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The advanced heat transfer applications of nanofluids make it important to investigate their viscous properties. For various engineering applications, accurate measurement of dynamic viscosity of n...

The heat transfer fluid's thermal properties are a significant topic of current research. In this study, coal fly ash nanoparticles of 14 nm average diameter were dispersed in water to prepare stab...

Thermal conductivity, dynamic viscosity, and density of TiN nanofluids (NFs) with different base mediums have been characterized for the prospect of developing new thermophysical property correlations in this work. Characterizations of morphology and crystal structure of nanopowder were made using scanning electron microspore and X-ray diffractometer. Set of NFs was prepared in a base liquid mixture of water–ethylene glycol W/EG 60:40 and 40:60 by an ultrasound-assisted two-step method. Meter Group KD 2 Pro analyzer operated on transient line heat source method was used for the thermal conductivity test. The viscosity and density of NFs were measured with Anton Paar rotational rheometer MCR 302 and oscillating densimeter DMA 4500M. All experiments were implemented for volume fractions of NF between 0.25 and 1.0 vol% in the temperatures range of 293.15–333.15 K. The findings indicate that density and viscosity decrease with increasing temperature, whereas the thermal conductivity of nanofluids is enhanced depending on NP concentration. The W/EG 60:40 base mixture exhibited higher thermal conductivity enhancement and 40:60 base mixture had greater viscosity growth among all analyzed NFs. Moreover, the difference in base fluid fractions does not lead to a significant variance in the density ratios of NFs. Empirical correlations developed for examined properties with effects of particle concentration, temperature, and base liquid ratio are capable of accurately reproducing the properties data within 15% deviation.

The experimental data on the viscosity and thermal conductivity (TC) of ethylene glycol (EG)-based hybrid nanofluids (HyNFs) dispersed with a SiC–CuO/C nanocomposite (NC) is reported for the first time. The rheological behavior and dynamic viscosity have been analyzed with a computer controlled rotational rheometer over a temperature range from 298.15–353.15 K and shear rate from 20 to 200 s−1. The TC was measured using transient hot-wire method for NF concentrations up to 3.13 wt%. The effect of the temperature and volume fraction of the nanoparticles (NPs) on the thermophysical properties were examined under atmospheric pressure. The experimental findings revealed that the TC increases with the concentration and temperature, while the viscosity increases with concentration and decreases with temperature as expected. HyNF exhibit substantially higher TC and viscosity enhancement compared to single-particle based NF under similar conditions. The enhanced properties of the HyNF could be attributed to the synergetic effects of the composite particles and the underlying physical mechanism in the fluid medium. The existing theoretical models failed to predict the experimental data. Herein, a new correlation is presented as a function of concentration and temperature for the TC and viscosity.

This paper reports experimental investigation on the viscosity, electrical and thermal conductivities of ethylene glycol and propylene glycol based β-SiC nanofluids. Two-step technique was used to formulate stable nanofluids at room temperature. The properties of nanofluids were measured at temperatures between 298.15 K and 353.15 K for different concentrations up to 3.0 wt.% loading (1.0 vol.%). The effect of temperature and base liquid was analysed on each of nanofluid sample. The experimental results showed that both electrical and thermal conductivity increase while viscosity decreases with temperature. The properties of the base liquid are found to influence the nanofluid properties. The underlying mechanisms have been established and discussed. Furthermore, some new empirical equations are derived to correlate the measured properties data. The results can be applied to predict the viscosity, electrical and thermal conductivities of ethylene glycol and propylene glycol-based β-SiC nanofluids.

The compound technique that combines nanofluids with wire coil inserts has proven itself in achieving double augmentation in heat transfer. This paper presents the thermal hydraulic performance of TiO2-SiO2 nanofluids with wire coil inserts. The experiments were conducted for Reynolds number from 2300 to 12,000 to determine the heat transfer performance and friction factor of TiO2-SiO2 nanofluids with wire coil inserts. The TiO2-SiO2 nanofluids were prepared by using the two-step method for volume concentrations of 0.5–3.0%. The wire coil inserts are designed at various ratios of pitch over diameter (P/D) in the range of 0.83–4.17. The heat transfer performance of nanofluids was enhanced for a maximum of 254.4%, while the friction factor was obtained in the range of 1.76–6.38 times higher than water/EG in a plain tube. The thermal performance factor (TPF), η for the nanofluids with wire coil inserts at all volume concentrations was observed greater than 1.0. The optimum performance of TiO2-SiO2 nanofluids with wire coil occurred at 2.5% volume concentration and 1.50 pitch ratio. At this condition, the TiO2-SiO2 nanofluids with wire coil inserts provide the highest TPF and represent the best condition for cooling system applications.

