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\"This book will be beneficial for students, researchers and scientists working in the field of green energy systems. In the last few decades, green energy technologies have gained significant interest. The increase of heat transfer in green energy technologies is one of the most important concerns in energy collection, energy storage, energy utilization, energy conservation, and optimum design. Since nanofluids/nano-enhanced phase change materials are used to increase heat transfer characteristics and thermal properties compared to conventional fluids/phase change materials, the performance of green energy technologies can be improved. These novel strategies are gaining interest to researchers and authors in recent years. This book presents the various applications of nanofluids, hybrid nanofluids, and nano-enhanced phase change materials in green energy technologies such as solar thermal energy storage, photovoltaic/thermal systems, tracking and non-tracking solar collectors, solar thermal power plant, and wind turbine cooling systems. The thermophysical properties of the nanofluids and nano-enhanced phase change materials are also presented. This book also overviews the challenges and opportunities in implementing the nanofluids/nano-enhanced phase change materials application in green energy technologies\"-- Provided by publisher.

AbstractBoth equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively) methods have been used to predict the thermal conductivity of nanofluids. However, there are considerable discrepancies among the results of these two methods. In this study, by estimating the effects of different mechanisms including the Brownian motion of nanoparticles, the micro-convection in the base fluid, the nanolayers around the nanoparticles, and the thermal boundary resistance at the surface of nanoparticle, we determine upper and lower physical limits for the thermal conductivity of a nanofluid with spherical nanoparticles. The prediction of the NEMD simulations is in the acceptable range, while the result of the EMD simulations is higher than the upper bound. Since the prediction of the EMD method is not physically justifiable, we conclude the inadequacy of the traditional EMD method in calculating the thermal conductivity of nanofluids. Consequently, we recommend the researchers to use a modified version of the EMD method or the NEMD method for new studies in this field. We also apply the NEMD method to investigate the effects of the shape of nanoparticles and the formation of percolation networks in enhancing the thermal conductivity of nanofluids. The interference of the effects of nanolayer and thermal boundary resistance on the thermal conductivity of nanofluids is a new phenomenon we introduce in this study.Graphic abstract

Non-Newtonian fluids with nanomaterials are studied to improve industrial efficiency and production by enhancing thermal conductivity. In addition, the titanium dioxide nanoparticles can easily penetrate cells and tissues due to their small size. Its photocatalytic activities can also be utilized to produce reactive oxygen species, which have potential applications in cancer treatment. So, the present investigation intends to analyze the water-based titanium dioxide power-law nanofluid flow over a thin needle. Further, the thermal radiation was incorporated and analyzed as a complete case study for linear, nonlinear, and quadratic radiation. The governing equations are reformed into a dimensionless form using suitable similarity variables. Numerical solutions were found by implementing the Bvp4c technique. The major conclusion drawn from the present investigation reveals that the temperature is enhanced by the radiation, needle size, and titanium dioxide volume fraction. The nonlinear radiation case plays a dominant role compared to the other two radiation cases. In order to provide further insight into the engineering quantities, multiple quadratic regression models are utilized to predict skin friction and thermal transmission rate. The quadratic regression term of radiation and temperature ratio parameters has a negative influence on the heat transmission rate. The outcomes of this investigation may help to get a better theoretical understanding of various scientific research and biomedical applications, especially in the treatment of tumors, sterilization of medical instruments, drug delivery systems, and cancer treatment. Graphical abstract

