通过焓-孔隙法建立数值模型,研究石蜡RT50在管壳式太阳能储热器的传热特性,并分析储热器安装形式、不同管径和管外肋片结构对相变储热过程的影响规律。结果表明,立式储热器在管径较大时（相变材料区域厚度较薄时）熔化速度比卧式储热器快;而在管径较小时（相变材料区域较厚时）熔化速度比卧式储热器慢。卧式储热器相变材料熔化过程的初始时间段和末尾时间段热传导占主导地位,而中间时间段自然对流换热占主导地位,且熔化速度主要由自然对流换热决定。此外,管外侧安装肋片能够显著提高传热系数,缩短熔化时间。相较于无肋片管道,卧式储热器采用环肋管道可缩短熔化时长31.6%;采用直肋管道可缩短熔化时长42.1%。直肋比环肋具有更好的传热效果,主要原因为直肋能够强化熔化过程中的自然对流。
Abstract
A numerical model is established using the enthalpy-porosity approach to study the heat transfer characteristics of a tube-and-shell phase-change heat exchanger filled with paraffin wax RT50. The influence of exchanger placement forms, tube diameters and fin structures on the phase change process of RT50 is analyzed. The results depicts that the vertical heat exchanger has a faster melting rate than the horizontal one as the tube diameter is large. However, the opposite results are obtained in case the tube diameter is small. For the horizontal exchanger, the heat conduction is dominant at the beginning and end of the melting process, while the natural convection plays a more important role at the intermediate stage of melting. Besides, the duration of the melting is mainly determined by the natural convection. In addition, the installation of fins on the outside of the tube can significantly increase the heat transfer coefficient and shorten the melting time. Compared with finless tube, the utilization of ring-fin tube in the horizontal heat storage device can shorten the melting time by 31.6%, and the utilization of straight-fin tube can shorten the melting time by 42.1%. Therefore, the straight fins have a better effect than the ring fins. The main reason is that straight fins can strengthen the natural convection during the melting process.
关键词
太阳能 /
相变材料 /
熔化 /
肋片 /
自然对流 /
热能储存
Key words
solar energy /
phase change material /
melting /
fins /
natural convection /
thermal energy storage
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