Heat transfer and flow visualizations in a flat confined two-phase thermosyphon

A transparent flat confined two-phase thermosyphon is experimentally investigated in order to analyze the link between the boiling flow patterns and the thermal performance of the system with several parameters such as the confinement, the saturation temperature, the filling ratio or the inclination angle. The device is constituted of a copper plate on which the heat sink and heat source are located, and of a transparent polycarbonate plate that enables the visualization of the boiling patterns. Two values of the inner thickness of the flat two-phase thermosyphon, 1 mm and 3 mm, are tested. The small values of the thickness induce confined boiling in the evaporator section, which leads to an enhancement of the heat transfer inside the thermosyphon. Two fluids are tested, water and n-pentane. The confinement difference between the two fluids enables to assess the influence of confinement on the boiling regime and heat transfer capacity, particularly its dependence on inclination. Confining the boiling in only one direction allows sufficient rewetting of the heated surface even for high confinements. It appears that the thermal performance of the two-phase thermosyphon is not affected by the inclination angle in the range 10 degrees-170 degrees (90 degrees being the vertical position) with a moderate confinement of the boiling process in only one direction. (C) 2019 Elsevier Ltd. All rights reserved.