本研究以數值模擬方式探討不同回流腔微流道散熱器之熱流性能。首先建立三種基本微流道結構，包含矩形微流道（R）、扇形回流腔微流道（F）與三角形回流腔微流道（T）。進一步以此三種基本幾何為基礎，設計多組二階與三階混合排列微流道，藉此分析回流腔幾何形狀與排列順序對流場發展、熱傳增強與流動阻力之影響。
本研究使用 ANSYS Fluent 進行數值模擬，工作流體為水，矽基板底部施加均勻熱通量 (0.6 MW/m²)，雷諾數範圍為 150 至 800。模擬採用穩態、層流、壓力基求解器，並考慮流體與固體之共軛熱傳效應。為確保數值結果之可靠性，本研究先針對網格獨立性進行分析，並將平均努塞爾數與表觀摩擦因子與 Chai 等人之實驗結果進行比較。結果顯示，約 9.6 百萬網格數可在計算精度與計算成本之間取得良好平衡，因此作為後續模擬分析之網格設定。
研究結果顯示，回流腔結構可有效擾動熱邊界層並促進冷卻流體混合，進而提升對流熱傳能力。相較於傳統矩形微流道，單一回流腔與混合排列微流道皆能降低壁面溫度與總熱阻。在代表性案例中，三角形–扇形混合微流道（TF）於 (Re=474.6) 時具有最低峰值溫度，可將 T 型微流道之最高溫度由 308.7 K 降至 303.7 K。三角形–扇形–矩形混合微流道（TFR）亦展現良好散熱能力，可作為三階混合排列設計之代表案例。
流場分析結果指出，混合式回流腔排列可維持較強之高速主流核心，並改善流道內之動量傳遞。渦度分析進一步顯示，矩形流道僅在壁面附近產生有限渦度，而扇形與三角形回流腔會因幾何變化產生不同程度之旋轉流動。其中，三角形回流腔可形成較強之局部渦度，而混合式排列則能延伸高渦度區域並增強流體混合。綜合而言，適當排列不同回流腔幾何可在維持合理流動阻力的同時，有效降低局部熱累積並提升微流道散熱器之整體熱流性能。

This study numerically investigates the thermal-hydraulic performance of microchannel heat sinks with different reentrant cavity configurations. Three basic microchannel geometries, including the rectangular microchannel (R), fan-shaped reentrant cavity microchannel (F), and triangular reentrant cavity microchannel (T), were first considered. Based on these basic structures, several two-stage and three-stage hybrid configurations were further developed to examine the influence of cavity geometry and arrangement sequence on flow development and heat transfer enhancement.
The numerical simulations were performed using ANSYS Fluent. Water was employed as the working fluid, and a uniform heat flux of 0.6 MW/m² was applied to the bottom surface of the silicon substrate. The Reynolds number ranged from 150 to 800. A steady, laminar, pressure-based solver with conjugate heat transfer was adopted. Mesh independence and model validation were conducted by comparing the predicted average Nusselt number and apparent friction factor with the experimental data reported by Chai et al. The mesh containing approximately 9.6 million cells was selected for subsequent simulations because it provided a suitable balance between numerical accuracy and computational cost.
The results show that the introduction of reentrant cavity structures enhances convective heat transfer by disturbing the thermal boundary layer and promoting coolant mixing. Compared with the conventional rectangular microchannel, both single-cavity and hybrid configurations reduce wall temperature and total thermal resistance. Among the representative configurations, the triangular–fan hybrid microchannel (TF) exhibits the lowest peak temperature at Re = 474.6, decreasing from 308.7 K for the T configuration to 303.7 K. The triangular–fan–rectangular configuration (TFR) also demonstrates improved thermal performance and provides a representative three-stage hybrid design.
Flow field analysis indicates that hybrid cavity arrangements maintain a stronger high-velocity core and improve momentum transport along the channel. The vorticity analysis further confirms that the rectangular channel generates limited rotational motion, while fan-shaped and triangular cavities produce different vortex characteristics. In particular, triangular cavities generate stronger localized vorticity, whereas hybrid arrangements extend the high-vorticity region and enhance fluid mixing. These findings demonstrate that properly arranged hybrid reentrant cavity structures can effectively improve heat transfer performance while maintaining acceptable hydraulic resistance, providing a useful design strategy for high-performance microchannel heat sinks.

[1] D. B. Tuckerman and R. F. W. Pease, "High-performance heat sinking for VLSI," IEEE Electron Device Letters, vol. 2, no. 5, pp. 126-129, 1981.
