Étude numérique et expérimentale du phénomène de la transition en convection mixte dans le cas d'un tube vertical pour un nombre de reynolds inférieur à 2000

Le transfert thermique en convection mixte (convection forcée et libre) pour l'air ascendant dans un tube vertical à bas nombre de Reynolds a été étudié numériquement et expérimentalement. La recherche a été concentrée sur l'étude de l'évolution axiale et radiale des paramètres hydrodynamiques et thermiques de l'écoulement à Re<2000 ; particulièrement, l'étude des phénomènes de transitions du champ d'écoulement à bas nombre de Reynolds. Par conséquent, on a proposé une formulation spéciale permettent de prévoir le régime laminaire aussi bien que le turbulent. La forme elliptique des équations gouvernantes a été également employée pour déterminer les paramètres de développement de l'écoulement. La capacité de la formulation et du procédé numérique de prévoir les caractéristiques de champ d'écoulement a été démontrée en comparant avec les résultats de mesure. Les résultats du calcul ont été comparés aux valeurs expérimentales trouvées dans le littérature pour un bas nombre de Reynolds (Re=380) et pour un nombre de Reynolds élève (Re=5000). Cependant, pour les nombres de Reynolds intermédiaires nous avons comparés nos résultats numériques avec nos valeurs mesurées. Les calculs ont déterminé deux nombres de Grashof critique pour lesquels des transitions se produisent (les transitions n'ont pas effectues pour Re=430). Pour le premier point (à Gr9xl06 pour Re=lOOO et à Gr2xl06 pour Re=l500), le régime d'écoulement change de laminaire en turbulent. Pour deuxième point critique (à Gr5x107 pour Re=lOOO et à Gr9xl07 pour Re=1500), le régime d'écoulement revient laminaire en raison de l'effet de laminarisation de la chaleur. Deux types d'inversion d'écoulement ont été prévus et discutés. Le premier s'est produit autour de la région de ligne centrale et le second autour de l'axe du tube et prés de parois. Malgré la solution analytique donnée par Hallman (1956) qui confirme le second cas, dans la littérature personne n'a prédit numériquement les résultats avant nos travaux. Un appareil expérimental a été conçu pour l'étude de la transition et le champ d'écoulement structuré de cette dernière. Les spectres de FFT de fluctuations de la température et de l'indicateur de vitesse ont distingué trois nombres critiques de Grashof pour lesquels le champ d'écoulement change de laminaire en turbulent. Ces trois nombres critiques de Grashof sont 3.78xl06, l.09x106, et 3.8lxl05 correspondant au Re I OOO, au Re 1300 et au Re 1600. Les fluctuations thermiques les plus importantes oscillent avec une fréquence de f=0.45Hz et ses multiples, tendis que pour la fluctuation de vitesse elle se détecte à f=l.8Hz (qui est aussi un multiple de f=0.45Hz) et ses multiples.Abstract: Combined forced and free convection (mixed convection) heat transfer for upward airflow through a vertical tube at relatively low Reynolds numbers was studied numerically and experimentally. The research focused on the axial and radial evolutions of hydrodynamic and thermal parameters of the flow field at Re < 2000, particularly on flow field transitions at such low Reynolds numbers. Therefore, a formulation based on Launder and Sharma Low Re [kappa]-[epsilon] turbulent model was proposed. Its main advantage is that it can predict laminar as well as turbulent flow fields. The elliptical form of the governing equations was also used in order to predict developing flow field parameters. The ability of the formulation and numerical procedure to predict the flow field characteristics was shown by comparison with experimental results. The calculated results were compared with experimental measurements that were found in the literature for very low Reynolds number (Re = 380) and high Reynolds number (Re = 5000). They were also compared with our experimental results at relatively low Reynolds number (Re = 1588). The calculated results for Re = 430, 1000 and 1500 established two critical Grashof numbers for which transitions occur (these transitions did not appear for Re = 430). At the first one (Gr [approximate] 9 × 10[superscript 6] for Re = 1000 and Gr [approximate] 2 × 10[superscript 6] for Re = 1500), the flow regime changes from laminar to turbulent. At the second critical point (Gr [approximate] 5 × 10[superscript]7 for Re = 1000 and Gr [approximate] 9 × 10[superscript 7] for Re = 1500), the flow regime comes back to laminar because of the accelerating effect of heating. Two flow reversal patterns were predicted and discussed. The first one includes the centerline while the second one occurs between the tube axis and the wall. In spite of the analytical solution by Hallman (1956), which confirms the existence of the second one, it had not been predicted numerically before. An experimental apparatus was designed and built to study the flow field transitions and their structure. FFT spectra of the temperature fluctuations and the velocity fluctuations indicator determined the critical Grashof numbers for which the flow field changes from laminar to turbulent. These critical Grashof numbers are 3.78 × 10[superscript 6] , 1.09 × 10[superscript 6], and 3.81 × 10[superscript 5] corresponding to Re [approximate] 1000, Re [approximate] 1300 and Re [approximate] 1600. The most important thermal fluctuations oscillate with f = 0.45Hz and its multiples while the velocity fluctuations oscillate with f = 1.8Hz (which is also a multiple of f = 0.45Hz) and its multiples

