采用脉冲示踪法研究离心泵的停留时间分布(RTD)，将离心泵与等径等体积空管对比，定性描述了离心泵的返混特征，考察了泵前阀控、泵后阀控、转速控制对RTD的影响. 结果表明，RTD曲线呈单峰分布，泵内有死区存在，返混大于等径等体积空管，无因次方差为0.39~0.61；离心泵的返混程度既不靠近平推流，也不靠近全混流，受流量影响显著，随流量增大，返混显著减小. 3种流量控制方式对离心泵返混有一定影响，转速控制的返混情况明显大于2种阀控方式，2种阀控方式的影响较接近；随流量减小，流量控制方式引起的RTD差异更显著，3种方式的无因次方差的最大相对偏差达13.6%.

The residence time distribution (RTD) of centrifugal pump was studied with a pulse tracer method. The back-mixing characteristics were described qualitatively by comparing the RTD of centrifugal pump with that of blank pipe. Three flow control modes, pre-pump valve, outlet valve, and motor speed, were selected to examine their effects on RTD. The experimental results indicate that the RTD curve of centrifugal pump shows a single-peak distribution, and dead zone is found. The back-mixing of centrifugal pump is greater than that of blank pipe with equal diameter and volume. The dimensionless variance ranges from 0.39 to 0.61, which is not close to ideal plug flow or complete mixing flow. The back-mixing is significantly affected by flow rate, it declines apparently with the increase of flow rate. Different flow control modes have a significant impact on the back-mixing. The back-mixing of centrifugal pump controlled by motor speed is greater than that regulated by valve, and pre-pump valve mode is similar to outlet valve mode. As the flow rate decreases, the difference of RTD among three control modes becomes more significant. The maximum relative deviation reaches 13.6%.