Fretting Wear Analysis of Different Tube Materials Used in Heat Exchanger Tube Bundle

Research on heat exchange is being 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. These vibration causes the interaction of tubes with the baffle resulting in a fretting wear of the tubes. Present study focuses on the 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

Experimental Investigation of the Internal Tube Flow Effect on the Vibration Response of the Tubes in Shell and Tube Heat Exchanger

In shell and tube heat exchangers, tube bundles often fail due to the flow-induced vibrations. In the current study, vibration response of the tubes, placed in the first and third row of the tube bundle, has been examined having a normal triangular arrangement with pitch-to-diameter (P/D) ratio of 1.44. Each tube is tested for three different inside tube flow velocities of 0.85, 0.9 and 1 m/s and five shell side velocities ranging from 0.9 to 1.3 m/s with an increment of 0.1 m/s. This is the first experiment of its kind that offers insight into the tube vibration behavior made of glass material. The experimental analysis shows that tubes with internal flow vibrate with higher amplitudes than tubes without internal flow. Furthermore, the vibration amplitude of the tube tends to rise with increase in internal tube velocity even for the same shell side velocity. For the current range of shell and tube side velocity, with the internal flow from the tube, the hydrodynamic mass of the tube increases significantly with enhanced damping and contributes towards the stability of the tubes in crossflow, the stability threshold is delayed and higher shell side velocities are allowed to enhance the heat transfer rate.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Vibration Based Gear Fault Diagnosis under Empirical Mode Decomposition and Power Spectrum Density Analysis

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

Investigation of the Effects of the Incident Flow Angle on Vibration Behavior in Heat Exchanger Tube Bundle

Experimental study of incident flow angle effects on vibration behavior has been 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 of 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 vibration behavior. The monitored tube was mounted flexibly in an array of rigid tubes. 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. Also it was observed that the damping response is dispersed with all positive values, indicating that there is no instability in the tube

Analysis of Flow-Induced Vibrations in a Heat Exchanger Tube Bundle Subjected to Variable Tube Flow Velocity

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

Physical health of preclinical medical students during covid-19

Due to the COVID-19 pandemic, several preventive measures have been put in place including movement restriction and closure of non-essential services in Malaysia including educational premises and shifting towards online learning. Physical inactivity may impact medical students’ quality of life, particularly their physical and mental health, as both are especially influenced by doing physical activity. This study aimed to assess the physical health of medical students during the pandemic. This study has been approved by the institutional research committee (Research ID: 735). All Year 1 and Year 2 International Islamic University Malaysia (IIUM) medical students were invited to participate in this cross-sectional study. Participants were asked to complete an online, self-administered abbreviated World Health Organisation Quality of Life (WHOQOL-BREF) questionnaire from July until August 2021. Data were analysed using IBM SPSS Statistics 26 (IBM, New York). We received 158 responses, consisting of 77 Year 1 and 81 Year 2 students. All participants were undertaking online remote learning at the time of study. The mean score for overall quality of life was 14.58 (3.23) whereas the physical health domain mean score was 14.18 (2.48). We found that the requirement for medical treatment scored the highest 17.70 (3.42) whereas work capacity scored the lowest 12.25 (3.95). There was no significant difference in the scores between 14.50 (2.56) and 13.87 (2.37) for Year 1 and Year 2 students in the individual items (p=0.107- 0.862). We concluded that despite the nationwide lockdown, the medical students in IIUM reported acceptable-good quality of life and physical health. This could be due to their adaptation to the new norms by applying the right coping strategy. Future study to re-assess their quality of life is due should the lockdown are further extended or tightened