Dispersion of nano sized metallic particles in to conventional base fluids, called nano-fluids, is expected to yield enhanced heat transfer properties. Experimental determination and subsequent correlations of thermo-physical properties such as viscosity, thermal conductivity, specific heat capacity etc., of these nano-fluids become necessary to estimate the heat transfer performance of these nano-fluids. Cu nano-fluids in Water-Glycerine base fluids are prepared at different volume concentrations of Cu nano particles. Two step dispersion synthesis method, without using any surfactant, is used to prepare nano-fluids consisting of Cu nano-particles in Water-Glycerine base fluid. Viscosity of these nano-fluids is determined experimentally at different temperatures of 20, 40, 60 and 80 °C using Brookfield Viscometer. Three different volume concentrations of Cu-based nano-particles in the base fluid are taken as 0.2%, 0.6% and 1.0%. SEM and EDS images show the particle size distribution and elemental analysis of Cu nano-particles. It has been observed that viscosity of nano-fluids increased with increase in particle volume concentration and decreased with increase in fluid temperature. Maximum viscosity value of 3.76 cP for 1.0% vol. concentration at 20 °C and minimum viscosity value of 0.94 cP at 80 °C for 0.2% vol. concentration is obtained for copper nano-fluids. Viscosity for Water-Glycerine base fluid also measured at different temperatures of 20, 40, 60 and 80 °C. This viscosity data of will be useful for the aspiring researchers to predict heat transfer properties of copper nano-fluids.

The energy gain of domestic solar water heating systems is determined by solar to thermal energy conversion and glazing optical efficiency. For this study, solar transmission properties of different transparent glazing materials such as acrylic, low-iron, medium-iron, and high-iron glasses were measured. The collector thermal efficiency under natural convection mode was compared for different transparent covers determined by numerical simulation using the Hottel–Whillier–Bliss equation. The low-iron glass (LiG-12 mm) has 16.3% and 20% higher thermal efficiency than medium- (MiG-12 mm) and high-iron glasses (HiG-12 mm), respectively, for a peak summer day. The effect of glass thickness on thermal performance is noteworthy in glasses than in acrylic glass sheets. Low-iron content glass with 6 mm thickness has the highest thermal and optical efficiency of 63.2% and 75.65%, respectively, for the collector optimum tilt for Vellore city in Tamil Nadu, India. The results are useful in the selection of glass covers for energy-efficient solar flat plate collectors.

Hybrid nanofluids are a novel class of colloidal fluids which have drawn significant attention due to potential tailoring of their thermo-physical properties for heat transfer enhancement by a combination of more than one nano-additive to meet specific requirements of an application. In the present work, ceramic copper oxide/carbon (SiO2-CuO/C) nanoparticles in 80:20 (wt%) composition were prepared by ultrasonic-assisted wet mixing technique. The hybrid nanofluid was formulated by dispersing the nanoparticles into a base fluid mixture of 60:40 (% by mass) glycerol and ethylene glycol (G/EG) using the two-steps method. The influence of nanoparticles on the augmentation of specific heat, thermal conductivity and viscosity was examined in the volume concentration range of 0.5–2.0% in the temperature range of 303.15–353.15 K. The results demonstrate that the synthesized SiO2-CuO/C hybrid nanoparticles enhanced the thermo-physical properties of the base fluid mixture which is higher than using SiO2 alone. In the case of SiO2–G/EG nanofluid, the specific heat capacity decremented by a maximum value of 5.7% whereas the thermal conductivity and viscosity incremented by 6.9% and 1.33-times as compared with G/EG at maximum volume concentration of 2.0% at a temperature of 353.15 K. Comparatively, a reinforcement of 80% SiO2 with 20% CuO/C in G/EG mixture led to thermal conductivity and viscosity enhancement by 26.9% and 1.15-times, respectively with a significant reduction of specific heat by 21.1%. New empirical correlations were proposed based on the experimental data for evaluation of thermophysical properties.

In the present work three different types of nanofillers such as multiwalled carbon nanotubes (MWCNTs), aluminum oxide nanoparticles and nanosize activated charcoal were mixed with UF resin and used in the preparation of medium density fiberboard(MDF). The process has improved heat transfer during hot pressing and achieved proper curing due to enhanced thermo physical properties of wood fibers. To improve the dispersion of nanofillers into UF matrix, high speed mechanical stirring and ultrasonic treatments were used. The MWCNTs were oxidized with nitric acid and the functional groups formed on its surface improved the dispersion and interaction with UF matrix. The dispersion of nanofillers in UF resin matrix was confirmed with XRD, FESEM, and DMA tests undertaken. The mixing of MWCNTs and Aluminum oxide with UF resin have reduced the curing time due to enhanced thermal conductivity of MDF matrix. The heat transfer during hot pressing of MDF improved significantly with the addition of MWCNTs and Al2O3 nanoparticle and activated charcoal did not have much effect on heat transfer. The curing rate of UF resin improved with all the three nanofillers, as the activation energy of UF curing decrease as shown by the DSC results. The physical and mechanical properties of MDF have improved significantly with MWCNTs and Al2O3 nanoparticle. The activated charcoal has significantly decreased the formaldehyde emission of MDF.

