高含盐废水降膜蒸发过程中液膜破裂的抑制
Suppression of liquid film rupture during falling film evaporation for high salinity wastewater
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摘要: 为解决高含盐废水降膜蒸发过程中液膜破裂产生的干区和结垢问题，采用高灵敏度的红外热成像仪实验研究了高含盐废水受热降膜破裂后的流动状态。结果表明，破裂降膜径向存在热Marangoni效应和溶质Marangoni效应。热Marangoni效应引起了液膜由侧面边缘向中心主流区的收缩，形成稳定的干区；而溶质Marangoni效应则导致了侧面边缘结垢的出现。在废水中添加50 mg/L表面活性剂2-乙基己醇（ETH）可有效抑制受热降膜的破裂。ETH的存在，改变了表面张力σ随温度的变化率的符号，在降膜径向产生的热Marangoni效应促使了液膜的扩展。同时，在径向形成的由表面活性剂蒸发引起的溶质Marangoni效应，使液膜进一步向外扩展，消除了干区和结垢的发生。
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关键词:
- 盐 /
- 废水 /
- 降膜蒸发 /
- Marangoni效应 /
- 表面活性剂
Abstract: To avoid the appearance of dry region and scaling caused by liquid film rupture during the falling film evaporation for high salinity wastewater, an experimental investigation was performed on the liquid film flow after heated falling film breaking by using a sensitive infrared camera technique. The results indicate that the thermal Marangoni effect and solutal Marangoni effect co-exit in transverse direction on the broken falling film surface. The thermal Marangoni effect induced the falling film shrinking from the lateral brim to the center bulk, generating stable dry region. And the solutal Marangoni effect caused the fouling along the lateral brim. Adding 50 mg/L surfactant of 2-ethyl-1-hexanol (ETH) into the salinity wastewater, the tendency of falling film breaking was effectively suppressed. The presence of ETH on the film surface varied the sign of change rate of surface tension σ with respect to temperature. Thus the thermal Marangoni effect generated in transverse direction caused the film spreading from the bulk to the lateral. Meanwhile, the solutal Marangoni effect, induced by the surfactant evaporating on the film surface, further promoted the film extending towards the lateral, preventing the occurrence of the dry region and scaling.-
Key words:
- salinity /
- wastewater /
- falling film evaporation /
- Marangoni effect /
- surfactant
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