硕士过热蒸汽饱和的研究与设计1.docVIP

工学 硕士学位论文 过热蒸汽饱和器的研究与设计 The Design and Research of the Superheated Steam Saturator 摘 要 本文着重研究了过热蒸汽饱和器内两相流动换热机理，尝试将单个水珠的微观蒸发过程与宏观的流动传热特性联系，在其中架设桥梁，以更好地了解过热蒸汽饱和器内(混合管)过热度的变化规律及其主要影响因素。 首先，从单一水珠角度探索分析蒸发模型。基于热质交换原理，从微观角度研究水珠蒸发模型，并系统比较了两种不同相际传热方式对水珠蒸发速率的影响。分析结果表明：对流换热方式下的蒸发速率要比导热方式下要高得多。并运用FLUENT软件仿真模拟了水珠蒸发过程，分析水珠直径随蒸发进程的变化规律，并研究了过热度对水珠蒸发的影响。 其次，建立了混合管内气液两相传热传质过程的简化物理模型。从单一水珠蒸发模型出发，推导出相际间不同传热方式下单位体积蒸发速率的具体表达式。并对连续方程和能量方程进行求解，获得了混合管内过热蒸汽质量流量和过热度的变化图。在此基础上， 对比分析了相际间不同传热方式对混合管长度（即饱和器结构特性）的影响；探讨了不同水珠初始直径（即雾化质量）对饱和化的影响。研究发现：混合管中的饱和水蒸发过程快慢，最主要取决于四个因素：水珠初始直径、饱和水质量流量、过热度和相对速度。有无相对速度决定了相际间不同的传热方式。并运用COMSOL软件模拟了混合管内气液两相流传热传质过程，数值模拟结果与上述求解结果基本吻合。 最后，选择一具体工况，对一种新型过热蒸汽饱和器进行了结构设计，确定了饱和器的外形尺寸与内部填料函的型式和高度。并依据不同的现场安装条件及用户需要，提出了重力水箱式和机械泵式两种饱和器供液装置。新型过热蒸汽饱和器改善原有装置的缺点和不足，扩大了饱和器使用范围，提高其工作性能。 关键词：过热蒸汽饱和器；两相流，过热蒸汽，蒸发速率  Abstract This paper is analyzed and studied the principle of flow and heat transfer in superheated steam saturator, trying to combine the microcosmic evaporation process of single water droplet and macroscopic character of flow and heat transfer, and better to understand the change regularity of superheated degrees and main influencing factors in superheated steam saturator which means in the mixing duct. First, the evaporation process of a single droplet is explored and analyzed. Based on the principle of heat and mass transfer, the evaporation rate of a single saturated water droplet is derived according to different heat transfer mode between phases. Compared with the thermal convection, the evaporation rate is 13 times higher than one by thermal conduction. Then, the evaporation process of water droplets with no relative speed is simulated by use of the FLUENT software. The droplet diameter changing with the degree of superheat is obtained due to the evaporation process. Secondly, the simplified two-phase model in the mixing duct is constructed between the superheated vapor and saturated liquid. On the basis of a single droplet evaporation model, the volume evaporation r