To find the sensitivity and dependence degree of the numerical simulation predictions on the property variations arising from the temperature gradients, a 3D conjugate heat transfer of Al2O3–water nanofluid convecting through rectangular microchannel heat sinks (MCHS) is considered in the present study. The Koo–Kleinstreuer–Li model is adopted to capture the temperature-dependent nature of thermophysical properties of the working nanofluid compared to the pure fluid (i.e., water). Both straight and width-tapered flow passages are studied using finite volume method within the laminar flow regime to see how sensitive are the predictions to the temperature dependency of the thermophysical properties for both the pure base fluid and nanofluid. Results show that the constant property assumption obtains unrealistic results up to 140% for the Reynolds number, which may mislead in predicting the flow regime (laminar/turbulent). The constant property approach predicts the convection heat transfer coefficient and the pumping power, respectively, 31% lower and 33% higher than those of the temperature-dependent property approach. In addition, the present study concludes that the MCHS should be simulated based on the temperature-dependent thermophysical property approach to be more realistic, especially for converging flow passages due to high-temperature gradients and for nanofluids for their induced temperature-dependent properties. The last two issues induced each other and increase the deviation of the predictions based on the constant property assumption. Finally, because of underestimating the heat transfer rate and overestimating the pumping power, the MCHS would be over-designed if one adopts the constant property assumption for conceptual design and the MCHS would perform under inefficient and off-design conditions.

In many processes such as microwave heating, chemical reaction, pasteurization, sterilization, heat transfer convection is occurred by means of purely internal heating sources, instead of heating solid surfaces. This paper deals with the analysis of the onset of MHD nanofluid convection inside a porous layer in the presence of purely internal heat source and chemical reaction. The nanofluid is enclosed between two solid surfaces and also incorporates the effect of Brownian motion along with thermophoresis. The simulation is performed for three cases of thermal boundary conditions, namely (I) isothermal condition for both surfaces, (II) isothermal condition for upper surface and insulated condition for lower surface, and (III) isothermal condition for lower surface and insulated condition for upper surface. Also, for all case studies, the zero nanoparticle flux condition under the thermophoretic effects is considered at the boundaries. In this study, the effect of chemical reaction and porosity parameters on the critical heat source Rayleigh number and critical wave number is investigated. It is found that the critical heat source Rayleigh number increases with an increase in the magnetic Chandrasekhar number, chemical reaction parameter, and porosity parameter.

In the current investigation, a (TiO 2 –Ag/water) hybrid nanofluid (NF), saturated porous medium filled wavy-walled enclosure, and an unstable magneto-mixed convective flow are examined. Heat radiation (Rd) is present with the constant magnetic field (B0), and the cavity, which is partially heated from its bottom wall and cooled from its wavy-left and right walls, contains a square solid block that is solidly surrounded on all sides. The governing PDEs, which are represented in terms of stream function, temperature, and nanoparticle volume percent, are numerically solved using a finite volume technique. It is discovered that as the dimensionless heat source length (B) rises, the streamlines' strength marginally changes while the isotherms in the wavy porous cavity grow increasingly obvious. The results show that increasing the number of undulations and hybrid NF generally produces a higher average Nusselt number when the wave amplitude parameter A  = 0.3 and the volume fractions of (TiO 2 − Ag/water) Hybrid NF = 0.05. Raising the volume percentage of Hybrid NF enhances the average Nusselt number while increasing the Hartmann number observed happened with decreases the average Nusselt number. One of the primary factors contributing to the production of entropy is the irreversibility of the magnetic force, which leads the isentropic lines to diffuse toward the interior of the enclosure as Ha rises. In comparison with previous case studies, the highest Nusselt number is at λ  = 3, and it rises in every case as the wave amplitude parameter and the percentage of hybrid NF volume increase. It was discovered that increasing porosity greatly increased local Nusselt numbers due to improved heat transfer within the enclosure. The lowest local Nusselt number has been determined to be Q  = − 2, which represents the heat generation/absorption factor.

