Search Results (337)

This paper presents a study on evaluating the effectiveness of nanofluid Minimum Quantity Lubrication (NF MQL) in machining Hastelloy C276 alloy—a difficult-to-cut material. The study compares NF MQL using different types of nanoparticles (Al₂O₃, MoS₂, SiC, and GrP) with dry and pure MQL conditions in terms of surface roughness, cutting force components, and especially the variation of cutting forces over time. Experimental results indicate that the graphene-containing nanofluid MQL showed the most superior performance in terms of surface roughness R_a with 54.3% and 34% reduction, followed by MoS₂ and Al₂O₃ nanofluid MQL conditions. Regarding the active cutting force F_a, Al₂O₃ nanofluid MQL achieves the largest reduction of about 18.4% and 22.1% when compared to dry and pure MQL, followed by GrP nanofluid MQL, MoS₂ nanofluid MQL, and then SiC nanofluid MQL. Meanwhile, GrP nanofluid MQL shows the highest percentage of F_z reduction at about 13.4% and 26% when compared to the dry and pure MQL conditions, followed by MoS₂ nanofluid MQL. Furthermore, the application of NF MQL also significantly improves tool life and extends about 36.4 ÷ 61.1% and 18.2 ÷ 50% compared to dry and pure MQL, respectively. Notably, through in-depth analysis of the variation of cutting forces, the study has elucidated the superior lubrication and cooling mechanism of the NF MQL method, confirming its potential application in machining advanced materials. Full article

Significance: This study addresses critical industrial and biomedical applications including glass blowing (thermal management of shrinking sheets), polymer sheet extrusion (controlled cooling), magnetic drug delivery (nanoparticle targeting), and nuclear reactor cooling (enhanced heat transfer). Aim: We present a novel nonlinear analysis of magnetohydrodynamic (MHD) boundary layer flow of a Jeffery Al₂O₃ nanofluid over a shrinking permeable plate with convective boundary conditions, uniquely integrating mixed convection, Ohmic dissipation, heat generation, Brownian motion, and thermophoresis within a non-Newtonian nanofluid framework. Methodology: The governing partial differential equations are transformed using similarity transformations and solved via the Adomian decomposition method (ADM). Comprehensive validation against RK4, RK45, and bvp4c demonstrates excellent agreement with maximum relative errors below $5\times {10}^{-4}$. Key Contribution: (i) Normal velocity decreases by 15–25% as the Biot number increases from $Bi=0.4$ to $0.6$; (ii) tangential velocity decreases by 20–30% as the magnetic parameter increases from $M=5$ to 15; (iii) temperature increases by 30–40% as the Eckert number increases from $Ec=0.5$ to $2.5$; (iv) ADM converges within 12–15 terms with $L_2$ errors $<{10}^{-5}$; (v) skin friction coefficient increases from $C_f=3.02713$ to $3.90082$ as $Q_0$ increases from 1 to 4; (vi) Nusselt number values: $Nu/\sqrt{Re}=0.4621$ at $Pr=0.7$, $0.8954$ at $Pr=2$, $3.2890$ at $Pr=20$. These quantitative findings provide design guidelines for engineers in thermal management and biomedical applications. Full article

Solar water heating systems (SWHS) offer a sustainable solution for reducing reliance on conventional energy sources; however, their performance is often limited by insufficient heat transfer within the collector. This study presents a CFD-based numerical investigation on the optimization of finned thermal collectors in a solar water heating system using Al₂O₃/water hybrid nanofluid. The effects of nanoparticle volume fraction (1–3%), fin geometry (triangular and hexagonal), and mass flow rate (5–20 kg/h) on the thermal and heat transfer performance of the system were analyzed. Key performance indicators including absorber/PV temperature, outlet fluid temperature, convective heat transfer coefficient, thermal efficiency, and improved daily efficiency were evaluated under transient operating conditions. The results show that increasing Al₂O₃ concentration enhances heat transfer and thermal efficiency due to improved thermophysical properties of the working fluid. Fin geometry significantly influences thermal behavior, with hexagonal fins generally producing higher outlet temperatures and thermal efficiency of 65%, while triangular fins provide higher daily efficiency improvement under optimized conditions. The convective heat transfer coefficient increased with both nanoparticle concentration and flow rate, reaching peak values during mid-day hours corresponding to maximum solar input. The study confirms that combining optimized fin structures with Al₂O₃/water nanofluids provides an effective strategy for improving the thermal performance of solar water heating collectors, while CFD modelling offers a reliable approach for system design and performance prediction. Full article

