本文選題：液滴　切入點(diǎn)：可視化　出處：《天津大學(xué)》2014年博士論文

【摘要】：質(zhì)子交換膜燃料電池(PEMFC)運(yùn)行過程中,在其流道內(nèi)部往往形成氣液兩相流,弄清該類氣液兩相流的特點(diǎn),對(duì)提高燃料電池水管理水平,具有重要的科學(xué)意義和應(yīng)用價(jià)值。在有關(guān)PEMFC的研究中,如何在不發(fā)生水淹的同時(shí)保證電解質(zhì)膜的質(zhì)子傳導(dǎo)性的水管理問題是一個(gè)十分重要的課題。雖然近年來有關(guān)燃料電池水管理方面的研究報(bào)告很多,但尚有很多深層次的機(jī)理問題并未弄清。這也嚴(yán)重的制約了相關(guān)研究的深入開展�；诖�,本文以燃料電池陰極流道氣液兩相流動(dòng)為研究基礎(chǔ),從對(duì)單一液滴的研究入手,進(jìn)而對(duì)流道內(nèi)的氣液兩相流動(dòng)進(jìn)行研究。液滴在微小流道內(nèi)的運(yùn)動(dòng)現(xiàn)象有很多應(yīng)用背景,包括化學(xué)工程、航空動(dòng)力工程等領(lǐng)域,而燃料電池也是其中的一個(gè)應(yīng)用背景。對(duì)于PEMFC,在運(yùn)行過程中,隨化學(xué)反應(yīng)的進(jìn)行,氣體擴(kuò)散層表面將逐漸產(chǎn)生小液滴,而且小液滴會(huì)逐漸長(zhǎng)大,并在來流作用下發(fā)生形變。本文將此現(xiàn)象提取出來,研究單一液滴在不銹鋼金屬底板上在來流作用下其出現(xiàn)、生長(zhǎng)、脫離乃至貼附、破碎的整個(gè)過程。為便于對(duì)單一液滴進(jìn)行研究,本文設(shè)計(jì)了可視化流道,研究液滴在流道內(nèi)在來流作用下且自身不斷長(zhǎng)大的過程中的變形情況以及脫離或者貼附行為。采用高速攝像系統(tǒng)獲取液滴變形這一瞬態(tài)過程中的動(dòng)態(tài)信息,而后對(duì)所獲取信息進(jìn)行處理,并變換參數(shù)的不同組合,做組合實(shí)驗(yàn),研究液滴的前進(jìn)接觸角、后退接觸角以及前后接觸角之差等液滴物性參數(shù)與液滴高度、來流雷諾數(shù)、液滴浸潤(rùn)直徑等之間的關(guān)系,并對(duì)現(xiàn)象產(chǎn)生的原因進(jìn)行具體分析,進(jìn)而總結(jié)出各物理參數(shù)之間的影響規(guī)律。對(duì)不銹鋼表面進(jìn)行疏水性處理,通過對(duì)比研究不同表面特性對(duì)液滴存在狀態(tài)的影響。為便于研究微小流道內(nèi)的氣液兩相流動(dòng),本文設(shè)計(jì)了微小流道氣液兩相流動(dòng)可視化實(shí)驗(yàn)系統(tǒng),對(duì)一個(gè)側(cè)面由透氣性多孔材料構(gòu)成的毫米尺寸的方形流道內(nèi),沿著流道內(nèi)氣體流動(dòng)方向液體水不斷地通過滲液側(cè)面滲入到氣體流道內(nèi)而形成的氣液兩相流動(dòng)現(xiàn)象進(jìn)行了實(shí)驗(yàn)研究。實(shí)驗(yàn)過程中,流道尺寸選擇了三種規(guī)格,氣液參數(shù)各選擇多組,并進(jìn)行組合,作為滲液側(cè)面的透氣性多孔材料共選擇兩種,一種是普通碳紙,另一種為經(jīng)PTFE浸潤(rùn)的碳紙。基于可視化觀察的結(jié)果,對(duì)這種特殊的兩相流動(dòng)的流型進(jìn)行了分類,并分析了氣體流量和滲液速度對(duì)流型的影響。同時(shí),發(fā)現(xiàn)由于液體的滲入流道兩端壓差表現(xiàn)出明顯的脈動(dòng)性,這種壓差脈動(dòng)的頻率不僅依賴于滲液量還依賴于氣體流量,但脈動(dòng)的振幅幾乎不受滲液量的影響。碳紙的PTFE浸潤(rùn)處理,主要作用不在于改變流道內(nèi)流型,而在于改變特定流型在流道中出現(xiàn)的位置。另外,兩種滲液側(cè)面特性下,壓降大小及其脈動(dòng)特性也存在很大的差異,反映了兩者排液機(jī)理的差異。
[Abstract]:In the process of PEMFC (Proton Exchange membrane fuel Cell) running, gas-liquid two-phase flow is often formed in the flow channel of PEMFC. The characteristics of this kind of gas-liquid two-phase flow are clarified, and the water management level of the fuel cell is improved. It has important scientific significance and application value. In the research of PEMFC, How to ensure the proton conductivity of electrolyte membrane without flooding is a very important issue, although there have been many researches on water management of fuel cell in recent years. However, there are still many deep-seated mechanism problems that have not been clarified. This also seriously restricts the further development of related research. Based on this, this paper takes the gas-liquid two-phase flow in the cathode channel of fuel cell as the research foundation, starting with the study of single droplet. Then the gas-liquid two-phase flow in the channel is studied. The motion of droplets in micro-channels has many application backgrounds, including chemical engineering, aerodynamics engineering and so on. The fuel cell is also one of the applications. For PEMFC, as the chemical reaction goes on, the surface of the gas diffusion layer will