Transformer reliability is strongly governed by the condition of insulating oil; however, limited studies have directly compared real-time aged transformer oil with standardized accelerated-aged oil or evaluated nanofluid performance in aged insulation systems. This study presents a novel comparative framework that first standardizes accelerated aging by matching its dielectric behavior and fault gas signatures with real-time aged transformer oil, and subsequently evaluates the effectiveness of mineral oil-based nanofluids in mitigating aging-induced degradation. Real-time aged and accelerated-aged oils were comparatively evaluated using dielectric constant, dielectric dissipation factor, resistivity, thermal conductivity, and dissolved gas analysis. To restore degraded insulation performance, nanofluids containing cerium oxide and zirconium oxide nanoparticles were prepared and aged under identical conditions. Optimal nanoparticle concentrations of 25 mg/L for cerium oxide and 37.5 mg/L for zirconium oxide were identified. At these concentrations, cerium oxide nanofluids exhibited improvements of + 21.05% in dielectric constant, + 88.47% in resistivity, − 39.27% in dielectric dissipation factor, and + 7.75% in thermal conductivity, while zirconium oxide nanofluids showed enhancements of + 28.07%, + 143.46%, − 40.24%, and + 9.58%, respectively, compared with aged mineral oil. Dissolved gas analysis further revealed a 30–40% reduction in key fault gas concentrations, resulting in a diagnostic shift from severe thermal faults to no-major-fault conditions. These improvements correspond to a 25–40% reduction in aging acceleration factor and an estimated 20–30% extension in insulation life. The results demonstrate the strong potential of cerium oxide- and zirconium oxide-based nanofluids as effective insulating fluids for enhancing the reliability and longevity of oil-immersed power transformers.

Purpose The purpose of this study is to theoretically analyze the laminar free convection heat transfer of nanofluids in a square cavity. The sidewalls of the cavity are subject to temperature difference, whereas the bottom and top are insulated. Based on the available experimental results in the literature, two new non-dimensional parameters, namely, the thermal conductivity parameter (Nc) and dynamic viscosity parameter (Nv) are introduced. These parameters indicate the augmentation of the thermal conductivity and dynamic viscosity of the nanofluid by dispersing nanoparticles. Design/methodology/approach The governing equations are transformed into non-dimensional form using the thermo-physical properties of the base fluid. The obtained governing equations are solved numerically using the finite element method. The results are reported for the general non-dimensional form of the problem as well as case studies in the form of isotherms, streamlines and the graphs of the average Nusselt number. Using the concept of Nc and Nv, some criteria for convective enhancement of nanofluids are proposed. As practical cases, the effect of the size of nanoparticles, the shape of nanoparticles, the type of nanoparticles, the type of base fluids and working temperature on the enhancement of heat transfer are analyzed. Findings The results show that the increase of the magnitude of the Rayleigh number increases of the efficiency of using nanofluids. The type of nanoparticles and the type of the base fluid significantly affects the enhancement of using nanofluids. Some practical cases are found, in which utilizing nanoparticles in the base fluid results in deterioration of the heat transfer. The working temperature of the nanofluid is very crucial issue. The increase of the working temperature of the nanofluid decreases the convective heat transfer, which limits the capability of nanofluids in decreasing the size of the thermal systems. Originality/value In the present study, a separation line based on two non-dimensional parameters (i.e. Nc and Nv) are introduced. The separation line demonstrates a boundary between augmentation and deterioration of heat transfer by using nanoparticles. Indeed, by utilizing the separation lines, the convective enhancement of using nanofluid with a specified Nc and Nv can be simply estimated.

