for the pulsating heat pipe. An experimental study from other work has been used for comparison and validation in three dimensional simulation.