Experimental study on thermo-hydrodynamic behaviors in miniaturized two-phase thermosyphons

• Thermo-hydrodynamics in miniaturized two-phase thermosyphons is investigated.
• Two-phase flow, heat transfer regimes and thermal performances are presented.
• Thermo-hydrodynamic behaviors are quantitatively recognized by a state diagram.
• Channel miniaturization triggers the oscillation state of gas–liquid two-phase flow.
• Oscillation state possesses random formation and oscillatory motion of liquid plugs.

In this paper, the thermo-hydrodynamic behaviors in miniaturized two-phase thermosyphons are experimentally investigated by a visualization system. The effects of heat load and channel dimension on the thermo-hydrodynamic behaviors are examined and further quantitatively recognized by a state diagram depending on the Weber number and Bond number. In addition, the vapor–liquid two-phase flow, heat transfer regimes and thermal performances are analyzed and discussed. The results indicate that, differing from the conventional two-phase thermosyphon, the state of working fluid in a miniaturized two-phase thermosyphon is no longer only in a fashion of pool and annular-flow states, but also in a fashion of oscillation state. The oscillation state is the characteristic two-phase flow regime of a miniaturized two-phase thermosyphon and possesses the feature of random formation and oscillatory motion of liquid plug in minichannels. The pool state occurs at small Weber number, the annular-flow state is observed at large Weber number, and the oscillation state takes place at medium Weber number when Bond number is approximately smaller than 0.7. The thermal performance of oscillation state is better than that of pool state but is less powerful than that of annular-flow state. The heat transfer regimes are the film evaporation and condensation combined with thermal conduction in the pool state, the forced evaporation and condensation in the oscillation state, and the film evaporation and condensation in the annular-flow state, respectively.