Search Results (2,195)

The use of nanofluids in components of absorption cooling systems enhances heat and mass transfer processes. Limited information exists on the thermophysical properties of the nanofluid prepared with water–lithium bromide (H₂O–LiBr) as the base fluid and CuO nanoparticles. Due to the limited data available, viscosity is experimentally assessed in this study, providing novel results. The nanofluid was formed using the two-step method, using first a magnetic stirrer and second a sonication bath. A high-accuracy sensor was utilized for viscosity measurements. The nanoparticle mass fraction in the nanofluid was 0.1 wt%, while the salt mass fraction in the base fluid ranged from 56.62 to 60.69 wt% and the temperature from 24 to 60 °C. A strong temperature and salt concentration dependence of viscosity was observed for the nanofluid, exhibiting a 3–9% lower viscosity than the base fluid. As an additional scientific novelty, the viscosity of both the H₂O–LiBr mixture and the CuO/H₂O–LiBr nanofluid was examined for variable shear rates, showing a slight dilatant behavior. To develop a method for predicting viscosity, machine learning techniques were used. The best performing model was the multi-layer perceptron, which closely reproduces the experimental data and was selected for creating a graphical user interface for viscosity prediction. Full article

This study presents a numerical investigation of heat transfer enhancement in a corrugated channel equipped with concave-up obstacles and hybrid nanofluids. The novelty of the present work lies in the combined evaluation of a new obstacle configuration with five different nanoparticles and hybrid nanofluids at two volume concentrations using both single-phase and two-phase numerical models. Numerical simulations were carried out using ANSYS Fluent 19.2 with a two-phase mixture model. Five types of nanoparticles (SiO₂, TiO₂, Al₂O₃, ZnO, and CuO) were tested at volume fractions of 1% and 2%, with obstacles optimized in size and position to enhance fluid mixing, over a Reynolds number range of 10,000–30,000. The combined application of concave-up obstacles and nanofluids increased the heat-transfer performance by approximately 244% in terms of percentage enhancement (PE) relative to the baseline corrugated channel using water without obstacles. Despite a considerable pressure drop (up to 15.5 times the baseline pressure ratio (PR)), the performance evaluation coefficient (PEC) indicates an effective trade-off, with the Al₂O₃–ZnO (50:50) hybrid nanofluid (Case 2) achieving a balanced thermal–hydraulic performance with a PEC of 1.28. These findings demonstrate that the combined application of corrugated channels, obstacles, and hybrid nanofluids is a highly effective strategy for improving heat exchanger efficiency in practical applications. Full article

Inconel 718 exhibits poor machinability due to its high strength and low thermal conductivity, which induce severe thermo-mechanical loads. Conventional cooling strategies struggle to concurrently regulate heat dissipation and interface lubrication. This paper proposes a machining method based on Active Thermal Conductive Media (ATCM), which simultaneously exerts the Rehbinder mechanochemical effect and solid-phase enhanced heat transfer effect by pre-coating a liquid graphene film on the workpiece surface. Orthogonal turning tests were conducted using a K313 carbide tool at a cutting speed of 30 m/min, cutting width of 2 mm, and undeformed chip thickness of 0.1 mm. The cutting force, cutting temperature, cutting power, and tool wear characteristics under six machining conditions—dry cutting, flood cutting, Minimum Quantity Lubrication (MQL), Cryogenic MQL (CMQL), Nanofluid MQL (NMQL), and ATCM-assisted cutting—are systematically compared. The results show that ATCM achieves a 21.6% reduction in cutting force, a 20% reduction in cutting temperature, and a 34.9% reduction in cutting power through the synergistic coupling effect of reduced heat generation and enhanced heat dissipation, with adhesive wear and diffusion wear of the cutting tool significantly suppressed. Full article

