We performed an independent failure analysis of quartz tubes used in a water purification system. The flow conditions around the quartz tubes were evaluated using ANSYS computational fluid dynamics software. Natural vibration frequencies of the quartz tube and stresses for various loading conditions, such as shell distortion and impact damage, were evaluated using the ANSYS structural software.

The natural frequencies of the hollow quartz tube were analyzed, in order to determine the flow rates at which shedding vortices would excite these frequencies. Mode shapes for each of these frequencies were obtained in order to determine whether the dynamic forces caused by shedding vortices would excite these mode shapes, causing the quartz tube to absorb energy from the flow.

The results show that only the first two mode shapes pick up significant energy from the shedding vortices. While the first two mode shapes are quite different, both have their primary deflections in the direction of the vortex forces.

The results show that the root cause of the fracture of the quartz tube was due to flow induced vibrations. In order to operate safely, it is necessary to raise the natural frequency of the tube, or reduce the local flow velocities.

 


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