NUMERICAL AND EXPERIMENTAL STUDY OF VIBRATION IN EXPANSION BELLOWS WITH DIFFERENT FABRICATION DESIGN

Abstract

Abstract Expansion bellows are widely used in applications of piping systems especially, the systems conveying fluid. The main function of bellows is to absorb the axial and transverse motions. Additionally, the flexibility of the expansion bellows make it sensible for vibration. This current work presents numerical model and experimental investigation study to analyze the vibration in expansion bellows. The main purpose of this research is to attempt to analyze the behaviour of U- shaped bellows under the influence temperature flow and mass flow rate. Firstly, a (MATLAB) code use to calculate numerically the bellows natural frequency depending on the material characteristics and design parameters of bellows. Furthermore, an experimental study is investigated on stainless steel 304L bellow type U-shaped with two inner diameters (10 and 20) mm to analyze the vibration under the effect of temperature and mass flow rate taking in consideration the bellow length and number of convolutions. For each diameter, three scenarios are prepared and tested in three types of supports (simple-simple), (fixed-free) and (fixed-fixed). The scenarios of the first diameters are included (100 mm pipe length with36 number of convolutions, 200 mm pipe length with75 number of convolutions and 300 mm pipe length with111 number of convolutions) while, the scenarios of the second diameter are included the same lengths of the first diameter with a difference in number of convolutions as (25, 54 and 82). Finally, response surface methodology (RSM) approach is employed to assess the effect of experimental parameters and their interaction on the frequency in expansions bellows. In addition, the( RSM) model is used to optimize the parameters and identify the optimal conditions for the frequency. Generally, the numerical results of (MATLAB) show that the natural frequency decreased with increasing the number of convolutions. But the percentage reduction in the natural frequency of (fixed-free) support is recorded higher than (simply-simply) support. According to the experimental tests, the frequency in case of IV ( simply-simply) increased with increasing the temperature regardless of design parameters but the frequency rapidly increased at small mass flow rate 1 LPM when the inner diameter 10 mm, length 100 mm and number of convolutions 36. In other words, the maximum percentage of increasing the frequency is about 40.7% when the temperature changed from 30C°to 80C° at length 100 mm. The analysis of (RSM) model results show that the minimum value of frequency is investigated at about 300 mm expansion bellow length, 7.5 LPM mass flow rate and temperature 55C°. In case of individual optimization, the responses obtained frequency is found to be 88.89 Hz with minimum desirability 0.992. The analysis of variance (ANOVA) results show a good match between the experimental data and proposed model, the value of observed determination coefficient (R2) and adjustment (R2) indicates that the developed model is a significant.