Study of Liquid–Vapor Oscillating Nature in a U-Shaped Tube for a Pulsating Heat Pipe

Being a two-phase flow passive heat transfer device, pulsating heat pipes can solve some of the current thermal management issues. Their distinctive feature involves thermally induced oscillations of the working fluid within a capillary tube connecting hot and cold ends. The effectiveness of heat transport in pulsating heat pipes is intricately linked to the amplitude and frequency of these oscillations. A U-shaped tube having one liquid slug and two vapor plugs is considered for mathematical modeling of the oscillatory flow in the present study. The amplitude of oscillations, the variation of mass, temperatures, and the pressure of vapor plugs are analyzed from the conservation of mass, energy, and momentum. A modified mass transfer equation for vapor plugs is introduced to account for the evaporation and condensation processes. The fourth-order Runge–Kutta method is employed to solve the non-dimensional form of the governing equations through a MATLAB program. A dimensionless time step of 0.0001 was considered for the time marching solution. The improvements are found in the amplitude of oscillation compared to the existing model. The plots for displacement of slug, mass, temperature, and pressure of plugs show the smooth variation having a phase difference around π.