Microchannel heat sinks provide the solution to the ever-increasing heat flux generated from micro-electric components. In this study, performance optimization of a microchannel heat sink with delta ...winglet vortex generators was carried out based on the data obtained from numerical CFD simulations. A total of 192 design points were generated by altering the fluid velocity in terms of Reynolds number (Re), winglet width (Wd), length (Ld), and the angle of attachment (β) of the winglet. The Artificial Neural Network (ANN) model coupled with Non-dominated Sorting Genetic Algorithm NSGA-II was used simultaneously to minimize the friction factor and increase the Nusselt number. The ANN model predicted the output values within the error limit of 10%. The Pareto optimal front generated by the algorithm contains the input parameters in the range 982 < Re < 988, 177 μm <Ld < 233 μm, 10 μm <Wd < 25 μm, 57° <β < 64°. Decision-making methods TOPSIS, LINMAP, and Shannon entropy were employed to calculate the optimal solution from the data set and the obtained points showcased 70%, 120% and 158% surge in Nusselt number while an increase of friction factor by 35%, 109%, and 140% respectively is reported. The Performance Evaluation Criteria (PEC) values obtained from the best solutions were 1.52, 1.72, and 1.92, respectively. Furthermore, the accuracy of the optimal solutions was verified numerically. The flow and thermal field of the microchannel are also analyzed, and results showed that the angle of attachment and width of the winglet played a crucial role in the overall performance.
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•Investigated the hydrothermal performance and optimization of the microchannel heat sink with delta winglets.•Analyzed 192 design points obtained by controlling four input variables.•Optimized solution points generated by the combination of ANN and NSGA-II.•Employed decision-making criteria to select the best solution in terms of overall performance.•PEC values of 1.52, 1.72, and 1.92 were achieved from the optimized best solution set.
The increasing fuel prices have led researchers to work on the efficiency and development of heat-transferring devices. One such device is the hot water radiator, which is familiar in the domestic ...arena. The study aims to increase the efficiency and cooling performance of hot water 3D radiators by modifying the design of their fins and adding perforations for better fluid mixing. CFD simulations were carried out on the radiators with modified fin geometries (Wavy, Spike-rib, Cut-sections, Straight) and with two different intensities of perforation (19 and 38 perforations) for each case at varying inlet flowrates of the radiator. The numerical model in this study was validated with experimental work. The hydrothermal performance of each radiator was measured in terms of fin surface temperature, entropy generation, heat transfer rate, and thermal enhancement factor. The temperature distributions and fluid flow streamlines have also been shown. The results show that modifying the fin geometries augments the overall heat transfer rate by up to 131 % while perforating the fins boosts the rate to 134 %. Moreover, the radiation heat transfer is seen to have surpassed the convection heat transfer by 60–160 % for the modified radiator cases. Finally, the most efficient radiator is found based on the thermal enhancement factor, which is the spike-fin arrangement.
This research aims to assess the in detail thermal performance and entropy generation of a helical heat exchanger with multiple rib profiles and coil revolutions using water-based Al2O3 nanofluid ...with 5% concentration. A steady-state computational fluid dynamic model was used in determining the thermal and hydraulic parameters. The numerical model was validated with a numerical study and an experimental study. Three multiple rib profiles (2 rib, 3 rib and 4 rib) and three different coil revolutions (10, 20 and 30) were considered to design nine cases of heat helical exchangers. The geometrical effect was assessed and further represented as the streamlines, isotherms, overall Nusselt number, friction factor, thermal enhancement factor, and entropy generation. It is found that with the growth of coil revolutions the overall heat transfer rate and friction factor rise. The most efficient heat exchanger found in terms of thermal enhancement factor is 3 rib 10 revolutions with the value of 1.34. The entropy generation increases with the rise of the coil revolution. The maximum entropy generation increased by 19.5% for varying the coil revolution with a constant rib profile. Finally, this study is a guide of choosing an efficient heat transfer in terms of thermo-hydraulic performance.
Oil-based nanofluids are used to strengthen the stability of nanofluids as well as their thermophysical properties when they are exposed to high temperatures. The time-dependent thermophysical ...characteristics of multiwalet carbon nanotubes for kerosine oil-based nanofluid are numerically explored in this study. Considering a constant magnetic field, the radiative domain is examined in a lid-driven squared shape cavity with a semicircular heater on the middle part of the bottom wall. The Galerkin residual technique based on finite elements is used to obtain nonlinear dimensionless governing equations. Thermal conductivity along with dynamic viscosity models integrate Brownian motion of nanoparticles. The Reynolds number, the Hartmann number, the Radiation Parameter and the Richardson number are assumed to be constant to account for the fluctuation in solid volume fraction (ϕ = 0% to 10%). The results demonstrated that particle concentration improves the nanofluid’s thermophysical properties from 1 to 9 times than the 0% concentration and the heat transfer rate from 1 to 3 times. In addition, dimensionless time enhances all except the heat transfer rate and drag force of the sliding lid. It is worth noting that the considered parameter exhibits consistent behavior after a while.
