Experimental studies on a high performance compact loop heat pipe with a square flat evaporator

A thorough experimental investigation was carried out on a copper–water compact loop heat pipe (LHP) with a unique flat, square evaporator with dimension of 30 mm (L)×30 mm (W)×15 mm (H) and a connecting tube having an inner diameter of 5 mm. Using a carefully designed experimental system, the startup process of the LHP when subjected to different heat loads was studied and the possible mechanisms behind the observed phenomena were explored. Two main modes, boiling trigger startup and evaporation trigger startup, were proposed to explain the varying startup behavior for different heat loads. In addition, an expression was developed to describe the radius of the receding meniscus inside the wick, to balance the increased pressure drop along the LHP with increasing heat loads. Finally, insight into how the compact LHP can transfer heat loads of more than 600 W (with a heat flux in excess of 100 W/cm2) with no occurrence of evaporator dry-out was provided.