Thin loop heat pipe with twisted wires as wick structure for microelectronics

The continuous miniaturization of consumer electronics has intensified the demand for thin, lightweight, and efficient thermal management solutions, being loop heat pipes (LHPs) a promising passive two-phase cooling technology. This work presents a thin diffusion-bonded LHP incorporating a novel twisted copper wire wick structure, specifically designed for microelectronics. The device features an external footprint of 76 × 60 mm 2 , a thickness of 0.5 mm, and an internal channel height of only 0.3 mm. The physical properties and fluid transport mechanisms of the twisted wire wick are investigated in detail using microtomography-based image processing, enabling a comprehensive characterization without additional experimental measurements. Thermal performance experiments were conducted using water as the working fluid, covering different filling ratios and orientations (horizontal, gravity-assisted, and against-gravity). The results demonstrate that a filling ratio of 60 % provides optimal performance, with stable startup at 2 W in all orientations. The proposed LHP achieved thermal resistances as low as 1.00 ± 0.12 °C/W and dissipated heat fluxes up to 8 W/cm 2 under natural convection. Comparative analyses with thicker LHPs and employing conventional sintered copper powder wicks reveal that, despite the increased pressure drop associated with the reduced channel height, the twisted wire wick maintains superior liquid pumping capability. Effective thermal conductivity values approaching 100,000 W/m·K were obtained, exceeding those thin two-phase devices reported in the literature. Overall, the results confirm that the proposed twisted copper wire wick enables high-performance operation in ultra-thin LHPs, offering a robust, low-cost, and scalable solution for next-generation compact electronic cooling applications.