  Numerical simulation has been conducted for the chaotic flow in a 3D
closed-loop pulsating heat pipe (PHP). Heat flux and constant temperature
boundary conditions were applied for evaporator and condenser sections,
respectively. Water and ethanol were used as working fluids. Volume of Fluid
(VOF) method has been employed for two-phase flow simulation. Spectral analysis
of temperature time series was carried out using Power Spectrum Density (PSD)
method. Existence of dominant peak in PSD diagram indicated periodic or
quasi-periodic behavior in temperature oscillations at particular frequencies.
Correlation dimension values for ethanol as working fluid was found to be
higher than that for water under the same operating conditions. Similar range
of Lyapunov exponent values for the PHP with water and ethanol as working
fluids indicated strong dependency of Lyapunov exponent to the structure and
dimensions of the PHP. An O-ring structure pattern was obtained for
reconstructed 3D attractor at periodic or quasi-periodic behavior of
temperature oscillations. Minimum thermal resistance of 0.85 degree/W and 0.88
degree/W were obtained for PHP with water and ethanol, respectively. Simulation
results showed good agreement with experimental results from other work under
the same operating conditions.