BLADDER INGUINAL HERNIA, HOSPITAL OF ZABOL, IRAN: A CASE REPORT

Herniation of the bladder into the inguinal canal is an uncommon phenomenon, accompanied by complications, such as the obstruction of the neck of the bladder caused by prostatic hypertrophy, that increase intra-abdominal pressure, which occurs in one fourth of all inguinal hernia. It is quite difficult to diagnose the involvement of the bladder during the first medical examination of the patient and it might even require a herniorrhaphy. The main objective of the present study is to report an untouchable case of bladder herniation without any specific symptoms which was randomly diagnosed using spinal CT scan. Knowing the possibility of the incidence of such a case can help assess requirements of a surgery and improve readiness to implement useful interventions. Key Words: Inguinal Hernia, Bladder, Case Report, Zabol

Numerical Study of CNT Micro Fin Array for Cooling Application

Heat removing from a microelectronic chip packaging has grand effect on performance and durability of the chip. Today’s microchips with high power densities would require efficient methods of cooling. Recently, vertical alignment CNTs, due to their superior thermal, electrical and mechanical properties, was suggested as an effective micro cooler on the level of modern electronics demands. In this paper, the cooling performance of the CNT fin structures is studied numerically. Flow of air was considered as the working fluid flow. CFD simulations have been carried out for a series of CNT micro-fin cooling architectures based on one and two dimensional fin array models. The modeling results indicate that fluid speed is the key factor in heat transfer capacity of the device. Also, the results of 2D carbon nanotube fin array model show more precise and greater thermal performance than that of 1D model. Finally, the examination of pressure drop between inlet and outlet of the cooling device is presented as an important factor which could limit the fluid speed and fin height effect on heat sink performance also investigated

The effect of placental location on placental weight and infant birth weight of pregnant mothers: a cross-sectional study.

Introduction The placenta is considered to be the most vital organ of the infant. The intrauterine fetal growth and development indicates a harmony between the fetus, placenta, and mother. Studies show that placenta has different effects on maternal and neonatal outcomes. This study aimed to investigate the effect of placenta location on placental weight (PW) and infant birth weight (IBW) in pregnant mothers. Material and Methods This descriptive study was performed on 370 pregnant mothers and their newborns referring to Amir-al- Momenin Hospital in Zabol, south of Iran from October to March 2018. The data collection tool included a researcher-made checklist consisting of two parts: maternal demographic information and infant information. The placenta location was determined by ultrasound and recorded by a radiologist and the Apgar’s score was measured by an obstetrician in the delivery room. The collected data were then analyzed using descriptive and analytical tests. Results The mean± SD of maternal age, maternal BMI, Apgar score, and IBW was 30.39±5.44. 25.24 ± 4.54, 9.65 ± 0.65, 3244.61 ± 204.116 gr, and 548.83± 104.65 gr, re- spectively. Most of the infants were male (50.3%). The placenta was mainly located in the fundal portion of the womb (44.9%). Results showed no significant relation- ship between the placental location and IBW (p = 0.555). However, the results showed a significant relationship between the placental location and PW (p = 0.028). Conclusion Since the results of this study indicate the relationship be- tween placental location and PW and infants' gender, spe- cialists are recommended to consider placental location as a factor affecting PW

Conjugate heat transfer of laminar mixed convection of a nanofluid through an inclined tube with circumferentially non-uniform heating

Laminar mixed convection of a nanofluid consisting of water and Al2O3 in an inclined tube with heating at the top half surface of a copper tube has been studied numerically. The bottom half of the tube wall is assumed to be adiabatic (presenting a tube of a solar collector). Heat conduction mechanism through the tube wall is considered. Three-dimensional governing equations with using two-phase mixture model have been solved to investigate hydrodynamic and thermal behaviours of the nanofluid over wide range of nanoparticle volume fractions. For a given nanoparticle mean diameter the effects of nanoparticle volume fractions on the hydrodynamics and thermal parameters are presented and discussed at different Richardson numbers and different tube inclinations. Significant augmentation on the heat transfer coefficient as well as on the wall shear stress is seen

Numerical Study of CNT Micro Fin Array for Cooling Application

Heat removing from a microelectronic chip packaging has grand effect on performance and durability of the chip. Today's microchips with high power densities would require efficient methods of cooling. Recently, vertical alignment CNTs, due to their superior thermal, electrical and mechanical properties, was suggested as an effective micro cooler on the level of modern electronics demands. In this paper, the cooling performance of the CNT fin structures is studied numerically. Flow of air was considered as the working fluid flow. CFD simulations have been carried out for a series of CNT micro-fin cooling architectures based on one and two dimensional fin array models. The modeling results indicate that fluid speed is the key factor in heat transfer capacity of the device. Also, the results of 2D carbon nanotube fin array model show more precise and greater thermal performance than that of 1D model. Finally, the examination of pressure drop between inlet and outlet of the cooling device is presented as an important factor which could limit the fluid speed and fin height effect on heat sink performance also investigated

