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    管壁波纹状形变后旋流液膜的厚度分布及波动特性

    Thickness distribution and fluctuation characteristics of swirling liquid film after corrugated deformation of the tube wall

    • 摘要: 洗涤冷却管在长期高温高压运行后会产生波纹状形变,降低湍流液膜附壁流动稳定性,使用旋流液膜可以改善液膜附壁流动和周向分布均匀性。本文利用超声波多普勒测速仪研究了湍流条件下波纹壁面结构参数(振幅和波长)及液膜雷诺数ReL对旋流液膜厚度分布及波动特性的影响。结果表明:当壁面发生波纹状形变后,旋流液膜的厚度大小(除液膜入口、波峰和波谷处)均小于平滑壁面上的液膜厚度。相比于平滑壁面,波纹壁面上旋流液膜的扰动波频率整体增大,无量纲最大膜厚εmax增大,无量纲最小膜厚εmin减小,液膜空间波动显著增强。当振幅增大或者波长减小时,液膜波动更加剧烈;ReL的增加使液膜离心力增大,抑制了液膜的波动。所建立的液膜厚度预测模型能较好预测湍流条件下(ReL = 8.73 × 103 ~ 1.22 × 104)波纹壁面上(振幅/波长= 0.015 ~ 0.03)的旋流液膜平均厚度,尤其可预测液膜最小厚度,为装置稳定运行提供可靠理论依据。

       

      Abstract: After long-term operation under high temperature and high pressure, the scrubbing-cooling tube undergoes corrugated deformation, which reduces the stability of turbulent liquid film flow along the tube wall. The swirling liquid film can make the liquid film adhere to the wall and improve the circumferential distribution uniformity of the liquid film. This paper employed the ultrasonic Doppler velocimeter to investigate the effects of corrugated wall surface structural parameters (amplitude and wavelength) and liquid film Reynolds number (ReL) on the thickness distribution and fluctuation characteristics of swirling liquid film under turbulent conditions. The results show that when the wall undergoes corrugated deformation, except for the inlet, crests, and troughs, the swirling liquid film thickness at other locations is generally thinner than that on the smooth wall. Compared with the smooth wall, the disturbance wave frequency of the swirling liquid film on the corrugated wall increases overall, the dimensionless maximum film thickness εmax increases, the dimensionless minimum film thickness εmin decreases, and the spatial fluctuation of the liquid film is enhanced. When the amplitude increases or the wavelength decreases, the liquid film fluctuation becomes more intense. The increase in Rel enhances the centrifugal force, thereby suppressing liquid film fluctuations. The established liquid film thickness prediction model can satisfactorily predict the average thickness of the swirling liquid film on corrugated walls (amplitude-to-wavelength ratio = 0.015 ~ 0.03) under turbulent conditions (ReL = 8.73 × 103 ~ 1.22 × 104), and can particularly predict the minimum film thickness, providing a reliable theoretical basis for the stable operation of the device.

       

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