In recent years, research is focused on enhancing the thermo-physical properties of single component nanofluids. Hence, the hybrid or composite nanofluids are developed to enhance the heat transfer performance. The thermo-physical properties of TiO 2 -SiO 2 nanoparticles suspended in a base fluid of water (W) and ethylene glycol (EG) mixture with 60:40 vol ratio are investigated. The experiments were conducted for 1.0% volume concentration of TiO 2 -SiO 2 nanofluids with different mixture ratios of 20:80, 40:60, 50:50, 60:40 and 80:20. The measurements of thermal conductivity and dynamic viscosity were performed in the temperature range of 30–80 °C by using KD2 Pro Thermal Properties Analyzer and Brookfield LVDV III Ultra Rheometer respectively. The highest thermal conductivity for TiO 2 -SiO 2 nanofluid was obtained with a ratio of 20:80 and the maximum enhancement exceeded up to 16% higher than the base fluids. The nanofluids with a ratio of 50:50 provided the lowest effective thermal conductivity. Meanwhile, the dynamic viscosity variation for all mixture ratios is always lower than the ones with a ratio of 50:50. The properties enhancement ratio suggests that TiO 2 -SiO 2 nanofluid with 1.0% volume concentration will aid the heat transfer for all mixture ratios except for the ratio of 50:50. As a conclusion, the optimum mixture ratios for TiO 2 -SiO 2 nanofluids are attained with 40:60 and 80:20 ratios where the combination of enhancement in thermal conductivity and dynamic viscosity had more advantages to heat transfer as compared to other ratios.

Solar thermal conversion technology harvests the sun’s energy, rather than fossil fuels, to generate low-cost, low/zero-emission energy in the form of heating, cooling or electrical form for residential, commercial, and industrial sectors. The advent of nanofluids and nanocomposites or phase change materials, is a new field of study which is adapted to enhance the efficiency of solar collectors. The concepts of thermal energy storage technologies are investigated and the role of nanomaterials in energy conversion is discussed. This review revealed that although the exploitation of nanomaterials will boost the performance of solar collectors almost in all cases, this would be accompanied by certain challenges such as production cost, instability, agglomeration and erosion. Earlier studies have dealt with the enhancement of thermal conductivity and heat capacity; however, less attention has been given to the facing challenges. Moreover, no exact criteria can be found for the selection of appropriate nanomaterials and their properties for a specific application. In most research studies, the nanoparticles’ material and properties have not been selected based on estimated values so that all the aspects of desired application could be considered simultaneously. The wide spread use of nanomaterials can lead to cost effective solutions as well. Therefore, it seems there should be a sense of techno-economic optimization in exploiting nanomaterials for solar thermal energy storage applications. The optimization should cover the key parameters, particularly nanoparticle type, size, loading and shape which depends on the sort of application and also dispersion technology.

The purpose of this research is to study the forced convection heat transfer and flow characteristics of water base fly ash-Cu (80:20% by volume) hybrid nanofluid (HNF) flow through a copper tube under a constant heat flux (CHF) of 7962W/m2 experimentally and numerically. The present work presents results for the concentrations of 0.5–2.0 vol% at a fluid inlet temperature of 30 °C in the flow rate range of 5–16 LPM. HNF stability, thermal conductivity, and viscosity were experimentally analyzed and compared with the established correlations. The maximum augmentation in Nusselt number (Nu) was 57.1% and 8.95% at a concentration of 2.0% relative to water for HNF and fly ash nanofluid (FANF), respectively. The total entropy generation varies inversely with the Reynolds number (Re). The pressure drop (Δp) of HNF is greater than the FANF and water. The development of correlations with experimental data is for determining Nu and friction factors of HNF. Bejan number (Be) of HNF and FANF varies inversely with concentration and Re improvement. The values of thermal performance factor (TPF) enhance with concentration, and a maximum TPF value observed is 1.52 at 2% concentration. The performance of the computational analyses is with ANSYS software gives a reasonable agreement between them.

This article presents experimental studies for the determination of heat transfer coefficient (HTC) and friction factor for the flow of a fly ash nanofluid in a copper tube under constant heat flux boundary condition. Fly ash/water nanofluid in the concentration range of 0.5–2.0 vol % is used. Stability, viscosity, and thermal conductivity have been found experimentally and validated with previously reported literature. Experimentation was performed at various flow rates and bulk fluid temperature of 30 °C . The highest thermal conductivity ratio and viscosity ratio of 1.21 and 1.18 were observed for a concentration of 2 vol% at 30 °C. The augmentation in Nusselt number (Nu) and friction factor was 46.9% and 9.89%, respectively at 2.0 vol%, when compared to the base fluid. With an increase in Reynolds number, the total entropy generation reduces, whereas the friction entropy generation increased. The maximum PEC value of 1.42 was observed at 2 vol% for fly ash nanofluid. The experimental findings are compared with CFD results, with good agreement between them. ANSYS Fluent software is used for computational validation.

Nanofluids are advanced fluids with novel properties useful for diverse applications in heat transfer. This article reports the experimental determination of thermal conductivity and viscosity for silica (SiO2) nanofluids in ethylene glycol (EG) and glycerol (G) as base fluids. A two-step method was applied to disperse the nanoparticles in the base fluids for the particle volume concentration of 0.5–2.0%. The dispersion stability of the nanofluids was evaluated by zeta potential analysis. All the measurements were performed in the temperature interval from 30 °C to 80 °C. It was found that the thermal conductivity increases with temperature. The SiO2-EG showed higher conductivity enhancement than SiO2-G nanofluids. Rheological analyses confirm Newtonian behavior for silica nanofluids within shear rate range of 20–100 s− 1. Viscosity decreases with an increase in operating temperature. The SiO2-EG demonstrated very weak temperature dependence compared to the SiO2-G nanofluids. Based on these measured properties, the criterion for heat transfer performance was determined. Furthermore, equations have been proposed with accuracy within ± 10% deviations to predict the thermal conductivity and dynamic viscosity of EG and G-based SiO2 nanofluids.

