Research on the capillary performance of the single-layer mesh wick in the ultrathin heat pipes

The capillary performance of single-layer mesh wicks in ultrathin heat pipes is strongly affected by shell confinement, which is not adequately represented by conventional wick models. Capillary rise experiments were conducted using ethanol to determine the effective capillary radius of five single-layer stainless-steel meshes (#100-#200), yielding values from 124.7 to 66.2 μm. A pore-scale VOF model was established, and qualitative comparison with microscopic observations showed that it reproduced the characteristic meniscus configurations during capillary migration. Under unilateral shell confinement, the main meniscus within the mesh holes exhibits an inclined configuration, while additional micro-menisci form between the mesh and the shell. Their combined effects produce periodic variations in capillary pressure as the meniscus migrates through successive mesh holes. A geometric analysis further reveals that the periodic evolution of the local effective capillary radius governs the alternating climbing behavior, which comprises three characteristic stages: the “steady climb”, “micro hole dominated climb”, and “transition” regions. Based on the capillary pressure superposition principle, a weighted correlation is proposed to characterize the peak-pressure equivalent capillary radius. With a correction coefficient of C = 0.42, the deviations between the correlation and VOF results for the #250 and #300 meshes are below 3.6%, demonstrating good extrapolative consistency with the present numerical framework outside the calibration range.