Fabrication and capillary characterization of micro-grooved wicks with reentrant cavity array

Micro-grooved wicks with reentrant cavity array (MGRAs) were fabricated with orthogonal Ploughing/Extrusion method for the application in the ultra-thin aluminum vapor chambers. Capillary rise tests using both ethanol and acetone as the working fluid were conducted by a novel IR-thermal imaging method. The experimental results indicated that the MGRAs yielded larger capillary height than the micro-grooved wicks (MGs) and the MGRA-1 exhibited the highest capillary rise rate of all samples studied. In addition, the permeability was characterized in the force flow tests. It was found that the MGRAs obtained comparable permeability to that for the MGs, revealing that they were able to enhance the capillary rise with little penalty of pressure drop. With regard to the capillary limited heat flux, the capillary parameter K·ΔPcap was employed to evaluate the performance of the wicks comprehensively. The comparison of K·ΔPcap between the prediction with/without the gravitational effect showed that the Washburn's Law greatly underestimated the K·ΔPcap after the initial stage, so the gravitational effect should be taken into account when comparing the samples. In this case, K·ΔPcap determined in the ethanol and acetone tests were similar. Besides, the MGRAs yielded higher K·ΔPcap than that for the MGs, except for the MGRA-3/MG-3 couple, justifying the prominent performance of the MGRAs. Despite the fact that the MGRA-2 failed to obtain the largest capillary height, it showed the largest K·ΔPcap among all MGRAs due to the good balance between the capillary pressure and permeability. Thus, it may be the optimum choice of all MGRAs in this study.