Hybrid nanofluids with enhanced thermal conductivity have emerged as promising candidates for efficient heat removal in advanced energy systems and next-generation thermal management technologies. In particular, the use of viscoelastic base fluids embedded with radiatively active nanoparticles enables improved thermal regulation in solar collectors, electronic cooling units, and high-temperature industrial processes. This study presents a comparative thermal investigation of mono- and hybrid nanofluids comprising the ferro-oxide (Fe₃O₄) and copper (Cu) metallic particles dispersed in ethylene glycol (C₂H₆O₂), under magnetohydrodynamic (MHD) viscoelastic flow over a stretched surface. Accurate modeling of heat and mass phenomena in such fluids arises from their growing application in advanced thermal systems, including cooling technologies, electronic devices, and renewable energy modules. Unlike conventional models, the current analysis incorporates the Cattaneo–Christov heat flux framework to capture non-Fourier thermal relaxation effects, alongside the influence of thermal radiation and solutal transport. The developed system is truncated into dimensionless form with the proper choice of appropriate quantities, whose solution methodology is based on the implementation of a Runge–Kutta scheme. Compiled observations suggest that the hybrid nanomaterial exhibits more pronounced thermal recovery, while mono nanofluid attributes lower impact. Moreover, increasing the viscoelastic and magnetic parameters leads to notable variations in temperature and concentration distributions. This work advances the current literature by simultaneously integrating viscoelastic rheology, dual nanoparticle suspensions, and non-classical heat conduction laws, providing new insights for optimizing thermal performance in engineering applications. Full article

In this study, the cooling performances of various nanofluids were compared under the operating conditions of a real automobile radiator, based on an internal combustion engine vehicle cooling system whose experiments had been previously completed. In the analyses, the radiator inlet fluid temperature was fixed at 70 °C, air inlet velocities were set to 6, 8, and 10 m/s, and fluid flow rates were taken as 17, 19, and 21 L/min. Under these conditions, the cooling capacities were evaluated for three different working fluids whose thermophysical properties were experimentally determined: 100% pure water, water-based 0.3% ZnO nanofluid, and water-based 0.3% ZnO + CuO hybrid nanofluid. Within the scope of this study, a Computational Fluid Dynamics (CFD) model was developed based on the aforementioned experimental parameters and validated with a maximum deviation of 6%. Using the validated model, additional CFD analyses were performed for water-based 0.3% Al₂O₃ and TiO₂ nanofluids, whose thermophysical properties were also experimentally determined, and their cooling performances were assessed. Based on the experimental and numerical results obtained, the highest cooling capacity was determined to be 20.8 kW in the 0.3% TiO₂ nanofluid, representing a 69.1% increase in cooling capacity compared to pure water. These findings clearly demonstrate that the use of nanofluids significantly enhances heat transfer performance in automotive cooling systems. Full article

This numerical study investigates the thermo-hydraulic and thermodynamic performance of a rectangular-channel heat exchanger incorporating isothermal circular tubes, with particular emphasis on geometric design strategies suitable for compact thermal systems. Two configurations with identical total heat transfer surfaces are analyzed: baseline geometry comprising four aligned tubes (G1) and an optimized geometry consisting of eight tubes arranged in two parallel rows (G2) maintaining the same exchange surface. Laminar forced convection is also considered. For the baseline configuration, results show a pronounced thermal shadowing effect, leading to a reduction of nearly 50% in the heat transfer contribution of downstream tubes.In contrast, optimized geometry significantly improves flow redistribution and temperature field uniformity. An optimal inter-row spacing, equal to 0.1, is identified as a robust design parameter, maximizing the total average Nusselt number. At this spacing, all heated surfaces actively contribute to heat transfer, resulting on an overall heat transfer enhancement of approximately 20–40% compared to the baseline configuration. Entropy production analysis shows that increasing Re strongly intensifies thermal irreversibility, while viscous irreversibility exhibits a moderate increase. The impact of nanoparticles addition, carried out on the optimal configuration of G2, shows that heat transfer increases by about 8% for a nanoparticle concentration of 4% at high Re values, with an insignificant change in the Bejan number. The present findings demonstrate that geometric optimization represents a more effective and energetically sustainable enhancement strategy than nanofluid addition for compact tubular heat exchangers. Full article

