Experimental investigation of heat transfer in three phase heat pipes

Two-phase heat pipes with high heat transfer capacity are widely used. While there are many experimental and theoretical studies on two-phase heat pipes with various application areas, there are very limited studies in the literature on three-phase heat pipes formed by adding solid particles to two-phase heat pipes. In order to contribute to the literature, the variation of thermal performance, thermal resistance and heat transfer coefficient in three-phase heat pipes were investigated. In this study, two different diameters of heat pipes, 15mm and 20mm, were used and the experiments were carried out at three different inclination angles (90°, 60° and 30°) and with 4 different working fluids: "Pure water", "Pure water+PA6", "Pure water+PA66" and "Pure water+PA6+PA66" mixtures. During the experiments, heat loads of 8.07 kW/m2, 16.99 kW/m2, 25.05 kW/m2 and 37.15 kW/m2 were gradually applied to the system from the evaporator area and measurements were recorded. As a result, when the changes in the heat transfer coefficient realized by boiling in the evaporator region in two-phase and three-phase heat pipes are compared, in general, three-phase systems have worsened compared to two-phase systems, but partial improvement has also been observed. In 20mm diameter heat pipes, the maximum improvement in the heat transfer coefficient was realized by 64% at a heat load of 16.99 kW/m2 in the case of "Pure water +PA6+PA66" mixture at 60° inclination. In the case of 15mm heat pipes, the maximum improvement was 96% at 8.07 kW/m2 with "Pure water+PA66" mixture at 60° inclination.