Efficient thermal management is critical for maintaining the safety, durability, and performance of lithium-ion batteries used in electric vehicles (EVs). In this study, a comprehensive numerical investigation is conducted to evaluate the heat transfer characteristics of mono- and hybrid-nanofluids in a microchannel-cooled lithium-ion battery module. A three-dimensional computational model of a 5S7P battery module composed of cylindrical 21700 cells is developed. Battery heat generation during 3C high discharge rate operation is predicted using the Newman-Tiedemann-Gu-Kim (NTGK) electrochemical model, while coolant flow and heat transfer are simulated using the governing conservation equations for mass, momentum, and energy. The cooling system consists of six liquid-cooling plates with circular microchannels. The performance of water-glycol (50/50) coolant is compared with several mono nanofluids of Al₂O₃ and Cu, and hybrid nanofluids of Al₂O₃-Cu, Al₂O₃-MWCNT, Al₂O₃-Graphene, Cu-MWCNT, and Cu-Graphene across multiple coolant flow rates from 1–5 LPM. The results demonstrate that nanofluids significantly enhance convective heat transfer and reduce battery temperature compared with the conventional water-glycol coolant. Among the investigated coolants, the Al₂O₃-Cu hybrid nanofluid (0.45–0.45%) operating at 1 LPM achieves the best overall thermo-hydraulic performance with a performance evaluation criterion (PEC) of 1.065. Further analysis of nanoparticle composition ratios shows that a Cu-dominant hybrid mixture (Al₂O₃-Cu: 0.27–0.63%) slightly improves the PEC to 1.0657, indicating marginally superior cooling performance. The findings highlight the potential of hybrid nanofluids as advanced coolants for microchannel-based battery thermal management systems in EVs, particularly under moderate coolant flow conditions. Full article

The escalating power density in Active Phased Array Radar has made the thermal management of Transmitter and Receiver (T/R) modules a critical bottleneck for radar performance. To address the thermal resistance of traditional cold plates, this study investigates an innovative embedded cooling strategy utilizing micro-pyramid arrays and advanced nanofluids. Thermal performance was evaluated using maximum temperature, maximum temperature difference and surface temperature standard deviation (ST). Higher pyramid density markedly enhances temperature uniformity, an effect that scales positively with the power load. Under a 100 W condition, the 8-circle micro-pyramids configuration (the densest structure with roughness Ra = 1.3) achieved a 22.58 K reduction in maximum temperature and a 22.5% improvement in temperature uniformity compared to the 2-circle structure, and outperformed the 4-circle structure by 16.98 K and 17.9%, respectively. Furthermore, a comparative analysis of nanofluids (Al₂O₃, CuO, graphene, and h-BN) is conducted and it is found that graphene nanofluid exhibits the best overall heat transfer enhancement because of its high thermal conductivity and moderate reduction in specific heat capacity. The thermal performance of the nanofluid is evaluated by comparing the maximum temperatures of the heat source at the 8-circle structure. The synergistic coupling of graphene nanofluid with the 8-circle array yields a remarkable 35.38% enhancement in temperature uniformity at 100 W. The enhancement mechanisms are mainly attributed to intrinsic thermophysical properties of the nanoparticles and convection caused by denser pyramid array. The aforementioned findings provide important guidance for the thermal management design of antenna and other high-density integrated electronic systems with embedded cold plate design demand. Full article

Global climate change has intensified the need for clean and stable energy sources. Geothermal energy, with its consistent availability, is crucial for the transition to renewable energy systems. This study aims to numerically evaluate the enhancement of heat extraction in a mid-deep coaxial geothermal heat exchanger (GHE) when using water-based Al₂O₃ and SiO₂ nanofluids. A comprehensive 1D pipe flow- and 3D subsurface heat transfer-coupled model was developed and validated against field experimental data. The results demonstrate that the nanofluids significantly enhanced heat extraction. The water–SiO₂ nanofluid achieved the highest outlet temperature, exceeding pure water by approximately 0.2 °C after 2000 h. A lower inlet temperature of 5 °C increased heat extraction by 88.57% compared to 25 °C, despite a lower outlet temperature. The thermal influence radius expanded from <2 m at 300 h to ~6 m at 1800 h. This study provides quantitative insights and a validated framework for optimizing GHE performance through nanofluid selection and operational control. Full article

