Dynamic Modeling of Tube-Support Interaction in Heat Exchangers

"RÉSUMÉ:" Les forces induites par écoulement dans les échangeurs de chaleur peuvent provoquer des vibrations excessives et des interactions avec les supports. Avec le temps, ces interactions peuvent entraîner de l'usure par frottement et éventuellement mener au bris des tubes. La prédiction précise de l'interaction tube-support est importante pour quantifier l'usure par frottement. Ainsi, l'étude détaillée du frottement et des forces d'impact à l'origine de ces effets est nécessaire à l'établissement d'un modèle d'usure précis. Cette étude porte sur le développement d'un modèle de frottement qui permet de reproduire fidèlement les différents états du phénomène de frottement, incluant les effets d'élasticité, de plasticité et de frottement partiel. Le modèle d'impact tube-support résultant est vérifié numériquement et expérimentalement. Un modèle de frottement fonction du taux d'amortissement d'un ressort hybride a été développé pour simuler précisément un phénomène de frottement d'une vitesse nulle à une vitesse de glissement importante. Cela a été obtenu en considérant différents phénomènes pendant le phénomène de friction incluant l'effet Stribeck, les forces variables de rupture, l'élasticité des micro-protubérances de paroi ainsi que les comportements de glissement plastique et partiel. Le temps de glissement dans le modèle de friction à limitation de vitesse a été comparé à celui obtenu par le modèle de friction de Lugre. L'incapacité du modèle de frottement à limitation de vitesse à détecter la zone d'adhérence a été expliquée par la dépendance du critère de limitation de la vitesse sur la force variable de rupture et l'effet Stribeck. Ceci a confirmé l'importance d'avoir une limitation de vitesse adaptative pour le modèle de frottement à limitation de vitesse. De plus, la distribution des contraintes à l'intérieur de la zone de contact a été étudiée en détails pour délimiter les différentes régions dans une zone de contact lors du frottement. Cette analyse a permis d'associer une signification physique à chaque composante de ce nouveau modèle de frottement hybride. La capacité du modèle à reproduire précisément le comportement adhérence-glissement a été évaluée à l'aide du modèle de frottement d'Ozaki et Hashigushi ainsi qu'avec les tests expérimentaux de Baumberger et al. Les résultats montrent une meilleure estimation du comportement adhérence-glissement, qualitativement et quantitativement, en utilisant le nouveau modèle hybride.----------"ABSTRACT:" Flow-induced forces in heat exchangers can cause excessive tube vibration and interaction with their supports. Long term interaction may develop fretting-wear and consequently lead to tube failures. An accurate prediction of the tube-support interaction behavior is important to quantify tube fretting-wear. Therefore, a detailed study of the related friction and impact forces is required for formulating a precise wear model. This study aimed to develop a friction model for accurate representations of various states of the friction process, including elastic, plastic and partial slipping states. In addition, the tube-support impact model is verified both numerically and experimentally. A hybrid spring-damper rate dependent friction model was developed to precisely simulate the friction process from zero velocity to the gross slip state. This was achieved by considering various physical phenomena during the friction process including the Stribeck effect, varying break-away force, bristle elastic, plastic and partial-slipping behaviors. The slipping time in the velocity-limited friction model was compared to the LuGre friction model. The inability of the velocity limited friction model to detect the sticking region was explained by the dependency of a limiting velocity criterion on the varying break-away force and the Stribeck effect. This confirmed the importance of having an adaptive limiting velocity for the velocity limited friction model. In addition, the stress distribution within the contact region was studied in detail to demarcate different regions within a contact area during the friction process. This analysis attributed a physical meaning to each component of the new hybrid friction model. The ability of the hybrid model to accurately reproduce stick-slip behavior was examined using the Ozaki and Hashiguchi friction model and the Baumberger et al. experimental tests. The result showed better estimation of the stick-slip behavior, both qualitatively and quantitatively, using the new hybrid friction model. In addition, the ability of the hybrid model, to reproduce pre-sliding displacements, was also examined using the Lim and Chen friction model and the experimental stability phase diagram, developed by Baumberger et al. The hybrid friction model reproduced the experimental phase diagram with qualitatively good agreement contrary to the Lim and Chen friction model

