發(fā)布時(shí)間：2018-08-17 10:50

【摘要】：在能源危機(jī)的背景下,新能源汽車得到了世界各國(guó)政府的大力支持并得到迅猛的發(fā)展。大容量鋰離子電池作為電動(dòng)汽車的動(dòng)力核心,其性能的優(yōu)劣在很大程度上決定了電動(dòng)汽車的性能,因此對(duì)鋰離子電池工作性能的研究尤為重要。溫度是影響鋰離子電池工作的重要因素之一。合理的溫度范圍能夠提高電池的輸出性能,延長(zhǎng)電池的使用壽命,因而需要對(duì)電池進(jìn)行有效的熱管理。相變蓄熱具有蓄熱密度大、結(jié)構(gòu)簡(jiǎn)單、無耗能、體積小和溫度變化小等優(yōu)點(diǎn),因此具有良好的發(fā)展前景。本文根據(jù)電動(dòng)汽車電池系統(tǒng)的發(fā)熱情況,搭建泡沫鋁-石蠟復(fù)合相變材料蓄熱可視化實(shí)驗(yàn)臺(tái),對(duì)泡沫鋁-石蠟復(fù)合相變材料蓄熱系統(tǒng)進(jìn)行相變界面的移動(dòng)、溫度變化、溫差變化的研究。實(shí)驗(yàn)結(jié)果表明:自然對(duì)流會(huì)對(duì)相變界面的移動(dòng)產(chǎn)生較大影響,并惡化復(fù)合相變材料底部的換熱,使得沿?zé)崃髅芏确较蛏系臏夭钶^大,在熱流密度垂直的方向上溫差較小。根據(jù)獲得的實(shí)驗(yàn)現(xiàn)象和實(shí)驗(yàn)數(shù)據(jù),對(duì)泡沫鋁的結(jié)構(gòu)進(jìn)行調(diào)整,優(yōu)化復(fù)合相變材料的蓄熱過程。鑒于實(shí)驗(yàn)手段有限,本文將重點(diǎn)采用數(shù)值模擬方法對(duì)復(fù)合相變材料的蓄熱過程進(jìn)行研究。根據(jù)泡沫鋁的實(shí)際結(jié)構(gòu)進(jìn)行簡(jiǎn)化,建立與實(shí)際結(jié)構(gòu)相近的十四面體多孔介質(zhì)模型,并與實(shí)驗(yàn)結(jié)果進(jìn)行對(duì)比驗(yàn)證。驗(yàn)證結(jié)果表明:模擬結(jié)果與實(shí)驗(yàn)結(jié)果高度一致,這表明簡(jiǎn)化的多孔介質(zhì)模型能夠很好的反映泡沫鋁的真實(shí)結(jié)構(gòu),數(shù)值模擬獲取結(jié)果的可靠性較好。通過多孔介質(zhì)模型對(duì)復(fù)合相變材料的相變界面的移動(dòng)、溫度均勻性及蓄熱性能進(jìn)行了研究,針對(duì)泡沫金屬的孔隙率變化對(duì)復(fù)合相變材料蓄熱過程的影響,并分析了不同均勻孔隙率泡沫鋁復(fù)合相變材料與孔隙率梯度變化的復(fù)合相變材料的蓄熱過程。研究結(jié)果表明:相變界面的移動(dòng)受孔隙率的影響較大。孔隙率越大,相變界面的移動(dòng)與加熱面的夾角越明顯。孔隙率越大,復(fù)合相變材料的溫度均勻性越差。孔隙率梯度變化(從底部到頂部,孔隙率呈0.86-0.90-0.94三段式和0.86-0.94線性增大)能有效改善底部傳熱較差,改善復(fù)合相變材料的內(nèi)部傳熱,加速相變材料的融化。孔隙率三段式梯度變化和孔隙率線性變化的復(fù)合相變材料的內(nèi)部溫差較均勻孔隙率為0.9的復(fù)合相變材料的內(nèi)部溫差降低了10.8℃。孔隙率梯度變化的蓄熱速率較均勻等效的孔隙率復(fù)合材料的蓄熱速率提高了142%。另外,研究表明:復(fù)合相變材料的熱傳遞主要通過泡沫金屬的導(dǎo)熱進(jìn)行傳遞。
[Abstract]:Under the background of energy crisis, new energy vehicles have been supported by governments all over the world and developed rapidly. As the power core of electric vehicle, the performance of large capacity lithium ion battery determines the performance of electric vehicle to a great extent, so it is very important to study the performance of lithium ion battery. Temperature is one of the important factors that affect the operation of lithium ion battery. The reasonable temperature range can improve the output performance of the battery and prolong its service life, so it is necessary to effectively heat manage the battery. Phase change heat storage has the advantages of high heat storage density, simple structure, no energy consumption, small volume and small temperature change, so it has a good development prospect. According to the heating condition of electric vehicle battery system, a visualized experimental platform for thermal storage of foam aluminum-paraffin composite phase change material is built, and the phase change interface and temperature change are carried out for the thermal storage system of aluminum foam and paraffin composite phase change material. The study of the variation of temperature. The experimental results show that natural convection will have a great effect on the movement of phase transition interface, and worsen the heat transfer at the bottom of the composite phase change material, which makes the temperature difference along the direction of heat flux larger and the temperature difference smaller in the vertical direction of heat flux. According to the experimental phenomena and experimental data, the structure of aluminum foam was adjusted to optimize the heat storage process of composite phase change materials. In view of the limited experimental means, the numerical simulation method will be used to study the heat storage process of the composite phase change materials. According to the actual structure of aluminum foam, a decahedron porous media model is established, which is similar to the actual structure, and the results are compared with the experimental results. The results show that the simulation results are in good agreement with the experimental results, which indicates that the simplified porous media model can well reflect the true structure of aluminum foam, and the reliability of the numerical simulation results is good. The movement, temperature uniformity and heat storage performance of phase change interface of composite phase change materials were studied by porous media model. The effect of porosity change on the heat storage process of composite phase change materials was studied. The heat storage process of aluminum foam composite phase change material with different uniform porosity and composite phase change material with different porosity gradient was analyzed. The results show that the movement of phase change interface is greatly affected by porosity. The larger the porosity, the more obvious the angle between the movement of phase change interface and the heating surface. The larger the porosity, the worse the temperature uniformity of the composite phase change material. The change of porosity gradient (0.86-0.90-0.94 three-stage porosity and 0.86-0.94 linear increase from bottom to top) can effectively improve the poor heat transfer at the bottom, improve the internal heat transfer of the composite phase change material, and accelerate the melting of the phase change material. The internal temperature difference of the composite phase change material with three-segment gradient of porosity and linear variation of porosity is 10.8 鈩，

本文編號(hào)：2187371