The effects of various surface corrugations and wall materials of the thick base wall of a trapezoidal cavity on conjugate natural convection have been examined in this study. Pinewood, plexiglas, ...dry concrete and glass fiber are considered as the materials of the solid bottom wall. In this cavity, both sidewalls are kept adiabatic, while the top wall is kept isothermally cold, and isothermal heating is applied at the bottom wall. Four types of regular surface corrugation, such as flat, rectangular, sinusoidal, and triangular-shaped corrugated surfaces are considered at the inner side of the base wall. The mathematical solutions of Navier-Stokes and thermal energy equations are obtained using Galerkin finite element method. Parametric simulation is carried out by varying Rayleigh number within laminar regime. The computed results are presented in terms of isotherm and streamline plots. The average Nusselt numbers along the solid-fluid interface, the average fluid temperature inside the cavity and the overall thermal performance ratio are also observed to assess the impact of wall materials and shapes of corrugation on convective heat transfer mechanism. From the viewpoint of overall heat transfer performance, the present results reveal that the surface material as well as the shape of the corrugation plays critically on the heat transfer enhancement of the trapezoidal cavity.
This study explores causal mechanisms of river metamorphosis and its impacts on regional landscapes. The study also investigates the implications of metamorphosis on associated ecological resources. ...Advanced GIS and remote sensing technologies were used to delineate morphological parameters describing metamorphosis of the Old Brahmaputra River from historical maps (i.e.,
Rannell's Map in 1776, Tassin's Map in 1840, Topographic Survey Map in 1943
) and remotely sensed optical satellite imagery
Sentinel-2 in 2022
. Flood frequencies were investigated for different periods by applying Gumbel’s Analytical Method (GAM), Log-Pearson Type III, and Log-Normal Method to estimate probability of flood vulnerability and impacts of flooding on morphodynamics in the central Bengal Basin. During the periods between 1776 and 2022, the area of sedimentation (77,999.43 ha) was greater than the eroded area (2983.29 ha).This difference was attributed to siltation of the channel bed morphology and corresponding accelerated flood vulnerability that accompanied river metamorphosis. Hydrological variables particularly annual average discharge significantly declined from 22 to ~ 18 m
3
/s per year during the period from 1965 to 2020. The study results demonstrated that the log-normal methods significantly overestimated peak flood discharge compared to Log-Pearson methods and Gumbel’s probability model. The extrapolation of the discharge for the 100-year flood by applying the three methods produced values of 712.66 m
3
/s, 1750.26 m
3
/s, and 2462.92 m
3
/s. Differences of these magnitudes may be critical for planning purposes because these differences in results will generate large-scale projected impacts on morphodynamics of the central Bengal Basin.
This work conducts a numerical analysis of thermal radiation with a semicircular heater on the middle part of the bottom wall and a sliding lid on the top in a square enclosure. Magnetohydrodynamic ...(MHD) unsteady mixed convection for kerosene oil-based CNT nanofluid is studied. The finite element-based Galerkin residual technique is used to obtain nonlinear dimensionless governing equations. The thermal conductivity and dynamic viscosity models incorporate nanoparticle Brownian motion. Simulations were conducted for Reynolds number = 100, Hartmann number = 10, Richardson number = 1, and particle concentration = 0.05. The effects of fluid velocity magnitude, pressure gradient, temperature gradient magnitude, average temperature, bulk temperature, drag force of the sliding lid, and Nusselt number of the semicircular heater were investigated for different radiation parameters and dimensionless time. Results showed that increasing radiation intensity and dimensionless time improves fluid velocity, pressure gradient, and temperature gradient but decreases the heat transfer rate of the semicircular heater. Furthermore, the drag force of the moving lid is likewise found to be substantially dependent on the radiation parameter as well as dimensionless time. It is worth noted that after a while, the considered parameter exhibits consistent behavior.
