【作者】 刘芸；

【导师】 王军； 于志家；

【作者基本信息】 大连理工大学 ， 化学工程， 2006， 硕士

【摘要】 本文对池核沸腾时的传热及加热面上CaCO₃垢的生成等复杂过程进行了实验研究与理论分析。主要工作如下： 采用极限扩散电流技术（LDCT）与直接传热测定同时进行的方法研究池核沸腾时的界面汽化热阱效应以及沸腾滞后和由自然对流向核沸腾转变过程中加热面上沸腾泡核的发展状况。结果表明，界面汽化热阱效应和对流是核沸腾传热的两个主要途径，界面汽化热阱效应对传热的贡献随着热通量的增大而增大，随着系统压力提高也增大。并从沸腾中所包含的各个子过程间相互作用，相互竞争的观点分析沸腾传热的机理。研究发现不同的加热方式对沸腾滞后影响明显：当热通量逐渐增加时，出现滞后现象，而此后逐渐降低热通量，会产生TD滞后（Temperature Deviation）。研究还发现在传热脱离自然对流至充分发展的沸腾阶段内界面汽化热阱效应是逐渐增强的，说明了在沸腾起始阶段，加热面上沸腾泡核的形成是一个渐进过程。另外，依据泡核激活机制的转变并结合界面汽化热阱效应对沸腾滞后进行机理分析。 针对池核沸腾时水平加热表面上CaCO₃的结垢过程，首先采用动态热阻法对结垢规律进行了系统的实验研究，考察了热通量、垢质浓度和溶液主体温度对结垢行为的影响。此外，分别在疏水的氟硅烷修饰紫铜基表面以及亲水的紫铜表面上进行了CaCO₃结垢实验，实验结果及理论分析均表明该疏水表面具有较好的抗垢性能。本文还对过冷池核沸腾条件下的结垢过程进行了实验研究，发现过冷沸腾时传热系数的变化趋势和饱和池核沸腾时相同，但传热系数及结垢速率均较饱和沸腾时的低。并分析了沸腾初期出现的负污垢热阻现象。根据沸腾传热的特点，分析界面汽化热阱效应以及对流传热效应各自作用下的结垢机理。此外还分析了传热面上污垢的形成和汽化核心之间的相互作用，进而解释污垢的生成对沸腾传热的影响机理，结果表明污垢的生成对沸腾传热的影响主要源于对可生成沸腾泡核的活化空穴数目和结构上的改变。更多还原

【Abstract】 Heat transfer and scale formation characteristics during nucleate pool boiling has been experimentally investigated and theoretically analyzed in this paper. The main work is as follows:The method of applying limiting diffusion current technology （LDCT） with heat transfer measuring simultaneously has been used to study the interfacial vaporization heat sink effect and hysteresis during nucleate pool boiling, and the spreading process of boiling nuclei on the heat transfer surface in boiling incipience. The results reveal that heat transfer during nucleate boiling is mostly contributed by the interfacial vaporization heat sink effect and convection, the contribution of interfacial vaporization heat sink effect to heat transfer increases with increasing heat flux or system pressure. The heat transfer mechanism has been analyzed by the interaction of fundamental processes contained in nucleate pool boiling. The heating methods have evident effects on hysteresis. Hysteresis occurs under the condition of increasing the heat flux with constant pressure, while TD hysteresis （Temperature Deviation） occurs when decreasing the heat flux. The results also revel that the interfacial vaporization heat sink effect enhances during boiling incipience, when the formation of boiling nuclei is a gradual process. The boiling hysteresis mechanism has been analyzed on the base of the interfacial vaporization heat sink effect and the change in activation way of boiling nuclei.The characteristics of CaCO₃ scale formation on a horizontal round heat transfer surface has been investigated systematically through dynamic thermal resistance experiments which reveal the effects of heat flux, solution concentration and solution bulk temperature on fouling resistance. The experiments of CaCO₃ scale formation were also carried out on a hydrophobic Cu-F₈₂₆₁ surface and a hydrophilic Cu surface. The experiments results and theoretical analysis both reveal the antifouling characteristic of Cu-F₈₂₆₁ surface. Study of CaCO₃ scale formation during subcooled nucleate pool boiling shows that the change trend of heat transfer coefficient is the same with which during saturated nucleate pool boiling, while the values of heat transfer coefficient and fouling rate are less than that of saturated nucleate pool boiling. The negative fouling resistance phenomenon has been found in boiling incipience and the mechanism is analyzed. Two different scale formation mechanism during nucleate boiling is further analyzed. The effect mechanism of scale formation on nucleate boiling heat transfer has been further analyzed on the base of the interaction between scale formation and bubble更多还原