本文選題：[降膜蒸發(fā)]　切入點(diǎn)：[液膜厚度]　出處：《天津大學(xué)》2014年碩士論文　論文類型：學(xué)位論文

【摘要】：本文基于國(guó)內(nèi)外節(jié)能減排和環(huán)境保護(hù)的大背景下,在制冷劑減量技術(shù)的思想上,進(jìn)行制冷系統(tǒng)水平管降膜蒸發(fā)研究。以降膜蒸發(fā)為研究對(duì)象,對(duì)降膜蒸發(fā)流動(dòng)及換熱理論進(jìn)行了歸納與總結(jié),為實(shí)驗(yàn)現(xiàn)象的分析奠定理論基礎(chǔ)。水平管外液膜厚度的大小對(duì)降膜過程非常重要。因此,本文建立二維物理模型,在忽略相變傳熱的前提下,以R134a為工質(zhì),對(duì)降膜過程中水平管外液膜厚度的分布情況進(jìn)行了研究。模擬結(jié)果表明:管外液膜厚度并非均勻分布,其厚度先由厚變薄,再由薄變厚,在管表面角度為150°左右時(shí),液膜厚度為最薄;管外薄膜厚度隨著制冷劑入口速度的增加而增加;在相同的入口速度下,液膜的厚度在本文模擬條件下基本不受管型的影響。在實(shí)際中,壓縮機(jī)出口的工質(zhì)是含有潤(rùn)滑油的,潤(rùn)滑油隨著工質(zhì)的流動(dòng)進(jìn)入蒸發(fā)器,勢(shì)必對(duì)蒸發(fā)器的換熱性能造成影響。針對(duì)這一問題,通過改造實(shí)驗(yàn)臺(tái),以R134a為工質(zhì)并對(duì)3種不同管型進(jìn)行研究,并分析潤(rùn)滑油對(duì)水平管降膜蒸發(fā)傳熱特性的影響。實(shí)驗(yàn)中蒸發(fā)溫度為6℃,含油率分別為0.5%、1.2%、5.1%。工質(zhì)噴淋密度分別為0.13、0.17和0.21kg?s~(-1)?m~(-1)。對(duì)測(cè)試結(jié)果進(jìn)行分析與對(duì)比發(fā)現(xiàn),在噴淋密度一定時(shí),對(duì)于光滑管和02號(hào)強(qiáng)化管,整體上表現(xiàn)出管外換熱系數(shù)隨著含油率的增加而增大。而對(duì)于01號(hào)強(qiáng)化管,在低噴淋密度下,管外換熱系數(shù)隨著含油率的增加而增大,一直到某一最佳含油率,然后隨著含油率增加而降低;在大噴淋密度下,含油率的變化對(duì)管外換熱系數(shù)影響不是特別明顯。出現(xiàn)這種情況的原因可能是由于管表面結(jié)構(gòu)不同所導(dǎo)致的。在較高含油率時(shí),對(duì)于光滑管,存在某一個(gè)合適的噴淋密度使管外換熱系數(shù)達(dá)到最大值;對(duì)于01號(hào)強(qiáng)化管與02號(hào)強(qiáng)化管,管外換熱系數(shù)的變化受噴淋密度的影響較小。在較低含油率時(shí),對(duì)于光滑管管外換熱系數(shù)受噴淋密度的影響不明顯;對(duì)于01號(hào)強(qiáng)化管,管外換熱系數(shù)隨著噴淋密度的增加而增大,直到某一值,然后隨著噴淋密度的增加而減小;對(duì)于02號(hào)強(qiáng)化管,在實(shí)驗(yàn)范圍內(nèi),管外換熱系數(shù)隨著噴淋密度的增大而增大。
[Abstract]:In this paper, based on the background of energy saving and environmental protection at home and abroad, based on the idea of refrigerant reduction technology, the study of falling film evaporation in horizontal tube of refrigeration system is carried out. The theory of falling film evaporation flow and heat transfer is summarized and summarized, which lays a theoretical foundation for the analysis of experimental phenomena. The thickness of liquid film outside the horizontal tube is very important for the falling film process. Therefore, a two-dimensional physical model is established in this paper. On the premise of neglecting phase change heat transfer, the distribution of outer liquid film thickness in horizontal tube is studied with R134a as working medium. The simulation results show that the thickness of liquid film outside the tube is not uniformly distributed, and its thickness first changes from thickness to thinning. When the surface angle of the tube is about 150 擄, the thickness of the liquid film is the thinnest; the thickness of the outer film increases with the increase of the inlet velocity of the refrigerant; at the same inlet velocity, the thickness of the liquid film increases with the increase of the inlet velocity of the refrigerant. The thickness of the liquid film is not affected by the pipe type under the simulated conditions in this paper. In practice, the working fluid at the outlet of the compressor contains lubricating oil, and the lubricating oil enters the evaporator with the flow of the working fluid. The heat transfer performance of evaporator is bound to be affected. In order to solve this problem, three different tube types are studied by modifying the test bench, taking R134a as the working fluid, and using R134a as the working medium. The effect of lubricating oil on the heat transfer characteristics of falling film evaporation in horizontal tube was analyzed. The evaporation temperature was 6 鈩，

本文編號(hào)：1591926