【摘要】：質(zhì)子交換膜燃料電池（PEMFC）是一種清潔高效的能源轉(zhuǎn)換裝置。PEMFC的水管理是影響其工作性能、穩(wěn)定性和可靠性的一個關鍵技術。液態(tài)水在PEMFC流道內(nèi)的高效傳輸和去除是PEMFC水管理的一個重要方面。研究和分析PEMFC陰極流道內(nèi)的氣液兩相流動問題，特別是液態(tài)水在流道內(nèi)的傳輸和去除過程，一方面有助于深入認識液態(tài)水在微觀流道內(nèi)的傳輸特點和去除機理，另一方面可以指導PEMFC流道的設計，進而改善PEMFC的水管理和提高PEMFC的工作性能。 本文以PEMFC流道內(nèi)的兩相流動問題為研究對象，在一個現(xiàn)有靜態(tài)潤濕模型（只包含一個靜態(tài)接觸角（Static Contact Angle）的作用）的基礎上，建立了PEMFC流道內(nèi)空氣-水兩相流動的動態(tài)潤濕模型（包含滑動角（Sliding Angle）和動態(tài)接觸角（Dynamic Contact Angle）的作用），并在此模型基礎上，開展了一系列的研究工作。本文的主要研究工作包括： 1. PEMFC流道內(nèi)兩相流的動態(tài)潤濕模型的建立和模擬。首先，采用橢圓形液固接觸面形狀和線性動態(tài)接觸角分布，推導出了滑動角和動態(tài)接觸角這兩個表征固體表面動態(tài)潤濕性的參數(shù)之間的理論關系式，明確了兩者之間的相互作用關系。其次，采用合適的數(shù)值方法，將由此關系式確定的滑動角和動態(tài)接觸角的作用應用到一個數(shù)值模型中，建立了PEMFC流道內(nèi)兩相流動的動態(tài)潤濕模型。采用此動態(tài)潤濕模型，研究了動態(tài)潤濕性對水滴在PEMFC流道中傳輸過程的影響。研究表明，在相同靜態(tài)接觸角下，滑動角越小，動態(tài)接觸角的變化范圍或接觸角差異（Contact Angle Hysteresis）越小，水滴的高度越大，水滴在氣體擴散層（GDL）表面的運動速度越大。因而，小的GDL表面滑動角有利于水滴在PEMFC流道中的傳輸和去除。 2.水滴在GDL表面的滲透位置對其傳輸過程的影響。詳細研究了水滴在GDL表面沿流道寬度方向不同位置處的傳輸過程。研究發(fā)現(xiàn)了水滴在流道寬度方向做周期性擺動的現(xiàn)象，并且，隨著水滴偏離GDL表面中心的距離變大，其擺動的幅度會變大。當水滴的滲透位置偏離GDL表面中心一定距離后，水滴會接觸到流道表面。此時，當流道表面接觸角較小時，水滴會由于流道表面毛細力的作用脫離GDL表面，最終運動到由流道側(cè)面和流道底面形成的流道角落處。這表明流道表面接觸角對液態(tài)水從GDL表面的去除有重要作用。 3.設計了兩種加快GDL表面除水的新型流道，分別為帶有親水針的流道和帶有親水薄板的流道。研究了水滴在這兩種新型流道中的傳輸過程，特別是從GDL表面的去除過程。研究發(fā)現(xiàn)在GDL表面上傳輸?shù)乃闻c親水針或親水薄板接觸后，會在親水針或親水薄板表面毛細力作用下從GDL表面去除。研究表明，采用在流道中安裝親水針或親水薄板的方法，可以在流道壓降增加較小的情況下，有效地起到GDL表面除水的作用，特別適合于在平行直流道中的應用。研究同時還表明，與帶有親水針的流道相比，帶有親水薄板的流道的GDL表面除水效果更好，，流道的壓降也更低。
[Abstract]:Proton exchange membrane fuel cell (PEMFC) is a clean and efficient energy conversion device. The water management of PEMFC is a key technology affecting the performance, stability and reliability of PEMFC. The problem of phase flow, especially the transfer and removal of liquid water in the channel, is helpful to understand the transport characteristics and removal mechanism of liquid water in the microchannel. On the other hand, it can guide the design of PEMFC channel, improve the water management of PEMFC and improve the performance of PEMFC.
In this paper, a dynamic wetting model (including Sliding Angle and Dynamic Contac Angle) for air-water two-phase flow in PEMFC runner is established based on a static wetting model (including only one static Contact Angle). On the basis of this model, a series of research work has been carried out.
1. Establishment and Simulation of dynamic wettability model of two-phase flow in PEMFC runner. Firstly, by using elliptical liquid-solid contact surface shape and linear dynamic contact angle distribution, the theoretical relationship between sliding angle and dynamic contact angle, which characterize the dynamic wettability of solid surface, is deduced, and the interaction between them is clarified. Secondly, a dynamic wettability model of two-phase flow in a PEMFC channel is established by applying the sliding angle and dynamic contact angle determined by the equation to a numerical model. The influence of dynamic wettability on the droplet transport in the PEMFC channel is studied by using the dynamic wettability model. Under the same static contact angle, the smaller the sliding angle, the smaller the range of dynamic contact angle or the difference of contact angle (Contact Angle Hysteresis), and the larger the height of water droplets, the greater the velocity of water droplets moving on the surface of gas diffusion layer (GDL).
2. The influence of the penetration position of water droplets on the GDL surface on its transport process is studied in detail. The transmission process of water droplets on the GDL surface is studied in different positions along the channel width direction. When the penetration position of the droplets deviates from the center of the GDL surface, the droplets will contact the runner surface. At this time, when the contact angle of the runner surface is small, the droplets will be separated from the GDL surface due to the capillary force of the runner surface, and eventually move to the corner of the runner formed by the runner side and the bottom of the runner. It plays an important role in the removal of liquid water from the surface of GDL.
3. Two kinds of new runners are designed to accelerate the surface dewatering of GDL, one with hydrophilic needle and the other with hydrophilic sheet. Hydrophilic needle or hydrophilic sheet can be removed from the surface of GDL by capillary force. The results show that the method of installing hydrophilic needle or hydrophilic sheet in the runner can effectively remove water from the surface of GDL when the pressure drop in the runner increases slightly. It is especially suitable for the application in parallel direct current channels. Compared with the runner with hydrophilic needle, the runner with hydrophilic thin plate has better surface dewatering effect and lower pressure drop.
【學位授予單位】：天津大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TM911.4

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