【摘要】：隨著環(huán)境問題的日益突出，制冷劑的替代問題也備受人們關(guān)注，新型低GWP和零ODP制冷工質(zhì)的研究成為了熱點課題。R32和R1234ze因其具有較好的熱力學性質(zhì)和環(huán)保性能，成為了較為理想的替代品。另一方面，換熱的微小型化也已成為一種必然的發(fā)展趨勢。隨著管徑的減小，重力、表面張力和切應(yīng)力對換熱影響的相對大小也發(fā)生變化，從而引起換熱時流型的轉(zhuǎn)換與常規(guī)通道不同，導致小通道內(nèi)的換熱機理和壓降特性與常規(guī)通道不同。因此，有必要進行實驗，對小通道內(nèi)換熱機理的研究提供數(shù)據(jù)基礎(chǔ)與理論支持。 本文用R32、R1234ze兩種制冷劑在2mm水平細圓管內(nèi)進行了冷凝換熱實驗，實驗時工質(zhì)流量為100-400kg/m2，飽和溫度設(shè)定為40℃、45℃和50℃，熱流密度范圍為4-30kW/m2，干度變化范圍為0~1。實驗測得了R32、R1234ze在不同工況條件下冷凝換熱系數(shù)和壓降，并觀測了R32兩相流的流型特性。 分析實驗結(jié)果，發(fā)現(xiàn)R1234ze和R32的冷凝換熱系數(shù)范圍分別在1.5~8kW/m2K和1~10kW/m2K之間，并且隨干度的增加而增加，隨飽和溫度的升高而降低，，隨質(zhì)量流量的增加而增大。測試段入口干度和熱流密度的變化對換熱系數(shù)的影響不太大。管內(nèi)摩擦壓降隨質(zhì)量流量增加而增大，隨飽和溫度的升高而降低，而且質(zhì)量流量越大時，這種影響越明顯。對R32流型實驗觀測中，觀察到了塞狀流、彈狀流、環(huán)波狀流和環(huán)狀流。并發(fā)現(xiàn)隨著干度的增加，流型逐漸由間歇流轉(zhuǎn)換為環(huán)波狀流，最后到環(huán)狀流。而且隨著質(zhì)量流量的增大，由間歇流轉(zhuǎn)換到環(huán)波狀流時的干度變小。 通過對比R32、R134a分別在不同管徑下的換熱系數(shù)，發(fā)現(xiàn)換熱系數(shù)隨著管徑的減小而增大。對比了R1234ze、R32、R1234yf和R134a四種制冷工質(zhì)在相同實驗工況下的換熱系數(shù)，發(fā)現(xiàn)R32的冷凝換熱系數(shù)最高， R1234ze與R1234yf的換熱系數(shù)大小比較接近，且都比R134a、R32小。 將本次實驗結(jié)果與六種經(jīng)典換熱預測模型、四種壓降預測模型和五種經(jīng)典流型圖模型進行了對比。發(fā)現(xiàn)對換熱系數(shù)預測較好的是Baird模型和Gerimella模型，對摩擦壓降預測較好的是Muller-Heck模型和Chisholm模型，并用這四個模型對其它文獻中的數(shù)據(jù)進行了預測與分析。對流型圖預測較好的是Yang-Shieh經(jīng)驗流型圖。同時引用無量綱數(shù)Xtt, Bd, Re，提出了一種新的由間歇流與環(huán)波狀流之間過渡曲線的預測公式。
[Abstract]:With the increasingly prominent environmental problems, the problem of refrigerant substitution has attracted much attention. The research of new low GWP and zero ODP refrigerants has become a hot topic. R32 and R1234ze have better thermodynamic properties and environmental protection properties. Has become the more ideal substitute. On the other hand, the micro-miniaturization of heat transfer has become an inevitable trend of development. With the decrease of pipe diameter, the relative magnitude of the influence of gravity, surface tension and shear stress on heat transfer also changes. The heat transfer mechanism and pressure drop characteristics in small channels are different from those in conventional channels. Therefore, it is necessary to carry out experiments to provide data basis and theoretical support for the study of heat transfer mechanism in small channels. In this paper, the condensation and heat transfer experiments were carried out in a 2mm horizontal thin tube with two refrigerants R32O / R1234ze. The working fluid flow rate was 100-400 kg / m ~ (2), the saturation temperature was 40 鈩

本文編號：2360247