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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 TEF o and TEF s 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. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) are frequently utilized in the thermal sector, especially for thermal energy storage (TES) applications. The purpose of this study was to analyze the thermal efficiency and melting characteristics of a leaf-vein-shaped fin in a triplex tube heat exchanger. The analysis focused on the use of pure molten salt PCM and a combination of molten salt PCM with MoS 2 and Fe 3 O 4 nanoparticles. The study utilized ANSYS Fluent software to conduct numerical simulations and analyze seven distinct fin arrangements. The simulations were employed to visualize and examine the liquid fraction, temperature, and fluid velocity. The findings indicated that the leaf-vein fin shape greatly improved the dispersion of liquid fraction, average temperature, and velocity in comparison to alternative fin designs. The addition of MoS 2 and Fe 3 O 4 nanoparticles significantly enhanced the melting and thermal characteristics of the PCM as a result of heightened thermal conductivity. This showcases the capability of the leaf-vein fin design and PCM nanocomposites to enhance the efficiency of thermal energy storage in triplex tube systems. About 2500 s PCM melt about 36% for case A, but melting rate enhance up-to 55% using nano particles. Melting rate enhance 91% in 1000 s in case of G using 8 fins as compare to case A having no fins. • Leaf-vein-shaped fins enhance PCM melting in triplex tube heat exchangers. • MoS 2 and Fe 3 O 4 nanoparticles improve thermal properties of molten salt PCM. • Ansys Fluent simulations reveal optimal fin configurations for heat transfer. • Eight-fin design with modified attachment points shows best melting performance, and the melting rate enhance 91%. • Nanoparticle integration promotes efficient flow patterns in TES systems. [ABSTRACT FROM AUTHOR]

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 (W d), length (L d), 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 μ m < L d < 233 μ m , 10 μ m < W d < 25 μ m , 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. [Display omitted] • 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. [ABSTRACT FROM AUTHOR]

• 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. [Display omitted] [ABSTRACT FROM AUTHOR]