电场作用下近换热表面区域的粒子吸附与传热特性研究

As the important heat transfer equipment between cold and hot fluids, heat exchanger is widely used in the industrial heating system. There are two outstanding problems with the heat exchanger, one is the fouling on the heat transfer surface and the other is the failure of heat transfer. In this project, the high voltage electric field is utilized into the heat exchanger, which is aiming at anti-fouling of the heat exchanger and enhancing the heat transfer. The target of this research is revealing the characteristics of the fouling particles adsorption as well as the heat transfer characteristics under the electric field. The CaCO3 crystallization fouling is chosen as the research object. The adsorption of the particles (Ca2+，CO32- and CaCO3) and the heat transfer near the heat exchanger surface under the multi-field coupling of the electric field, flow field and temperature field can be obtained by experimental measurements and molecular dynamics simulations. The microstructure difference of the fouling particles and the heat transfer under the electric field can be directly observed in the experiment. The interaction force between the microscopic particles and the motion of microscopic particles can be tracked by the molecular dynamics simulations. The effect of the electric force on the adsorption of the particles and the heat transfer process are studied in the sight of microscopic view. Thus, the mechanism of the anti-fouling and the heat transfer enhancement under the electric field can be revealed in this project. Moreover, several effective methods of controlling the particles adsorption and the heat transfer can be designed by changing the electric field. For the actual heat exchanger structure, the reasonable and effective form of the electric field is designed. As a conclusion, this project builds the theoretical foundation of the effective applications of the electric field for the heat exchangers.

换热器作为冷热流体之间的热交换设备，被广泛应用在工业热力系统中。针对换热器换热表面结垢与传热性能下降的两个突出问题，本项目将高压电场引入到换热器中，同时实现电场作用下换热器换热表面的抑垢与传热强化。项目以“电场作用下近换热表面区域的粒子吸附与传热特性”为研究主题，以换热器中常见的CaCO3析晶污垢为研究对象，采用实验与分子动力学模拟相结合的方法，获得电场、流场与温度场耦合作用下近换热表面区域的污垢粒子（Ca2+，CO32-与CaCO3）吸附与传热规律；实验观测电场作用下换热表面污垢的微观形貌差异，结合分子动力学模拟跟踪微观粒子的受力与运动，从分子角度分析电场对粒子吸附与传热行为的作用机制，揭示电场抑垢与强化传热的物理机理；改变电场分布形式，获得粒子吸附与传热行为的有效调控方法；针对实际的换热器结构，设计合理与有效的抑垢与强化传热的电场形式，为高效换热器中电场的有效施加提供坚实的理论基础。

换热设备污垢问题广泛存在于能源、化工与食品加工等领域，换热表面污垢的形成显著降低换热设备换热效率，造成巨大的能源浪费与经济损失，换热表面高效抑垢是换热设备节能减排的重要研究方向。针对换热器换热表面结垢与传热性能下降的两个突出问题，本项目将高压电场引入到换热器中，同时实现电场作用下换热器换热表面的抑垢与传热强化。项目以换热器中常见的CaCO3析晶污垢为研究对象，采用实验与分子动力学模拟相结合的方法，获得电场、流场与温度场耦合作用下近换热表面区域的CaCO3污垢吸附规律。实验观测电场作用下换热表面污垢的微观形貌差异，结合分子动力学模拟跟踪微观粒子的受力与运动，从分子角度分析电场对粒子吸附与传热行为的作用机制，揭示电场抑垢与强化传热的物理机理。.项目获得电场作用下近换热表面区域的CaCO3污垢特性的实验研究数据，总结电场抑垢规律与关键影响因素。当换热表面入口温度为313 K，实验段前外加圆筒电极的最佳抑垢电压500 V，最佳抑垢率为83 %。因此合理设计电场形式，可有效实现换热表面的高效抑垢效果。此外，外电场作用下换热表面CaCO3结晶形貌存在差异，这为CaCO3合成研究方面给予新的思路。本项目采用分子动力学方法模拟CaCO3预团簇形成过程，分析CaCO3团簇的结构与性质的演化过程。这部分工作揭示了CaCO3成核过程中其纳米团簇团聚的重要作用，为CaCO3非经典成核提供有力支持。此外，外加电场可调控固-液界面处水分子的定向排列与水分子的数密度，可以有效提高固-液界面换热与强化液膜蒸发。当将施加的直流电场改为交流电场，可进一步提高液膜的蒸发速率。项目执行期间，指导毕业硕士研究生2名，其中一名毕业生获国家奖学金，被评为校优秀毕业生；辅助指导毕业博士研究生1名，硕士研究生3名，其中，博士研究生博士期间获国家奖学金，被评为校优秀毕业生。在项目资助下共发表8篇学术论文，其中SCI论文7篇。