COVID-19 VACCINATION IN THREE SITES IN SASKATCHEWAN: A PATIENT-ORIENTED REALIST EVALUATION

The purposes of this research were to evaluate the COVID-19 vaccination campaign in three pilot sites (Regina, Saskatoon, Prince Albert) in Saskatchewan and construct program theories for vaccine uptake among the recipients and vaccine delivery by the Saskatchewan Health Authority (SHA) stakeholders who were involved in the planning and delivery of the vaccines. The program theories contain contextual factors and causal mechanisms that influenced vaccine uptake and delivery. Traditional evaluations oversimplify characteristics of interventions and the environment surrounding them (1). Finding solutions to complex problems needs a through understanding of the nature of the problem, interventions, and the implementation contexts (2). Problems operate at various levels (individual, local, organizational, societal) which makes the relevant interventions complex (2). Literature has shown that targeted efforts are needed to increase vaccine uptake (3). In a theory-driven realist evaluation, evaluators raise the question of “for whom, under what circumstances, how and why do interventions work or not work?”, and build program theories to answer the question (2,4,5). Realist evaluation requires considerable researcher reflection, creativity, judgment, and inferences (6,7). By using a novel combination of patient-oriented research (POR) strategy and the realist evaluation, three and six initial program theories (IPTs) for the vaccine recipients and the SHA stakeholders, respectively, were developed collaboratively with three patient and family partners (PFPs). We refined and finalized the IPTs into seven program theories (PTs) by collecting insights from six vaccine recipients and six SHA stakeholders via realist evaluation interviews. We identified salient contextual factors that evoked mechanism chains resulting in intermediate outcome of vaccine hesitancy or willingness among the recipients. These contextual factors and causal mechanisms demonstrate the complex reality of Saskatchewan’s COVID-19 vaccination campaign, show causal pathways for vaccine strategies, and help policymakers to enhance vaccination programs for other jurisdictions

Effects of porous superhydrophilic surfaces on flow boiling critical heat flux in IVR accident scenarios

Critical Heat Flux (CHF) plays a key role in nuclear reactor safety both during normal operation as well as in accident scenarios. In particular,when an in-vessel retention (IVR) strategy is used as a severe accident management strategy, the reactor pressure vessel (RPV) cavity is flooded with water, to remove the decay heat from the corium relocated in the lower plenum by conduction through the RPV wall and flow boiling on the outer surface of the RPV. The CHF limit must not be exceeded to prevent RPV failure.Therefore, knowledge of the CHF under realistic conditions is necessary to assess coolability margins. Previous studies for prediction of CHF in the IVR situation were mostly based on data for as fabricated un-oxidized stainless steel. However, the RPV is made of low carbon steel and its surface has an oxide layer that results from pre-service heat treatment as well as oxidation during service. This oxide layer introduces significant differences in surface wettability, porosity, and roughness in comparison to an un-oxidized stainless steel surface. In this study, test heaters were fabricated out of RPV low carbon steel, pre-oxidized in a controlled high temperature wet air environment, which emulates the surface oxides present on the outer surface of the actual RPV; the heaters were then tested in a flow boiling loop designed specifically for the IVR conditions. Up to 70% enhancement in CHF value was observed for the oxidized in low carbon steel in comparison to the stainless steel

Bacteriophage as a Novel Antibacterial Agent in Industry and Medicine

Bacteriophage is a kind of virus that infect bacteria, and is distinct from the animal and plant viruses that could have either lytic or lysogenic cycle. Lytic phages known as candidates for phage therapy, since they rapidly replicate into their host and lyse them. Theoretically, phages have more than a few benefits over routine antibiotics. They are extremely specific and for their targeted hosts and also are safe for human, because they have no activity against eukaryote cells. Over this time, phages were used to treat various infections. Although, phages have a lot of advantages against antibiotics, their industrial production as a commercial production have been ceased in most of the western European countries.These days, by raising of antibiotics resistance and inefficiency of antibiotic to overcome bacteria biofilm,  there is renewed global attention in phage applications as a potentially powerful antibacterial agents. Different published paper through the world indicates bacteriophage could be recruited as suitable agent for therapeutic purposes in medicine and food industry. Therefore, here we tried to review most of these ideas about phage application as a rapid review

Sensorless Commutation Method for Low-Voltage BLDC Motors Based on Unfiltered Line Voltage

