以二流體模型模擬鎂基固態儲氫系統中的鎂粉末運動

Abstract

本研究旨在模擬鎂基固態儲氫系統中鎂粉末的運動行為。固態儲氫技術因其高儲氫密度和良好的安全性，已成為能源儲存技術的研究熱點。鎂基儲氫材料因其豐富的地殼含量和較高的儲氫能力，成為研究的重點。然而，過去的實驗發現，在高溫高壓環境下，鎂粉末易在儲氫罐體底部燒結，導致氫氣吸附效率下降，影響儲氫性能。為解決此問題，本研究提出在儲放氫入口處增加側壁開孔盤管的設計，使氫氣在注入時能夠攪動粉末，均勻化粉末濃度，從而提高儲氫效率。 為了模擬氫氣與鎂粉間的氣固耦合運動，本研究採用二流體模型 （Two-Fluid Model）。與傳統的拉格朗日法將粉末個別離散化不同，二流體模型將粉末視為連體，利用體積分數表示不同相所佔據的空間。氣相和固相分別滿足各自的質量、動量及能量守恆定律，並通過如動量交換係數、阻力模型計算氫氣與鎂粉之間的作用力，而透過固體壓力、顆粒溫度、顆粒黏度、徑向分佈函數使顆粒群能夠以連體的方式計算。本研究通過對不同邊界條件和盤管幾何設計的模擬，分析了這些因素對粉末均勻度的影響，從而提出優化鎂基固態儲氫系統的方法。 為了評估二流體模型對於儲氫系統的適用性，本研究首先進行了一系列的定性實驗，比較模擬結果與實驗結果後，證明其能夠成功預測盤管於不同邊界條件下，吹動粉末或是堵塞之情形。 將二流體模型應用在鎂基固態儲氫系統後，其成果顯示，在不同的邊界條件和盤管幾何設計下，鎂粉末的均勻度存在顯著差異。盤管開孔的角度、罐體的擺放方式及不同的邊界條件對於粉末的攪動效果皆有一定程度地影響。較大的質量流率和罐體倒置有助於提高粉末的均勻度；而將盤管之孔洞改為45°能夠進一步減少壁面的粉末聚集，減少燒結現象的發生。此外，利用脈衝式的質量流率作為邊界條件則能夠有效增加粉末混和效果及延長其混和時間。 綜上所述，本研究通過二流體模型模擬鎂基固態儲氫系統中粉末的運動行為，提出了通過設計側壁開孔盤管來改善粉末均勻度的方法。研究結果為鎂基固態儲氫系統的優化設計提供了新的思路，具有重要的實際應用價值。本研究的成果可用於提高鎂基儲氫材料的使用效率，推動固態儲氫技術的發展，並為未來的氫能應用提供可靠的技術支持。

This study aims to simulate the motion behavior of magnesium powder in magnesium-based solid-state hydrogen storage systems. Solid-state hydrogen storage technology has become a research hotspot in energy storage due to its high hydrogen storage density and excellent safety. Magnesium-based hydrogen storage materials have been a focus of research owing to their abundant crustal content and high hydrogen storage capacity. However, previous experiments have found that under high-temperature and high-pressure environments, magnesium powder tends to sinter at the bottom of storage tanks, leading to decreased hydrogen adsorption efficiency and impaired storage performance. To address this issue, this study proposes a design incorporating side-wall perforated coiled tubes at the hydrogen inlet/outlet, allowing hydrogen gas to agitate the powder during injection, thereby homogenizing powder concentration and improving storage efficiency. To simulate the gas-solid coupled motion between hydrogen and magnesium powder, this study employs the Two-Fluid Model (TFM). Unlike traditional Lagrangian methods that discretize individual powder particles, the TFM treats the powder as a continuum, using volume fractions to represent the space occupied by different phases. The gas and solid phases each satisfy their respective mass, momentum, and energy conservation laws. Interactions between hydrogen gas and magnesium powder are calculated through parameters such as momentum exchange coefficients and drag models. Solid pressure, granular temperature, granular viscosity, and radial distribution functions enable the particle groups to be calculated as a continuum. This study analyzes the effects of various boundary conditions and coiled tube geometries on powder uniformity through simulations, proposing methods to optimize magnesium-based solid-state hydrogen storage systems. To evaluate the applicability of the TFM to hydrogen storage systems, a series of qualitative experiments were first conducted. Comparison of simulation results with experimental data validated the model's ability to successfully predict powder agitation or clogging under different boundary conditions for the coiled tubes. Application of the TFM to magnesium-based solid-state hydrogen storage systems revealed significant differences in magnesium powder uniformity under various boundary conditions and coiled tube geometries. The angle of coiled tube perforations, tank orientation, and different boundary conditions all influenced powder agitation to varying degrees. Higher mass flow rates and inverted tank orientation contributed to improved powder uniformity, while changing the coiled tube perforations to a 45° angle further reduced powder accumulation on walls, mitigating sintering phenomena. Moreover, using pulsed mass flow rates as boundary conditions effectively enhanced powder mixing effects and prolonged mixing time. In conclusion, this study simulates the motion behavior of powder in magnesium-based solid-state hydrogen storage systems using the Two-Fluid Model, proposing a method to improve powder uniformity through the design of side-wall perforated coiled tubes. The research results provide new insights for optimizing the design of magnesium-based solid-state hydrogen storage systems, offering significant practical application value. The outcomes of this study can be applied to improve the efficiency of magnesium-based hydrogen storage materials, promote the development of solid-state hydrogen storage technology, and provide reliable technical support for future hydrogen energy applications.