直接空冷单元空气流场优化

摘要

直接空冷系统空冷单元空气流场具有明显的旋转上升特点，且呈中心对称分布，使空冷单元翅片管束的冷却空气流量分配极不均匀，翅片管束传热面利用效率低，空冷凝汽器流动传热性能差。对此，利用 CFD 软件，对直接空冷单元内部的空气动力学特性进行研究，发现，由于风机出口流通面积的突变，在空冷单元底部形成了流动死区和涡流，在单元中心形成了严重的回流，导致流动阻力增加，阻碍了风机出口冷却空气向翅片管束方向的顺利流动。为此，提出4种导流方案，对4种导流方案的空冷单元热力性能进行研究。结果表明，经过空冷单元内冷却空气导流后，空气流场得到优化，管束表面流量和温度场更为均匀，空冷单元流动传热性能得到了改善。4种导流方案中，方案3的效果最为显著。%The air flow field of air cooling unit in direct air cooling systems has dramatic spiral trend and is cen-trosymmetric distributed,resulting in a very uneven distribution of cooling air volume in finned tube bundles,a real-ly low utilization efficiency of the heating surface of finned tubes and quite poor flow and heat transfer performance of air cooled condenser.Thus,the CFD software was applied to investigate the dynamic characteristics of air flow field inside the direct air cooling unit.It finds that due to sudden change of flow area at the fan outlet,flow dead zone and vortexes form at the air cooling unit bottom and serious reflux occurs in the unit center,causing an increase in flow resistance,which impedes the cooling air to flow from the fan outlet toward the finned tube bundles.There-fore,four flow guidance schemes were put forward and thermal performance of the air cooling unit in these four schemes were analyzed.The results show that,after guidance of the cooling air inside the air cooling unit,the air flow field is optimized,the bundles'surface flow and temperature field are more uniform and the flow and heat trans-fer property of the air cooling unit are significantly improved.