In this paper, the three-dimensional vapor–liquid two-phase interface reconstruction of the micro-grooved heat pipe is investigated by a visualization system based on the principle of optical sectioning microscopy. Three-dimensional distribution characteristics of the vapor–liquid interface and heat transfer regimes are analyzed. In addition, the effects of heat load on transport characteristics of the liquid phase between evaporator and condenser are examined. The results indicate that gravity has weak effects on distribution of the liquid layer in direction of axial and radial, the liquid layer distributes in sharp corners of the square groove or covers the wall of the groove almost symmetrically. Differing from gravity, the effect of surface tension on distribution of the liquid phase is significant, the vapor–liquid two-phase interface of the condensate liquid plug distributes in central region of grooves symmetrically as a shape of the bullet, and the warhead points to condenser. Driven by the capillary pressure difference, the condensate flows from condenser through the adiabatic to evaporator. And the thickness of the liquid layer covering the inner wall of the groove decreases gradually from condenser to evaporator. The increase of heat load strengthens the circulation of the working medium, increases the thickness of the liquid layer in condenser, and even leads to no liquid plug in condenser. Meanwhile, the increase of heat load can also promote evaporation in evaporator and reduce the thickness of the liquid layer in evaporator.
