發(fā)布時(shí)間：2018-09-02 06:26

【摘要】：隨著全球工業(yè)和經(jīng)濟(jì)的飛速發(fā)展,各國(guó)對(duì)能源的需求量越來(lái)越多,煤炭和石油等傳統(tǒng)不可再生能源的消耗逐漸增加,能源短缺和環(huán)境污染問題日益加劇,因此,節(jié)能減排、提高能源利用率迫在眉睫。相變儲(chǔ)能材料能夠解決熱能供求在時(shí)間和空間上不匹配的問題,可以有效地提高能源的利用率,在工業(yè)余熱回收、太陽(yáng)能熱利用、建筑節(jié)能、電子元器件的熱管理、動(dòng)力電池?zé)峁芾淼确矫婢哂袕V闊的應(yīng)用前景。通過(guò)微膠囊技術(shù)對(duì)相變儲(chǔ)能材料進(jìn)行封裝制備出相變微膠囊,能夠有效解決相變儲(chǔ)能材料的泄漏對(duì)環(huán)境和設(shè)備造成污染的問題。但是目前相變微膠囊芯材大多為石蠟類等有機(jī)相變材料,導(dǎo)熱性能普遍較低,致使熱能的存儲(chǔ)和運(yùn)輸效率不高,從而限制了相變儲(chǔ)能技術(shù)在實(shí)際中的應(yīng)用。本論文針對(duì)上述問題開展了相變微膠囊強(qiáng)化傳熱、潛熱型功能熱流體的傳熱與流動(dòng)特性研究和無(wú)機(jī)水合鹽相變微膠囊的制備及其熱物性研究等相關(guān)方面的工作。主要研究?jī)?nèi)容與結(jié)論如下:(1)采用納米銅、石墨烯和膨脹石墨三種高導(dǎo)熱材料對(duì)石蠟/密胺樹脂相變微膠囊進(jìn)行了傳熱強(qiáng)化研究,并分析了高導(dǎo)熱材料的種類及質(zhì)量分?jǐn)?shù)對(duì)相變微膠囊的熱物性和儲(chǔ)熱/釋熱性能的影響。結(jié)果表明,當(dāng)納米銅、石墨烯和膨脹石墨的含量均為2.5 wt.%時(shí),相變微膠囊的導(dǎo)熱系數(shù)分別提高了8.72%、28.27%、39.62%。在儲(chǔ)熱/釋熱測(cè)試中,膨脹石墨對(duì)相變微膠囊儲(chǔ)熱/釋熱效率的提升也明顯高于納米銅和石墨烯。當(dāng)膨脹石墨添加含量為2.5 wt.%時(shí),膨脹石墨/Micro EPCM復(fù)合材料的儲(chǔ)熱和釋熱效率與相變微膠囊相比分別提高了14.98%和26.63%,并且儲(chǔ)熱/釋熱效率隨著膨脹石墨添加含量的提高而增大。(2)以石蠟/密胺樹脂相變微膠囊為基材,制備了不同微膠囊質(zhì)量分?jǐn)?shù)下的相變微膠囊懸浮液作為潛熱型功能熱流體,并對(duì)其熱物性和管內(nèi)的傳熱與流動(dòng)特性進(jìn)行了研究。結(jié)果表明,潛熱型功能熱流體的密度、導(dǎo)熱系數(shù)隨著相變微膠囊含量的增大而減小,而相變潛熱則隨著相變微膠囊質(zhì)量分?jǐn)?shù)的增大而增大。其粘度也隨著相變微膠囊質(zhì)量分?jǐn)?shù)的增大而升高,當(dāng)相變微膠囊的含量為20 wt.%、30 wt.%和40 wt.%時(shí),潛熱型功能熱流體的粘度迅速增加。通過(guò)搭建對(duì)流換熱實(shí)驗(yàn)平臺(tái),對(duì)潛熱型功能熱流體在管內(nèi)的傳熱性能進(jìn)行了研究,結(jié)果表明潛熱型功能熱流體的對(duì)流換熱系數(shù)隨著相變微膠囊含量的增大而增大。當(dāng)相變微膠囊的添加含量為5 wt.%和10 wt.%時(shí),其對(duì)流換熱系數(shù)分別約為基液的2倍和3倍。(3)以七水合硫酸鎂為芯材,脲醛樹脂為壁材,采用乳液聚合法制備出了相變微膠囊。并對(duì)不同工藝條件下制備的相變微膠囊微觀形貌、物性參數(shù)進(jìn)行了研究。結(jié)果表明,乳化劑的含量對(duì)相變微膠囊的微觀形貌和粒徑分布有很大的影響。當(dāng)乳化劑的含量為0.5 g時(shí),微膠囊呈現(xiàn)規(guī)則的球狀結(jié)構(gòu),且表面光滑緊湊、粒徑相對(duì)均勻,此時(shí)微膠囊的平均粒徑為34.99μm,其包覆率為36.5%。(4)以五水合硫代硫酸鈉為芯材,聚苯乙烯為壁材,采用溶劑揮發(fā)法制備出了相變微膠囊。并對(duì)不同乳化劑含量和攪拌速率下制備的微觀形貌、熱穩(wěn)定性等進(jìn)行了分析。研究表明,所制備的相變微膠囊均成規(guī)則的球狀結(jié)構(gòu),且表面光滑緊湊。隨著乳化劑含量的增加和攪拌速率的加快,微膠囊的粒徑呈現(xiàn)出減小的趨勢(shì)。隨著乳化劑含量的增大,微膠囊的相變溫度也隨之降低;而微膠囊的相變潛熱則隨著乳化劑天機(jī)含量的增加先增大后減小。五水合硫代硫酸鈉經(jīng)聚苯乙烯包覆后,熱穩(wěn)定性也明顯的提高。微膠囊中五水合硫代硫酸鈉的包覆率為26.4%。(5)以五水合硫代硫酸鈉為芯材,二氧化硅為壁材,采用溶膠凝膠法制備出了相變微膠囊。并對(duì)不同乳化劑含量、芯材與壁材質(zhì)量比、攪拌速率下制備的相變微膠囊微觀形貌、熱物性等進(jìn)行了分析。結(jié)果表明,乳化劑含量、芯材與壁材質(zhì)量比、攪拌速率對(duì)膠囊的微觀形貌和粒徑分布均有很大的影響。當(dāng)芯材、壁材、乳化劑的質(zhì)量比為1:0.4:0.04時(shí),相變微膠囊呈規(guī)則的球形結(jié)構(gòu),表面光滑緊湊,且粒徑分布最為均勻。芯壁比對(duì)相變潛熱影響較大,隨著芯壁比的減小相變微膠囊的相變潛熱逐漸增大。所制備的相變微膠囊相變潛熱最大為199.47k J/kg,包覆率為94.65%。五水合硫代硫酸鈉經(jīng)二氧化硅包覆后,其過(guò)冷度和導(dǎo)熱系數(shù)均有所改善,熱穩(wěn)定性也明顯提高,同時(shí)解決了芯材熔化后流動(dòng)造成泄漏的問題,從而延長(zhǎng)了無(wú)機(jī)水合鹽在實(shí)際應(yīng)用中的循環(huán)壽命。綜上,本文針對(duì)相變微膠囊的強(qiáng)化傳熱、潛熱型功能熱流體的流動(dòng)與傳熱和無(wú)機(jī)水合鹽相變微膠囊的制備及其熱物性分析三方面開展了相關(guān)的研究工作,研究結(jié)果和方法在儲(chǔ)能過(guò)程傳熱與流動(dòng)的強(qiáng)化、新型無(wú)機(jī)鹽類相變微膠囊材料的制備等方面具有一定的參考價(jià)值。
