279 INTRODUCTION Flow-induced vibrations (FIV) are a primary concern while designing the heat exchanger tube bundle. The main purpose to conduct this study was to understand the tube failure patterns against diferent tube and shell side fow velocities as well as no-fow conditions. The observations and results of this study shall act as guidelines for a safer heat exchanger design and consequently helps in avoiding the currently prevailing fail- ure modes in heat exchanger operation. The dif- ferent mechanisms that act as excitation sources to cause tubular vibrations in the heat exchang- ers are turbulence, vortex-induced instability, acoustic resonance, and fuid elastic instability [1] but the acoustic resonance is not considerable for single-phase liquid fow because this source of excitation is more signifcant in multi-phase fow and the gas fows. As the chances of fail- ure in tube bundles due to FIV are quite higher, thus it is a prime concern for the designers and engineers to study this phenomenon in detail. In a single-span tube bundle, support is provided using bafe plates to each tube just like the tube sheets are supported in multi-span tube bundles. The designer’s concern is to identify the natural frequency of the tube bundle and the severity of vibrations in it. This research has been carried out to study fow-induced vibrations to analyze their Analysis of Flow-Induced Vibrations in a Heat Exchanger Tube Bundle Subjected to Variable Tube Flow Velocity Akmal Hafeez 1* , Shahab Khushnood 2 , Luqman Ahmad Nizam 3 , Muhammad Usman 4 , Muhammad Mohsin Rashid 4 , Hasan Farid Khan 4 , Muhammad Ayub 4 , Adeel Qadir 4 1 Department of Mechanical and Aeronautical Engineering, University of Engineering and Technology (UET), Taxila, 47080, Pakistan 2 Department of Mechanical Engineering, University of Wah, Wah Cantonment 47040, Pakistan 3 Department of Mechanical Engineering, HITEC University, Taxila, Rawalpindi, Punjab 47080, Pakistan 4 Department of Mechanical engineering, The University of Lahore, Lahore 54000, Pakistan * Corresponding author’s e-mail: mianakmal77@gmail.com ABSTRACT Tube bundles of shell and tube-type heat exchangers often fail because of vibrations produced in tubes due to fow. The turbulence in the fow 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°) confguration having a pitch to diameter (P/D) ratio of 1.44. The internal tube fow 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 fow inside the tube is less as compared to the amplitude with the fow. Furthermore, as the velocity of internal tube fow escalates; the amplitude of tube vibrations tends to escalate as well even when the shell side fow 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 confrmed 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 fow. Keywords: Cross-fow; parallel-triangular confguration; internal tube fow; damping; glass tube heat exchanger. Advances in Science and Technology Research Journal Advances in Science and Technology Research Journal 2023, 17(2), 279–288 htps://doi.org/10.12913/22998624/161278 ISSN 2299–8624, License CC-BY 4.0 Received: 2022.12.30 Accepted: 2023.03.15 Published: 2023.04.01