有限通道内热空气顺流掺混NaCl水溶液喷射闪蒸的数值模拟  

Numerical Simulation of Aqueous NaCl in Parallel Hot Air Mixing and Spray Flashing within Finite Rectangle Tube

作　　者：郑巨淦 张丹[1] 袁洋 王一笑 杨庆忠 ZHENG Jugan;ZHANG Dan;YUAN Yang;WANG Yixiao;YANG Qingzhong(School of Energy and Power Engineering,Xi’an Jiaotong University,Xi’an 710049,China;School of Mechanical Engineering,Tianjin University of Commerce,Tianjin 300134,China)

机构地区：[1]西安交通大学能源与动力工程学院,西安710049 [2]天津商业大学机械工程学院,天津300134

出　　处：《西安交通大学学报》2023年第2期173-183,共11页Journal of Xi'an Jiaotong University

基　　金：国家自然科学基金资助项目(51976162)。

摘　　要：为实现高浓度含盐废水的高效脱盐,开展了对有限通道内NaCl水溶液在喷射闪蒸和顺流掺混热空气共同作用下的蒸发性能研究。在实验研究的基础上,从该过程中过热度控制的非平衡蒸发到对流控制的平衡蒸发建立了贯通的数学物理模型,计算结果与实验结果的主体偏差小于5%。使用该模型在液滴群初始粒径为30~110μm、初始温度为120℃、初始盐质量分数为0~0.1、初始速度为20 m/s、掺混热空气速度为5~15 m/s、温度为100~200℃的范围内开展了数值模拟。结果表明:液滴群的温度、速度、粒径以及盐质量分数的分布均呈现雾羽边缘变化快、喷射轴线处变化慢的特点;随着喷射距离的增大,液滴群粒径、速度、温度的截面平均值均降低,而平均盐质量分数升高;液滴初始盐质量分数的增大对上述参数的沿程变化无明显影响。定义蒸发效率为给定喷射距离内液滴群总蒸发质量与初始质量之比,减小液滴初始粒径、提高掺混热空气温度的同时降低热空气流速是提高蒸发效率、强化液滴浓缩的有效途径。蒸发效率的半经验计算数值与模拟值主体误差小于±15%。该研究结果可为工业脱盐装置的设计和运行提供一定的参考。In order to improve desalination efficiency,aqueous NaCl solution is selected as the working fluid for investigation on its evaporation characteristics under the combined effect of spray flashing and parallel hot air mixing within finite rectangle tube.Based on experimental results,a comprehensive mathematical model is set up for the entire evaporation process from the non-equilibrium evaporation stage controlled by superheat to the equilibrium evaporation stage controlled by hot air convection.The relative error between the calculation and experimental results is mainly less than 5%.With this model,numerical simulations were carried out with initial droplet size between 30 and 110μm,initial droplet temperature of 120℃,initial salt concentration between 0 and 10%,initial droplet speed of 20 m/s,initial mixing hot air speed between 5 and 15 m/s,and initial temperature between 100 and 200℃.Results suggest that the droplet temperature,velocity,particle size as well as salt concentration all change rapidly at the edge of the spray plume,but slowly along the spray axis.With the increase of spray distance,the average droplet size,velocity as well as temperature decrease,but the average salt mass fraction increases.The increase of initial salt mass fraction shows no obvious effect on the evolution with distance of the aforementioned parameters.The evaporation efficiency is introduced as the ratio of the total evaporation mass of droplets to the initial mass of droplets within a given spray distance.Results suggest that reducing the initial droplet size,increasing the hot air temperature and at the same time reducing the hot air velocity are effective to improve the evaporation efficiency and enhance concentrating of droplets.A semi-empirical formula for evaporation efficiency is proposed,yielding a main error within±15%between its calculated value and the simulation results.The research results above are applicable to design and operation of industrial desalination systems.

关 键 词：喷射闪蒸 顺流掺混 有限通道 雾羽流场 蒸发效率 

分 类 号：TK124[动力工程及工程热物理—工程热物理]