Investigation of boiling heat transfer on small diameter tubes and tube bundles

Boiling heat transfer on the outside of small diameter tubes in the range of 1.8-3.Omm has been investigated. Pool boiling was investigated at nominal atmospheric pressure for each of the tubes in isolation. The experiment was varied by investigating the effect of bubbles from a second tube mounted below by varying the heat flux on the upper tube. The upper tube diameter was changed from 3.00 to 2.32 and 1.83mm and in each case the lower tube was 3.00mm. Experimental results showed that the upper tube heat transfer coefficient was enhanced due to the combined mechanism of translating bubbles and turbulent convection at low to moderate heat fluxes. A compact tube bundle made up of 30 stainless steel tubes of outer diameter 3mm, pitch diameter ratio 1.5 and heating length of 50mm. was designed to permit the measurement of flow boiling heat transfer coefficient from tubes within the bundle. The heat flux tested was in the range of 4-21 kW/m2 and mass flux of 5.6-32.8 k g/M2 s using distilled water, R-113 and Flutec PPI at nominal atmospheric pressure as the working fluids. Results obtained showed that the heat transfer coefficient was predominantly dependent on the heat flux as opposed to mass flux. Macro scale models were compared with the experimental results and none of these models predicted the experimental results well. The Confinement number (Co developed for flow boiling inside micro channels was applied to compact tube bundles and it was shown that confinement is expected to be significant for Co>0.63. Photographic studies also showed that the diameter of the bubbles that were generated within the bundle were greater than the tube diameter. As such, the sliding bubbles mechanism played less significant role in contributing to the heat transfer coefficient. The recent three-state correlation developed by Thome et al for flow boiling heat transfer in micro channels was modified to predict the experimental results obtained using a compact tube bundle and it has been shown that the thin film evaporation was the dominant mechanism compared to the nucleate boiling. The results from the twin tube and compact bundle arrangement showed two regions coexist at any point in time; that part of the tube covered with liquid subject to nucleate boiling and the other part completely enveloped with vapour. This latter part is designated by the introduction of a factor p and this has been demonstrated experimentally and theoretically corroborated by a model based on a liquid part (1-p) and vapour part p

Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell.

The present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian two-phase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area. The volume of fluid interface tracking model has then been implemented to investigate the emergence of water droplets from the gas diffusion layer into the cathode channel and the subsequent removal of water from the channel. Further, the effects of the location of water emergence in the cathode channel on the dynamic behavior of liquid water have been investigated. The present study shows that the water emerging into the channel near the side walls greatly reduces the surface water coverage of the channel. In order to control the water path into the channel near side walls, a further discussion has been provided that a gas diffusion layer design based on hydrophilic fibres distributed inside a hydrophobic fibre matrix could provide a precisely controlled water path through the gas diffusion layer

Old age and depression in Ghana: assessing and addressing diagnosis and treatment gaps

Background: There is limited evidence about the prevalence of depression among older people in sub-Saharan Africa, about access to treatment or the potential efficacy of community-based interventions. Objective: Using nationally representative data from the WHO SAGE survey, examine the prevalence of and factors associated with depression among people aged 50 and over in Ghana. Compare self-reported diagnosis and a symptom algorithm to assess treatment gaps and factors associated with the size of gap. Assess the feasibility of a small community-based intervention specifically for older people. Method: Prevalence and treatment data were taken from the WHO SAGE 2007 survey in Ghana, including 4,725 people aged 50 or over. Outcomes of interest were self-reported depression and diagnosis of depression derived from a symptom-based algorithm. The data were subjected to bivariate and multivariate analysis. In parallel, a pilot intervention was conducted with 35 older people, which included screening by a trained psychiatrist and follow-up group sessions of psychotherapy. Results: The symptomatic algorithm reported an overall rate of 9.2 per cent for the study population, with associations with female sex and older age. The treatment gap for these cases was found to be 83.0 per cent. The implementation of the pilot study was perceived as effective and replicable by stakeholders and there was so evidence of enhanced outcomes for people with mild depression. Conclusions: Large numbers of older people in Ghana experience depression, but very few have access to treatment. There is an urgent need to develop and validate community-based services for older people experiencing this condition