Nanofluids have been widely researched in recent years to improve the heat transfer rate in heat exchangers. However, no research is seen on improving heat transfer rate using nanofluids by ...incorporating multi-ribbed geometry with coil revolution into helical heat exchangers. This study thus numerically investigates the heat transfer performance of a helical heat exchanger using various water-based nanofluids, considering multiple head-ribbed geometries with different coil revolutions. The numerical results have been validated against experimental correlations and a published numerical study. A total of nine cases are initially modelled to compare and identify the most efficient heat exchanger design under various heating conditions. The helical heat exchanger with 2 head ribbed and 30 coil revolution is found to be the most effective among all the cases and is selected for the nanofluid study. The heat transfer rate could be enhanced by 20%–80% utilizing 2 rib head geometry and by 17%–66% using 30 coil revolutions. Four different water-based nanofluids, namely Al2O3, CuO, SiO2, and ZnO with 4% nanofluid concentration, are introduced in the most effective helical heat exchanger. It is revealed that Al2O3 offers the highest heat transfer rate while SiO2 provides the lowest. The heat transfer rate enhances when the number of the ribbed head reduces and the coil revolution increases.
Metabolic syndrome (MetS) is a group of medical conditions that increase the risk of cardiovascular disease, stroke, and type 2 diabetes. While there are numerous studies on the prevalence of MetS in ...the general adult population worldwide, limited information exists regarding its prevalence among university students and academic staff. This study aimed to determine the prevalence of MetS and associated risk factors among Bangladesh university students and academic staff. For this cross-sectional study, 583 participants were randomly selected from university students (n = 281) and academic staff (n = 302) in Bangladesh. The participants' fasting blood samples were collected, and their serum lipid profile levels, fasting blood glucose, and other parameters were measured using standard methods. MetS was defined according to the NCEP-ATP III model guidelines. Additionally, a questionnaire was administered to the participants to gather information on socio-demographics, lifestyle risk behaviours, and personal medical history. Multivariate logistic regression models were used to determine the risk factors associated with MetS. Overall, the prevalence of MetS was 27.7% in students and 47.7% in staff. There was a significant difference (p < 0.01) in MetS prevalence between male students (34.8%) and female students (17.2%). In contrast, it was comparatively higher in female staff (52.3%) than in male staff (45.8%), although the difference was not statistically significant. The prevalence of MetS and its components increased with age in student and staff groups. The most common component of MetS was low levels of HDL-C, which affected 78% and 81.4% of the students and staff, respectively. Logistic regression modelling showed that increased age, BMI, hypertension, dyslipidemia, low physical activity, and smoking were significantly associated with MetS in students (at least p < 0.05 for all cases). On the other hand, increased age and BMI, hypertension, and dyslipidemia were significantly associated with MetS in academic staff (at least p < 0.05 for all cases). In conclusion, this study indicates a high prevalence of MetS in university students and staff in Bangladesh. Age, BMI, hypertension and dyslipidemia were independently associated with the risk of MetS in both groups. The findings emphasize the importance of interventions for students and staff in academic settings in Bangladesh. It is crucial to implement health promotion activities such as healthy diet and exercise programs more rigorously. Further research with more representative samples is needed to get more clear insights into MetS prevalence in this particular population subgroup for targeted interventions.
Childhood anemia is a global public health issue. In this study, we assessed the potential sociodemographic and dietary factors associated with the prevalence of anemia among children aged 6-59 ...months in Nigeria.
In this cross-sectional study, we collected dietary information and demographic data on 6,338 children with anemia from the Nigerian Demographic and Health Surveys (2018). The association between the occurrence of anemia and the demographic and dietary factors was determined by conducting Chi-squared tests. Additionally, bivariate and multivariate order logit models were constructed and reported as odds ratios.
The results of the multivariate analysis showed that the risk of anemia was reduced by 13% and 44% in children aged 13-36 months (OR = 0.87; 95% CI = 0.77-0.98; p = 0.019) and 37-59 months (OR = 0.56; 95% CI = 0.49-0.63; p < 0.001), respectively, compared to the risk of anemia in children aged 6-12 months. Anemia was 28% less likely in children of non-anemic mothers (OR = 0.72; 95% CI = 0.66-0.80; p < 0.001) than children of anemic mothers. Children fed pumpkin, carrot, squash, and sweet potato showed a lower occurrence of anemia by 17% (OR = 0.83; 95% CI = 0.70-0.99; p = 0.036) compared to those who were not fed these vegetables. Chances of anemia increased by 14% in children who were fed white potatoes, white yams, manioc, cassava, and other root-based foods (OR = 1.14; 95% CI = 1.01-1.29; p = 0.036).
This study highlighted the impact of a plant-based diet on the high prevalence of childhood anemia in Nigeria. Therefore, reformation of dietary habits, the inclusion of nutritional supplements, and food-fortification programs with reductions in maternal anemia are recommended.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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