A systematic review of composite wick designs for enhancing capillary and thermal performance in heat pipes

With the surge in heat flux densities in compact electronic and contemporary thermal systems, heat pipes have emerged as vital passive thermal management solutions. The wick, critical to heat pipe performance, governs liquid circulation and capillary pumping. However, conventional mono-wick designs often demonstrate a trade-off between capillary force and permeability, limiting their effectiveness. Composite wick structures, combining two or more wicks such as sintered powder, mesh, grooves, and spiral woven mesh (SWM), have received significant attention for facilitating an optimised balance between these conflicting properties. Despite this growing research on composite wicks, no review has analysed their advancement and influence on heat pipe performance in comprehensive detail. Addressing this gap, the present work systematically reviews the performance of composite wick designs in cylindrical, flat, and looped heat pipes, with a focus on hydrodynamic and thermal performance characteristics such as permeability, thermal resistance, and heat transport capacity. Studies show that composite wicks can achieve up to 56 % higher performance and thermal resistances as low as 0.02 K/W for some cases. The review also underlines how operating conditions such as fluid charge ratio, orientation, and heat input affect the thermal performance of heat pipes with composite wicks. By synthesising key insights from different studies, this study provides a thorough assessment on the design and fabrication of composite wick-based heat pipes. The findings underscore the critical role of composite wicks in advancing next-generation thermal management systems and shaping future directions for scalable and highly effective heat pipe devices.