This study presents a filterless and sensorless commutation method for low-voltage brushless DC motors. The proposed method utilizes controlled DC-link inverter instead of the Pulse-Width Modulation (PWM) scheme. Therefore, motor voltages and currents become free from the high-frequency noise of PWM switching, thereby decreasing motor losses. Consequently, the method does not require any Low-Pass Filter (LPF) and it does not involve speed-dependent phase delay caused by the LPF. However, current commutation deteriorates waveform of line voltages. Thus, specific functions are defined to compensate for the current commutation spikes and remove false zero-crossing points of line voltages. Furthermore, the use of unfiltered line voltages eliminates the requirement of any phase shifter. Hence, the main superiority of the proposed method over preceding sensorless commutation methods is the simultaneous elimination of the phase shifter and LPF, which makes the method simple and cost-effective. The simulation and experimental results show the effectiveness and validity of the method

Seroprevalence of Toxoplasmosis among Women Referring to Shahid Beheshti Hospital, Hamadan, Iran

Background: Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The aim of this study was investigate the prevalence of toxoplasmosis among young women who referred to check up for toxoplasmosis attended in Shahid Beheshti hospital, Hamadan during 2013-2014.Materials and Methods: This study was performed on 2523 pregnant women who referred to laboratory of Shahid Beheshti hospital in Hamadan province (western of Iran) during 2013-2014. Age, level of education and place of residence were recorded in the relevant forms. Antibodies serum levels for all samples were examined by ELISA. IgG titer equals and more than 1:200 was presumed as seropositive. Data were analyzed using by SPSS version 19.0 software.Results: 26.1% of IgG seropositive persons were city residents while 32.3% of them lived at village and suburb of city. 1.4% and 1.1% of at risk persons (based on IgG titration) were city and village residents, respectively. 1.3% and 1.9% of IgM seropositives were city and village residents, respectively. The percentage of at risk persons of city and village (based on IgM titration) were 0.3% and 0.6%, in a row. 29.7% of IgG seropositives did not have academic education while 30.4% of them graduated from high school, at least. The seropositive IgM percentage of non-academic educated persons and graduated/academic ones were 1.7% and 1.4%, respectively.Conclusion: Our funding indicates the association between age of women and their level of education with percentage of contamination and prevalence. IgM seropositive is lesser than IgG. It means that toxoplasmosis is chronic or there is previous contact. To avoid the risk of toxoplasmosis infection particularly in pregnant women should be examined and the necessary preventive measures and training for young women should be presented

Dynamics of bacteriophages as a promising antibiofilm agents

Pseudomonas aeruginosa is an ubiquitous organism which has emerged as a major threat in the hospital environment. Overuse of antibiotics has also significantly increased the emergence of antimicrobial multiresistant bacteria. P. aeruginosa has an innate ability to adhere to surfaces and form virulent biofilms. Bacteriophage might represent one attractive solution to this problem. In this study, P.aeruginosa phage were utilized to Biofilm inhibition and remove.Sample collected from University sewage. Isolation was done according to Martha.R.J.Clokie protocol. Serial dilution prepared, then equally incubated with bacteria to investigate Biofilm inhibition potential. Biofilm formed base on Microplate Biofilm Assay. The effect of isolated phage investigated on biofilm remove of Pseudomonas putida, E.coli and Acinetobacter baumanii. P.aeruginosa biofilm had OD: 1.688 in 492n.m. Pure phage, 10-2 and 10-3 diluted phage decreased OD to 1.587, 1.341 and 1.461, respectively. Isolated phage dramatically decline OD of Biofilm of all strains.Phages have various affinity to attach to hosts, thereby it is supposed to phages compete for their receptors. Therefore it is supposed phages have most efficiency in optimum concentration to remove biofilm or growth inhibition

Global, regional, and national burden of disorders affecting the nervous system, 1990–2021: a systematic analysis for the Global Burden of Disease Study 2021

