Effects of fluidized solid particles on vibration behaviors of a graphite tube evaporator with an internal vapor–liquid flow

Abstract

Equations of motion for a straight graphite tube with an internal vapor–liquid–solid flow were derived and discussed for vibration analysis when the tube was fixed at both ends, and a model of “mixed phase flow” was used to deal with fluid parameters. To study the vibration behavior of the tube subjected to multiphase flow, an experimental program was also carried out. Numerical calculations indicate that under the present experimental conditions, the critical flow velocity is 0.85 m/s. Divergence motion appears when the flow velocity is from 0.85 to 1.14 m/s. The coupled mode flutter occurs when flow velocity is above 1.14 m/s. Parameter sensitivity analysis of the model shows that length of the tube has the most significant impact on the natural frequency of the tube. The natural frequency increases with the increase of void fraction, and decreases with the increase of solid holdup. Experimental results indicate that the addition of solid particles enlarges the amplitude of the vibration acceleration at the same pressure of boiler steam due to collision motions of solid particles with tube walls. The addition of solid particles has little influence on the natural frequencies of the graphite tube, which is in agreement with the model calculation results. The value of the vibration frequency excited by vapor–liquid–solid flow is about 8 Hz. Flow velocity should be controlled less than 0.78 m/s to avoid possible destructive resonance. The value 0.78 m/s is lesser than the critical flow velocity.