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Cooling channel (CC) design is an effective measure to improve the internal thermal management of proton exchange membrane fuel cells (PEMFC). In this paper, a new elliptical dimple (EDC) cooling channel structure is proposed. The heat transfer and flow characteristics of EDC, circular dimpled cooling channel (CDC), and smooth cooling channel (SC) are compared by numerical simulation method, and the influence of elliptical dimple structural parameters on their performance is discussed. The serpentine CC with elliptical dimples is further compared with the traditional serpentine CC. The results indicate that the EDC is more effective than the other two types due to the narrow surface of the elliptical dimple, which enhances fluid flow and creates a region at the trailing edge of the vortex that promotes heat exchange. It is worth noting that lengthening the elliptical dimple leads to reduced performance, while elongating it initially improves but eventually decreases performance. This study found that the EDC with an elliptical dimple of 0.1 mm depth and 0.6 mm length outperformed the SC, resulting in a 10.6% improvement. Furthermore, the elliptical dimple serpentine cooling channel was found to enhance heat transfer and reduce pressure loss. [ABSTRACT FROM AUTHOR]

Active and passive cooling are the two possible methods for removing heat. An active cooling system is the one that involves the use of energy as opposed to passive cooling that uses no energy. Passive cooling methods are cost effective and more reliable than active cooling due to the absence of moving parts. Microchannel heat sink is one of high-tech devices that have widely considered passive cooling methods especially for electronics cooling. In this paper, the use of passive cooling methods in microchannel heat sink is comprehensively discussed. This paper also present the effects of some important parameters such as the type of channel types, surface roughness, fluid additives, and Reynolds number on the rate of heat transfer in microchannel heat sink. Finally, the conclusions and important summaries were presented according to the data collected. [ABSTRACT FROM AUTHOR]

In this article, turbulent flow characteristic of nanofluids is thoroughly reviewed. Turbulent flows have unique characteristics and are preferred in many industrial applications. Therefore, this paper reviews different techniques used to enhance heat transfer using nanofluids within turbulent regime. This paper also presents the effects of some important parameters such as nanoparticle type, nanoparticles concentration, and Reynolds number on heat transfer rate. Studies on numerical techniques are also discussed. Finally, the conclusions and important summaries are presented according to the data collected. [ABSTRACT FROM AUTHOR]

This paper is a continuation of the authors' previous work on the thermophysical properties, heat transfer, and pressure drop of nanofluids [Experimental Thermal and Fluid Science 52 (2014) 68–78]. In this paper, an experimental study is carried out to study the turbulent flow of COOH-functionalized multi-walled carbon nanotubes/water nanofluid flowing through a double tube heat exchanger. For this purpose, first, the thermophysical properties of the nanofluid, including the thermal conductivity and dynamic viscosity, have been measured at various temperatures and concentrations. Using the measured data, new correlations as a function of temperature and concentration are presented to predict the thermophysical properties. In the next step, the effects of low volume fractions of the nanofluid (from 0.05% to 1%) on the heat transfer rate are studied at the Reynolds numbers between 5000 and 27,000. The experimental results reveal that with increasing the nanofluid concentration, the heat transfer coefficient and thermal performance factor increase. On average, a 78% increase in heat transfer coefficient, a 36.5% increase in the average Nusselt number, and a 27.3% penalty in the pressure drop are recorded for the highest concentration of MWCNTs in water. [ABSTRACT FROM AUTHOR]

Comprehensive research work on heat transfer in heat pipe using traditional working fluids has been carried out over the past decade. Heat transfer in heat pipes using suspensions of nanometer-sized solid particles in base fluids have been experimentally and theoretically investigated in recent years by various researchers across the world. The suspended nanoparticles effectively enhance heat transfer characteristics and the transport properties of base fluids in heat pipes. The objective of this paper is to present an overview of literature dealing with recent developments in the study of heat transfer using nanofluids in heat pipes and some important inferences from the various papers are also highlighted. It also discusses the mechanism of heat transfer enhancement or degradation, the existing problems for various heat pipes utilizing nanofluids, and explores the possible application prospects. [ABSTRACT FROM AUTHOR]

Abstract: Nanofluids attract researchers in many ways for their enhanced heat transfer properties. Nanorefrigerant is one kind of nanofluids. It has better heat transfer performance than traditional refrigerants. Thermal conductivity, viscosity and density are the basic thermophysical properties that must be analyzed before performance analysis. This paper presents a comprehensive review of nucleate pool boiling, flow boiling, condensation and two-phase flow of refrigerant-based nanofluids. The effects of nanolubricants on boiling and two-phase flow phenomena are presented as well. Furthermore, studies of applications and preparation of refrigerant-based nanofluids are presented. For the limited studies done so far, there are some controversies from one study to another. Based on results available in the literatures, it has been found that nanorefrigerants have a much higher and strongly temperature-dependent thermal conductivity at very low particle concentrations than conventional refrigerant. This can be considered as one of the key parameters for enhanced performance for refrigeration and air conditioning systems. Because of its superior thermal performances, latest up to date literatures on this property has been summarized and presented in this paper as well. [Copyright &y& Elsevier]