[Abstract]:With the rapid development of global industry and economy, more and more countries are demanding energy, the consumption of traditional non-renewable energy such as coal and oil is increasing, energy shortage and environmental pollution are becoming increasingly serious. Therefore, it is urgent to save energy, reduce emissions and improve energy efficiency. Phase change microcapsules can be prepared by encapsulating phase change energy storage materials with microcapsule technology. However, most of the core materials of phase change microcapsules are organic phase change materials, such as paraffin wax. Their thermal conductivity is generally low, resulting in low thermal energy storage and transport efficiency, which limits the practical application of phase change energy storage technology. The main research contents and conclusions are as follows: (1) Paraffin/melamine resin was prepared by using nano-copper, graphene and expanded graphite as high thermal conductive materials. The heat transfer enhancement of phase change microcapsules was studied, and the effects of the kinds and mass fraction of high thermal conductivity materials on the thermal properties and heat storage/release properties of phase change microcapsules were analyzed. The results showed that the thermal conductivity of phase change microcapsules increased by 8.72%, 28.27% and 39.62% respectively when the contents of nano-copper, graphene and expanded graphite were 2.5 wt%. When the content of expanded graphite was 2.5 wt.%, the thermal storage and release efficiency of expanded graphite / micro EPCM composites were 14.98% and 26.63% higher than that of phase change microcapsules, respectively. (2) Phase change microcapsule suspensions with different mass fractions of microcapsules were prepared as latent functional thermal fluids, and their thermophysical properties and heat transfer and flow characteristics in tubes were studied. The density and thermal conductivity of the fluid decrease with the increase of the content of phase change microcapsules, while the latent heat increases with the increase of the mass fraction of phase change microcapsules. The results show that the convective heat transfer coefficient of latent functional heat fluids increases with the increase of the content of phase change microcapsules. When the content of phase change microcapsules is 5 wt.% and 10 wt.