Oscillating heat pipe simulation considering bubble generation Part I: Presentation of the model and effects of a bubble generation

Oscillating heat pipe (OHP) simulations with and without a bubble generation are performed to investigate both the flow behaviors of liquid slugs, vapor plugs and liquid films, and the heat transfer characteristic of an OHP. A closed-looped OHP without an adiabatic section is adopted. The simulations are performed under the boundary condition of constant wall temperature. The results show that a bubble generation causes the large pressure difference between two neighboring vapor plugs (driving force). This produces oscillating motions of liquid slugs and vapor plugs with large amplitude, which are very different from all previous simulation results (only a simple sinusoidal oscillating motion with small amplitude). The frequency of oscillating motions also increases due to the continuous bubble generation. By the large amplitude and the more frequent of oscillating motions, the amount of latent and sensible heat transfer rates from the heating section to the cooling section increase. The latent heat transfer rate increases due to the large evaporation rate from liquid film during a bubble growth, while the sensible heat transfer rate increases due to the large amplitude motions of liquid slugs and vapor plugs. In the simulation with a bubble generation, heat is transferred by the sensible heat (74%) and latent heat (26%). On the other hand, in the simulation without a bubble generation, heat is transferred mainly by the sensible heat (95%) and only 5% by the latent heat, which agrees with the previous simulation results.