渦集式捕集法製備碳系奈米流體及其特性與應用研究

Abstract

本研究旨在開發出屬於一階合成法的渦集式捕集法製造系統（MSVTM）去製備碳系奈米流體。針對製造系統的可行性、產出物的材質與形貌、基本理化性質以及實用性等方面進行深入的分析與探討。 本研究主要分為三個部分。第一部分為使用自行開發之渦集式捕集法製造系統製備碳系奈米流體。此法是以氧乙炔火焰為碳源，並利用氣流導引燃燒產生含碳微粒的氣體進入渦集結構產生水霧與碳微粒的混合及收集而生成碳系奈米流體。接著再檢測產製材料的形貌、材質、粒徑、物理化學性質以及穩定性等基本性質以瞭解製程參數與碳系奈米流體各種基本性質之間的關係。本製造系統製備碳系奈米流體濃度可達0.055 wt%以上且平均粒徑約為20~50 nm。碳系奈米流體中所懸浮的奈米碳包含非晶碳、氧化石墨烯及還原氧化石墨烯等成份，且有良好的穩定性。 第二部為分散劑的選用評估。為了達到長期的穩定性以提高碳系奈米流體的實用性，本研究選用六種常用於奈米碳材的分散劑(CTAB、SDBS、SDS、CH、GA及PSS)加入碳系奈米流體中並進行穩定性測試及評估以尋求最佳穩定性的分散劑與濃度。實驗結果發現，含有分散劑的碳系奈米流體加熱到85℃後的穩定性明顯優於未加熱的樣本，且當分散劑濃度在0.4 wt%以上時，靜置35天以上仍然保持良好的穩定性。 最後分別選定SDBS及PSS作為機械（磨潤與切削）與能源領域（儲冷與熱交換）應用研究所使用的分散劑。結果顯示，含SDBS的碳系奈米油水混合液在磨潤實驗時可以比未加奈米碳系材料的油水混合液減少2.36倍以上的磨耗量。鑽削加工則顯示當碳系奈米材料濃度提升時，磨耗及表面粗糙度有降低的趨勢。在儲冷方面，使用含SDBS之碳系奈米流體的平均過冷卻度低於水0.93 ℃。含有PSS之碳系奈米流體使用在扁管及圓管氣冷式熱交換器進行熱交換性能評估時，碳系奈米流體在熱交換系統的效率因子之整體趨勢優於水。歸結上述研究結果顯示本系統製備之碳系奈米流體未來在相關應用領域應具有相當的發展潛力與實用性。This study developed a manufacturing system for the vortex trap method (MSVTM) for the preparation of carbon-based nanofluids (CBNFs) through a single-step synthesis method. The feasibility of the MSVTM, product material and morphology, fundamental physicochemical characteristics of CBNFs, and practicality of CBNFs were comprehensively analyzed and evaluated. This study was mainly divided into three parts. The first part involved the preparation of CBNFs by using a self-developed MSVTM. In this method, an oxygen–acetylene flame was used as the carbon source. Moreover, gas flow was used to guide combusted gas containing carbon particles into a vortex trap structure for generating a mixture of water mist and carbon particles and thereby forming a CBNF. The fundamental properties of the produced materials, such as their morphology, material, particle size, physicochemical properties, and stability were then examined to clarify the relationship between the process parameters and various fundamental properties of CBNFs. The concentration of CBNFs prepared with the MSVTM could exceed 0.055 wt%, with an average particle diameter of approximately 20–50 nm. The suspended nanocarbon in the CBNFs contained amorphous carbon, graphene oxide, and reduced graphene oxide, and the CBNFs had superior stability. The second part of the study involved the evaluation of dispersant selection. To achieve long-term stability and thus improve the practicality of the CBNFs, six types of dispersants (CTAB, SDBS, SDS, CH, GA, and PSS) commonly used in nanocarbon materials were selected and added to the CBNFs for stability testing and evaluation to determine the optimal stability and concentration of the dispersant. The experimental results revealed that after heating to 85 ℃, the CBNFs with dispersants had a significantly higher stability than the unheated sample. Moreover, the dispersant maintained superior stability for more than 35 days when the concentration exceeded 0.4 wt%. Finally, SDBS and PSS were selected as the optimal dispersants for use in mechanical (tribology and cutting) and energy (cold storage and heat exchange) applications. The results indicated that the carbon-based nanocutting fluid containing SDBS could reduce the wear loss by 2.36 times or more compared with the original cutting fluid during the tribology test. The cutting test results revealed that the wear loss and surface roughness tended to decrease as the carbon-based nanomaterial concentration increased. In terms of cold storage, the average subcooling temperature of the CBNFs containing SDBS was lower than the 0.93 °C subcooling temperature of water. CBNFs containing PSS were used in flat- and circular-tube air-cooled heat exchangers to evaluate the heat-exchange performance. The overall trend of the efficiency factor of the CBNFs in the heat-exchange systems was superior to that of water. These research results indicate that CBNFs prepared with the MSVTM should have considerable development potential and practicability in related future applications.