Molten salts are essential heat transfer and storage media in high-temperature applications such as Concentrated Solar Power (CSP), owing to their high boiling points, low vapor pressures, and excellent thermal stability. The overall performance of such systems is largely governed by the convective heat transfer characteristics of molten salt fluids. This review systematically synthesizes recent advances over the past five years in enhancing the thermophysical properties and convective heat transfer of molten salts, focusing on two primary strategies: improving the intrinsic properties of molten salts through nanoparticle doping, and optimizing the structural design of heat exchangers. The enhancement of thermophysical properties is mainly achieved by preparing molten salt-based nanofluids. Dispersing low concentrations (typically 0.1–1.0 wt.%) of nanoparticles such as SiO₂, Al₂O₃, and carbon nanotubes (CNTs) can yield significant improvements—thermal conductivity increases of up to ~100% (e.g., 0.5 wt% SiO₂ in NaNO₃-KNO₃) and specific heat capacity enhancements of 20–30% (e.g., 1.0 wt% Al₂O₃ in carbonates). Multiscale simulations, particularly molecular dynamics (MD), have revealed key enhancement mechanisms, including the formation of ordered ionic layers on nanoparticle surfaces that create efficient nanoscale heat conduction pathways, and the modulation of ion–ion interactions. Concurrently, significant heat transfer enhancement can be achieved through structural optimization. Single-method technologies, such as enhanced heat transfer tubes, improve performance by disrupting the thermal boundary layer. For instance, spirally grooved tubes can increase the Nusselt number (Nu) by 19% for Re > 25,000, while twisted tape inserts can enhance laminar flow heat transfer by up to 8.6 times. Composite strategies that couple nanofluids with enhanced geometries demonstrate superior overall performance, with Performance Evaluation Criterion (PEC) values reaching up to 1.48 for converging–diverging tubes with SiO₂ nanofluids and 1.21 for trefoil-shaped U-tubes with Cu-based nanofluids. Compact heat exchangers (CHEs) offer high efficiency, achieving PEC values of 1.07–1.4 in optimized designs, but face challenges such as clogging risks in large-scale applications. Future research directions include the development of advanced composite molten salts, the application of artificial intelligence and multiscale simulations for mechanistic analysis and design optimization, the fabrication of novel heat exchanger structures via additive manufacturing, and cross-disciplinary integration for full-chain system optimization. These concerted efforts are essential for realizing efficient, cost-effective, and reliable molten salt-based energy systems. Full article

An experimental investigation was conducted to evaluate the thermal conductivity (TC) and local heat-transfer coefficients (LHTCs) of nanofluids containing alumina (Al₂O₃), hematite (Fe₂O₃), and copper oxide (CuO) nanoparticles dispersed in deionized water. A newly developed non-invasive LHTC probe was integrated into the inner wall of the test section to enable direct quantification of interfacial heat-transfer performance. The measurements were conducted under laminar and turbulent flow conditons across Reynolds numbers ranging from 1000 to 10,000. The selected nanoparticles were chosen based on their high intrinsic thermal conductivity, cost effectiveness, and, in the case of Fe₂O₃, magnetic recoverability. The nanoparticles enhanced both TC and LHTCs through improved thermophysical propoerties and possible interfacial effects. Maximum TC enhancements of 19%, 21%, and 25% were achieved for Al₂O₃/distilled water (DW), Fe₂O₃/DW, and CuO/DW nanofluids, respectively, at 0.05 vol% and 55 °C, while the corresponding LHTC enhancements reached 44%, 50%, and 53%. Under turbulent flow, CuO/DW exhibited the highest heat-transfer performance, attributed to a 25% increase in TC and corresponding improvement in connective heat transfer. Since the boundary-layer thickness exceeded the nanoparticle diameter (30 nm), nanoparticles penetrated the interfacial film, inducing localized micro-convection and catalytic micro-mixing, which intensified interfacial heat transport. The experimentally determined Nusselt numbers showed strong agreement with the Xuan–Qiang correlation at 55 °C, suggesting that the nanoparticle volume fraction governs the catalytic interfacial heat-transfer mechanism. Full article

