The Simulation Of Pulse Ultrasonic Anti-scaling In Soft Scale Prevention On Chemical Equipment

Fouling is a common problem in chemical equipment.Fouling is divided into hard scale and soft scale which is composed of slime and microorganism.As a new kind of anti-scaling technology,Pulsed ultrasonic technology has good anti-scaling effect on the hard scale,but doesn't work well in removing soft scale.In this paper,the shear and cavitation effects of long pulse ultrasonic anti-scaling are simulated and the effects on the removal of soft scale for different parameters are analyzed and some valuable results are obtained.The shear effect which is caused by the different propagation velocities of the pulse ultrasonic wave in two different mediums is an important mechanism of descaling.The viscoelastic constitutive model is used to simulate the soft scale,and the propagation of pulse ultrasonic vibration in the pre-stressed heat exchanger shell is simulated based on ANSYS/LS-DYNA implicit-display sequence solution.It is found that the increase of pulse width can enhance the effect on descaling,while the change of intermittent ratio has little influence based on the study of shear stress variation between the scale layer and the shell wall.Secondly,the influences of frequency and amplitude on the shear action are calculated by using the same method and it reveals that the amplitude affects the intensity of the sound field,and the frequency affects the sound field distribution.Finally,the cavitation effects of the fluid in the heat exchanger tube box under different pulse ultrasonic waves are simulated based on mixture model coupled with cavitation in FLUENT.It is found that the low-frequency and high acoustic pressure working state can enhance the effects of cavitation and descaling,and the change of fluid temperature has little influence on the cavitation field in the tube box.The results are of reference value for further improvement of the application of pulse ultrasonic anti-scaling technology.