Search Results (13)

Phase change materials (PCMs) are widely used in latent heat thermal energy storage systems (LHTESSs), but their low thermal conductivity limits performance. This study numerically investigates the enhancement of thermal efficiency in LHTESSs using nano-enhanced PCM (NePCM), composed of paraffin wax embedded with copper (Cu) nanoparticles. The NePCM is confined within a trapezoidal cavity, with the base serving as the heat source. Four different cavity heights were analyzed: cases 1, 2, 3, and 4 with the heights D of 24 mm, 18 mm, 15 mm, and 13.5 mm, respectively. The finite element method was employed to solve the governing equations. The influence of two hot base temperatures (333.15 K and 338.15 K) and Cu nanoparticle volume fractions ranging from 0% to 6% was examined. The results show that incorporating Cu nanoparticles at 6 vol% (volume fraction) enhanced thermal conductivity and reduced melting time by 10.71%. Increasing the base temperature to 338.15 K accelerated melting by 65.55%. Among all configurations, case 4 exhibited the best performance, reducing melting duration by 15.12% compared to case 1. Full article

Carbon dioxide (CO₂) has been recognized as one of the potential working fluids to operate power generation cycles, either in supercritical or transcritical configuration. However, a small concentration of some of the additives to CO₂ have shown promising improvements in the overall performance of the cycle. The current study is motivated by the newly proposed additive silicon tetrachloride (SiCl₄), and so we perform a detailed investigation of SiCl₄ along with a few well-known additives to CO₂-based binary mixtures as a working fluid in transcritical organic Rankine cycle setup with internal heat regeneration. The additives selected for the study are pentane, cyclopentane, cyclohexane, and silicon tetrachloride (SiCl₄). A comprehensive study on the energy and exergy performance of the cycle for warm regions is conducted at a turbine inlet temperature of 250 °C. The performance of the heat recovery unit is also assessed to highlight its importance in comparison to a simple configuration of the cycle. This study shows that the cycle operating with binary mixtures performs significantly better than with pure CO₂, which is mainly due to its better heat recovery in the heat recovery unit. The results show that the optimal molar concentration of the additives is in between 20% and 25%. Besides having better thermal stability, SiCl₄ shows an improvement in the cycle thermal efficiency by 6% points which is comparable to cyclopentane (7.3% points) and cyclohexane (7.8% points). The optimal cycle pressure ratio for SiCl₄ is also relatively lower than for other additives. The energy efficiency of the cycle with pure CO₂ is around 45% which is also increased to 58%, 63%, 64%, 60% with pentane, cyclopentane, cyclohexane, and SiCl₄, respectively. These results suggest that additives like SiCl₄ could make CO₂-based cycles more viable for power generation in warm regions. Full article

Aluminum AA7075, graphene nanoplates (GNP), boron nitride (BN), and vanadium carbide (VC) are used to fabricate hybrid nanocomposite matrices. BN and VC serve as secondary reinforcement particles in the fabrication of hybrid composites, with graphene (GNP) as a key component of the hybrid process. Friction stir processing (FSP) was used to manufacture the composite matrix; it also has a major role in improving the microstructure’s grain refinement, as well as the reinforcing of the particles, which play a crucial role in limiting grain growth during the dynamic recrystallization process. Consequently, the grain sizes of the nanocomposite AA7075/GNPs, hybrid composites AA7075/GNPs+BN, and hybrid composites AA7075/GNPs+BN+VC were decreased by an average of 10.3 times compared to the base alloy. The SEM analysis demonstrated that the dispersion of the hybrid reinforcement particles was performed, and the particles were dispersed uniformly throughout the metal matrix. The mechanical characteristics of the hybrid AA7075/GNPs+BN+VC include the highest compression stress and hardness values due to the homogeneity of the hybridization process between the BN and VC particles. The GNPs reduce the electrical conductivity by 7.3% less than the base alloy. In comparison, when hybridized with BN and VC, it is reduced by 24.4% and 31.1%, respectively. In addition, the inclusion of thermally insulating materials, such as BN and VC, decreases the thermal conductivity of the hybrid composite metal matrices. Full article