Association of barriers of learning during COVID-19 pandemic with mental health

On March 11, 2020, World Health Organization (WHO) declared that COVID-19 has become a pandemic. Therefore, online learning (OL) has replaced face-to-face teaching and learning sessions in many schools and colleges. This has forced the students to adapt to a new environment and overcome some barriers during the OL. However, the increase in suicidal rate among students is a disturbing phenomenon due to mental vulnerability experienced during the current worldwide situation. This study was done to investigate the association between barriers of learning during Covid-19 with mental well-being among International Islamic University Malaysia (IIUM) pre-clinical medical students. A cross-sectional study was conducted among the Year 1 (n=77) and Year 2 (n=81) medical students of IIUM, from July until August 2021. They were recruited to answer self-administered online questionnaires based on 5 remote learning barriers (inadequate interaction with classmates and teachers, lack of peer support and confidence to handle online tasks, and difficulty in applying taught concepts). The survey includes Generalised Anxiety Disorder (GAD-5) and Well Being Index (WHO5) to assess mental well-being and was approved by the institutional ethical committee (Research ID: 735). The results were analysed using IBM SPSS Statistics 26 (IBM, New York). The prevalence of depression and anxiety among medical students were 27.8% and 86.7% respectively. More than half of the respondents agreed with all learning barriers listed. However, the difficulty in applying taught concepts is the only significant barrier associated with depression (p<0.05). In conclusion, although only one item was identified as significant, it was an undeniable factor. Corrective measures must be taken to minimize it as continuous exposure may deteriorate mental health among medical students. Careful evaluation is required in order to ensure the quality of education remains upheld to its highest standards without jeopardizing the students’ psychological well-being

Association between sleep quality and mental health among IIUM medical students during COVID-19

Medical students usually sacrifice their sleep to adjust to their workloads. It is worth noting the importance of a good night's sleep to ensure the body and mind's optimum performance. However, depriving oneself of much-needed sleep in exchange for productivity has been shown to have deleterious consequences on the students' physical health and their state of mind. The objective of this study was to investigate the association between sleep quality and mental health among International Islamic University Malaysia (IIUM) medical students in the COVID-19 era. A cross-sectional study was conducted from July 2021 until August 2021 in IIUM and all year 1 and year 2 medical students were invited to participate. A total of 158 students responded, consisting of 77 first-year and 81 second-year medical students. The survey was distributed to assess the sleep quality using Pittsburgh Sleep Quality Index (PSQI), the mental health status was measured using WHO-Five Well Being Index (WHO-5) for the depression level and the General Anxiety Disorder-7 (GAD-7) for the anxiety level. The association between sleep quality and mental health was tested using Pearson's chi-square test and Fisher's Exact test. The findings showed a significant association between sleep quality and the mental health of medical students. A higher proportion of participants (86.4%) with depressive symptoms had poor sleep quality. Similarly, 81.8% of participants with anxiety symptoms had poor sleep quality. There was significant association between sleep quality and depression and/or anxiety (p<0.001). This study has shown a significant association between sleep quality and mental health status among IIUM medical students. It is highly recommended that the university provide interventions including advertising good sleep hygiene and coping mechanisms to support students' mental health in this COVID-19 era

Satisfaction of IIUM medical students towards online learning and its facilitating factors

The declaration of COVID-19 as a pandemic on 11th March 2020 has left a significant mark on the global education ecosystem. The transition from conventional to online learning is challenging for the administrators, teachers and students. The purpose of this study is to determine the satisfaction towards online learning and its facilitating factors among medical students in the International Islamic University Malaysia (IIUM). We conducted a cross-sectional study among first- and second-year medical students in IIUM from July to August 2021. The study protocol has been approved by the institutional research committee (Research ID 735). We asked the participants to complete a web-based self-administered Online Learning Experience Questionnaire (OLEQ) and rated the items using the 4 and 5-Likert scales. We used IBM SPSS Statistics 26 (IBM, New York) to describe and analyse the data. We received 50% (n=77) and 59% (n=80) responses from first- and secondyear medical students respectively. In general, the satisfaction of the students towards online learning was positive (mean 2.84-3.87 out of 4). In both cohorts, access to information and learning material scored the highest satisfaction followed by interaction with teachers. Meanwhile, the topmost factor facilitating online learning was being encouraged to take responsibility for their learning [4.11 (0.82) out of 5] followed by electronic communication with the teacher [3.92 (0.91)]. We found a positive association between the satisfaction score towards online learning and the facilitating factors score (r=0.635, p<0.001). In a nutshell, we can see that the IIUM medical students’ satisfaction towards online learning was positive and this could be attributed to the facilitating factors. This finding could be useful for policy-makers and administrators in education to focus on these factors to keep the system relevant in this current pandemic situation