摘要:本「固液二相流實驗室」(Solid-Liquid Two-phase flow Lab)的近期研究目標旨在探討受重力驅動的固體液體二相混合流之動態行為與理論模型的推論與建構。在大自然界及眾多尖端工業製程中,我們常會發現固體液體混合流的動態模式。這種固液二相共存混合體的宏觀運動,除了受到內部顆粒直接碰撞的影響,顆粒間黏性流體細部的流動行為也可能造成二相流整體動態行為關鍵性的改變。 當共存的兩相由密度相近的材料所組成時,顆粒和流體的運動有著緊密的相關性。這種高度非線性的相互作用產生了單相物質運動所沒有的多尺度動態特性。
本研究預計為期兩年,擬藉系統的實驗來探討顆粒運動對二相混合體宏觀行為的影響。鑒於當今的二相流實驗多限於穩態行為的探討,本實驗室將突破致力於二相流動態行為的研究。本計畫預計建構一個室內坡道,藉調整傾斜角賦予上游混合體不同的驅動力。除了坡道角度的操控,本計劃亦將選用不同大小和不同材質的固體圓球,搭配不同密度的混合液,以探討不同的流動條件下的二相流行為。
本研究的二相流速度較快且為時短暫,本實驗室將研發創新的觀測技術及影像處理分析方法。本研究的觀測重點將為於二相流中固體顆粒分離(particle segregation)及固液兩相的分相現象(phaseseparation); 探究這兩種微觀的機制如何影響二相流宏觀的行為,更是此實驗的重要目標。為獲得更完整的結論,本研究亦將進行實驗數據的無因次分析來檢測影響二相流體的關鍵參數,期能完成運動方程式理論與模型的推論與建構。預擬探討的參數有平均雷諾數、顆粒Stokes number、Archimedesnumber和Savage number。
Abstract: A solid-liquid flow is the motion of a mixture that is composed of solid particles and filling liquids (gas or fluid). Flow of this kind can be found in various geophysical and environmental problems, as well as in industrial applications. In addition to direct particle collisions in a flowing mixture, the co-existing liquid may greatly modify the particle contact giving rise to new flow phenomena. When the two phases possess comparable inertia, the particle interactions are inevitably coupled with the surrounding liquid motion. The strong solid-liquid interaction introduces the mixture new mechanisms for momentum transport and energy dissipation, which results in rich flow rheology. Despite the prevalence of solid-liquid flows, our knowledge of their bulk macroscopic and microscopic behavior is still fragmental. Even less understood are the mixture
dynamic behavior and transient responses to varying boundary and flow conditions.
As a first step to tackle the non-linear, multi-dimensional, but yet important problem, we propose to examine how the mixture constituents affect the flow dynamic behavior through systematic experiments. To be more specific, this two-year long project will first focus on how the solid particles segregate in a two-phase flow. Then we will analyze how this “particulate wave” affects the overall bulk rheology. Since most of the existing research on particle segregation is specialized in flows at steady states, we plan to investigate the phenomena within an unsteadily flowing mixture. We plan to build one or two lab-scale flumes (3-10m long and 0.3-1m wide) that can be tilted at specific angles from the horizontal to initiate the flow. To prepare the sample, solid spheres of different sizes (5-30 mm in diameter) and materials (steel, glass, and Nylon) and materials will be used with premixed water-glycerin mixtures or silicon oils (with a viscosity range of 1-25 cP). We will start with mixtures of mono-sized spheres and then extend to dual- or poly-disperse systems. By properly choosing the mixture constituents and the flume angle, we shall achieve a wide range of flow conditions in the lab.
In the following theoretical work, we aim to develop a dynamic flow model that characterizes the flow behavior, especially the mixture run-out time and distance. The dimensionless parameters that we will examine include mean flow Reynolds number, particle Stokes number, Archimedes number, and Savage number. The long term goal of this two-year long research is to identify the crucial mechanisms and flow parameters that govern the solid-liquid flow under varying driving and boundary conditions.
The findings will undoubtedly shed lights on the fundamentals of complex fluids and nonlinear dynamic systems. The obtained knowledge may al