There has been a rising trend for recovering waste heat, especially after the invention of new types of semiconductors. Among all available utilization options, thermoelectric generation (TEG) systems are promising for recovering waste heat. Thermoelectric devices are environment-friendly, operate silently, and are suitable for low- to high-power applications. This review paper presents a comprehensive study of TEGs, starting with the current problem, state of the art, advantages, disadvantages, generation and related principles, and applications, and covers different arrangements (individual and combined) and working fluids. Furthermore, this article systematically covered various experimental and numerical studies, including optimization, offering insights into heat exchanger configurations, working fluids, and performance parameters. Here, an effort is made to describe the contributions of individual/coupled TEG systems. As a coupled system, the individual TEG system is used with other systems like solar, distillation, solar pond, etc., for cogeneration and enhanced efficiency. The thermal/system parameters of individual/coupled systems are thoroughly discussed, and their impact on efficiency and power generation is illustrated. It was found that the design of the heat exchanger configuration varies from plate type to an efficient liquid-based electricity generation system in these TEG systems. The working fluid inside the fluid loop of a thermoelectric generation system varies from simple fluids to nanofluids. The current state of thermoelectric generation technology is facing challenges in module materials, equipment cost optimization, and commercialization. The progressive TEG generation capabilities have improved with recent advancements in these areas. The power densities are increasing from 0.5 to 1.2 W/cm² in earlier standalone TEGs to 2.5–4.8 W/cm² in recent optimized hybrid configurations, and overall system efficiencies are rising from an average of 5.2% (standalone) to 18.7% in coupled solar-TEG or waste heat recovery systems. The reported maximum ZT values are also improved from ~1.2 to 2.1–2.8 in next-generation materials. Liquid-based heat exchangers in conjunction with nanofluids are the most efficient way to maximize temperature gradient coefficient (0.75–0.92) and minimize parasitic losses. While flexible, ionic, and hybrid next-generation material platforms are still in the early phases of development (TRL 3–5), liquid-based heat exchanger systems improved with nanofluids are closest to commercialization (Technology Readiness Level, TRL 6–8). Therefore, further research in these areas is required to mitigate these challenges. Finally, the recent developments in the thermoelectric generation field and future research direction are briefly discussed. Full article

This paper presents a parametric numerical study on the cooling performance of photovoltaic panels using water and an Al₂O₃-based nanofluid. The increase in operating temperature leads to a decrease in electrical efficiency, making thermal management a key factor in optimizing these systems. The analysis was carried out through numerical simulations in ANSYS, aiming to evaluate the influence of volumetric flow rate and inlet temperature of the cooling fluid on the panel cooling time under transient conditions. The results show that the performance of the Al₂O₃ nanofluid depends on the flow rate of the cooling fluid. At a low flow rate of 0.05 m³/h and a concentration of 4%, the cooling time is reduced by approximately 18–22% compared to water, while this advantage diminishes as the flow rate increases. A favorable operating region was also observed within the investigated laminar and near-transitional range, beyond which increasing the flow rate produced only limited additional reductions in cooling time under the assumptions of the numerical model. The findings highlight the importance of correlating the thermophysical properties of the fluid with flow parameters in order to optimize the thermal management of photovoltaic panels. Full article

This research analyzes the wavy, axisymmetric flow of a Ree–Eyring non-Newtonian nanofluid, infused with motile microorganisms, within a porous, tapered cylindrical channel under a transverse magnetic field. This investigation presents a theoretical framework that may inform the improvement of energy efficiency and thermal management in biomedical engineering applications, such as drug delivery systems and microfluidic biosensors. The work provides an extended insight by a contribution to the evaluation of entropy generation, explicitly considering the influence of motile microorganisms, thereby bridging a gap in the existing literature. The comprehensive physical model further incorporates the combined effects of Joule heating, viscous dissipation, nonlinear thermal radiation, and chemical reactions. Methodologically, the governing nonlinear equations of the system were rendered tractable under long-wavelength and low-Reynolds-number assumptions and subsequently solved using the numerical Runge–Kutta–Fehlberg technique. The key conclusion is that, based on the present numerical model, careful selection of magnetic field strength and microorganism motility parameters may reduce irreversible energy losses, potentially improving the net usable work in advanced nanofluid transport systems for biomedical applications, subject to experimental validation. The most significant finding reveals that the magnetic field serves as a dual-purpose control parameter: increasing its strength boosts total entropy generation by 20–30% while simultaneously raising the Bejan number, confirming heat transfer as the dominant irreversibility mechanism in the system. Additionally, nanoparticle concentration diminishes substantially with elevated chemical reaction rates and Schmidt numbers, while microorganism density is highly sensitive to the Péclet number, which causes flow disruptions. Full article

