The expansion of environment-friendly materials based on natural sources increases dramatically in terms of biodegradable, recyclable, and environmental disputes throughout the world. Plant-based ...natural fiber, a high potential field of the reinforced polymer composite material, is considered as lightweight and economical products as they possess lower density, significant material characteristics, and extraordinary molding flexibility. The usage of plant fibers on the core structure of composite materials have drawn significant interest by the manufacturers to meet the increasing demand of the consumers for sustainable features with enhanced mechanical performances and functionalities. The plant fiber-based composites have widespread usage in construction, automotive, packaging, sports, biomedical, and defense sectors for their superior characteristics. Therefore, this critical review would demonstrate an overview regarding the background of natural fiber composites, factors influencing the composite properties, chemical interaction between the fiber and matrices, future potentiality, and marketing perspectives for triggering new research works in the field of biocomposite materials.
•Methods to design new generation of energy absorbing and dissipating helmet liners with PA12 lattice structures.•Generation of high fidelity finite element lattice liner models predicting ductile to ...brittle transition behavior due to strain rate effects.•Linear high energy and oblique impact simulations based on a state-of-the-art helmet standard.•Helmet liners using PA12 lattice structures exhibit improvement in head protection, particularly against the rotational effects.
Existing helmets have a significant but limited ability to reduce the severity of brain injury and the fatality rate during motorcycle accidents. Helmet designs with a special focus on reducing head injuries caused by rotational effects have attracted great interest in recent times. This paper uses a computational approach to study the generation of new helmet designs with lattice liners made of polyamide12 (PA12) material. Three design possibilities and three distinct unit cell topologies were used to create the liners as the energy absorbing and dissipating part of the helmet. PA12 lattice samples were additively manufactured and tested under quasi-static and dynamic compression loads. The test data, showing ductile to brittle transition due to strain-rate effects, were used to validate the finite element models of the lattices. Simulations of the linear high energy and oblique impacts on the coupled headform and liner were carried out following the state-of-the-art helmet standard ECE R22.06. The findings of this study suggest that PA12 lattice liners have an excellent capability of reducing peak rotational acceleration. Many liners can outperform the protection levels offered by existing expandable polystyrene foam liners for single impacts, but at the expense of weight. The performance of the liners can be improved by choosing the topology in such a way that the stress can be distributed through the struts. Moreover, a lattice liner having a balanced energy absorption capability and stiffness would perform better than other lattice liners.
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The thermal efficiency of gas turbine engines depends heavily on the cooling performance of the internal channels of turbine blades. In the present study, the effects of bidirectionally arranged ribs ...on the flow and heat transfer mechanism in a two-pass cooling channel are investigated numerically. The channel aspect ratio is kept constant at 1:2 (W: H), and the rib pitch-to-height ratio (P/e) is 10. Comparative analysis is performed for three different cross-sectioned (Square, triangular and Curved) ribs with Reynolds numbers ranging from 10,000-50,000. The results indicate that the bidirectional ribbed channel provided 69% better thermal performance compared to horizontal-only ribs due to its potential to induce secondary flow in both vertical and horizontal directions. The square and triangular ribs show similar characteristics, but the thermal performance of curved ribs drops by 11%. The pressure loss phenomenon is also lowest in the case of the curved ribs. The obtained Nusselt number and friction factor for all cases are normalized with the Dittus-Boelter correlation, Blasius correlation and the smooth channel. The detailed analysis of area-averaged normalized Nusselt number indicates that the best thermal performance occurs at the bend region due to the combined contributions of the ribs and the 180° turn. Furthermore, in terms of the overall thermohydraulic characteristics, the curved-bidirectional ribbed channel is noticed to have the best results with values of 1.38 and 1.25 for TEFo and TEFs respectively.
•Numerical flow and heat transfer mechanisms of a bidirectional ribbed two-pass channel have been investigated.•Comparative analysis among three different types of rib cross-sections is generated.•Detailed analysis of the effects of rib arrangements on normalized Nu and f are presented.•Curved-bidirectional ribs show superior performance in terms of overall thermohydraulic characteristics.
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.
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.
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.
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 mortality of coronavirus disease 2019 (COVID‐19) disease is very high among the elderly or individuals having comorbidities such as obesity, cardiovascular diseases, lung infections, ...hypertension, and/or diabetes. Our study characterizes the metagenomic features in severe acute respiratory syndrome coronavirus‐2 (SARS‐CoV‐2)‐infected patients with or without type 2 diabetes, to identify the microbial interactions associated with its fatal consequences.This study compared the baseline nasopharyngeal microbiome of SARS‐CoV‐2‐infected diabetic and nondiabetic patients with controls adjusted for age and gender. The metagenomics based on next‐generation sequencing was performed using Ion GeneStudio S5 Series and the data were analyzed by the Vegan‐package in R. All three groups possessed significant bacterial diversity and dissimilarity indexes (p < 0.05). Spearman's correlation coefficient network analysis illustrated 183 significant positive correlations and 13 negative correlations of pathogenic bacteria (r = 0.6–1.0, p < 0.05), and 109 positive correlations between normal flora and probiotic bacteria (r > 0.6, p < 0.05). The SARS‐CoV‐2 diabetic group exhibited a significant increase in pathogens and secondary infection‐causing bacteria (p < 0.05) with a simultaneous decrease of normal flora (p < 0.05). The dysbiosis of the bacterial community might be linked with severe consequences of COVID‐19‐infected diabetic patients, although a few probiotic strains inhibited numerous pathogens in the same pathological niches. This study suggested that the promotion of normal flora and probiotics through dietary supplementation and excessive inflammation reduction by preventing secondary infections might lead to a better outcome for those comorbid patients.
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.
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.
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