Fabrication and testing of a miniature flat evaporator loop heat pipe with polydimethylsiloxane and molding

Abstract

Two main approaches have been proposed to fabricate miniature loop heat pipes: a mechanical-manufacturing-based approach (traditional approach) and a microelectromechanical-system-based approach. However, both of these approaches have problems, such as complexity, expensive equipment, and difficult control. Polydimethylsiloxane and molding are good candidates for solving these problems because they have a low cost and require simple materials and processing. In this study, substrates with high thermal conductivity were combined with Polydimethylsiloxane for the fabrication of a 3.4 mm thick loop heat pipe evaporator. The effect of the molding conditions on the loop heat pipe thermal performance was discussed and the suitable conditions were identified. The heat transfer performance of the miniature loop heat pipe in different orientations was investigated. A long-term performance test was carried out. It was found that the miniature loop heat pipe could operate stably for a long time (three weeks) in different orientations. The maximum heat transfer capacity reached 9 W (4.5 W/cm2) and a thermal resistance of 5.7 K/W was obtained. The maximum heat flux is 2–4 times higher while the thermal resistance is the same order as with the corresponding values of other polymer heat pipes. Further improvement was required for practical applications. However, there was evidence of a high degree of potential with this approach for the miniaturization of loop heat pipes.