制冷系統(tǒng)水平管降膜蒸發(fā)理論分析和實驗研究
發(fā)布時間：2018-08-07 22:01
【摘要】：在當前嚴峻的環(huán)境壓力下，制冷劑的替代和新型制冷劑的開發(fā)已經刻不容緩，而減量延續(xù)技術可以作為當前形式下對制冷劑替代工質的補充與過渡。通過統(tǒng)計和調查發(fā)現(xiàn)，在相同制冷量前提下，降膜蒸發(fā)所消耗的制冷工質要低于滿液式蒸發(fā)器的四分之一。 本文以制冷劑的減量替代作為研究背景，針對水平管降膜蒸發(fā)的流動機理、傳熱特性、強化方式進行了深入的分析和總結，并對制冷系統(tǒng)中降膜蒸發(fā)技術的應用以及系統(tǒng)含油對傳熱系數(shù)的影響等幾個方面逐一進行總結和說明。在不同的運行工況下，降膜蒸發(fā)的傳熱特征具有不同的變化規(guī)律，同時系統(tǒng)所含潤滑油會對其傳熱特性產生一定影響，發(fā)現(xiàn)潤滑油的存在會明顯降低了換熱系數(shù)。通過搭建R134a的制冷循環(huán)系統(tǒng)，將水平管降膜蒸發(fā)器應用于系統(tǒng)的蒸發(fā)器中，從而進行水平管降膜蒸發(fā)的實驗研究，以制冷劑的噴淋量、熱流密度、蒸發(fā)溫度作為研究變量進行實驗對比分析，總結實驗規(guī)律。 此外，根據(jù)水平管降膜蒸發(fā)的傳熱機理，改變管外表面結構可以不同程度提高管外對流換熱系數(shù)，因此在實驗過程中加入了機械加工的TJX管、EX管、測試1管、測試2管進行實驗研究。分析表明，強化管的降膜蒸發(fā)傳熱特性主要與熱流密度、工質噴淋量以及管型的不同強化特征有關，而隨著熱流密度的增加，管外傳熱系數(shù)均出現(xiàn)升高趨勢，但經過臨界熱流密度后，強化管的傳熱系數(shù)均呈現(xiàn)出不同程度的下降趨勢，同時強化表面的傳熱系數(shù)要明顯優(yōu)于光滑管，不同強化管的傳熱系數(shù)也不盡相同，說明強化表面結構對實驗結果也具有一定影響。 最后，利用光滑管變工質噴淋量的實驗數(shù)據(jù)與Ribatski和Thome預測的傳熱模型進行對比計算，并在此基礎上進行公式擬合，擬合結果與實驗數(shù)據(jù)之間的誤差在±20%以內，并在此基礎上提出了適用于強化管的強化系數(shù)，，為強化管的傳熱特性研究提供參考。
[Abstract]:Under the severe environmental pressure, the replacement of refrigerant and the development of new refrigerant are urgent, and the technology of deweighting continuation can be used as the supplement and transition of refrigerant substitute in the current situation. Through statistics and investigation, it is found that the refrigerant consumption of falling film evaporation is lower than 1/4 of the full liquid evaporator under the same refrigerating capacity. Based on the research background of refrigerant reduction substitution, the flow mechanism, heat transfer characteristics and strengthening methods of falling film evaporation in horizontal tube are analyzed and summarized in this paper. The application of falling film evaporation technology in refrigeration system and the influence of oil content on heat transfer coefficient are summarized and explained one by one. Under different operating conditions, the heat transfer characteristics of falling film evaporation have different laws, and the lubricating oil contained in the system will have a certain influence on its heat transfer characteristics. It is found that the existence of lubricating oil will obviously reduce the heat transfer coefficient. By setting up the refrigeration cycle system of R134a, the horizontal tube falling film evaporator is applied to the evaporator of the system, and the experimental study of the horizontal tube falling film evaporation is carried out. The evaporation temperature is used as the research variable to carry on the experiment contrast analysis, summarizes the experimental rule. In addition, according to the heat transfer mechanism of falling film evaporation in horizontal tube, the convection heat transfer coefficient can be improved in varying degrees by changing the outer surface structure of the tube. Therefore, the machined TJX tube ex tube is added in the experiment, and the 1 tube is tested. Test 2 tubes for experimental study. The analysis shows that the heat transfer characteristics of falling film evaporation of the enhanced tube are mainly related to the heat flux density, the amount of liquid spray and the different strengthening characteristics of the tube type, but the heat transfer coefficient outside the tube increases with the increase of the heat flux density. However, after the critical heat flux, the heat transfer coefficient of the strengthened tube is decreased in different degrees, and the heat transfer coefficient of the strengthened surface is obviously better than that of the smooth tube, and the heat transfer coefficient of the different strengthened tubes is also different. It shows that the strengthened surface structure also has a certain influence on the experimental results. Finally, the experimental data of variable working fluid spray quantity in smooth tube are compared with the heat transfer model predicted by Ribatski and Thome, and the formula fitting is carried out on the basis of which, the error between the fitting result and the experimental data is less than 鹵20%. On this basis, the enhancement coefficient suitable for the enhanced tube is put forward, which provides a reference for the study of the heat transfer characteristics of the enhanced tube.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB657;TB611
