Effect of Sagging on Dynamic Characteristics of Silicone Tube Conveying Fluid

Abstract

Flexible silicone tubes are nowadays broadly employing in medical applications such as drugs or blood-conveying tubes, various infusions as well as medical pumps, and ventilators tubes. Due to better resistance to corrosion and erosion, the subsequent diminishing of wall thickness and change in stiffness of silicone tubes are negligibly small. Hence, these tubes provide trouble-free operations for a prolonged period. Commonly, the fundamental frequency of fluid conveying tubes is influenced by various flow parameters. Recognizing the parameters affecting the fundamental frequency and estimating the extent of the impact of these parameters on the natural frequency are extremely important. This information is vital in the design of precision flow measuring instruments such as Coriolis flowmeter (CFM), which uses vibration techniques for flow measurements. Owing to higher accuracy and the direct fluid flow rate measurements, CFMs are universally accepted in industries for flow measuring applications. When the flexible silicone tube is excited in its sagged condition, there exists a difference in natural frequency in horizontal and vertical planes. Applying pre-stretch decreases the difference in natural frequency, which reduces the sagging and facilitates the tube to regain its cylindrical shape. This paper shows the experimental research on the influence of sagging of the silicone tube conveying fluid, the feasible methods to overcome these effects, and an effective means to capture the deformed shape of a flexible tube. Numerical analysis is carried out in ANSYS using the deformed shape acquired from the laser scanning technique, and the result shows excellent agreement with the experimental values. The damping ratio of the tube is identified by experimenting with varying flow velocities and pre-stretches. This study reveals that it is essential to eliminate the effect of sagging and the subsequent impact of frequency difference in flexible tubes when the principle of Coriolis flowmeter employs for measuring flow rates through flexible tubes.