gradually produce small droplets, and small droplets will gradually grow up. This phenomenon is extracted from this phenomenon to study the appearance, growth, detachment and even attachment of a single droplet on the stainless steel metal substrate under the action of the incoming flow. The whole process of fragmentation. In order to facilitate the study of a single droplet, a visual flow channel is designed in this paper. This paper studies the deformation of droplets in the process of internal flow in the channel and their growing up. The dynamic information of the transient process of droplet deformation is obtained by using a high-speed camera system, which is used to obtain the dynamic information during the transient process of droplet deformation. Then the obtained information is processed, the different combinations of parameters are transformed, and combined experiments are done to study the drop physical parameters and drop height, such as the forward contact angle, the backward contact angle and the difference between the front and back contact angles, and the flow Reynolds number. The relationship between droplet wetting diameter and so on, and the causes of the phenomenon are analyzed in detail, and the influence laws among various physical parameters are summarized. The surface of stainless steel is treated with hydrophobicity. In order to study the gas-liquid two-phase flow in micro-channel, a visualized experimental system for gas-liquid two-phase flow in micro-channel is designed. In the case of a square passage of millimeter size on the side of a porous material, The gas-liquid two-phase flow phenomenon formed by the continuous infiltration of liquid water into the gas channel through the seepage side along the gas flow direction in the channel has been studied experimentally. In the course of the experiment, three specifications have been selected for the flow channel size. Each of the gas-liquid parameters is composed of two kinds of porous materials, one is ordinary carbon paper, the other is carbon paper infiltrated by PTFE, which is based on the results of visual observation. The flow patterns of this special two-phase flow are classified, and the effects of gas flow rate and seepage velocity on the convection pattern are analyzed. It is also found that the pressure difference between the two ends of the liquid permeating channel shows obvious pulsation. The frequency of the differential pressure pulsation depends not only on the amount of seepage but also on the flow rate of gas, but the amplitude of the pulsation is almost independent of the amount of percolation. The main function of the PTFE soakage treatment of carbon paper is not to change the flow pattern of the flow channel. In addition, the pressure drop and its pulsation characteristics are also very different under the side characteristics of the two kinds of seepage, which reflects the difference of the drainage mechanism between them.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TM911.4

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