本研究以實驗量測方式，探究平行與漸擴毫米流道熱沉內奈米相變化乳液強制對流熱傳遞特性。實驗所使用之工作流體為純水與奈米相變化乳液，而奈米相變化乳液係利用超音波震盪1至2小時之製程，製作出懸浮於水中粒徑大小為130nm左右之相變化液滴。熱傳遞實驗所用之毫米流道熱沉係以無氧銅為材料，利用線切割機械加工技術，製造出各具八條長度50 mm流道之平行與漸擴型熱沉，兩熱沉之單位流道入口皆為寬為1 mm、高為1.5 mm之矩形截面，而漸擴型熱沉內各流道係其寬度呈線性增加方式至出口形成寬2.8 mm、高1.5 mm之矩形截面，各漸擴流道之漸擴角度為2.06°。本研究探討之相關參數與其變化範圍為：奈米相變化乳液質量分率= 2%、5%、10%；熱沉進口體積流量=60 cm3/min、180 cm3/min、300 cm3/min、420 cm3/min、600 cm3/min；熱沉底部加熱通率=3.2W/cm2、4.0 W/cm2、4.8 W/cm2。本研究所得熱傳實驗結果顯示，相較於純水，奈米乳液在適當的實驗參數條件下，奈米相變化乳液通過平行或漸擴流道熱沉均能有所效提升平均熱傳遞係數，其最大增益可達17.6%；此外，肇因奈米相變化乳液壓降相較於水呈巨幅上升情形，致使其流經平行或漸擴流道熱沉之壓降亦大幅劇增。由於其相較於平行流道熱沉之壓降上升幅度較小，利用奈米相變化乳液於漸擴型流道熱沉可具較高熱散逸效能指標(FOM)與性能因子(COP)。

In the present study, the force convection heat transfer characteristics of water-based nano-PCM emulsions in the multi-channel heat sinks with parallel and divergent rectangular mini-channels, respectively, are examined experimentally to explore their cooling efficacies. The water-based nano-PCM emulsions were formulated by dispersing n-eicosane as the phase change material (PCM) nanoparticles in the pure water as the base fluid in an ultrasonic vibrator for 1-2 hours, producing the water-based emulsions with the PCM nanoparticle size of about 130 nm. The two multi-channel heat sinks with eight parallel and divergent mini-channels of 50 mm in length, respectively, were fabricated of oxygen-free copper. Each rectangular mini-channel of the parallel and divergent heat sinks has an inlet cross section of 1 mm in width and 1.5 mm in height. For the divergent mini-channel heat sink, each channel was machined such that the channel width is linearly expanded in width from the inlet, leading to a width of 2.8 mm at the channel outlet. As a result, each transversely divergent channel has a divergent angle of 2.06 over the channel length. The forced convection heat transfer experiments for the mini-channel heat sinks have been undertaken for the relevant parameters in the following ranges: the volumetric flow rate into the heat sinks,= 60 cm3/min, 180 cm3/min, 300 cm3/min, 420 cm3/min, 600 cm3/min; and the heat flux imposed over the bottom surface of the heat sinks,=3.2W/cm2、4.0 W/cm2、4.8 W/cm2; and the mass fraction of PCM nanoparticles dispersed in the water-based emulsions, ωpcm = 2%, 5%, 10%. Experimental results obtained clearly reveal that the nano-PCM emulsion through both parallel and divergent mini-channel heat sinks under the appropriate conditions can be markedly effective for averaged heat transfer enhancement compared to the pure water. Further comparing with the parallel heat sink, the figure of merit (FOM) and coefficient of performance (COP) obtained for the divergent channel heat sink can effectively mitigate the pressure drop penalty due to the highly increased dynamic viscosity arisen for the nano-emulsions formualted.

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