【作者】 刘磊；

【导师】 王恩禄；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2015， 硕士

【摘要】 本文在分析纯对流式换热器强化换热机理、纯凝结换热方式换热器强化换热机理、以及对流冷凝换热方式换热器强化换热机理基础上,根据各种换热器的特点,分析研究了对流冷凝换热过程的影响因素:烟气流动速度、壁面温度、水蒸气体积份额。并以上述影响因素作为变量,选取了两种结构形式换热器进行对流冷凝传热特性实验研究,探讨了理论凝结率与实际凝结率的关系,最后以理论结合实验得出了低烟气流速和大比表面积换热器有利于水蒸气凝结的结论。天然气燃烧得到的烟气作为研究对象,控制天然气流量与空气流量之比使烟气的流率稳定在要求的范围。蒸汽发生器产生水蒸气并以可调流量喷入烟气中实现的对烟气湿度的调节。在此基础上,研究光管管外壁面温度、管间烟气流速、水蒸气体积份额对对流冷凝换热系数以及冷凝水收集率的影响,对该类型换热器由于水分回收时,受热面布置的经济性进行了分析。并对低烟气流速下的水平布置翅片管外的对流冷凝换热特性进行了研究。实验过程将烟气的水蒸气体积份额控制在为14%,烟气平均温度控制在85.6-88.3℃,将换热管基管表面温度控制在28.8-29.8℃。研究的换热管管型为基管外径12m,翅片高度分别为0、3、4、5、6mm翅片管。结果表明,错列竖直布置光管换热器管外烟气流速减小,冷凝水捕集率增大。烟气流速为8m/s的条件下,水蒸气体积份额增大,冷凝率也会增大。当水蒸气份额从5.4%增大到18.3%,水蒸气的体积份额增大了3.4倍,而冷凝水的流率从0.2g/s增大了8倍达到1.6g/s。水平布置单排翅化比为8.9的翅片管管外对流冷凝换热过程水蒸气的冷凝率是光管管外水蒸气冷凝率的6.2倍;水平布置翅片管存在一个最佳烟气流速使得水蒸气凝结率达到最大;高翅片高度越高,烟气流速对对流冷凝换热系数的影响越小;随着翅片高度增加水蒸气凝结率趋于稳定;存在一个最佳翅片高度,使得翅片强化换热效率达到最大。更多还原

【Abstract】 This paper carries on experimental study on convective condensing heat-transfer effects of two kinds of heat exchangers’ structural form and further discusses the selecting principle of convective condensing heat exchanger’s structural type used in the flue gas of boiler on the basis of heat transfer enhancement mechanism of pure convective, pure condensing and convective condensing heat exchangers.In this paper, flue gas obtained by natural gas combustion was taken as research object, through controlling the ratio of the gas flow and air flow to guarantee the stability of flue gas components within the experimental requirements. To adjust humidity is realized by steam generator’s producing an adjustable mount of steam and injecting into flue gas. The experimental temperature at the inlet was kept around 100℃. The gas velocity, steam volume fraction, average temperature of cooling medium, influence of the flow type of cooling medium on convective condensation heat transfer coefficient and condensed water collection rate of vertical-cross arrangement smooth-tube heat exchanger were investigated, meanwhile the economy of heating surface arrangement when the water was recycled in this kind of heat exchanger was analyzed.Then the outer surface convective condensation heat transfer characteristics of horizontal arrangement finned-tubes was studied with different height of fin under the low flue gas velocity. The volume fraction of vapor in flue gas was controlled at 14%, and average flue gas temperature was controlled at 86.6-86.3℃. the average temperature of based tubes was controlled at 28.8-29.8℃. The finned-tubes include five types of 0, 3, 4, 5, 6mm fin height with the diameter of based tube was 12 mm.Experimental result shows that the condensation rate is increasing with the flue gas velocity decreasing in the staggered vertically arranged tube heat exchanger. The condensation rate increases as the volume fraction of vapor in flue gas increasing, under the 8m/s flue gas velocity condition. When water vapor share increased from 5.4% to 18.3%, the volume fraction of water vapor increases by 3.4 times, while the condensate flow rate from 0.2g / s increased eight-fold to reach 1.6g / s.The condensation rate of finned-tubes with 8.9 finned ratio is 6.2 times larger than that of tubes. There is an optimum flue gas velocity that makes condensation rate reaching largest in the convective condensation heat transfer process of outer finned tubes. The effect of flue gas velocity on convective condensation heat transfer coefficient decreases with increasing fin height. The condensate rate tends to be stable as increasing fin height. There is an optimum fin height that makes fin heat transfer enhancement efficiency reaching to maximum.更多还原