Film thickness and heat transfer characteristics of R1233zd(E) falling film with nucleate boiling on an inclined plate
Film thickness and heat transfer characteristics of R1233zd(E) falling film with nucleate boiling on an inclined plate
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DOI：
10.1016/j.ijheatmasstransfer.2022.123423
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发表时间：
2022-12
影响因子：
5.2
通讯作者：
Tsutomu Ubara;K. Sugimoto;H. Asano
中科院分区：
文献类型：
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作者：
Tsutomu Ubara;K. Sugimoto;H. Asano
降膜蒸发是一种以较少制冷剂实现大热流密度、大面积制冷的有效传热方法。随着液膜厚度和壁厚的增加，液膜内发生核态沸腾。在这种情况下，由于气泡的存在，表面液膜厚度变厚。虽然这种表观膜厚度是表示膜结构的重要参数，但氢氟烃和氢氟烯烃制冷剂在核态沸腾条件下的液膜厚度尚未报道。以R1233 zd（E）为工质，在饱和温度为20°C时，对宽50 mm、长75 mm的倾斜平板上的液膜厚度和传热系数进行了实验研究。进口气膜雷诺数在4.4 × 102 ~ 2.7 × 103之间变化，热流密度在5.6 ~ 138 kW/m2之间变化。结果表明，在绝热条件下，随着流量的增加或倾角从30°减小到15°，平均油膜厚度增加，其变化范围为0.14 ~ 0.37 mm，与已有的理论和关联式吻合较好。在无沸腾的加热条件下，膜厚与绝热条件下的膜厚基本相同，传热系数略高于典型的饱和水降膜传热关联式。在高热流密度范围内，核态沸腾时，汽泡所在位置的表观膜厚可达1-3 mm。厚度超过1 mm的频率随着热通量的增加而增加，因为核态沸腾变得更加活跃;因此，平均厚度也增加。核态沸腾条件下的换热系数主要受热流密度的影响，与现有的池沸腾关联式吻合较好。
Falling film evaporation is an effective heat transfer method for achieving high heat flux and wide-area cooling with less refrigerant. As the film thickness and wall superheat increase, nucleate boiling occurs in the liquid film. In this case, the superficial liquid film thickness becomes thicker due to the existence of vapor bubbles. Although such superficial film thickness is an important parameter for expressing the film structure, the liquid film thickness of hydrofluorocarbon and hydrofluoroolefin refrigerants under nucleate boiling conditions has not yet been reported. This study experimentally investigated the liquid film thickness and heat transfer coefficients on an inclined plate with the width of 50 mm and the length of 75 mm. R1233zd(E) was used as the working fluid at a saturation temperature of 20°C. The film Reynolds number at the inlet was varied from 4.4 × 102to 2.7 × 103, and the heat flux was varied from 5.6 to 138 kW/m2. As a result, the mean film thickness under adiabatic conditions increased when the flow rate increased or the inclination angle decreased from 30° to 15°, and ranged from 0.14 to 0.37 mm. The values were in good agreement with preexisting theories and correlations. Under heating conditions without boiling, the film thickness was almost equal to that under adiabatic conditions, and the heat transfer coefficients were slightly higher than the typical heat transfer correlation of the saturated falling film of water. With nucleate boiling in the high heat flux range, the superficial film thickness reached 1–3 mm at the location where vapor bubbles existed. The frequency of the thickness exceeding 1 mm increased with the heat flux as nucleate boiling became more active; thus, the average thickness also increased. The heat transfer coefficients under the developed nucleate boiling conditions were dominated by heat flux and were in good agreement with the existing pool boiling correlation.