In the present study, titanium oxide-copper oxide/carbon (TiO 2 -CuO/C) nanocomposite particles have been prepared via wet-mixing protocol. The nanocomposite was characterized by using scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray powder diffraction (XRD). Subsequently, hybrid nanofluids were prepared by dispersing the nanocomposite in ethylene glycol (EG) as a base liquid. The thermal conductivity and viscosity of the nanofluids was measured in various volume concentrations (0.5, 1.0, 1.5, and 2%) and temperatures ranging from 303.15 K to 333.15 K. The experimental results showed the sensitivity of thermal conductivity and viscosity with respect to variations in volume concentration and temperature. The maximum enhancement of thermal conductivity of TiO 2 -CuO/C hybrid nanofluid is 16.7%, while the viscosity increased nearly by 80% at 2.0% volume concentration compared to base liquid at 313.4 K. The rheological analysis established that the hybrid nanofluid conforms to Newtonian classification of fluids. Finally, correlations for thermal conductivity and viscosity of nanocomposite based hybrid nanofluids were formulated which represent a satisfactory agreement between the experimental and calculated data with average absolute deviation ranging from 1% to 4%.

An analytical method is proposed to estimate the ignition time of the fuel droplet injected in to the combustion chamber of an I.C. engine. The first phase of analysis related to the case of thermal conservation to raise its temperature up to the ignition temperature with non-vaporization from its spherical surface. The ignition temperature depends on the fuel characteristics like specific heat, density, vapor pressure, thermal conductivity, latent heat etc. Subsequently, the mass diffusion of the vapors is included in the investigation. The non –dimensional parameter Fourier number F o is associated with mass diffusion of vapor from the spherical surface π m , the convective heat transfer π h and the thermal radiation π e from the compressed medium are observed to be the significant criteria in determining the ignition time. For a range of parameters analyzed the ignition time is observed to be a fraction of second. The results show that the term dimensionless radius R + decreases with increase in Fourier number. Further a correlation is established between the non-dimensional numbers Fourier number and π m , π h , π e T i g + , R + of the droplet to predict the ignition time is proposed based on the physical configuration of the droplet.

Thermal conductivity and viscosity of the Al2O3-SiO2/PAG composite nanolubricants for 0.02 to 0.1% volume concentrations at a temperature range of 303 to 353 K were investigated. Al2O3 and SiO2 nanoparticles were dispersed in the Polyalkylene Glycol (PAG 46) lubricant using the two-step method of preparation. Thermal conductivity and viscosity were measured using KD2 Pro Thermal Properties Analyzer and LVDV-III Rheometer, respectively. The result shows that the thermal conductivity and viscosity of composite nanolubricants increase with volume concentration and decreases with temperature. Composite nanolubricants behave as Newtonian in the range of the temperatures and volume concentrations studied. The highest thermal conductivity increment is 2.41% at 0.1% concentration and temperature of 303 K. A maximum value of 9.71% in viscosity at 0.1% concentration is observed at temperature of 333 K. A new correlation model to predict the properties of composite nanolubricants has been proposed for applications in refrigeration systems.

In this paper, laminar nanofluid flow in 3D copper microchannel heat sink (MCHS) with rectangular cross section, and a constant heat flux, has been treated numerically using the computational fluid dynamics software (FLUENT). Results for the temperature and velocity distributions in the investigated MCHS are presented. In addition, experimental and numerical values are compared in terms of friction factors, convective heat transfer coefficients, wall temperature and pressure drops, for various particle volume concentrations and Reynolds numbers. The numerical results show that enhancing the heat flux has a very weak effect on the heat transfer coefficient for pure water, but an appreciable effect for the case of a nanofluid. For all considered volume fractions, the sink friction factor decreases by increasing the Reynolds number and slightly increases by increasing the volume fractions, and, with increasing the volume fractions and the Reynolds number, the pressure drop increases.

Nanofluids are developed to meet the challenges of improving the efficiency of the cooling system subsequently minimizing the energy waste. This paper aims to investigate the forced convection heat transfer for Al2O3 nanofluids in different based ratio of water (W) and ethylene glycol (EG) mixture. The Al2O3 nanofluids are formulated using the two-step method for three based mixture ratio of 60:40, 50:50 and 40:60 (W:EG) by volume. The forced convection experiments are conducted under constant heat flux conditions for operating temperatures of 30–70 °C and Reynolds numbers of 3000–25,000. The heat transfer coefficient of nanofluids is enhanced with concentration compare to its base fluid at all designated temperature. It is observed to be improved further with the increase of temperature. The effect of different base mixture ratio display that nanofluids in 60:40 base mixture have the highest percentage of performance with 24.6% enhancement at 1.0% concentration and temperature of 70 °C. The increment of concentration for nanofluids shows a slight rise in friction factor. As a conclusion, the thermo-physical properties and the forced convection heat transfer for nanofluids in various base mixture is significantly influenced by concentration, temperature and base ratio of mixture.