BackgroundDisorders affecting the nervous system are diverse and include neurodevelopmental disorders, late-life neurodegeneration, and newly emergent conditions, such as cognitive impairment following COVID-19. Previous publications from the Global Burden of Disease, Injuries, and Risk Factor Study estimated the burden of 15 neurological conditions in 2015 and 2016, but these analyses did not include neurodevelopmental disorders, as defined by the International Classification of Diseases (ICD)-11, or a subset of cases of congenital, neonatal, and infectious conditions that cause neurological damage. Here, we estimate nervous system health loss caused by 37 unique conditions and their associated risk factors globally, regionally, and nationally from 1990 to 2021.MethodsWe estimated mortality, prevalence, years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life-years (DALYs), with corresponding 95% uncertainty intervals (UIs), by age and sex in 204 countries and territories, from 1990 to 2021. We included morbidity and deaths due to neurological conditions, for which health loss is directly due to damage to the CNS or peripheral nervous system. We also isolated neurological health loss from conditions for which nervous system morbidity is a consequence, but not the primary feature, including a subset of congenital conditions (ie, chromosomal anomalies and congenital birth defects), neonatal conditions (ie, jaundice, preterm birth, and sepsis), infectious diseases (ie, COVID-19, cystic echinococcosis, malaria, syphilis, and Zika virus disease), and diabetic neuropathy. By conducting a sequela-level analysis of the health outcomes for these conditions, only cases where nervous system damage occurred were included, and YLDs were recalculated to isolate the non-fatal burden directly attributable to nervous system health loss. A comorbidity correction was used to calculate total prevalence of all conditions that affect the nervous system combined.FindingsGlobally, the 37 conditions affecting the nervous system were collectively ranked as the leading group cause of DALYs in 2021 (443 million, 95% UI 378–521), affecting 3·40 billion (3·20–3·62) individuals (43·1%, 40·5–45·9 of the global population); global DALY counts attributed to these conditions increased by 18·2% (8·7–26·7) between 1990 and 2021. Age-standardised rates of deaths per 100 000 people attributed to these conditions decreased from 1990 to 2021 by 33·6% (27·6–38·8), and age-standardised rates of DALYs attributed to these conditions decreased by 27·0% (21·5–32·4). Age-standardised prevalence was almost stable, with a change of 1·5% (0·7–2·4). The ten conditions with the highest age-standardised DALYs in 2021 were stroke, neonatal encephalopathy, migraine, Alzheimer's disease and other dementias, diabetic neuropathy, meningitis, epilepsy, neurological complications due to preterm birth, autism spectrum disorder, and nervous system cancer.InterpretationAs the leading cause of overall disease burden in the world, with increasing global DALY counts, effective prevention, treatment, and rehabilitation strategies for disorders affecting the nervous system are needed

A fundamental study on heat transfer characteristics of magnetite nanofluids

Research Doctorate - Doctor of Philosophy (PhD)This study investigated the heat transfer behaviour of nanofluids with focus on a magnetite nanofluid as an alternative for the next generation of cooling applications. The very first aim of this study was to shed light on conflicting data reported in the literature about the thermal conductivity of conventional nanofluids (non-magnetic). For this purpose, the thermal conductivity of different nanofluid samples were measured under different conditions (namely particle volume fractions, temperature and pH) and results were compared with theoretical prediction of mixture theory. Shortcomings of different hypotheses were examined, analysed and explained. All of the experimental data were within the ±10% boundary of theoretical mixture theory (i.e. Maxwell model). It was shown that higher thermal conductivity in the conventional nanofluids can be achieved by controlling the aggregation size (i.e. pH value). To test this hypothesis, artificial aggregates were generated by applying an external magnetic field to the magnetite nanofluid. Thermal conductivity enhancement by up to 160% was observed for 0.86 vol% magnetite nanofluids (Fe3O4-water), subjected to the magnetic field intensity of 32 mT parallel to the temperature gradient. On the other hand, the thermal conductivity of magnetite nanofluid is almost constant under the applied magnetic field perpendicular to the temperature gradient. Convective heat transfer coefficient of magnetite nanofluid under laminar flow condition was also considered in the absence and presence of an external magnetic field. Heat transfer in magnetite nanofluids with and without magnetic field has been performed previously. However, the extent of the experiments and analysis is the main goal which has been achieved through this study. It has been shown that the experimental data in the absence of an external magnetic field follows the prediction of standard correlation for laminar flow heat transfer (Shah equation) using the thermophysical properties of nanofluid. Up to 300% enhancement in convective heat transfer enhancement has been observed at Re=745 and the magnetic field gradient of 32.5 mT/mm. Moreover, the effect of magnetic field on pressure drop was insignificant. It is concluded here that aggregation is the main mechanism of heat transfer in nanofluids. The thermal conductivity and convective heat transfer coefficient of magnetite nanofluids can be altered far beyond the prediction of traditional theories by applying an external magnetic field