Introduction Chronic lung disease is a major cause of morbidity in African children with HIV infection; however, the microbial determinants of HIV-associated chronic lung disease (HCLD) remain poorly understood. We conducted a case–control study to investigate the prevalence and densities of respiratory microbes among pneumococcal conjugate vaccine (PCV)-naive children with (HCLD +) and without HCLD (HCLD-) established on antiretroviral treatment (ART). Methods Nasopharyngeal swabs collected from HCLD + (defined as forced-expiratory-volume/second < -1.0 without reversibility postbronchodilation) and age-, site-, and duration-of-ART-matched HCLD- participants aged between 6–19 years enrolled in Zimbabwe and Malawi (BREATHE trial-NCT02426112) were tested for 94 pneumococcal serotypes together with twelve bacteria, including Streptococcus pneumoniae (SP), Staphylococcus aureus (SA), Haemophilus influenzae (HI), Moraxella catarrhalis (MC), and eight viruses, including human rhinovirus (HRV), respiratory syncytial virus A or B, and human metapneumovirus, using nanofluidic qPCR (Standard BioTools formerly known as Fluidigm). Fisher's exact test and logistic regression analysis were used for between-group comparisons and risk factors associated with common respiratory microbes, respectively. Results A total of 345 participants (287 HCLD + , 58 HCLD-; median age, 15.5 years [IQR = 12.8–18], females, 52%) were included in the final analysis. The prevalence of SP (40%[116/287] vs. 21%[12/58], p  = 0.005) and HRV (7%[21/287] vs. 0%[0/58], p  = 0.032) were higher in HCLD + participants compared to HCLD- participants. Of the participants positive for SP (116 HCLD + & 12 HCLD-), 66% [85/128] had non-PCV-13 serotypes detected. Overall, PCV-13 serotypes (4, 19A, 19F: 16% [7/43] each) and NVT 13 and 21 (9% [8/85] each) predominated. The densities of HI (2 × 10 4 genomic equivalents [GE/ml] vs. 3 × 10 2 GE/ml, p  = 0.006) and MC (1 × 10 4 GE/ml vs. 1 × 10 3 GE/ml , p  = 0.031) were higher in HCLD + compared to HCLD-. Bacterial codetection (≥ any 2 bacteria) was higher in the HCLD + group (36% [114/287] vs. (19% [11/58]), ( p  = 0.014), with SP and HI codetection (HCLD + : 30% [86/287] vs. HCLD-: 12% [7/58], p  = 0.005) predominating. Viruses (predominantly HRV) were detected only in HCLD + participants. Lastly, participants with a history of previous tuberculosis treatment were more likely to carry SP (adjusted odds ratio (aOR): 1.9 [1.1 -3.2], p  = 0.021) or HI (aOR: 2.0 [1.2 – 3.3], p  = 0.011), while those who used ART for ≥ 2 years were less likely to carry HI (aOR: 0.3 [0.1 – 0.8], p  = 0.005) and MC (aOR: 0.4 [0.1 – 0.9], p  = 0.039). Conclusion Children with HCLD + were more likely to be colonized by SP and HRV and had higher HI and MC bacterial loads in their nasopharynx. The role of SP, HI, and HRV in the pathogenesis of CLD, including how they influence the risk of acute exacerbations, should be studied further. Trial registration The BREATHE trial (ClinicalTrials.gov Identifier: NCT02426112 , registered date: 24 April 2015).

We examine thermal management in the heat exchange of compact density nanoentities in crude base liquids. It demands the study of the heat and flow problem with non-uniform physical properties. This study was conceived to analyze magnetohydrodynamic Eyring–Powell nanofluid transformations due to slender sheets with varying thicknesses. Temperature-dependent thermal conductivity and viscosity prevail. Bioconvection due to motivated and dynamic microorganisms for Eyring–Powell fluid flow is a novel aspect herein. The governing PDEs are transmuted into a nonlinear differential structure of coupled ODEs using a series of viable similarity transformations. An efficient code for the Runge–Kutta method is developed in MATLAB script to attain numeric solutions. These findings are also compared to previous research to ensure that current findings are accurate. Computational activities were carried out with a variation in pertinent parameters to perceive physical insights on the quantities of interest. Representative outcomes for velocity, temperature, nanoparticles concentration, and bioconvection distributions as well as the local thermal transport for different inputs of parameters are portrayed in both graphical and tabular forms. The results show that the fluid’s velocity increases with mixed convection parameters due to growing buoyancy effects and the fluid’s temperature also increased with higher Brownian motion Nb and thermophoretic Nt. The numerical findings might be used to create efficient heat exchangers for increasingly challenging thermo-technical activities in manufacturing, construction, and transportation.