In the past decade, research on nanofluids has been increased rapidly and reports reveal that nanofluids are beneficial heat transfer fluids for engineering applications. The heat transfer enhancement of nanofluids is primarily dependent on thermal conductivity of nanoparticles, particle volume concentrations and mass flow rates. Under constant particle volume concentrations and flow rates, the heat transfer enhancement only depends on the thermal conductivity of the nanoparticles. The thermal conductivity of nanoparticles may be altered or changed by preparing hybrid (composite) nanoparticles. Hybrid nanoparticles are defined as nanoparticles composed by two or more different materials of nanometer size. The fluids prepared with hybrid nanoparticles are known as hybrid nanofluids. The motivation for the preparation of hybrid nanofluids is to obtain further heat transfer enhancement with augmented thermal conductivity of these nanofluids. This review covers the synthesis of hybrid nanoparticles, preparation of hybrid nanofluids, thermal properties, heat transfer, friction factor and the available Nusselt number and friction factor correlations. The review also demonstrates that hybrid nanofluids are more effective heat transfer fluids than single nanoparticles based nanofluids or conventional fluids. Notwithstanding, full understanding of the mechanisms associated with heat transfer enhancement of hybrid nanofluids is still lacking and, consequently it is required a considerable research effort in this area.

The limitation of the conventional fluids to facilitate cooling/heating rates remains the primary basis for exploring alternative heat transfer nanofluids. Research efforts on nanofluids have evolved over the past two decades in establishing extensive literature. Several models for thermophysical properties were made available to characterize the behaviors of diverse individual nanofluids. However, lack of reasonable agreement between theory and experimental results has been a limiting factor for the development of a unified nanofluid model for thermal conductivity. Existing models for thermo-physical properties of nanofluids such as density, specific heat, thermal conductivity, and viscosity are critically surveyed and appropriate equations are extended for composite nanofluids. Consequently, based on reliable models identified predictions for thermal conductivity and viscosity for composite nanofluids are presented. Overall results show that existing thermophysical models for density and specific heat are valid for all water based oxide nanofluids for both single material and composites whereas models for thermal conductivity and viscosity show selective response but have the versatility for predicting the behavior of single and composite nanofluids within acceptable deviation.

The objective of the present work is to evaluate the experimental convective heat transfer coefficient and friction factor of the nanofluids flowing through a copper tube under a uniform heat flux of 7962 W/m2. Water-based stable fly ash and fly ash– Cu (80:20% by vol.) hybrid nanofluids were used as working fluids in the concentration range of 0.5 to 2.0 vol%. Experiments in the Reynolds number range of 6800 to 45,200 were performed at fluid inlet temperatures in the temperature range of 30 to 60 °C. The findings suggest that compared to water and fly ash nanofluid, thermal conductivity, viscosity, and the heat transfer rate of hybrid nanofluid is higher. At fluid inlet temperature of 60 °C, the maximum Nusselt number augmentation for fly ash-Cu hybrid nanofluid is 15.6% and 93.5% was observed at a concentration of 2.0% compared to fly ash nanofluid and water, respectively. A maximum thermal performance factor of 1.65 and 1.87 is observed for fly ash and hybrid nanofluid respectively at 60 °C with a 2.0% volume concentration. Correlations for evaluating the Nusselt number and friction factor of hybrid nanofluid were developed with the experimental data.

The article presents the heat transfer coefficient and the friction factor for the flow of water-base fly ash nanofluid in the concentration range of 0.5 to 2.0 vol%. Experiments are undertaken for flow in a horizontal copper tube subject to uniform heat flux in the Reynolds number range of 7000 to 45,200, for inlet fluid temperatures of 30, 45, and 60°C. The results revealed that in contrast to base fluid, nanofluids exhibit greater heat transfer coefficients which increase with concentration and fluid inlet temperatures due to augmentation in nanofluid thermal conductivity. The maximum amplification in Nusselt number and pressure drop of 67.4% and 11.9% are observed with 2% nanofluid concentration as compared to base liquid, for an inlet fluid temperature of 60°C and 30°C respectively. The values of Efficiency Index (EI) are evaluated for different concentrations and inlet fluid temperatures. Correlations are reported based on the experimental data for the estimation of dynamic viscosity, thermal conductivity, Nusselt number, and the friction factor of fly ash nanofluid.

In the present work, medium density fiberboard (MDF) panels were produced using multiwalled carbon nanotubes (MWCNT) reinforced urea formaldehyde resin. Response surface methodology was employed to optimize the relationship between the three variables, viz. pressing time, percentage of UF resin and percentage of MWCNT, used in the fabrication of MDF, and the influence of variables on the internal bonding (IB) and modulus of rupture (MOR) was studied. The optimum conditions based on the IB strength were determined as 8.18 % of UF resin, pressing time of 232 s, and MWCNT of 3.5 %. Similarly, the optimized conditions for MOR are also reported in this paper.