%, the convective heat transfer system is established. The number is about 2 times and 3 times that of the base solution. (3) with seven hydrated Magnesium Sulfate as core material and urea formaldehyde resin as wall material, phase change microcapsules were prepared by emulsion polymerization. The micromorphology and physical parameters of phase change microcapsules prepared under different technological conditions were studied. When the content of emulsifier was 0.5 g, the microcapsules showed regular spherical structure, smooth and compact surface, and the particle size was relatively uniform. At this time, the average diameter of microcapsules was 34.99 micron, and the coating rate was 36.5%. (4) Sodium thiosulfate pentahydrate was used as core material, polystyrene as wall material, and solvent evaporation method was used to prepare microcapsules. The phase change microcapsules were prepared. The morphology and thermal stability of the microcapsules prepared under different emulsifier content and stirring rate were analyzed. The results showed that the phase change microcapsules had regular spherical structure and smooth and compact surface. With the increase of emulsifier content, the phase transition temperature of microcapsules decreases, while the latent heat of microcapsules increases first and then decreases with the increase of emulsifier content. 4%. (5) Phase change microcapsules were prepared by sol-gel method with sodium thiosulfate pentahydrate as core material and silica as wall material. When the mass ratio of core material, wall material and emulsifier is 1:0.4:0.04, the phase change microcapsules have regular spherical structure, smooth and compact surface, and most uniform particle size distribution. The latent heat of phase change increases gradually. The maximum latent heat of phase change microcapsules is 199.47kJ/kg and the coating rate is 94.65%. The supercooling and thermal conductivity of sodium thiosulfate pentahydrate coated with silica are improved, and the thermal stability is also improved obviously. The leakage problem caused by the flow of core material after melting is solved, thus the coating rate is prolonged. In summary, this paper focuses on the enhanced heat transfer of phase change microcapsules, the flow and heat transfer of latent functional heat fluids, the preparation and thermophysical properties analysis of phase change microcapsules of inorganic hydrate salts. It has a certain reference value in strengthening the preparation of new inorganic salt phase change microcapsule materials.
【學(xué)位授予單位】：中國(guó)礦業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TK124

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