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The Nusselt number, overall heat transfer, and convective heat transfer coefficients of glycerol-water-based Cu nanofluids flowing in a parallel flow double pipe heat exchanger are estimated using CFD analysis. Single-phase fluid approach technique is used in the analysis. Ansys 19.0 workbench was used to create the heat exchanger model. Heat transfer tests with nanofluids at three flow rates (680

In the present work, the thermal conductivity (TC) of stable water base fly ash and fly ash-Copper (80:20 vol.%) nanofluid was determined experimentally in the temperature range of 30–60 °C for the...

The heat transfer and flow characteristics of water-based fly ash nanofluid for concentrations of 0.1–1.5 vol.% that flow through a copper tube at an inlet fluid temperature of 303 K with constant heat flux boundary conditions are estimated numerically. Stability, viscosity, and thermal conductivity of fly ash nanofluid have been determined experimentally and compared with correlations available in the literature. STAR CCM + software was used to solve the governing equations using the finite volume method (FVM). Water and stable fly ash nanofluid were used as working fluids for the Reynolds number range of 4500–16,000. The Nusselt number and friction factor at 1.5% volume concentration are greater than the base fluid by 36% and 9.4%, respectively. The fly ash nanofluid showed a performance index ( $$\eta$$ ) value of more than 1 at all concentrations undertaken, indicating that the use of fly ash nanofluid in heat transfer applications is beneficial. The highest $$\eta$$ value is determined to be 1.5 approximately for a nanofluid concentration of 1.5 vol.%. The fly ash nanofluid exhibits enhanced heat transfer performance contrasted to SiO2 nanofluid. The utilization of fly ash particles for heat transfer enhancement can aid in the reduction of environmental pollution to a certain extent. Novel correlations are suggested for the estimation of fly ash nanofluid Nusselt number and friction factor.

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...

Dynamic viscosity of SiO2/22nm nanofluids prepared in a glycerine-water (30:70 by volume) mixture base liquid, referred to as GW70, is measured experimentally. Nanofluids with concentrations of 0.2, 0.6, and 1.0 percent are produced, and viscosity measurements are carried out at temperatures ranging from 20 to 80 oC using a LVDV-2T model Brookfield Viscometer. The particle size and elemental composition of nanoparticles are determined using FESEM and EDX. XRD images confirm the SiO2 peaks in the crystalline structure. The rheology of nanofluids is influenced by the nanoparticle’s concentration. In the experimental temperature and concentration range, nanofluids show Newtonian behavior. The viscosity of nanofluids enhanced as particle concentration increased and reduced as temperature increased. For 1.0 percent vol. concentration at 20oC, the maximum viscosity value is achieved, and for 0.2 percent vol. concentration at 80oC, the lowest viscosity value is observed. The viscosity of the glycerine-water base fluid was also determined at 20, 40, 60, and 80 degrees Celsius. The viscosity ratio of nanofluids to the base liquid is found to be more than one for all the nanofluids. This viscosity data is useful to estimate HTC of glycerine-water-based silica nanofluids.

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.

A numerical model has been developed for turbulent flow of hybrid nanofluids in a tube with wire coil inserts. The model was developed from van Driest eddy diffusivity equation. The model can be im...

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.

The hybrid nanofluids were used as absorber fluids in solar energy applications, which could further increase the efficiency of solar devices. The use of nanofluids in solar devices with the laminar and turbulent flow has received much attention. Presently, the effect of temperature and concentration on thermal conductivity and viscosity of fly ash-copper (80:20% by volume) hybrid nanofluid is investigated. The thermal conductivity and viscosity measurements were carried in the temperature range of 30–60 °C for a concentration range of 0–4.0 vol%. The nanoparticles and nanofluids were characterized by XRF, XRD, SEM, TEM, zeta potential, and DLS techniques. The maximum augmentation in the hybrid nanofluid's dynamic viscosity and thermal conductivity at a concentration of 4 vol% is 45.18% and 49.8%, respectively, at 30 and 60 °C. Correlations to estimate the hybrid nanofluid's dynamic viscosity and thermal conductivity have been proposed considering the results obtained from the present study. A radial basis function-based neural network is used to model nanofluids' effective thermal conductivity and relative viscosity. The outcomes of the experiments were used to calculate the Mouromtseff number and heat transfer efficiency for solar energy applications.

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.

The study is aimed to understand the heat transfer coefficient and thermal entropy generation analyses of plate heat exchanger by using water-based nanodiamond nanofluids. The experiments were conducted in the volume concentration range: 0 ≤ ϕ ≤ 1.0%, the Reynolds number range: 140 ≤ Re ≤ 610, the mass flow rate range: 0.05 ≤ m ≤ 0.183 kg / s , and the Peclet number range from 895.78 ≤ Pe ≤ 3882.72, respectively. The effect of Reynolds number, Peclet number and particle volume loadings of nanodiamond nanofluids on heat transfer characteristics and entropy generation has been investigated. Water and nanodiamond nanofluids were considered as hot and cold medium in the plate heat exchanger, respectively, for the experimental study. The study reveals considerable augmentation in heat transfer coefficient and Nusselt number with an increase of nanofluid particle loadings. The study showed 32.50%, 55.47%, 35.11%, 22.80%, and 18.93% enhancements in overall heat transfer coefficient, heat transfer coefficient, Nusselt number, pressure drop and pumping power compared to base fluid at a Reynolds number of 526.37 at ϕ = 1.0%. Improved effectiveness, number of transfer units and exergy efficiency of 14.41%, 32.81% and 19.72% was observed at ϕ = 1.0% and at a Reynolds number of 526.37 against base fluid data. The thermal entropy and friction entropy generation was showed decreasing and increasing trends respectively, in the measured particle volume loadings. The Bejan number and entropy generation number demonstrated the roles of heat transfer and friction factor in the entropy generation. From the experimental results a new Nusselt number and friction factor correlations were proposed.

