Thermal performance evaluation of a parylene-coated polydimethylsiloxane loop heat pipe featuring a micropillar evaporator

• Created a 1.5 mm parylene/PDMS loop heat pipe with a micropillar evaporator. • Developed a MEMS-based process for durable seals, sustaining high vapor pressure. • Demonstrated reliable heat transport across all orientations, ensuring adaptability. • Achieved 3.0 W transport in a bending device, advancing wearable device technology. The thermal management of flexible electronic devices represents a major barrier to their applications. Thus, in this study, a parylene-coated polydimethylsiloxane (PDMS)-based loop heat pipe (LHP), parylene/PDMS-LHP, equipped with a micropillar evaporator was developed. A newly developed one-dimensional steady-state numerical model was used and the parylene/PDMS-LHP (thickness: 1.5 mm) was designed based on the model. Flow channel of PDMS was formed by a mold using conventional photolithography technique. Parylene is vapor-deposited on the inner surface of the flow channel to improve the liquid barrier properties and hydrophilicity. Ethanol was selected as the working fluid from the viewpoint of the contact angle with parylene surface. Heat input tests were conducted in six different orientations (five without bending and in different orientations, and one with bending) to verify the effect of operating direction on performance, assuming that the Parylene/PDMS-LHP will be mounted on flexible electronic devices. The maximum heat-transport of the parylene/PDMS-LHP was 3.0 W, and the heat source temperature decreased to ∼ 60°C compared with that of a non-fluid-charged device in a horizontal orientation. In tests in five orientations without bending and one orientation with bending, continuous heat transfer from 1.0 W to 2.5 W or 3.0 W was achieved in all orientations, confirming the applicability of the proposed Parylene/PDMS-LHP to wearable devices.