凝汽器水侧流动的三维数值模拟

建立了某一凝汽器实际管束的流动计算模型,运用计算流体力学的方法,对该凝汽器水侧流场进行了三维数值模拟。采用分区对称计算方法,大大降低网格数量,从而详细预测了凝汽器水侧进出口水室以及其连接管和冷却水管束内的流动特性。计算结果可以清楚地表明:该凝汽器进口水室存在大量漩涡,使流动阻力增加,流动恶化;水室速度分布不均匀,进口水室管板中心区域流体流速较高而边缘区域较低,结构上存在一定问题;而出口水室的结构较为合理。这与采用多孔介质模型模拟的结论一致,进一步验证了采用多孔介质模型对凝汽器进行计算是正确可行的。计算结果同时表明,冷却水管束内流量和流速的分布是不均匀的,位于中心位置的冷却水管流量较大,而周边区域较小,最大流量差别可达到38%,且相邻管路的流量减小幅度与冷却水管布置有关。冷却水管内冷却水流量和流速的差异将会影响换热器的换热性能。计算结果可为分析研究管排流动不均而引起的换热效率问题提供条件,也可为凝汽器设计和结构优化提供依据。

A Three-dimensional Numerical Simulation of Water Flows at the Water Side of a Condenser

A model for the calculation of flows in tube bundles of a condenser has been established and by employing a CFD (computational fluid dynamics) method,a three-dimensional numerical simulation conducted of the flow field at the water side of the condenser.By using a sub-regional symmetric calculation method,the number of mesh can be greatly reduced,making it possible to conduct a detailed prediction of the flow characteristics in the inlet and outlet water chambers and their connecting pipes at the condenser water side as well as in the cooling water tube bundles.The calculation results clearly indicate that there exist numerous vortexes in the inlet and outlet water chambers of the condenser,resulting in an increase of flow resistance and a deterioration of the flow conditions.The velocity distribution inside the water chambers is not uniform.As a result,the flow velocity in the tubesheet central area of the inlet water chamber is relatively high and that in the marginal area is relatively low,indicating the presence of a certain structural problem.The structure of the outlet water chamber,however,is relatively rational.This fully corresponds with the conclusion of the simulation conducted by using a porous medium model,giving further proof that it is correct and feasible to use the porous-medium model to calculate the condenser.The calculation results show simultaneously that the distribution of flow rates and velocity in the cooling water tube bundles is not uniform,i.e.the cooling water tubes in the central area have a relatively big flow rate while those in the peripheral area a relatively small flow rate.The biggest difference in flow rates can amount to 38%.The margin of decrease in the flow rate of neighboring tubes has something to do with the layout of the cooling water tubes.The difference in cooling water flow rate and velocity in the cooling water tubes will influence the heat exchange performance of a heat exchanger.The calculation results can provide a foundation for the analysis of heat exchange efficiency problems caused by a non-uniform flow in tube banks and also a basis for the design and structural optimization of condensers.