本文編號：2171478
[Abstract]:Under the severe environmental pressure, the replacement of refrigerant and the development of new refrigerant are urgent, and the technology of deweighting continuation can be used as the supplement and transition of refrigerant substitute in the current situation. Through statistics and investigation, it is found that the refrigerant consumption of falling film evaporation is lower than 1/4 of the full liquid evaporator under the same refrigerating capacity. Based on the research background of refrigerant reduction substitution, the flow mechanism, heat transfer characteristics and strengthening methods of falling film evaporation in horizontal tube are analyzed and summarized in this paper. The application of falling film evaporation technology in refrigeration system and the influence of oil content on heat transfer coefficient are summarized and explained one by one. Under different operating conditions, the heat transfer characteristics of falling film evaporation have different laws, and the lubricating oil contained in the system will have a certain influence on its heat transfer characteristics. It is found that the existence of lubricating oil will obviously reduce the heat transfer coefficient. By setting up the refrigeration cycle system of R134a, the horizontal tube falling film evaporator is applied to the evaporator of the system, and the experimental study of the horizontal tube falling film evaporation is carried out. The evaporation temperature is used as the research variable to carry on the experiment contrast analysis, summarizes the experimental rule. In addition, according to the heat transfer mechanism of falling film evaporation in horizontal tube, the convection heat transfer coefficient can be improved in varying degrees by changing the outer surface structure of the tube. Therefore, the machined TJX tube ex tube is added in the experiment, and the 1 tube is tested. Test 2 tubes for experimental study. The analysis shows that the heat transfer characteristics of falling film evaporation of the enhanced tube are mainly related to the heat flux density, the amount of liquid spray and the different strengthening characteristics of the tube type, but the heat transfer coefficient outside the tube increases with the increase of the heat flux density. However, after the critical heat flux, the heat transfer coefficient of the strengthened tube is decreased in different degrees, and the heat transfer coefficient of the strengthened surface is obviously better than that of the smooth tube, and the heat transfer coefficient of the different strengthened tubes is also different. It shows that the strengthened surface structure also has a certain influence on the experimental results. Finally, the experimental data of variable working fluid spray quantity in smooth tube are compared with the heat transfer model predicted by Ribatski and Thome, and the formula fitting is carried out on the basis of which, the error between the fitting result and the experimental data is less than 鹵20%. On this basis, the enhancement coefficient suitable for the enhanced tube is put forward, which provides a reference for the study of the heat transfer characteristics of the enhanced tube.
【學位授予單位】：天津大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TB657;TB611
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本文編號：2171478
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