The purpose of the current research work is to investigate the various properties like thermal conductivity, stability and viscosity of copper and a mixture of fly ash-Copper (FA:Cu) nanoparticles (NP) suspended in water. The research experiments were conducted for a concentration of 1.0 vol% of FA:Cu hybrid nanofluid (HNF) with various mixture ratios. The measurements of thermal conductivity and viscosity were performed in the 30–60 °C temperature range. The highest thermal conductivity and viscosity values for HNF with a mixture ratio of 20:80 were obtained with a maximum amplification exceeding 83.2% and 65% than the base fluid, respectively. The properties enhancement ratio (PER) reveals that HNF with 1.0 vol% concentration enhances heat transfer for all defined mixture ratios in the reported research work. Finally, the predictability potential of an ensemble-based machine learning technique called Boosted Regression Tree (BRT), based on nanofluids temperature (T) and mixture ratio (R), were compared with the classical regression approach to simulate the thermo-physical properties of HNF. The outcomes of the BRT model in terms of (r(viscosity) = 0.9953 and r(thermal conductivity) = 0.9991) superior to the regression method with (r(viscosity) = 0.9695 and r(thermal conductivity) = 0.9539) over the viscosity and thermal conductivity prediction process.

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.

Convective and overall heat transfer coefficients of SiO2 nanofluid flowing in a concentric DTHE are determined experimentally. The tests are carried out in the 8002/22nm nanofluids prepared in 0.2, 0.6 and 1.0% volume concentrations in 30:70 ratio glycerol-water mixture base liquid. The thermal and physical properties of silica nanofluids are determined in the range of 20-80°C. Viscosity, thermal conductivity, and density of nanofluids increased with particle concentration whereas specific heat decreased. Thermal conductivity and specific heat of nanofluids increased with temperature while viscosity and density decreased. Heat transfer experiments are conducted using nanofluids at a bulk temperature of 35°C in a laminar developing flow region. Overall heat transfer coefficient and convective HTC of 1.0% silica nanofluids are increased by 21.2 and 36.3% compared to base liquid.

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.

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.

From a regression analysis perspective, this paper focused on literature about TiO2 nano particles. The particles on focus entailed those that had been suspended in ethylene glycol and water – at a ratio of 60:40. Indeed, regression analysis has gained application in contexts such as the turbulent Reynolds number, especially with the aim of establishing the impact of the ratio of the base fluid on heat transfer coefficients, as well as the target materials’ thermal properties. From the findings, this study infers that when the water-ethylene glycol mixture is used at a ratio of 60:40, the rate of heat transfer is higher than that which is obtained when water is used solely. Additional findings established from the examination of the impact of material concentration and temperature on the rate of nanofluids’ heat transfer suggested that as temperature increases, the rate of heat transfer decreases. However, it was noted that an increase in concentration exhibits a positive correlation with the nanofluids’ rate of heat transfer whereby an increase in the former parameter (concentration) leads to an increase in the latter (rate of nanofluids heat transfer).

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 current numerical study is aimed to examine the forced convection heat transfer of fly ash-Copper (80:20% by volume) water-based hybrid nanofluids flowing in a horizontal circular copper tube under a constant heat flux of 7962W/m2 using STAR CCM+ software. The volume concentrations of 0.5% and 1% are considered for the analysis within the Reynolds number range of 6900-26500. The findings show that the heat transfer coefficient and the Nusselt number of hybrid nanofluid at a concentration of 1 vol.% are increased by about 66.0% and 36.67% compared to that of water.

STAR CCM+ software is used to investigate the forced convection heat transfer of fly ash/Water nanofluids flowing through a horizontal circular tube in the turbulent flow regime under the constant heat flux of 707 W/m2. The volume concentrations of nanofluid are 0.3, 0.5, 1.0, and 1.5 vol. %, used in this analysis. The results revealed that both the Reynolds number and concentration intensify the Nusselt number of fly ash nanofluids. The highest heat transfer coefficient augmentation is about ∼60% observed at 1.5% concentration in comparison to the water.

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.

A numerical model for determining the characteristics of flow and heat has been presented by modifying the eddy diffusivity equation of Sarma et al. The experimental data of thermo-physical properties determined using spherical particles in a wide range of concentration, particle size, materials and operating temperatures are available in the literature. The numerical analysis employed equations, which were developed using the experimental data of thermo-physical properties, friction factor and Nusselt number. Based on the agreement of the numerical results with the experimental data, the influence of concentration and temperature on the turbulent characteristics is presented. It is observed that SiO2 nanofluid attained higher velocity and lower eddy diffusivity compared to Cu nanofluid at a concentration. The temperature gradient increases with concentration and decreases with temperature.

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.