發(fā)布時間：2018-08-13 19:40

【摘要】：如何有效地利用陰極反應(yīng)生成的水和加濕的反應(yīng)氣體對膜進行適當?shù)乃献饔?并及時地排出陰極液態(tài)水,是提高質(zhì)子交換膜燃料電池性能的關(guān)鍵。作為氣體擴散層中一種典型的流動形式,交叉流能夠有效地排出陰極液態(tài)水。同時,由于氣體擴散層的疏水處理工藝,會導(dǎo)致其表面的接觸角分布不均勻。交叉流以及非均勻接觸角對氣體擴散層微觀結(jié)構(gòu)中液態(tài)水的傳輸過程均有影響,目前,與此相關(guān)的研究還很少。本研究基于已經(jīng)開發(fā)的氣體擴散層真實微觀結(jié)構(gòu)的重建模型和VOF方法,建立了一個三維、兩相流瞬態(tài)模型,研究接觸角(固定和漸變)、壓力差(毛細壓力)對交叉流在氣體擴散層微觀結(jié)構(gòu)中傳輸特性的影響。研究結(jié)果表明,交叉流在氣體擴散層的傳輸過程中,會先通過一些容易滲透的孔隙,形成“毛細指進模式”;然后越來越多的液態(tài)水侵入到氣體擴散層中,填滿其余的大部分孔隙,形成“穩(wěn)定傳輸模式”。研究證實,對液態(tài)水的傳輸模式來說,壓力差比接觸角具有更顯著的影響。較高的壓力差和較小的接觸角能夠加快液態(tài)水的侵入過程,使交叉流動過程達到穩(wěn)定狀態(tài)所需的時間縮短;對于漸變接觸角工況,在垂直于流道方向的不同橫截面上,氣體擴散層表面的接觸角也不相同。在這些截面上,交叉流的傳輸特性與其在相對應(yīng)的固定接觸角工況下具有相同的變化規(guī)律;對于交叉流在氣體擴散層中的整個傳輸過程,漸變接觸角工況與其相對應(yīng)的固定接觸角中間值工況下的變化規(guī)律相似。當交叉流的傳輸過程接近結(jié)束時,達到規(guī)定的穩(wěn)定狀態(tài)。在穩(wěn)定狀態(tài)下,毛細壓力(壓力差)隨液態(tài)水體積分數(shù)的增加而增大,這個趨勢在液態(tài)水體積分數(shù)較大的時候更加明顯;在穩(wěn)定狀態(tài)下,氣體擴散層中液態(tài)水的質(zhì)量流量與壓力差呈正比例,且當接觸角較小時,氣體擴散層中液態(tài)水的質(zhì)量流量更高�？傮w來說,對于漸變接觸角及其相對應(yīng)的固定接觸角中間值的工況,壓力差對交叉流穩(wěn)態(tài)傳輸特性的影響規(guī)律相似。
[Abstract]:The key to improve the performance of proton exchange membrane fuel cells is how to effectively use the water generated by the cathodic reaction and the humidified reaction gas for proper water cooperation and timely discharge of cathode liquid water. As a typical flow form in gas diffusion layer, cross flow can effectively discharge cathode liquid water. At the same time, due to the hydrophobic treatment of the gas diffusion layer, the surface contact angle distribution is not uniform. Cross-flow and non-uniform contact angle affect the transport process of liquid water in the microstructure of gas diffusion layer. Based on the developed reconstruction model of the true microstructure of the gas diffusion layer and the VOF method, a three-dimensional and two-phase flow transient model is established. The effects of contact angle (fixed and gradual) and pressure difference (capillary pressure) on the transport characteristics of cross flow in the microstructure of gas diffusion layer are studied. The results show that the cross flow in the gas diffusion layer will first pass through some easily permeable pores to form a "capillary pointing mode", and then more and more liquid water will invade into the gas diffusion layer. Fill most of the remaining pores to form a "stable transport mode". It is confirmed that the pressure difference is more significant than the contact angle in the transport mode of liquid water. Higher pressure difference and smaller contact angle can speed up the invasion process of liquid water and shorten the time required for the cross flow process to reach a stable state. For the gradual contact angle condition, at different cross sections perpendicular to the direction of the flow channel, The contact angle of the gas diffusion layer surface is also different. On these sections, the transport characteristics of cross flow are the same as those under the corresponding fixed contact angle, and for the whole transmission process of cross flow in gas diffusion layer, The variation law of the gradual contact angle is similar to that of the fixed contact angle. When the transmission process of the cross-flow is near the end, the specified stable state is reached. Under steady state, capillary pressure (pressure difference) increases with the increase of liquid water volume fraction, which is more obvious when the volume fraction of liquid water is larger; in stable state, the capillary pressure (pressure difference) increases with the increase of liquid water volume fraction. The mass flow of liquid water in the gas diffusion layer is proportional to the pressure difference, and when the contact angle is small, the mass flow rate of liquid water in the gas diffusion layer is higher. As a whole, the influence of pressure difference on the steady state transmission characteristics of cross flow is similar for the condition of gradual contact angle and its corresponding intermediate value of fixed contact angle.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TM911.4

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本文編號：2181980