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Evaporation heat transfer characteristics of falling film in small diameter fabricated tubes of absorption refrigeration system: An experimental investigation
International Journal of Heat and Mass Transfer ( IF 5.2 ) Pub Date : 2021-02-01 , DOI: 10.1016/j.ijheatmasstransfer.2020.120618
Syed Muhammad Ammar , Chan Woo Park

Abstract Absorption refrigeration system is going through optimization. The evaporator is one of the core components of the absorption refrigeration system, and its optimization can be done by improving the wettability and reducing the uneven distribution of liquid film. Enhanced tubes are often helpful in mitigating the film thickness and ensuring proper wetting of the tubes, thus enhancing the heat transfer performance. Using a smaller tube diameter also significantly affects the heat transfer performance because of the increasing ratio of the developing boundary layer to the fully developed boundary layer. In this study, seven small-diameter (12.7 mm) tubes were used to optimize the performance of the evaporator. The parameters observed are as follows: falling-film Reynolds number (10–100), wall superheat (2.2–5.1 °C), and saturation pressure (0.9–1.20 kPa). The heat transfer coefficient exhibited a peak point at a falling-film Reynolds number, called transition Reynolds number (Retransition) mostly at a value of ~42. The wall superheat is increased by increasing the wall temperature and, as a result, the heat transfer coefficient remains unchanged; however, the heat flux increases almost linearly. The heat transfer coefficient increases with the increase in the saturation pressure. One of the fabricated tubes was tested with corrosion, and a negligible change in the heat transfer coefficient was observed when compared with the uncorroded tube. Both droplet and jet modes are observed when viewing the falling-film phenomena through a glass window. Smooth tube data reveal a reasonable comparison with the jet and droplet mode of Hu et al. Of all the tubes, the heat transfer coefficient of Tube_Z is the highest. Tube_Y1 exhibited the highest heat flux; however, Tube_Z exhibited the highest ratio of heat flux to friction factor. Empirical correlations were developed based on the current experimental perimeters, and correlations predicted the data within ±20%.

中文翻译:

吸收式制冷系统小口径管降膜蒸发传热特性的实验研究

摘要 吸收式制冷系统正在经历优化。蒸发器是吸收式制冷系统的核心部件之一,其优化可以通过提高润湿性和减少液膜分布不均来进行。增强型管通常有助于减轻薄膜厚度并确保管的适当润湿,从而提高传热性能。使用较小的管径也会显着影响传热性能,因为发展的边界层与完全发展的边界层的比率增加。在这项研究中,使用七个小直径 (12.7 mm) 管来优化蒸发器的性能。观察到的参数如下:降膜雷诺数 (10–100)、壁面过热度 (2.2–5.1 °C)、和饱和压力 (0.9–1.20 kPa)。传热系数在降膜雷诺数处表现出峰值点,称为过渡雷诺数(Retransition),大部分值为~42。提高壁温会增加壁面过热度,因此传热系数保持不变;然而,热通量几乎呈线性增加。传热系数随着饱和压力的增加而增加。其中一个制造的管子进行了腐蚀测试,与未腐蚀的管子相比,观察到传热系数的变化可以忽略不计。通过玻璃窗观察降膜现象时,可以观察到液滴和喷射模式。光滑管数据揭示了与 Hu 等人的射流和液滴模式的合理比较。在所有的管子中,Tube_Z 的传热系数最高。Tube_Y1 表现出最高的热通量;然而,Tube_Z 的热通量与摩擦系数的比率最高。经验相关性是基于当前的实验周长开发的,相关性预测数据在 ±20% 以内。
更新日期:2021-02-01
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