海水淡化系统中水平管降膜蒸发器流动与传热特性数值研究

Numerical Study on Flow and Heat Transfer Characteristics of Horizontal-tube Falling-film Evaporators in Seawater Desalination System

为了解和改善水平管降膜蒸发器内局部区域流体流动和传热状况,建立适用于蒸发器实体的三维分布参数模型,详细分析了管束内部加热蒸汽流量分配和外部海水流场特性,给出了蒸发器内部的工作过程以及复杂流动与换热现象。通过数值解与实际值的比较对模型进行验证,计算结果表明:管内工质质量流速与热负荷相互匹配,反映出管内工质的流动具有"自补偿特性",管外海水表现出喷淋密度"上高下低"、盐度"上小下大"的规律;总结了供入海水流量、加热蒸汽流量与二次蒸汽产量等参数之间的依变关系,并探讨其对蒸发器热力性能和装置结垢的影响,为蒸发器经济运行以及进一步的结构优化提供了理论依据。

A three-dimensional distributed parameter model of a horizontal-tube falling-film evaporator was set up to understand and improve the flow and heat transfer performance of the fluid in key local region. The mass flow rate distribution of heating steam and characteristics such as flow field of seawater were analyzed in detail using the self-built software, which was helpful to intuitively investigate the working process and complex flow and heat transfer phenomena. The present model was verified by operating results. Furthermore, the numerical results show that the mass flow rate and thermal load of the fluid is mutually matched, which indicates that the self-compensation characteristics exist in the first and second tube-pass bundle. The distributed parameters show that the flow density becomes less and the seawater gets saltier with falling film flowing. In addition, the dependent relationship between the heating steam flow rate, the intake seawater flow rate and the amount of vapor formed in the effect is summarized to evaluate its influence on the thermal performance and scaling of evaporators, which can provide the theoretical basis for economic operation and further stucture optimization.