Abstract: The particle image velocimetry (PIV) system was used for the flow field tests of step diffuser at different flow rates, velocity distributions of axial cross section, resistance loss and cavitation were obtained.The results showed that outlet velocity distribution became uniform at the cross section with length-diameter ratio of 3—5 with varying inlet velocity between 8 m·s^-1 and 24 m·s^-1, and further changed from uniform into non-uniform for circular tube, while outlet velocity distribution of square tube still remained uniform.Fiber deflocculated better with the increase of inlet velocity, but pressure loss increased rapidly.Cavitation intensified after the expansion, so inlet velocity should not exceed the critical cavitation velocity.The test results indicated that step diffuser with square tube was more suitable for high-speed paper machine, and appropriate high-speed slurry, geometric shape and size were guarantee of quantitatively uniform and evenness good paper..

Key words:

粒子图像测速, 纸机流浆箱, 阶梯扩散器, 流场试验

摘要：

采用粒子图像测速（PIV）系统对两种出口段型式阶梯扩散器的内流场进行了测试，得到了多种流量工况下阶梯扩散器轴向水平截面的速度分布、阻力损失及阶扩处空化等情况。测试结果表明，入口浆速为8～24 m·s^-1时，出口段横向速度分布在长径比为3～5时达到均匀，随后圆管出口段横向速度分布再由均匀发展到不均匀，而方管出口段的横向速度在达到均布后，后续流动没有明显不均匀的横向速度分布。入口浆速越大，对纤维的解絮越有利，但随着入口浆速的增大，流动阻力急剧增加，阶扩处空化区域增大，故在纤维充分分散的前提下，入口浆速以不超过空化的临界浆速为宜。研究表明，方管出口阶梯扩散器更适用于高速纸机，适当高的浆速和合适的形状尺寸是获得定量均匀、匀度好纸张的保证。

关键词:

粒子图像测速, 纸机流浆箱, 阶梯扩散器, 流场试验