Nanofluids as a new coolant have overcome the limitations in thermal performance faced by conventional fluids such as water, ethylene glycol (EG) and oil based fluids. The objective of the study is to investigate the properties and heat transfer performance of TiO2 nanofluids in water-EG mixture at different operating temperatures. The study is carried out through experimental determination on heat transfer coefficient of TiO2 nanofluids in a circular tube under turbulent flow. The thermal conductivity and viscosity measurements were undertaken for temperature in the range of 30–80 °C. The maximum enhancement of thermal conductivity achieved was 15.4% at 1.5 vol% concentration and temperature of 60 °C. The relative viscosities fluctuate at a range of 4.6–33.3% with variation of temperature. The Nusselt number showed an enhancement up to 22.8% and 28.9% for temperatures of 50 °C and 70 °C, respectively. The friction factor for the nanofluids is slightly increased with concentration. Thermal conductivity, viscosity and heat transfer coefficient of TiO2 nanofluid are strongly influenced by working temperature and concentration.

This paper introduces the historical background about the development of water based, ethylene glycol (EG) based and EG:water mixture nanofluids for the past 20 years. The primary consideration is to review the salient of research work related to EG:water mixture nanofluids and their applications. Nowadays, the fundamental studies of nanofluids are increasing rapidly for engineering applications. The determination of the forced convection heat transfer and pressure drop was reviewed for nanofluid flow in a tube. The experimental and numerical heat transfers of nanofluids were presented. A review of other relevant research studies is also provided. Substantial heat transfer literature has been studied on water based nanofluids used in the fundamental study for engineering applications. However, there are limited studies that use EG:water mixture nanofluids in evaluation of forced convection heat transfer. A number of research studies have been performed to investigate the transport properties of EG:water mixture nanofluids either in experimental or numerical approach. As the performance of EG:water mixture nanofluids could be verified through experimental studies, researchers have conducted the experimental works using several types of potential nanofluids. As a result, nanofluids have been used in certain engineering applications such as in automotive, transportation, cooling of electronics components, solar, and nuclear reactor coolant.

Nanofluid as a new brand of cooling fluid consisting of nanometer-sized particles dispersed in base fluid. In this study, the thermal conductivity and electrical conductivity of BioGlycol (BG)–water (W) mixed nanofluids containing Al 2 O 3 nanoparticles were studied. Nanofluids with 0.5–2.0% concentrations were prepared by the two-step method. The nanofluids demonstrated excellent stability over the temperature range of 30–80 °C after using the long term sonication process. Comparisons of the experimental data with many existing models illustrated that they do not display good agreement. Therefore, a new nonlinear model has been developed with 5% maximum deviation for the thermal conductivity of nanofluids as a function of temperature and volume concentration. The results of BG:W mixtures have displayed improvement in thermal performance of 7.5% in comparison with propylene glycol (PG):W in similar circumstances. The thermal conductivity of nanofluid increased as a function of volume concentration and temperature. The maximum thermal conductivity enhancement using 40:60% (BG:W) mixture ratio was twice as high as 60:40% in the same conditions. Electrical conductivity was observed to decrease as the volume concentration increased. Thermo-electrical conductivity ratio (TEC) has been evaluated theoretically based on thermal and electrical conductivity results.

The use of nanofluids is essential in heat transfer study due to its effective performance. The performance of nanofluids in mixture based fluids is yet to be explored hence; the study was carried out to provide a wider knowledge and information on heat transfer performance of TiO 2 nanofluids. The forced convection heat transfer is conducted at Reynolds number of 3000 to 24,000 under constant heat flux boundary conditions. The TiO 2 nanofluid is prepared at 0.5 to 1.5% volume concentration and the thermal conductivity and dynamic viscosity were measured for 30 to 70 °C. The heat transfer performance was evaluated at three different bulk temperatures for its heat transfer coefficient and friction factor; 30, 50 and 70 °C. The thermal conductivity and viscosity enhanced with the increase in volume concentration. The heat transfer performance for temperature at 30 °C experienced low enhancement compared to the base fluid when the nanofluid concentration was less than 1.2%. However, at temperatures of 50 and 70 °C for all volume concentrations, the heat transfer performance improved with a value of h ′ greater than 1. As the working temperature increased, the enhancement became more noticeable for higher concentrations. The friction factor of TiO 2 nanofluids is slightly increased with the increase of concentration at approximately 1.1 times of base fluid. The performance factor, h ′ of the TiO 2 nanofluids is significantly influenced by the thermal properties, concentration, temperature, and Reynolds number.

The determination of thermo-physical properties and especially thermal conductivity and viscosity were important for evaluating heat transfer coefficients either for single or two phase flow. The thermo-physical properties measurements and heat transfer observations were mostly obtained with nanoparticles above 10 nm. Various researchers measured and modelled for the determination of thermal conductivity and viscosity of nanofluids. Most of the investigators developed equations for the estimation of thermal conductivity and viscosity as a function of percentage volume concentration, temperature and sometimes with the consideration of particle size valid in their experimental range. Nanofluids are considered to have great potential for heat transfer enhancement and are applied in heat transfer processes. Many studies were carried out to investigate this phenomenon. The main aim of this study is to give a comprehensive review on the research progress on the enhancement of effective thermal conductivity and effective dynamic viscosity of nanofluids.