Effect of waste landfill site on surface and ground water drinking quality

Drinking water quality of surface and underground water within 1.34 km from a waste landfill site in Kumasi, Ghana was investigated. Physico‐chemical properties and heavy metal concentrations were analysed to determine water quality and pollution indices. It was found that turbidity of 83% of hand dug wells, 50% of the streams and 33% of boreholes were higher than World Health Organisation (WHO) standards for drinking water. Water quality index (WQI) showed that 25% of the water sources are of excellent quality, while 50%, 15% and 5% are good quality, poor quality, very poor quality and unsuitable for drinking, respectively. Heavy metal pollution index (HPI) indicated that the water sources were above the critical limit for drinking water (HPI > 100). Principal component analysis (PCA) revealed 75.30% and 70.88% of the total variance for the physico‐chemical parameters and heavy metals, respectively. The findings concluded that cadmium concentrations in all the water sources were extremely higher (0.0122–0.1090 mg/L) than WHO limit (0.003 mg/L), rendering them unwholesome for consumption

A fractional order Monkeypox model with protected travelers using the fixed point theorem and Newton polynomial interpolation

This study formulates a Monkeypox model with protected travelers. The fixed point theorem is used to obtain the existence and uniqueness of the solution with Ulam–Hyers stability for the analysis of the solution to the model. The Newton polynomial interpolation scheme is employed to solve an approximate solution of the fractional Monkeypox model. The numerical simulations and the graphical representations suggest that the fractional order affects the dynamics of the Monkeypox. The fractional order shows other underlining transmission trends of the Monkeypox disease. We conclude that the result obtained for each compartment conforms to reality as the fractional order approaches unity

Prenatal and postnatal small-quantity lipid-based nutrient supplements and childrens social-emotional difficulties at ages 9-11 y in Ghana: follow-up of a randomized controlled trial.

BACKGROUND: Provision of small-quantity lipid-based nutrient supplements (SQ-LNSs) during early life improves growth and development. In the International Lipid-Based Nutrient Supplements DYAD-Ghana trial, prenatal and postnatal SQ-LNS reduced social-emotional difficulties at age 5 y, with greater effects among children in less-enriched home environments. OBJECTIVES: We aimed to investigate the effect of prenatal and postnatal SQ-LNS on childrens social-emotional problems at age 9-11 y. METHODS: In 2009-2011, 1320 pregnant women ≤20 wk gestation were randomly assigned to receive the following daily until 6 mo postpartum: 1) iron and folic acid until delivery, then placebo, 2) multiple micronutrients (MMNs), or 3) SQ-LNS (20 g/d). Children in group 3 received SQ-LNS from 6 to 18 mo. In 2021, we evaluated childrens social-emotional outcomes with 6 assessment tools that used caregiver, teacher, and/or self-report to measure socioemotional difficulties, conduct problems, temperament, mood, anxiety, and emotion management. RESULTS: We assessed outcomes in 966 children, comprising 79.4% of 1217 participants eligible for re-enrolment. No significant differences were found between the SQ-LNS and control (non-LNS groups combined) groups. Few children (<2%) experienced high parent-reported social-emotional difficulties at 9-11 y, in contrast to the high prevalence at age 5 in this cohort (25%). Among children in less-enriched early childhood home environments, the SQ-LNS group had 0.37 SD (-0.04 to 0.82) lower self-reported conduct problems than the control group (P-interaction = 0.047). CONCLUSIONS: Overall positive effects of SQ-LNS on social-emotional development previously found at age 5 y are not sustained to age 9-11 y; however, there is some evidence of positive effects among children in less-enriched environments. The lack of effects may be owing to low prevalence of social-emotional problems at preadolescence, resulting in little potential to benefit from early nutritional intervention at this age in this outcome domain. Follow-up during adolescence, when social-emotional problems more typically onset, may yield further insights. This trial was registered at clinicaltrials.gov as NCT00970866. https://clinicaltrials.gov/ct2/show/record/NCT00970866