A parabolic trough collector (PTC) is a linear concentrating system consisting of a parabolic-shaped reflector with a receiver tube positioned along the focal axis. In this study, the performance of a parabolic trough solar collector is evaluated, with aperture area, collector length, breadth, Rim angle, and inner and outer absorber diameters of 5.54 m², 3.65 m, 1.52 m, 70°, 0.048 m, and 0.05 m, respectively. The experiment was conducted at Ranchi, India (23.35° N and 85.30° E). During this day, marked by a cloudless sky, the ambient temperature ranged from 27 °C to 39 °C. The global solar radiation ranged from (630 W/m² to 975 W/m²), and the wind speed varied between (0.8 m/s and 1 m/s). Aluminium oxide (Al₂O₃) and Therminol VP-1-based nanofluid were employed as the working fluid. The different volume fractions of nanoparticles were taken, and the evacuated tube PTC performance was analysed. When Al₂O₃–Therminol VP-1 of varying concentration (0–4%) and mass flow rate of 0.041 kg/sec is used, it has been observed that the receiver’s heat transfer performance improved with an increment in nanoparticle volume fraction. Temperature-dependent properties were applied to the thermal efficiency, exhibiting a notable increase of approximately 7.2% when the volume fraction ascends from 0 to 4%. At elevated Reynolds numbers, the efficiency decreases compared to lower volume fractions. These results contribute to understanding the effect of nanoparticle concentration on PTC performance. Full article

This study investigates the effect of R141b-Al₂O₃ nanorefrigerant with mass fractions of 0.1%, 0.3%, 0.5% and 0.9% (w/w%) on the refrigeration time, energy consumption and performance coefficient of a vapor compression refrigeration system (VCRS). The effects of span80 and Tween80 surfactants on the stability of the nanorefrigerant were also investigated, and the optimum sonication time required to prepare stable nanofluids was determined. The results showed that Span-80 is more effective than Tween 80 at producing a stable nanorefrigerant. Then, the effect of span80 surfactant on the efficiency of VCRS was investigated. The results showed that upon using the nanorefrigerant, COP increased by up to 214% compared to the pure refrigerant. Furthermore, using the nanorefrigerant with a surfactant improved the performance coefficient by 52% compared to the nanorefrigerant without a surfactant. Full article

The current research first investigates the flow in the fractional order of a vertical artery with atherosclerosis using a Casson-based penta-hybrid nanofluid. Gold (Au), copper (Cu), silver (Ag), magnesium oxide (MgO), and alumina (Al₂O₃) nanoparticles are dispersed in blood to make the hybrid nanofluid. It is assumed that the flow is very pulsatile. The mathematical model is constructed by using differential forms of the conservation laws of mass, momentum, energy, and irreversibility analysis. By applying the mild stenosis approximation, the governing equations are transformed into dimensionless form. To generalize the classical model to its fractional counterpart, the Caputo–Fabrizio fractional derivative (C-FFD) is employed. Closed-form solutions for the velocity and temperature fields are realized by the joint application of the Laplace and Hankel transforms. The impact of essential physical parameters on velocity, temperature, and entropy generation is displayed through figures. The physical significance of enhanced thermal characteristics is shown, emphasizing their potential relevance to thermal regulation, targeted drug delivery, and minimization of irreversible energy losses in biomedical flow systems. The velocity profile elevates with the increase in the Casson parameter, while the temperature drops as the fractional-order parameter rises. Entropy generation is observed to amplify with the increasing values of the thermodynamic parameter in question, whereas an opposite tendency is seen for the Bejan number. The Bejan number decreases as the control parameter becomes higher. The novelty of the present investigation lies in the simultaneous incorporation of Caputo–Fabrizio fractional dynamics, penta-hybrid nanoparticle suspension, and entropy generation analysis in a stenosed arterial configuration. Unlike existing fractional Casson blood flow models that primarily focus on single or hybrid nanofluids, the present framework highlights the synergistic enhancement of thermal transport and irreversibility control achieved through penta-hybrid nanoparticles, which may be relevant for advanced biomedical and targeted therapeutic applications. Full article