Nanofluids are a new class of engineered thermal fluids with enhanced thermal properties and heat transfer capabilities exceeding those of the base liquid. Studies related to the effect of temperature on the thermophysical and rheological properties of ethylene glycol and glycerol nanofluids have been documented in various articles. In this paper, the thermal and physio-chemical behavior of SiC nanofluid dispersed in glycerol and ethylene mixture of 60:40 wt.% ratio was determined. The influence of temperature on the p H, viscosity, electrical and thermal conductivity of nanofluid was undertaken for a maximum concentration of 1.0 vol.% in the temperature range of 15-75 o C. It was found that, the base liquid electrical conductivity and p H were unaffected by temperature; whereas the nanofluid electrical and thermal conductivity increased with temperature. The viscosity of the base liquid and nanofluid decreased significantly while the decrease in p H is not significant with temperature.

Emerging nanotechnology with solar collector technology has attracted the attention of researchers to enhance the performance of solar systems in order to develop efficient solar thermal systems for future sustainability. This paper chronologically reviews the various research works carried out on the performance enhancement of nanofluid-filled flat-plate solar collectors (FPCs). Gaps in the radiation exergy models and maximum exergy of FPCs, the importance of pressure drops in collector manifolds in exergy analysis, and the economics of nanofluid-laden FPCs have been addressed. The necessity of replacing currently used chemically derived glycol products with a renewable-based glycol has not been reported in the current literature thoroughly, but it is pondered in the current paper. Moreover, the thermophysical properties of all common metal and metal oxide nanoparticles utilized in various studies are collected in this paper for the first time and can be referred to quickly as a data source for future studies. The different classical empirical correlations for the estimation of specific heat, density, conductivity, and viscosity of reported nanofluids and base liquids, i.e., water and its mixture with glycols, are also tabulated as a quick reference. Brief insights on different performance criteria and the utilized models of heat transfer, energy efficiency, exergy efficiency, and economic calculation of nanofluid-based FPCs are extracted. Most importantly, a summary of the current progress in the field of nanofluid-charged FPCs is presented appropriately within two tables. The tables contain the status of the main parameters in different research works. Finally, gaps in the literature are addressed and mitigation approaches are suggested for the future sustainability of nanofluid-laden FPCs.

In previous scholarly studies, the water and ethylene glycol mixtures as base liquids have been considered in the ratio of 40:60 (60EGW), with specific investigations focusing on a nanofluid in the form of Silicon dioxide (SiO2) in relation to its thermo-physical properties, besides its nature of the heat transfer coefficients (HTC). In this study, the main aim lies in SiO2 heat transfer coefficient prediction. With the approach of computational fluid dynamics (CFD) considered, the experimental conditions constitute 40EGW. For SiO2 nanoparticles, their viscosity and thermal conductivity are experimentally assessed, having been dispersed in 60EGW and 40EGW. Also, the existing literature and experimental values are used to conduct regression analysis. With thermal features on the focus, there is also the formulation of correlations. Furthermore, there is the invocation of correlations in heat transfer coefficients and CFD simulations that target Al2O 3 and SiO 2 nanoparticles, with predictions entailing their dispersion in 40EGW and 60EGW base fluids. The inlet temperature is set at 60 to 80 °C, and it is at this stage that there is CFD simulation implementation. For the volume concentration, the ranges include 0.0 percent to 1.5 percent. The existing literature is relied upon relative to the validation of the coefficients of heat transfer, besides previously predicted nanofluids. From the results, compared to the case of 40EGW base fluid, there is 51 percent and 53 percent enhancement when the experimental conditions are set at 1.0 percent volume concentration, with temperatures being 80 °C. From the computational outcomes, Al2O3/40EGW nanofluids tend to be associated with significant heat transfer coefficients. Specifically, the enhancement of heat transfer for these materials stands at 52.9%. On the other hand, the enhancement of heat transfer when the base fluid of SiO2/40EGW is considered stands at 51.0%. These values are obtained when the experimental conditions are considered at 80 °C, as well as a volume concentration of 1.0%. Therefore, when aspects of heat transfer coefficients and thermal conductivity are considered, the superiority of 40EGW is confirmed. As such, the study confirms the impact of the base nanofluids set at 40EGW relative to the coefficients of heat transfer and also the thermal properties of materials.

This paper involves a numerical study of several water – ionic liquids mixtures and nanoparticle enhanced ionic liquids starting from a less studied ionic liquid: 1-Ethyl-3-methylimidazolium Methanesulfonate, [C2mim][CH3SO3]. The research start point was several previous published experimental results in regard to the water – ionic liquid mixtures and alumina based nanoparticle enhanced ionic liquids thermophysical properties. Consequently, all the considered fluids are completely described and can be successfully implemented in a numerical analysis using the single phase approach. The numerical analysis was performed in a cylindrical enclosure considering laminar steady state and results were collected in terms of Nusselt number, convective heat transfer coefficient, pressure drop and temperature on tube exit. Results were discussed in terms of heat transfer enhancement and pumping power requirement variation, as well as field synergy. Concluding, it can clearly say that mixing water with [C2mim][CH3SO3] ionic liquid it gets a decrease in laminar convective heat transfer coefficient, while adding nanoparticles the heat transfer is enhanced by maximum 50%, depending on the alumina mass concentration.

