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<p>Rising heat fluxes in computing and communication devices have made thermal management a critical bottleneck. In this study, two vapor chambers (VCs) with identical envelopes and an overall thickness of ~ 5.12&#xa0;mm were designed and fabricated. VC-1 serves as the baseline and employs a radially graded sintered copper-powder wick together with a hydrophobic condenser surface. VC-2 is identical in geometry and materials, except that a 0.02-mm-thick ultrafine powder sublayer (1200-mesh) is sintered at the base of the evaporator wick adjacent to the heating surface. Under forced water cooling, the effects of cooling-water inlet temperature (20/25/30°C), orientation (horizontal /−45°/−90°), and heat load (30–180&#xa0;W) on thermal performance were systematically investigated. Relative to VC-1, VC-2 exhibits a consistently lower thermal resistance across the entire operating range. In the horizontal orientation, the average thermal resistance reductions achieved by VC-2 are 25.4%, 25.6%, and 30.4% at inlet temperatures of 20, 25, and 30&#xa0;°C, respectively. Under anti-gravity orientations, the performance advantage of VC-2 becomes more pronounced at high heat loads, yielding reductions of 18.4–44.9%. At 180&#xa0;W, the thermal resistance of VC-2 is 0.062, 0.069, and 0.070&#xa0;°C/W at horizontal, − 45°, and − 90°, respectively, which is markedly lower than that of VC-1 (0.091, 0.118, and 0.127&#xa0;°C/W). One possible explanation for this improvement is that the ultrafine powder sublayer modifies the near-wall pore-scale phase-change environment. First, it establishes a capillary-pressure gradient from ultrafine pores near the heated surface to coarser pores outward, thereby improving liquid return pathways and enhancing liquid replenishment. Second, the reduced effective pore-throat size constrains the characteristic size and spatial distribution of vapor structures, while the increased density of active nucleation sites promotes more vigorous nucleate boiling and a more spatially distributed vaporization process. These coupled effects strengthen liquid supply and mitigate vapor–liquid pathway competition in confined passages, enabling VC-2 to maintain low thermal resistance and stable operation under high heat fluxes and unfavorable anti-gravity conditions.</p>

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Vapor chamber with axial graded capillarity for low thermal resistance and orientation-robust high-heat-flux cooling

  • 期刊论文

  • 发表日期：

    2026年4月27日

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  • Shaotong Du,
  • Xiaoyu Cui,
  • Bingyao Lin,
  • Zhenhua Jiang

摘要

Rising heat fluxes in computing and communication devices have made thermal management a critical bottleneck. In this study, two vapor chambers (VCs) with identical envelopes and an overall thickness of ~ 5.12 mm were designed and fabricated. VC-1 serves as the baseline and employs a radially graded sintered copper-powder wick together with a hydrophobic condenser surface. VC-2 is identical in geometry and materials, except that a 0.02-mm-thick ultrafine powder sublayer (1200-mesh) is sintered at the base of the evaporator wick adjacent to the heating surface. Under forced water cooling, the effects of cooling-water inlet temperature (20/25/30°C), orientation (horizontal /−45°/−90°), and heat load (30–180 W) on thermal performance were systematically investigated. Relative to VC-1, VC-2 exhibits a consistently lower thermal resistance across the entire operating range. In the horizontal orientation, the average thermal resistance reductions achieved by VC-2 are 25.4%, 25.6%, and 30.4% at inlet temperatures of 20, 25, and 30 °C, respectively. Under anti-gravity orientations, the performance advantage of VC-2 becomes more pronounced at high heat loads, yielding reductions of 18.4–44.9%. At 180 W, the thermal resistance of VC-2 is 0.062, 0.069, and 0.070 °C/W at horizontal, − 45°, and − 90°, respectively, which is markedly lower than that of VC-1 (0.091, 0.118, and 0.127 °C/W). One possible explanation for this improvement is that the ultrafine powder sublayer modifies the near-wall pore-scale phase-change environment. First, it establishes a capillary-pressure gradient from ultrafine pores near the heated surface to coarser pores outward, thereby improving liquid return pathways and enhancing liquid replenishment. Second, the reduced effective pore-throat size constrains the characteristic size and spatial distribution of vapor structures, while the increased density of active nucleation sites promotes more vigorous nucleate boiling and a more spatially distributed vaporization process. These coupled effects strengthen liquid supply and mitigate vapor–liquid pathway competition in confined passages, enabling VC-2 to maintain low thermal resistance and stable operation under high heat fluxes and unfavorable anti-gravity conditions.