This paper aims to study the hygrothermal buckling of smart graphene/piezoelectric circular nanoplates lying on an elastic medium and subjected to an external electric field. The circular nanoplates are made of piezoelectric polymer reinforced with graphene platelets that are uniformly distributed through the thickness of the nanoplate. The material properties of the nanocomposite plate are determined based on the modified Halpin-Tsai model. To capture the nanoscale effects, the nonlocal strain gradient theory is applied. Moreover, the principle of virtual work is employed to establish the nonlinear stability equations in the framework of classical theory. The differential quadrature method is utilized to solve the governing equations. Among the important aims of the paper is to study the influences of various parameters such as graphene weight fraction, elastic foundation parameters, external applied electric field, humid conditions, and boundary conditions on the thermal buckling of the smart nanocomposite circular nanoplates. It is found that the increase in graphene components and elastic foundation stiffness enhances the strength of the plates; therefore, the buckling temperature will increase. Full article

This paper presents exact solutions for the nonlinear bending problem, the buckling loads, and postbuckling configurations of a perfect and an imperfect bioinspired helicoidal composite beam with a linear rotation angle. The beam is embedded on an elastic medium, which is modeled by two elastic foundation parameters. The nonlinear integro-differential governing equation of the system is derived based on the Euler–Bernoulli beam hypothesis, von Kármán nonlinear strain, and initial curvature. The Laplace transform and its inversion are directly applied to solve the nonlinear integro-differential governing equations. The nonlinear bending deflections under point and uniform loads are derived. Closed-form formulas of critical buckling loads, as well as nonlinear postbuckling responses of perfect and imperfect beams are deduced in detail. The proposed model is validated with previous works. In the numerical results section, the effects of the rotation angle, amplitude of initial imperfection, elastic foundation constants, and boundary conditions on the nonlinear bending, critical buckling loads, and postbuckling configurations are discussed. The proposed model can be utilized in the analysis of bio-inspired beam structures that are used in many energy-absorption applications. Full article

This article establishes the vibrational behavior of functionally graded plates embedded in a viscoelastic medium. The quasi-3D elasticity equations are used for this purpose. The three-parameter Visco-Winkler-Pasternak model is employed to give the interaction between the viscoelastic foundation and the presented plate. Hamilton’s principle is applied to derive the governing dynamic equations. Many validation examples are presented. Additional benchmark results are tabulated for future comparisons. The effects of various parameters like geometrical, material properties, and viscoelastic foundations on the vibrational frequencies of homogeneous and functionally graded plates are investigated. The frequencies increase as all parameters increase except the functionally graded power-law index for which its increase causes a decrease in the frequency value. Full article

In this study, two successive methods were used to improve the grain structure and the mechanical and physical properties of Al 5052 aluminum alloy. The modifying elements, 0.99 wt.% of titanium (Ti) and 0.2 wt.% of boron (B), were added during the casting process. After solidification, single- and double-pass friction stir processing (FSP) were performed to achieve additional grain refinement and disperse the newly formed phases well. The addition of Ti–B modifiers significantly improved the mechanical and physical properties of the Al 5052 aluminum alloy. Nevertheless, only a 3% improvement in microhardness was achieved. The ultimate strength (US), yield strength (YS), and elastic modulus were investigated. In addition, the electrical conductivity was reduced by 56% compared to the base alloys. The effects of grain refinement on thermal expansion and corrosion rate were studied; the modified alloy with Ti–B in the as-cast state showed lower dimension stability than the samples treated with the FSP method. The grain refinement significantly affected the corrosion resistance; for example, single and double FSP passes reduced the corrosion rate by 11.4 times and 19.2 times, respectively. The successive FSP passes, resulting in a non-porous structure, increased the bulk density and formed precipitates with high bulk density. Full article