The solar flat plate collector operating under different convective modes has low efficiency for energy conversion. The energy absorbed by the working fluid in the collector system and its heat transfer characteristics vary with solar insolation and mass flow rate. The performance of the system is improved by reducing the losses from the collector. Various passive methods have been devised to aid energy absorption by the working fluid. Also, working fluids are modified using nanoparticles to improve the thermal properties of the fluid. In the present work, simulation and experimental studies are undertaken for pipe flow at constant heat flux boundary condition in the mixed convection mode. The working fluid at low Reynolds number in the mixed laminar flow range is undertaken with water in thermosyphon mode for different inclination angles of the tube. Local and average coefficients are determined experimentally and compared with theoretical values for water-based Al2O3 nanofluids. The results show an enhancement in heat transfer in the experimental range with Rayleigh number at higher inclinations of the collector tube for water and nanofluids.

This paper discuss the tool life and wear mechanism in the end-milling of AISI304 stainless steel using a TiN-coated carbide insert with water-soluble coolant and nanoparticle-based coolant (TiO2/EG). The cutting variables are cutting speed, feed rate, and axial depth. The end-milling operation using nanoparticle-based coolant (TiO2/EG) obtains a high tool life compared with the end-milling operation using water-soluble coolant. In general, the tool failure when milling with water-soluble coolant was flank wear, cracking, chipping, and fracture at a cutting distance of 720 mm, but the milling process with nanoparticle-based coolant (TiO2/EG) showed chipping and fracture at a cutting distance of 1200 mm. According to ISO 8688-2-1989 (E), the wear criterion for milling with water-soluble coolant is reached at an average cutting distance of 800 mm, but milling with nanoparticle-based coolant (TiO2/EG) reached the ISO 8688-2-1989 (E) wear criterion at a cutting distance of 1300 mm. The SEM and EDX spectra show that there are nanolayers of Ti nanoparticles from the nanofluid embedded in and filling the holes in the insert, forming a layer which acts as a thermal bridge for the cutting insert. Attrition and oxidation at the cutting edge were the main tool wear mechanisms present during the end-milling operation with nanoparticle-based coolant (TiO2/EG). An oxide layer formed during the oxidation wear which shielded the cutting tool from impact during the milling process.

Cities in Sub-Saharan Africa suffer from widespread disparities in water supply due to depletion in groundwater and global-warming-induced changes in weather patterns. The offset of water head from the design considerations of water pumping systems has increased energy requirements leading to worsening of the situation with respect to availability of energy and water. Consequently, highly capitalized water supply schemes, which have been designed to meet the demand, are underutilized leading to operational inefficiencies. Robust empirical equations can help detect inefficiencies in water pumping systems, and this paper discusses the equations which were developed by analysing data obtained from various water supply utilities facing water scarcity. These equations provide cost-benefit analysis for decision making in water utilities and can bring about energy efficiency in municipal pumping operations.

The properties such as viscosity, thermal conductivity, specific heat, and density of nanofluids have been determined by various investigators through experiments. An equation developed for specific heat and density employing the law of mixtures is observed to be valid when compared with the experimental data. However, the experimental data of viscosity and thermal conductivity reported by investigators are observed to vary by more than 25 % for certain nanofluids. Theoretical models for the estimation of properties are yet to be developed. The nanofluid properties are essential for the comparison of heat transfer enhancement capabilities. Equations are developed for the estimation of viscosity and thermal conductivity by Corcione and Sharma et al. These equations are flexible to determine the nanofluid properties for a wide range of operating parameters which can predict the experimental data of water-based nanofluids with a maximum deviation of 12 %.

Hot corrosion arises when metals are excited in the temperature range 700–900 °C in the existence of sulphate deposits, formed as a result of the reaction among sodium chloride and sulphur mixtures in the gas phase adjoining the metals. No alloy is resistant to hot corrosion occurrence indefinitely even though there are certain alloys that require a prolonged origination time at which the hot corrosion progression from the beginning stage to the circulation stage. Superalloys have been established for high-temperature applications. However, these alloys are not constantly able to meet both the high-temperature strength and high-temperature corrosion resistance simultaneously, so the need is to protect from hot corrosion. The high-temperature guarding system must meet numerous benchmarks, provide satisfactory environment resistance, be chemically and mechanically compatible with the substrate, be practically applicable, reliable and economically viable. This chapter briefly reviews the hot corrosion of some Ni- and Fe-base superalloys to recognise the occurrence. Extensive reviews on the hot corrosion of coatings have looked regularly since early 1970; the purpose of this chapter is not to repeat the published resources but relatively to emphasis on research developments and to point out some research forecasts.