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.

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.

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.

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%.

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.