Abstract: In this paper, the problem of steady two-dimensional magnetohydrodynamic (MHD) stagnation-point flow and heat transfer, with thermal radiation, of a nanofluid past a shrinking sheet is investigated numerically. Both the effects of Brownian motion and thermophoresis are considered simultaneously. A similarity transformation is used to transform the governing partial differential equations to a system of nonlinear ordinary differential equations which are solved numerically using a shooting technique. A similarity solution is presented which depends on the magnetic parameter (M), radiation parameter (R), Brownian motion number (Nb), thermophoresis number (Nt), Prandtl number (Pr), Lewis number (Le) and the ratio of the rate constants of the shrinking velocity to the free stream velocity (α). Interesting solution behavior is observed with multiple solution branches for certain parameter domain. The results of the present paper show that the velocity, temperature, the wall shear stress, the Nusselt number and the Sherwood number are strongly influenced by the magnetic parameter. A comparative study between the previously published results and the present results for a special case is found to be in good agreement. [Copyright &y& Elsevier]

Abstract: In this paper, different types of entropy generations in the circular shaped microchannel and minichannel are discussed analytically using different types of nanoparticles and base fluids. In this analysis, Copper (Cu), alumina (Al2O3 ) as the nanoparticle and H2O, ethylene glycol (EG) as the base fluids were used. The volume fractions of the nanoparticles were varied from 2% to 6%. In this paper, the irreversibility or entropy generation analysis as the function of entropy generation ratio, thermal entropy generation rate and fluid friction entropy generation rate for these types of nanofluids in turbulent flow condition have been analyzed using available correlations. Cu–H2O nanofluid showed the highest decreasing entropy generation rate ratio (36%) compared to these nanofluids flow through the microchannel at 6vol.%. The higher thermal conductivity of H2O causes to generate much lower thermal entropy generation rate compared to the EG base fluid. The fluid friction entropy generation rate decreases fruitfully by the increasing of volume fraction of the nanoparticles. Cu–H2O and Cu–EG nanofluid gave the maximum decreasing rates of the fluid friction entropy generation rate are 38% and 35% respectively at 6% volume fraction of the nanoparticles. Smaller diameter showed less entropy generation in case of all nanofluids. [Copyright &y& Elsevier]

In view of the fact that thermocapillary convection is an important heat transfer mechanism in nucleate boiling, and nanofluids is used to be heat transfer medium extensively. The present paper reports the numerical investigation of nanofluids thermocapillary convection around a gas bubble in a cavity, and the effects of nanoparticles volume fraction and size on flow characteristics, heat transfer performance and entropy generation are studied. The results show that, with more nanoparticles add to base fluid can enhance the heat transfer performance of gas bubble thermocapillary convection, the convective intensity is reduced, and the local entropy generation decreases and its distribution becomes more uniform. However, with larger nanoparticles diameter the results are just the opposite, namely, the heat transfer performance is weakened, the convective intensity is enhanced and the total entropy generation increases and its distribution becomes more nonuniform. These findings are of significance for the heat transfer enhancement in nanofluid boiling heat transfer. [ABSTRACT FROM AUTHOR]

Abstract This paper deals with heat transfer and fluid flow of natural convection in enclosures (square enclosure and enclosures with concave/convex walls) filled with water based Cu, and subjected to a constant imposed wall temperature. The governing equations of momentum and energy are formulated using the dimensionless form of transport equations in bipolar coordinates for a laminar two-dimensional incompressible and Newtonian flow which is expressed in terms of stream-function, vorticity and temperature. The resulting equations are numerically solved using the finite volume method (FVM) implemented in an in house-built computer code. The key parameters governing the problem are the Rayleigh number up to 105, the Prandtl number of 6.2 and nanoparticles' volume fraction from 0 to 0.2. The relevant results are presented in terms of isotherms and streamlines. It is found that the heat transfer increases with nanoparticles' volume fraction for the entire range of Rayleigh number considered. Besides this, heat transfer in the square enclosure remains better than for the other enclosures with curved walls. Highlights • Use of bi-polar coordinates. • Rise of heat transfer with nanoparticles' volume fraction for the Rayleigh number range considered. • The square cavity exhibits the best heat transfer regardless of Ra and ϕ. • Cavity B involves a lower heat transfer (lowest Nu). • The average Nusselt number's sensitivity to the walls' shape (straight or curved). [ABSTRACT FROM AUTHOR]