This paper presents the effects of temperature and the nonlocal coefficient on the bending response of functionally graded (FG) nanoplates embedded in an elastic foundation in a thermal environment. The effects of transverse normal strain, as well as transverse shear strains, are considered where the variation of the material properties of the FG nanoplate are considered only in thickness direction. Unlike other shear and deformations theories in which the number of unknown functions is five and more, the present work uses shear and deformations theory with only four unknown functions. The four-unknown normal and shear deformations model, associated with Eringen nonlocal elasticity theory, is used to derive the equations of equilibrium utilizing the principle of virtual displacements. The effects due to nonlocal coefficient, side-to-thickness ratio, aspect ratio, normal and shear deformations, thermal load and elastic foundation parameters, as well as the gradation in FG nanoplate bending, are investigated. In addition, for validation, the results obtained from the present work are compared to ones available in the literature. Full article

Using nano-enhanced phase change material (NePCM) rather than pure PCM significantly affects the melting/solidification duration and the stored energy, which are two critical design parameters for latent heat thermal energy storage (LHTES) systems. The present article employs a hybrid procedure based on the design of experiments (DOE), computational fluid dynamics (CFD), artificial neural networks (ANNs), multi-objective optimization (MOO), and multi-criteria decision making (MCDM) to optimize the properties of nano-additives dispersed in a shell and tube LHTES system containing paraffin wax as a phase change material (PCM). Four important properties of nano-additives were considered as optimization variables: volume fraction and thermophysical properties, precisely, specific heat, density, and thermal conductivity. The primary objective was to simultaneously reduce the melting duration and increase the total stored energy. To this end, a five-step hybrid optimization process is presented in this paper. In the first step, the DOE technique is used to design the required simulations for the optimal search of the design space. The second step simulates the melting process through a CFD approach. The third step, which utilizes ANNs, presents polynomial models for objective functions in terms of optimization variables. MOO is used in the fourth step to generate a set of optimal Pareto points. Finally, in the fifth step, selected optimal points with various features are provided using various MCDM methods. The results indicate that nearly 97% of the Pareto points in the considered shell and tube LHTES system had a nano-additive thermal conductivity greater than 180 Wm⁻¹K⁻¹. Furthermore, the density of nano-additives was observed to be greater than 9950 kgm⁻³ for approximately 86% of the optimal solutions. Additionally, approximately 95% of optimal points had a nano-additive specific heat of greater than 795 Jkg⁻¹K⁻¹. Full article

PTSCs (parabolic trough solar collectors) are widely employed in solar-thermal applications to attain high temperatures. The purpose of this study is to determine how much entropy is created when Powell-Eyring nanofluid (P-ENF) flows across porous media on a horizontal plane under thermal jump circumstances. The flow in PTSC was generated by nonlinear surface stretching, thermal radiation, and Cattaneo-Christov heat flux, which was utilized to compute heat flux in the thermal boundary layer. Using a similarity transformation approach, partial differential equations were converted into ordinary differential equations with boundary constraints. Then, the boundary restrictions and partial differential equations were merged to form a single set of nonlinear ordinary differential equations. To obtain approximate solutions to ordinary differential equations, the Keller-Box approach is utilized. Nanofluids derived from silver- and copper-based engine oil (EO) has been employed as working fluids. The researchers observed that changing the permeability parameter reduced the Nusselt number while increasing the skin frictional coefficient. Total entropy variation was also calculated using the Brinkman number for flow rates with Reynolds number and viscosity changes. The key result is that thermal efficiency is inversely proportional to particular entropy production. For example, using Cu-EO nanofluid instead of Ag-EO nanofluid increased the heat transport rate efficiency to 15–36%. Full article