CARDIOPULMONARY RESUSCITATION-REVIEW ARTICLE

Introduction: Cardiac arrest is one of the major causes of increased mortality and morbidity worldwide Regarding the occurrence of physiological changes in the vital system of pregnant mothers and reminders, it must be stated that the fact that heart disease in pregnant women can endanger two lives simultaneously, it is clearly indicative of the importance of taking correct remedial and precautionary measures. On the other hand, since the implementation of cardiopulmonary arrest on pregnant women cause incidents, timely and correct remediation is associated with a high percentage of success. Therefore, the purpose of this study was to review the recovery of heart rhythm in pregnant mothers. Methods: In this review article, the databases Medline, Cochrane, Science Direct, and Google Scholar were thoroughly searched to identify the studies investigating Pulmonary cardiopulmonary resuscitation. In this review, the papers published until early January 2017 that were conducted to study the Paget's disease were selected. In searching for the articles, those English papers were selected that had investigated Pulmonary cardiopulmonary resuscitation. Results: . Side effects such as heart rhythm disorders and pulmonary edema usually arise in the context of old heart disease and follow physiological changes in the cardiovascular and pulmonary causes which, unless treated timely and correctly, may lead to cardiac arrest. Conclusion: In case of cardiac arrest, ventilation of pregnant mothers is initially performed by mask and bag valve mask and the oxygen core. If additional ventilation is needed, intubation of the trachea should be done as soon as possible and the ventilation must continue through the tracheal tube and bag valve mask; finally, in case of prolonged cardiac and respiratory difficulty, long-term ventilation can be used. Keywords: Pulmonary, cardiopulmonary, resuscitatio

Effect of Source Solution Components on Quality of Electrospun PVDF Nanofibers for Nanogenerator Application

High surface area flexible thin films of Polyvinylidene Difluoride (PVDF) nanofibers are vastly used because of low cost, simple, safety and environmentally friendly production methods. PVDF nanofibers are inherently piezoelectric when produced by high voltage electrospinning method. In this paper, PVDF nanofibers are synthesis in a electrospinning apparatus, using a solution that contains PVDF dissolved in two solvents, THF (Tetrahydroforan) and DMF (N,N-Di-Methyl Formamid), which DMF has a higher boiling point than THF. The effects of THF to DMF ratio in the solution, and also, PVDF concentration on the morphology and diameter of the synthesised nanofibers are studied. Field emission scanning electron microscopy analysis of the nanofiber thin films indicates that by adding THF in the source suspension, smoother and more uniform nanofibers with lower diameter are resulted. However, by further increasing THF ratio, the cone-jet mode is formed on the tip of the needle, rapidly dried, before reaching the collector substrate. Results of the further experiments indicate that decreasing of PVDF concentration in the deposition source solves the latter problem. On the other hand, by decreasing the THF ratio to DMF, the solution cannot completely be dried, before collecting by the substrate. The best and uniform nanofibers with the diameter of 200 to 300 nm are obtained from a ratio of 3:1 For THF:DMF and 10 % PVDF concentration. Fabricated nanogenerator, based on the best mentioned sample, shows an output power of 0.56 W/m2 when actuated by a vibration mechanical force with the frequency of 8 Hz

Emerging Nano-Theranostic Strategies against Non-Alcoholic Fatty Liver Disease: a review

As a major global cause of liver damage, non-alcoholic fatty liver disease (NAFLD) is associated with excessive hepatocellular accumulation of lipids in the liver, elevated levels of hepatic enzymes,and the fibrotic evidence. The primary therapies for NAFLD are changing lifestyle or managing comorbid-associated diseases. Lately, nanotechnology has revolutionized the art of nanostructure synthesis for disease imaging, diagnosis, and treatment. Loading drugs into nanocarriers hasbeen established as a promising strategy to extend their circulating time, particularly in treating NAFLD. In addition, considering a master modulator of adipogenesis and lysosomal biogenesis and function, designing novel nanostructures for biomedical applications requires using biodegradable materials. Various nanostructures, including inorganic nanoparticles (NPs), organic-based NPs, metallic nanocarriers, biodegradable polymeric nanocarriers, polymer-hybrid nanocarriers, and lipid-based nanocarriers have been designed for NAFLD treatment, which significantly affected serum glucose/lipid levels and liver function indices. NPs modified with polymers, bimetallic NPs, and superparamagnetic NPs have been used to design sensitive nanosensors to measure NAFLD-related biomarkers. However, certain limitations are associated with their use as diagnostic agents. The purpose of this review article is to shed light on the recent advancements in the field of nanomedicine for the early diagnosis, treatment, and prognosis of this progressive liver disease