This study experimentally investigates the mixed convection heat transfer performance of CuZnFe₂O₄–water-based magnetic nanofluids in a cylindrical minichannel under the influence of external magnetic fields. Nanofluids with three different volumetric concentrations (0.25%, 0.50%, and 0.75%) were synthesized and characterized in terms of thermophysical properties. The experiments were conducted within the Richardson number range of 0.1–10 to ensure mixed convection conditions, while magnetic field intensities of 220 G, 300 G, and 380 G were applied using custom-built electromagnets. Results show that suspending CuZnFe₂O₄ nanoparticles significantly enhances the heat transfer rate compared to pure water, mainly due to increased thermal conductivity and particle–fluid interactions. The application of a magnetic field further augments the Nusselt number by disturbing the thermal boundary layer and intensifying particle motion, leading to up to 64.4% improvement compared with pure water at similar Reynolds numbers. In addition, Analysis of Variance (ANOVA) and Response Surface Methodology (RSM) were employed to determine the most influential parameters on heat transfer performance and to develop a predictive correlation for the Nusselt number as a function of Reynolds number, nanoparticle concentration, and magnetic field intensity. The findings highlight the combined effects of nanoparticle suspension and magnetic field application as a promising approach for enhancing heat transfer in low-flow mixed convection regimes, offering valuable insights for thermal management in miniaturized cooling systems. Full article

We conducted a theoretical analysis on the diffusiophoretic motion of a dielectric droplet in a cylindrical pore in the presence of an induced diffusion potential, such as that in a NaCl electrolyte solution. The fundamental electrokinetic governing equations are solved using a patched pseudo-spectral method based on Chebyshev polynomials, coupled with a geometric mapping scheme to handle the irregular solution domain. The impact of the boundary confinement effect on droplet mobility is examined in detail. Interesting electrokinetic phenomena are found in this work, such as mobility reversal in narrow cylindrical pores with the droplet moving against the direction expected based on the classical Coulomb electrostatic law due to the strong boundary confinement effect. Moreover, “solidification phenomenon” is also found at some specific pore radius where the droplets move as rigid particles with no interior recirculating vortex flows regardless of the droplet viscosities. Corresponding critical points of ${\mathrm{R}}_{\mathrm{w}}^{\mathrm{*}}$, the ratio of droplet radius to the cylindrical radius are found where the spinning orientation on the droplet surface changes each time as it passes them. The profound boundary confinement effect, both electrostatically and hydrodynamically, is responsible for these peculiar phenomena. The results presented here have direct applications in microfluidic and nanofluidic operations as well as drug delivery applications. Full article

Oil recovery from carbonate reservoirs is one of the critical challenges in the oil industry due to the strongly oil-wet nature, natural fractures, and the heterogeneity of carbonate rocks. Subsequently, waterflooding can only displace oil from large fractures, leaving the majority of oil trapped in the rock matrix. This work suggests that nanofluid flooding, as a predesigned flooding method, is an alternative to conventional waterflooding. Various concentrations of silica nanofluid at different nanoparticle concentrations were formulated and systematically investigated for their characteristics, stability at reservoir conditions, and their influence on wettability and oil recovery. Silica nanoparticles were sustainably synthesized from waste materials to ensure the feasibility and environmental friendliness of the process. Results indicated that the synthesized silica has an amorphous crystalline nature characterized by nano-sized particles. Additionally, treating silica nanoparticles with a silane group significantly enhances the stability of nanofluids in a high-salinity environment. Most interestingly, by comparing the amount of oil recovered, the results revealed that implementing nanofluid flooding as a secondary oil recovery, rather than waterflooding, can produce around 12% more oil, in addition to eliminating a whole waterflooding step. This is the first study to alter the traditional flooding scenario and directly conduct nanofluid flooding as secondary oil recovery, without being preceded by waterflooding, using sustainably synthesized nanoparticles. Considering the water crisis in the Middle East, this approach can save substantial amounts of water, which improves the sustainable development of communities. Full article