Abstract Ionanofluids (ionic liquid-based nanofluids) as newly introduced types of nanofluids with promising potential for heat transfer and thermal storage applications are created through complex dispersion of ultrafine nanometer-sized particles in ionic liquids. As innovative agents for development of energy sustainability, ionanofluids are widely employed in some applications, i.e., solar panels, catalysts, heat insulators and so forth. Non-flammability and non-volatility features of ionic liquids, make them applicable as green working fluids for any chemical processes. In the present paper, an experimental investigation was conducted on some thermophysical properties (viscosity, electrical conductivity and surface tension) of graphene based ionanofluid as main effective parameters in performance analysis. For this purpose, ionanofluid was prepared at three levels of weight fractions (1%, 2% and 3%) by adding and dispersing polycarboxylate functionalized graphene nanoplatelets (GNPs) in BMIM-PF 6 (1-Butyl-3-methylimidazolium hexafluorophosphate) with 98 + % purity as the base fluid. The experimental data was acquired within the temperature range of 293.15 to 333.15 K and at atmospheric pressure (~101 kPa). The results show that the viscosity of ionanofluid decreases with enhancement of temperature and nanoparticle concentration. On the other hand, electrical conductivity of ionanofluid augments as temperature and particle loading increase. For instance, EC at 1% wt. nanoparticles and 303.15 K enhances around 64% compared to the pure IL. Surface tension of the ionanofluids was also determined experimentally as a function of temperature for different mass loadings of nanoparticles. The results reveal that surface tension of ionanofluids decreases slightly as temperature enhances and it reduces with enhancement of nanoparticle fraction as well. [ABSTRACT FROM AUTHOR]

In this paper, an experimental and numerical study was conducted to evaluate the impacts of momentum and thermal diffusivity comparing to the thermal conductivity of various types of nanofluids on turbulent forced convection heat transfer. 1%, 2%, and 3% volumetric concentrations of different nanofluids such as Al 2 O 3 -DW, SiO 2 -DW, and Cu-DW were considered in this study and their properties were evaluated numerically at the flow inlet temperature of 30 °C. The experimental works were conducted with distilled water as a working fluid to validate the 2-D numerical model. A two-dimensional domain was constructed using ANSYS-Fluent package, and the standard k–ε turbulence model was employed to solve the continuity, momentum, and energy equations. The flow was maintained in the Reynolds range between 6000 and 12,000, and the data obtained experimentally were validated by results from empirical correlations. The numerical solutions for the average Nusselt number and pressure drop presents a good agreement with the experimental results as the average error was less than 5% for both the cases of heat transfer and pressure loss data. The results showed that Al 2 O 3 -DW nanofluid has the best enhancement in convection heat transfer coefficient compared with the DW and other nanofluids of the same concentration while Cu-DW nanofluids shown the lowest enhancement though it shown the highest value of thermal conductivity. Also, the results showed that the product of kinematic and dynamic viscosities had the greatest effect on pressure drop in the fluid domain. [ABSTRACT FROM AUTHOR]

In this paper, the convective heat transfer and flow characteristics of nanofluids consisting of distilled water and 0.25, 0.5 wt% and 1 wt% Al 2 O 3 nanoparticles were studied experimentally and compared to predicted results using computational fluid dynamics (CFD) that using laminar model was performed to examine the heat transfer characteristics. The Al 2 O 3 nanoparicles with a nominal diameter of 40 nm are dispersed in distilled water to form stable suspensions containing various kind of volume concentrations of nanoparticles. For the even dispersion of the nanoparticles in the base liquid, ultrasound was applied for 3 h. The nanoparticle dispersion on alumina concentration was measured using UV spectroscopy. Thermal conductivities of nanofluid solutions are measured by the transient hot wire method. Heat transfer characteristics were investigated by changing pressure pulsation at each concentration. Finally, calculated heat transfer characteristics results using CFD are compared to experimental results and discussed successfully. Results indicate that the heat transfer coefficient and Nusselt number increase with increasing the Reynolds number and it is also seen that the Prandtl number is getting down when the concentration of nanofluids enlarge and showed the equation by the linear method of the result value. [ABSTRACT FROM AUTHOR]