Nanofluids have better surface stability, thermal absorption, and distribution capacities are produced as heat transfer fluids. In current nanofluid-transport studies, together with the heat transfer mechanisms, entropy reduction in thermo- and non-Newtonian nanofluid models with changing thermophysical characteristics is heavily addressed. The entropy production is examined as thermodynamically stable first-grade viscoelastic nanofluid (FGVNF) flow over a flat penetrable, porous barrier. The uniform porous horizontal stretching of the surface in a Darcy type of pore media results in a fluid motion disturbance. In addition, this study also includes the effects of thermal radiation, viscous dissipation, and slip conditions at the border. Under boundary layer flow and Rosseland approximations, the governing mathematical equations defining the physical features of the FGVNF flow and heat transfer models are summarized. The governing nonlinear partial differential equation is transformed by similarity variables to achieve solutions in nonlinear ordinary differential equations. Approximative solutions for reduced ordinary differential equations are obtained by the Keller Box Scheme. Two distinct types of nanofluids, Copper-Engine Oil (Cu-EO) and Zirconium Dioxide-Engine Oil (ZrO₂-EO), are considered in this research. The graphs are produced to examine the effects of the different physical factors for the speed, temperature, and entropy distributions. The significant findings of this study are that the critical characteristics of (boundary layer) BL collectively promote temperature variation, including slip speed, diverse thermal conductivity, and non-Newtonian first-grade viscoelastic nanofluid, the concentration of nanoparticles as well as thermal radiation, and a high porous media. The other noteworthy observation of this study demonstrates that the (Cu-EO) FGVNF is a better conductor than (ZrO₂-EO) FGVNF transmission. The entropy of the system grows the Deborah number and volume fraction parameter. Full article

In the present study, a novel configuration of a rotating tube bundle was simulated under non-isothermal hydrodynamic conditions using a mixture model. Eight fins were considered in this study, which targeted the hydrodynamics of the system. An aqueous copper nanofluid was used as the heat transfer fluid. Various operating factors, such as rotation speed (up to 500 rad/s), Reynolds number (10–80), and concentration of the nanofluid (0.0–4.0%) were applied, and the performance of the microchannel heat exchanger was assessed. It was found that the heat transfer coefficient of the system could be enhanced by increasing the Reynolds number, the concentration of the nanofluid, and the rotation speed. The maximum enhancement in the heat transfer coefficient (HTC) was 258% after adding a 4% volumetric nanoparticle concentration to the base fluid and increasing Re from 10 to 80 and ω from 0 to 500 rad/s. Furthermore, at Re = 80 and ω = 500 rad/s, the HTC values measured for the nanofluid were 42.3% higher than those calculated for water, showing the nanoparticles’ positive impact on the heat transfer paradigm. Moreover, it was identified that copper nanoparticles’ presence had no significant effect on the system’s pressure drop. This was attributed to the interaction of the fluid flow and circulated flow around the tubes. Finally, the heat transfer coefficient and pressure drop had no considerable changes when augmenting the rotation speed at high Reynolds numbers. Full article

In this study, thermal performance and flow characteristics of a shell and tube heat exchanger equipped with various baffle angles were studied. The heat exchanger was operated with distilled water, and a hybrid nanofluid at three concentrations of 0.04% and 0.10% of GNP-Ag/water within Reynolds numbers ranged between 10,000 and 20,000. The thermophysical properties of nanofluid varied with temperature and nanoparticles’ concentration. The baffle angles were set at 45°, 90°, 135°, and 180°. Results showed that the calculated Nusselt number (Nu) could be improved by adding nanoparticles to the distilled water or increasing the fluid’s Reynolds number. At a low Re number, the Nu corresponding to baffle angle of 135° was very close to that recorded for the angle of 180°. At Re = 20,000, the Nu number was the highest (by 35% compared to the reference case), belonging to a baffle angle of 135°. Additionally, results related to friction factor and pressure drop showed that more locations with fluid blocking were observed by increasing the baffle angle, resulting in increased pressure drop value and friction. Finally, the temperature streamlines counter showed that the best baffle angle could be 135° in which maximum heat removal and the best thermal performance can be observed. Full article