This paper presents the results of numerical and experimental studies of forced convection of water/EG-Al₂O₃ nanofluids through a horizontal stainless steel tube (8 mm inner diameter; 2000 mm length). As a base fluid, distilled water/EG mixture of three volume ratios (90:10, 80:20, and 60:40) is used. Nanoparticle mass concentrations are 0.1%, 1%, and 5%. The tested nanofluids are prepared by use of the two-step method. No dispersant is used to stabilize the suspension. Transition and turbulent flow regimes are tested. The commercial code Ansys Fluent 19.3 is used to conduct numerical simulations. A k-ε turbulence model with an expanded boundary layer function is adopted. A homogeneous nanofluid model is assumed, with thermophysical properties depending on the mean fluid temperature and nanoparticle concentration. The nanofluids are treated as incompressible Newtonian fluids. Both experimental and numerical studies showed an increase in the average Nusselt number with the addition of Al₂O₃ nanoparticles to each of the water/EG mixtures. However, the experimental results indicated that, at the maximum mass nanoparticle concentration of 5%, the Nusselt number increased by 42%, whereas the numerical simulations showed an increase of only 16% compared with the base fluid. Both experimental studies and numerical simulations show the flow resistance of the nanofluid increases with increasing nanoparticle concentration. Similarly to heat transfer, the numerical calculations predict lower pressure drops than those observed experimentally. For the maximum nanoparticle mass concentration of 5%, the experimental results indicate an increase in nanofluid flow resistance of about 95%, while numerical simulations predict an increase of about 50%, compared to the base liquid. The generalized correlation equations are proposed to calculate the average Nusselt number and the friction factor valid for the turbulent flow of water-based nanofluids and water/EG mixtures with a volumetric water fraction above 60% and a mass concentration of nanoparticles in the range of 0.1% ≤ φ_m ≤ 5%. Full article

Many studies on solar heating systems have examined individual techniques to enhance the performance of solar water collectors, such as flow obstructions, increased turbulence, nanofluids, and investment in thermal storage. The benefits of integrating these sustainability strategies into a single, sustainable system have yet to be fully established. This work displays a hybrid water-heating system that contains a solar water collector (SWC) and an electric water heater (EWH), a photovoltaic panel (PV), and nano-additives to increase the outlet water temperature and improve thermal efficiency. Numerical and experimental analyses were used to estimate the influence of water flow rate (2.5, 3.5, and 4.5 L/min) and different Al₂O₃ concentrations (0.1%, 0.2%, and 0.3%) on system performance using U-shaped pipe in SWC model. The results highlight that lower flow rates consistently yield higher ΔT values because water spends a longer time in the collector, allowing it to absorb more heat. Also, when using water only, the collector efficiency increases pro-aggressively with flow rate. A significant performance enhancement is observed upon incorporating Al₂O₃ nanoparticles into the fluid, with a 0.1% Al₂O₃ volume concentration improving efficiency by ~7.4% over water. At 0.3%, the highest improvement is recorded, yielding a ~9.3% gain in efficiency compared to the base case. Full article

This study aimed to prepare water-based nanofluids using Al₂O₃ nanoparticles with different types of surfactants, and to investigate the colloidal and thermophysical properties of the obtained nanofluids. In this context, water-based Al₂O₃ nanofluids have been prepared using six surfactants with anionic, cationic, and nonionic characteristics SDS, CTAC, PVP, Tween 80, PVA, and Triton X-100. The electrostatic colloidal stability of the prepared samples has been determined by zeta potential and particle size measurements. To understand the interactions at the molecular level and the stabilities in terms of interaction Gibbs free energy, nanoparticle–surfactant interactions have been modeled using the DFT (Density Functional Theory) method. The overall colloidal stability rankings of nanofluids have been performed using both zeta potential measurements and DFT analysis. Furthermore, the thermophysical properties of nanofluids, which are crucial for industrial applications, have been measured. The results showed that the type of surfactant has a significant effect on the colloidal and thermophysical properties of nanofluids. It has been concluded that Al₂O₃-SDS and Al₂O₃-CTAC nanofluids can be used in cooling systems due to their high zeta potential and thermal conductivity, and low viscosity and size. Full article

The present paper investigates the steady laminar flow and thermal mixing performance of non-Newtonian Al₂O₃ nanofluids within a two-layer cross-channel micromixer, employing three-dimensional numerical simulations to solve the governing equations across a low Reynolds number range (0.1 to 50). It also addresses secondary flows and thermal mixing performance with two distinct inlet temperatures for thin nanofluids. Additionally, it explores how fluid properties and varying concentrations of Al₂O₃ nanoparticles impact thermal mixing efficiency and entropy generation. Simulations were conducted to optimize performance by adjusting the power law index (n) across different nanoparticle concentrations (1–5%). The findings show that magnetohydrodynamics can enhance mixing efficiency by generating vortices and altering flow behavior, providing important guidance for improving microfluidic system designs in practical applications. Full article