[2] G. Morini, "Single-phase convective heat transfer in microchannels: A review of experimental results," International Journal of Thermal Sciences, vol. 43, no. 7, pp. 631-651, 2004.
[3] S. G. Kandlikar, "High flux heat removal with microchannels - A roadmap of challenges and opportunities," Heat Transfer Engineering, vol. 26, no. 8, pp. 5-14, 2005.
[4] W. Dong, X. Zhang, B. Liu, B. Wang, and Y. Fang, "Research progress on passive enhanced heat transfer technology in microchannel heat sink," International Journal of Heat and Mass Transfer, vol. 220, 125001, 2024.
[5] U. Ghani, A. N. M. Karim, and M. M. Rahman, "Microchannel heat sinks - A comprehensive review," Eng, vol. 5, no. 4, pp. 1076-1101, 2024.
[6] W. Qu and I. Mudawar, "Experimental and numerical study of pressure drop and heat transfer in a single-phase micro-channel heat sink," International Journal of Heat and Mass Transfer, vol. 45, no. 12, pp. 2549-2565, 2002.
[7] P. S. Lee and S. V. Garimella, "Thermally developing flow and heat transfer in rectangular microchannels of different aspect ratios," International Journal of Heat and Mass Transfer, vol. 49, no. 17-18, pp. 3060-3067, 2006.
[8] J. Koo and C. Kleinstreuer, "Viscous dissipation effects in microtubes and microchannels," International Journal of Heat and Mass Transfer, vol. 47, no. 14-16, pp. 3159-3169, 2004.
[9] J. Xu, Y. Song, W. Zhang, H. Zhang, and Y. Gan, "Numerical simulations of interrupted and conventional microchannel heat sinks," International Journal of Heat and Mass Transfer, vol. 51, pp. 5906-5917, 2008.
[10] L. Chai, G. Xia, M. Zhou, and J. Li, "Optimum thermal design of interrupted microchannel heat sink with rectangular ribs in the transverse microchambers," Applied Thermal Engineering, vol. 51, no. 1-2, pp. 880-889, 2013.
[11] L. Chai, G. D. Xia, and H. S. Wang, "Laminar flow and heat transfer characteristics of interrupted microchannel heat sink with ribs in the transverse microchambers," International Journal of Thermal Sciences, vol. 110, pp. 1-11, 2016.
[12] L. Chai, G. Xia, M. Zhou, and J. Li, "Numerical simulation of fluid flow and heat transfer in a microchannel heat sink with offset fan-shaped reentrant cavities in sidewall," International Communications in Heat and Mass Transfer, vol. 38, pp. 577-584, 2011.
[13] M. Pan, H. Wang, Y. Zhong, M. Hu, X. Zhou, G. Dong, and P. Huang, "Experimental investigation of the heat transfer performance of microchannel heat exchangers with fan-shaped cavities," International Journal of Heat and Mass Transfer, vol. 134, pp. 1199-1208, 2019.
[14] G. D. Xia, L. Chai, M. Z. Zhou, and H. Y. Wang, "Effects of structural parameters on fluid flow and heat transfer in a microchannel with aligned fan-shaped reentrant cavities," International Journal of Thermal Sciences, vol. 50, no. 3, pp. 411-419, 2011.
[15] G. D. Xia, L. Chai, H. Y. Wang, M. Z. Zhou, and Z. Z. Cui, "Optimum thermal design of microchannel heat sink with triangular reentrant cavities," Applied Thermal Engineering, vol. 31, no. 6-7, pp. 1208-1219, 2011.
[16] Y. L. Zhai, G. D. Xia, X. F. Liu, and Y. F. Li, "Heat transfer in the microchannels with fan-shaped reentrant cavities and different ribs based on field synergy principle and entropy generation analysis," International Journal of Heat and Mass Transfer, vol. 68, pp. 224-233, 2014.
[17] Y. F. Li, G. D. Xia, D. D. Ma, Y. T. Jia, and J. Wang, "Characteristics of laminar flow and heat transfer in microchannel heat sink with triangular cavities and rectangular ribs," International Journal of Heat and Mass Transfer, vol. 98, pp. 17-28, 2016.
[18] Q. Wang, J. Tao, Z. Cui, T. Zhang, and G. Chen, "Numerical simulation of fluid and heat transfer characteristics of microchannel heat sink with fan-shaped grooves and triangular truncated ribs," International Communications in Heat and Mass Transfer, vol. 155, 107580, 2024.