Hybrid nanofluids combining thermally conductive nanoparticles with latent heat-storing nanocapsules have attracted growing interest for near-ambient liquid-based thermal management, yet direct comparisons between mono and hybrid phase-change-material-containing systems on a common experimental basis remain scarce. In this work, water-based mono Al₂O₃, mono polyurethane-nanoencapsulated n-nonadecane (PU-NEPCM), and Al₂O₃/PU-NEPCM hybrid nanofluids were prepared under identical surfactant, sonication, and dispersion conditions, and their thermal conductivity, dynamic viscosity, and Day-1 colloidal stability were characterized over 298–313 K at total volume fractions of 0.1, 0.3, and 0.5 vol.%, with the hybrids prepared at a 50:50 volumetric ratio. At 0.5 vol.% and 313 K, the hybrid (NFH3) exhibited the highest thermal conductivity enhancement (+8.27%), exceeding the corresponding mono Al₂O₃ and mono PU-NEPCM nanofluids by 4.6 and 5.2 percentage points, respectively, while maintaining a moderate viscosity penalty. The hybrid formulations also achieved |ζ| = 32–37 mV, exceeding the conventional electrostatic-stabilization threshold and outperforming both mono families. A two-factor analysis of variance (ANOVA) identified particle concentration as the dominant factor governing both properties (p < 0.001), with temperature becoming statistically significant only for the hybrid viscosity (p = 0.043). The synergy index varied between 0.85 and 1.43 across the tested conditions—reaching values of 1.20–1.43 for the lowest-loaded hybrid (NFH1)—while the performance index remained close to unity (0.97–1.01). These results identify low-loaded Al₂O₃/PU-NEPCM hybrid nanofluids as a balanced and stable candidate for near-ambient liquid-based thermal management applications. Full article

DNA extraction is a critical prerequisite for reliable downstream analyses such as Polymerase Chain Reaction (PCR), sequencing, and genotyping. Conventional methods often require labor-intensive protocols, large sample volumes, or costly automation. Microfluidic approaches offer an alternative by reducing reagent consumption and enabling faster, more integrated workflows. Here, we present a passive lab-on-a-chip device that performs DNA extraction from complex biological media and enables subsequent on-chip single-molecule analysis. The chip integrates a magnetophoresis-based solid-phase extraction module with a fluorescence detection section capable of quantifying DNA molecules in microchannels and visualizing stretched molecules in nanochannels. The multi-level micro/nanofluidic architecture is fabricated in polymer using a single-step nanoimprinting process with a total manufacturing time of two minutes per chip, enabling scalable production. As a proof of concept, the device extracted DNA from samples spiked into buffer or plasma. On-chip transfer efficiency of DNA–bead complexes to the elution buffer reached 86%, and quantitative analysis of the recovered liquid showed an overall extraction efficiency of 40% (including DNA recovery off-chip), with intact 48 kbp DNA confirmed in both micro- and nanochannel measurements. This platform offers a promising foundation for point-of-care and point-of-interest applications, where integrated DNA extraction and analysis can reduce sample loss and support streamlined, automated workflows. Full article

This paper reviews emerging dielectric fluids for power transformers, including natural and synthetic esters, silicone oils, gas-to-liquid oils, and nanofluids, driven by environmental regulations, fire safety concerns, and the need for extended asset life. The review synthesizes technical data from standards and field experience, including a case study of an Eskom transformer energized in 2016 with natural ester fluid. Analysis confirms these fluids offer significant benefits in fire safety, biodegradability, and dielectric performance, with the case study demonstrating natural esters’ effectiveness in preserving solid insulation. However, trade-offs involving cost, material compatibility, and operational protocols require careful management. Full article