冰泥冷媒之熱傳與壓降

Abstract

強勁的經濟增長和電力需求的激增使夏季高峰電力需求成為全球一項重大挑戰。空調佔據建築物總能源消耗的40%以上，冰儲冷空調已成為減少高峰電力需求和建築物能源消耗的重要方法之一，它利用非高峰時段的電力來製冰和儲存冰，然後在高峰時段作為冷卻源使用。冰泥是一種由小冰粒子和載體液體組成的固液兩相混合物，是冰儲冷空調的工作流體，它在多方面優於傳統冷媒，例如非氟氯碳化合物、卓越的能量儲存能力和優越的熱傳特性，然而冰泥在冷卻系統中的應用仍受流動和熱傳特性理解不足的限制，目前文獻中對於冰泥是牛頓流體還是非牛頓流體沒有定論，因此本研究旨在建立一個冰泥系統，並在不同運行條件下研究其壓降和熱傳特性。 本研究建立了一套水平管路的冰泥量測系統，使用密度流量計來量測冰泥的蓄冰率(IPF, Ice packing factor)，並建立了可視化系統，在可視化系統中不僅量測冰泥壓降及熱傳，也可觀察冰泥在管路內的流動情況；本研究使用5%乙二醇作為載體容液，並包含不同的蓄冰率，平均冰顆粒大小約為200 μm，實驗系統之管路為14mm之正方管，並且雷諾數操作在1900以下時，我們的研究結果顯示，當蓄冰率低於15%時，冰泥的流動行為呈牛頓流體特性，冰泥的壓降值相較於單相水有4至12倍的上升，壓降值隨著蓄冰率的升高而增加，此外，在熱通量恆定400 W、三面加熱的情況下，我們發現冰泥的熱對流係數以及努塞數約為單相水的1.2倍至1.7倍，熱對流係數隨著蓄冰率的升高而增加，努塞數在雷諾數大於1200時才隨著蓄冰率的升高而增加，然而造成此熱傳現象之機制尚不確定。

The robust economic growth and the surge in electricity demand have caused summer peak power demand to be a significant global challenge. Air conditioning accounts for over 40% of a building''s total energy consumption. Ice storage air conditioning has emerged as an important approach to reduce peak power demand and energy consumption in buildings. It utilizes non-peak electricity to produce and store ice, which can be used as a cooling source during peak hours. Ice slurry, a two-phase mixture of small ice particles and carrier liquid, is the working fluid for ice storage air conditioning. It has several advantages over conventional refrigerants, such as being free of CFCs, excellent energy storage capabilities, and superior heat transfer characteristics. However, the application of ice slurry in cooling systems is still limited by the lack of understanding of its flow and thermal behavior. The debate on whether ice slurry behaves as a Newtonian or non-Newtonian fluid remains unresolved in the current literature. Therefore, this study aims to establish an ice slurry system and investigate its pressure drop and heat transfer properties under different operating conditions. The study implemented a horizontal pipeline ice slurry measurement system, employing a Coriolis flowmeter to measure the ice packing factor (IPF) and establishing a visualization system. This system not only measured pressure drop and heat transfer but also allowed observation of the ice slurry flow within the pipeline. The ice slurries in this work use 5% ethylene glycol as the carrier liquid and consist of various ice packing factors(IPFs). The average ice particle size is approximately 200 μm. The experimental system employed a 14mm square pipe, and Reynolds numbers were kept below 1900. The results indicate that when the IPF is below 15%, the flow behavior of ice slurry resembles that of Newtonian fluid characteristics. The pressure drop of ice slurry was 4 to 12 times higher compared to single-phase water, increasing with higher IPF. Additionally, under a constant heat flux of 400 W and three-sided heating, the heat transfer coefficient and Nusselt number of ice slurry were approximately 1.2 to 1.7 times that of single-phase water. The heat transfer coefficient increases with higher ice packing factor, and the Nusselt number increases only when the Reynolds number exceeds 1200. However, the mechanism causing this heat transfer phenomenon remains uncertain.