[19] L. Chai and L. Wang, "Thermal-hydraulic performance of interrupted microchannel heat sinks with different rib geometries in transverse microchambers," International Journal of Thermal Sciences, vol. 127, pp. 201-212, 2018.
[20] C. Bi, G. H. Tang, and W. Q. Tao, "Heat transfer enhancement in mini-channel heat sinks with dimples and cylindrical grooves," Applied Thermal Engineering, vol. 55, no. 1-2, pp. 121-132, 2013.
[21] I. A. Ghani, N. Kamaruzaman, and N. A. C. Sidik, "Heat transfer augmentation in a microchannel heat sink with sinusoidal cavities and rectangular ribs," International Journal of Heat and Mass Transfer, vol. 108, pp. 1969-1981, 2017.
[22] I. A. Ghani, N. Kamaruzaman, and N. A. C. Sidik, "Heat transfer enhancement in microchannel heat sink using hybrid technique of ribs and secondary channels," International Journal of Heat and Mass Transfer, vol. 114, pp. 640-655, 2017.
[23] N. R. Kuppusamy, H. A. Mohammed, and C. W. Lim, "Numerical investigation of trapezoidal grooved microchannel heat sink using nanofluids," Thermochimica Acta, vol. 573, pp. 39-56, 2013.
[24] Z. Dai, D. F. Fletcher, and B. S. Haynes, "Impact of tortuous geometry on laminar flow heat transfer in microchannels," International Journal of Heat and Mass Transfer, vol. 83, pp. 382-398, 2015.
[25] N. O. El-Saeh, F. Alnaimat, B. T. Chew, and B. Mathew, "Performance evaluation of MEMS heat sinks having straight microchannels integrating rectangular sidewall cavities in in-line pattern," Applied Thermal Engineering, vol. 266, 125696, 2025.
[26] X. Yan, Y. Wu, Z. Zhang, K. Cui, H. Zhao, and K. He, "Experimental study of flow boiling heat transfer in rectangular ribbed micro-channels with rectangular cavities," International Journal of Heat and Mass Transfer, vol. 236, 126402, 2025.
[27] Y. Liu, D. Ma, G. Xia, J. Song, and H. Zhang, "Thermo-hydraulic analysis of a novel microchannel with zigzag cavities and waterdrop-shaped ribs for electronic chip cooling," Thermal Science and Engineering Progress, vol. 71, 104567, 2026.
[28] G. Xie, F. Zhang, B. Sunden, and W. Zhang, "Constructal design and thermal analysis of microchannel heat sinks with multistage bifurcations in single-phase liquid flow," Applied Thermal Engineering, vol. 62, no. 2, pp. 791-802, 2014.
[29] L. Chai, G. Xia, L. Wang, M. Zhou, and Z. Cui, "Heat transfer enhancement in microchannel heat sinks with periodic expansion-constriction cross-sections," International Journal of Heat and Mass Transfer, vol. 62, pp. 741-751, 2013.
[30] M. Fiebig, P. Kallweit, N. K. Mitra, and S. Tiggelbeck, "Heat transfer enhancement and drag by longitudinal vortex generators in channel flow," Experimental Thermal and Fluid Science, vol. 4, no. 1, pp. 103-114, 1991.
[31] J. M. Wu and W. Q. Tao, "Effect of longitudinal vortex generator on heat transfer in rectangular channels," Applied Thermal Engineering, vol. 37, pp. 67-72, 2012.
[32] A. Ebrahimi, E. Roohi, and S. Kheradmand, "Numerical study of liquid flow and heat transfer in rectangular microchannel with longitudinal vortex generators," Applied Thermal Engineering, vol. 78, pp. 576-583, 2015.
[33] H. E. Ahmed, H. A. Mohammed, and M. Z. Yusoff, "An overview on heat transfer augmentation using vortex generators and nanofluids: Approaches and applications," Renewable and Sustainable Energy Reviews, vol. 16, no. 8, pp. 5951-5993, 2012.
[34] L. Lin, J. Zhao, G. Lu, X. D. Wang, and W. M. Yan, "Heat transfer enhancement in microchannel heat sink by wavy channel with changing wavelength/amplitude," International Journal of Thermal Sciences, vol. 118, pp. 423-434, 2017.
[35] I. A. Ghani, N. Kamaruzaman, N. A. C. Sidik, R. Mamat, G. Najafi, and W. H. Azmi, "The significant effect of secondary flow in wavy microchannel heat sink," Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, vol. 25, no. 1, pp. 1-18, 2016.