Heat transfer characteristics of flat evaporator loop heat pipe under high heat flux condition with different orientations

Highlights: • Heat transfer characteristics of high heat flux LHP with flat evaporator is studied. • A designed porous wick in an evaporator has 84 grooves of 0.3 mm width. • The LHP was tested with six different orientations. • The maximum heat transfer capacity reached 280 W (19.6 W/cm²). • The effect of LHP orientation on heat transfer performance is discussed. -- Abstract: This paper reports an experimental study on a high heat flux loop heat pipe (LHP) with different orientations. A flat rectangular evaporator with a dimension of 51 mm (L) × 68 mm (W) × 15 mm (H) was designed. To enhance a heat transfer performance at a high heat flux, width and number of vapor groove which is processed in a porous wick designed to 0.3 mm and 84, respectively. The LHP was tested in six orientations such as (1) Evaporator under condenser, (2) Wick above liquid core, (3) Evaporator under CC, (4) Evaporator above condenser, (5) Wick under liquid core, and (6) Evaporator above CC. The main originality of this paper is to evaluate the effect of LHP orientation on the heat transfer performance under high heat flux condition. As results of the experiment, it was confirmed that the LHP successfully started up at 50 W for all orientations. In the case of orientation (3) and (5), the maximum heat transfer capacity became the highest value such as 280 W (19.6 W/cm²). The lowest thermal resistances of them were 0.094 K/W and 0.064 K/W, respectively. It was found that the LHP orientation and liquid-vapor phase distribution in the liquid core significantly affected the heat transfer performance when the high heat flux was applied.