基于PIV技术对换热器入口流场的可视化研究

为了提高板翅式换热器物流分配的均匀性,本文利用粒子图像测速仪(PIV),并采用两帧互相关的分析方法,对换热器封头结构改进前后的流场进行实验测量.经过大量的实验数据处理,获得封头内部不同剖面处的流场速度矢量和流线分布图,发现了原始封头内部流场的流动与分布规律.由于封头结构的不合理导致漩涡、回流等现象存在,使得封头内部轴向以及径向的物流分配极不均匀.而对于在封头1/2高度处添加打孔挡板的改进型封头,物流分配的均匀性有了很大改善,速度场分布更加合理.在相同的入口条件下,全局不均匀系数S由改进前的1.210降至0.209,最大流速与最小流速之比由23.163降至1.756.此研究结果对于板翅式换热器的优化设计具有重要意义,同时也验证了PIV技术非常适合于研究复杂的流动结构.

Investigation of flow patterns in the entrance of heat exchanger by PIV technology

To improve the uniformity of fluid distribution in plate-fin heat exchanger,flow characteristics of flow field in the header were investigated by Particle Image Velocimetry(PIV).The velocity fields were measured using the two-frame cross-correlation technique.A series of velocity vector and streamline graphs of different cross-sections were achieved in the experiments.The results indicate that the improved header with punched baffle can effectively improve the performance of fluid flow distribution in the header.The global flow maldistribution parameter S in plate-fin heat exchanger is reduced from 1.210 to 0.209,and the ratio of the maximum velocity to the minimum is reduced from 23.163 to 1.756 by installing the punched baffle.The results validate that PIV is well suitable to investigate complex flow pattern,and the conclusion is of great significance in the optimum design of plate-fin heat exchanger.