Fabrication and capillary characterization of multi-scale micro-grooved wicks with sintered copper powder

Capillary wick is a key component of loop heat pipes, and its structure design is essential to improve the thermal performance of the devices. In this work, a novel micro-grooved wick with multi-scale structures was fabricated by powder sintering technique and two-step chemical treatment processes. The effect of structure parameters on the capillary performance of sintered-powder wicks was investigated including the particle size and microstructural features, i.e., nanograss and microcavities. The results indicated that the microstructure features had a minimal effect on the permeability of samples. Under the same particle size, compared with the plain sintered-powder wicks (PCPWs) and sintered-powder wicks covered by nanograss (NGPWs), the composite wick covered by microcavities (MCPWs) showed a higher capillary pumping amount and higher wicking velocity in the capillary pumping process. For the nine sintered-powder wicks, MCPW2 and PCPW1 showed the maximum and the minimum capillary pumping amount, respectively, leading to a 73% of increasement in capillary pumping amount. In the comprehensive evaluation of capillary performance, MCPW2 showed the optimal capillary performance, which increased by more than 260% compared with PCPW1. Finally, we predicted the critical size of the microscale gap to enhance the boiling heat transfer and obtained an optimal structure of capillary wick. The optimized capillary wick could significantly improve the capillary limit, providing an ideal option for capillary wicks of loop heat pipes.