583 / 2019-01-19 11:16:40

Field test on raindrop size distribution in the rain zone of natural draft wet cooling tower

field test; natural draft wet cooling tower; rain zone; raindrop size distribution; crosswind

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Field test on raindrop size distribution in the rain zone of natural draft wet cooling tower
Xuehong Chen1, Fengzhong Sun*, Dongqiang Lyu
1 School of Energy and Power Engineering, Shandong University, 17923 Jingshi Road, Jinan 250061, China; cxh@mail.sdu.edu.cn, Tel: 18366119835, Fax: +86 0531 88395691.
* School of Energy and Power Engineering, Shandong University, Jinan 250061, China; sfzh@sdu.edu.cn.
Abstract: Affected by the raindrop size distribution, the thermodynamic characteristics and pressure loss performance of the rain zone in a natural draft wet cooling tower (NDWCT) are material to the tower thermal performance. However, existing research on the thermodynamic and aerodynamic calculation of rain zone is mainly based on the equivalent raindrop diameter rather than the raindrop size distribution, thus skewing the results. In this paper, field test was performed on a NDWCT of a 600MW unit to investigate the raindrop size distribution in the rain zone. A test rig for the field test was designed and constructed, with due consideration of variable test positions (3 altitudinal positions ?3 radial positions ?6 circumferential positions), sampling times (15s, 30s, 60s, 300s), and crosswind conditions. The test results manifest that the raindrops in the rain zone have a particle size distribution between 0.3 mm and 15 mm, with a sensitivity to crosswind. Under no wind and low wind conditions, the raindrop size distribution is determined by the residence time of raindrops. As the altitude of test position increases, the raindrops residence time decreases, and the proportion of raindrops with smaller particle size decreases. This phenomenon is most noticeable within the raindrop size range from 1.4 mm to 5.5 mm. At the same test position, the raindrop size distribution rule is arguably immutable across sampling time. At different radial and circumferential test positions with the same altitude, the raindrop size distributions have the same pattern. Under strong crosswind condition, the main factor affecting the raindrop size distribution is no longer the residence time of raindrops but the crosswind. This occurs because the horizontal velocity component of air motion not only breaks and deforms the raindrops, but increases the collision frequency between raindrops, hence, the raindrop size distribution in the rain zone is basically consistent at different altitudinal positions, and the proportion of raindrops with smaller particle size increases significantly on windward side. This field test can provides reliable support for the further study of the rain zone.
Keywords: field test; natural draft wet cooling tower; rain zone; raindrop size distribution; crosswind.