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Tube bundles of shell and tube-type heat exchangers often fail because of vibrations produced in tubes due to flow. The turbulence in the flow is the primary cause of vibrations in the tubes. In this study, a tube positioned in the third row of the tube bundle was considered to determine the vibrational response of the heat exchanger tubes. The tube bundle was parallelly arranged in a triangular (60°) configuration having a pitch to diameter (P/D) ratio of 1.44. The internal tube flow velocity ranges from 0 to 0.371 m/s and the shell side velocity ranges from 0.5 m/s to 2 m/s. The experimentation shows that the amplitude of vibration without flow inside the tube is less as compared to the amplitude with the flow. Furthermore, as the velocity of internal tube flow escalates; the amplitude of tube vibrations tends to escalate as well even when the shell side flow velocity is kept constant. The data points from experiments tend to reside in the unstable region of the stability map and particularly on the map’s left side, although the tube shows stable vibration behaviour as confirmed by the experimental results. Thus, further, development can be done by modifying the theoretical models to predict the realistic stability behaviour of tubes with internal tube flow. [ABSTRACT FROM AUTHOR]

Rotating machinery plays a significant role in industrial applications and covers a wide range of mechanical equipment. A vibration analysis using signal processing techniques is generally conducted for condition monitoring of rotary machinery and engineering structures in order to prevent failure, reduce maintenance cost and to enhance the reliability of the system. Empirical mode decomposition (EMD) is amongst the most substantial non-linear and non-stationary signal processing techniques and it has been widely utilized for fault detection in rotary machinery. This paper presents the EMD, time waveform and power spectrum density (PSD) analysis for localized spur gear fault detection. Initially, the test model was developed for the vibration analysis of single tooth breakage of spur gear at different RPMs and then specific fault was introduced in driven gear under different damage conditions. The data, recorded by means of a wireless tri-axial accelerometer, was then analyzed using EMD and PSD techniques and the results were plotted. The results depicted that EMD algorithms are found to be more functional than the ordinarily used PSD and time waveform techniques. [ABSTRACT FROM AUTHOR]

An experimental study on the incident flow angle effects on the vibration behavior was carried out on aluminum tube in parallel triangular tube bundle with P/D ratio of 1.375. Fluid elastic instability is the most fatal mechanism from all the vibration mechanisms and therefore must be dealt with a lot of attention. Experiments were performed on low speed water tunnel with the velocity of water ranges from 0.3 m/s to 0.7 m/s. The experiments were designed in a unique way to study the effects of incident flow angle on the vibration behavior. The monitored tube was mounted flexibly in an array of rigid tubes. The experiments were conducted on a flexible tube for different velocities ranging from 0.3 m/s to 0.7 m/s with different array rotated angles (0 to 90 degrees). It was observed that the vibration level was significantly high at 75 degree configuration as compared to other rotated angle configurations. It was also observed that the damping response is dispersed with all positive values, indicating that there is no instability in the tube. [ABSTRACT FROM AUTHOR]

Experiments have been designed to investigate the fluidelastic instability in a flexibly mounted tube in a parallel triangular tube bundle with a tube diameter of 12:7 mm and pitch-to-diameter (P/D) ratio of 1:45. The monitored tube, placed in the centre of the tube bundle, was equipped with a wireless accelerometer to acquire the vibration response under air cross-flow in a wind tunnel. The vibration response of the monitored tube was captured by changing the surrounding flexible tube location and the mass ratio. This experiment is the first of its kind, as it has not yet been reported in the literature. It is observed that the fluidelastic instability occurs for all the surrounding tube locations and mass ratios and is strongly dependent on the location and mass ratio. A strong tube-to-tube coupling exists, as indicated by the amplitude analysis of the monitored tube. The stability analysis suggests that increasing the mass ratio of the surrounding tubes seems to have an effect on the stability of the monitored tube. [ABSTRACT FROM AUTHOR]

Research on heat exchange has been carried out for more than five decades because of its importance in process industries and power generation plants. Heat exchanger experiencing cross flow are vulnerable to flow-induced vibration. This vibration causes the interaction of tubes with the baffle resulting in a fretting wear of the tubes. The present study focuses on fretting wear analysis of different tube materials. Fretting wear tests were performed on aluminum, copper and stainless steel instrumented central tubes against mild steel baffle. For each tube material the tests were performed for three different test durations i.e. 60 minutes, 120 minutes and 180 minutes at a cross flow velocity of 0.55 m/s. It was observed that vibrational amplitude of the flexible test tube is affected by its weight. A scanning electron microscope was used to analyze and measure the sizes of wear scar. The results indicated that wear loss in case of aluminum tube is the highest while that in case of stainless steel tube is the lowest. [ABSTRACT FROM AUTHOR]