Presented research paper is an investigation of water, paraffin and ethylene glycol based Al 2 O 3 nanofluid. Heat transfer coefficient is measured using shell and tube heat exchanger under the conditions of fully developed laminar and turbulent flow. Concentration of nanoparticles in the respective base fluids was varied from 0.01 vol% to 0.08 vol% in the step of 0.1%. Nanofluids were used as the working fluid and sent to tubular side. The effects of Reynold's number and concentration of nanoparticles in nanofluid on heat transfer characteristics were studied. A significant enhancement in heat transfer coefficient and thermal conductivity of nanofluid over base fluid is found in the study. As the concentration of nanoparticles was increased, heat transfer coefficient was also improved marginally. At greater turbulence, the improvement in the heat transfer coefficient of nanofluid over base fluid was found to be more than that at lower turbulence. This is due to homogeneous distribution of nanoparticles in a base fluid at higher temperatures was achieved. The various factors that were considered in the characterization of nanofluid heat transfer coefficients are: sonication time, temperature, pressure difference, base fluid (water, paraffin and EG). Pressure drop in case of nanofluid was higher than base fluid in the turbulent regime; however, no significant change was observed in the laminar region. [ABSTRACT FROM AUTHOR]

The heat transfer and flow of nanofluids in microchannel heat sink is usually numerically investigated by the single-phase model. The thermal conductivity and viscosity of nanofluids are calculated in the whole computational region because the single-phase model, assumes the nanofluids is static and nanoparticles concentration is uniform. However for the actual forced flow process, the concentration distribution of the nanofluids is not uniform. So the thermal properties of the nanofluids vary within different computational regions. With the increase of the velocity of the nanofluids, the deviation between the prediction of single-phase model and experimental results increases. In this paper, a new simulation method is proposed to consider the inhomogeneous and dynamic thermophysical properties of the nanofluids by obtaining the nonuniformly distributed nanoparticle concentration in each numerical cell. At the same time, it takes into account the following factors: the interactions between the nanoparticles, the solid wall and the base fluid, the axial conduction, the slip boundary conditions and fluid-solid coupling. The results show that the proposed numerical simulation method further improve the simulation accuracy for the forced flow and heat transfer process of nanofluids in the microchannel in a wider range. The effects of the nanoparticles concentration, Reynolds number and axial heat transfer on the thermophysical properties of the nanofluilds, the flow and heat transfer characteristics of a rectangular microchannels with hydraulic dimensions of 341 μm were analyzed using the proposed simulation model. The main results are as follows: the nanoparticles are enriched at the near wall for the fully developed region; the nonuniformity of the nanofluilds thermal conductivity coefficient distribution at the channel cross section increases with the increase of the mass flow rate and the inlet centration; under the same Reynolds number, the higher the nanofluids concentration the better the heat transfer characteristics, but there is no linear relationship between the enhancement amplitude and concentration; the heat transfer coefficient of nanofluid with 1% and 2% alumina nanoparticles concentration is about 5.86% and 8.49% higher than that of deionized water, respectively; the axial conduction effect cannot be ignored for the microchannel, which significantly affects the inlet and outlet region of the microchannel especially when the Reynolds number is low. The nanofluilds temperature in the microchannel increases with the curve and does not match the conventional linear growth hypothesis. [ABSTRACT FROM AUTHOR]

In order to avoid the costs of experimental evaluations, soft computing methods like artificial neural network (ANN) and genetic algorithm have remarkably grabbed the attentions of investigators for predicting the hydrothermal characteristics of different types of nanofluids. In this paper, the implementation of ANN and genetic algorithm for modeling and multi-criteria optimizing the hydrothermal behavior of SiO 2 /water nanofluid has been investigated. Using the data obtained from the experimental analysis, an ANN model is developed to estimate the pressure drop and Nusselt number as a function of volume concentration, Reynolds number, and inlet temperature. Different network structures were assessed and it has been achieved that a network with 2 hidden layers and 6 neurons in every layer provides the most accurate prediction. It is revealed that the developed network is satisfactorily accurate to determine the Nusselt number and pressure drop of SiO 2 /water nanofluid compared to the empirical correlations. To optimize the hydrothermal behavior of the nanofluid (i.e. to find the optimal cases with highest Nusselt number and the relatively least pressure drop), the genetic algorithm coupled with compromise programming approach has been implemented considering decision maker's attitude. [ABSTRACT FROM AUTHOR]

In the present work, the effect of channel cross section on the heat transfer performance of an oblique finned micro-channel heat sink was investigated. Water and Al 2 O 3 /water nanofluid of volume fraction 0.25% were used as a coolant. The oblique finned microchannels are designed with three channel cross-sections namely square, semicircle and trapezoidal. The primary work of this paper is to study the heat transfer and hydrodynamic characteristics in the oblique finned microchannel. The experimental setup and procedure are validated using water as coolant in a micro-channel heat sink. Heat transfer and flow characteristics are examined for three cross-sections of varying mass flux. The trapezoidal channel cross-section increases the considerable heat transfer rate improvement for both water and nanofluid by 3.133% and 5.878% compared to square and semicircle cross section. Also, the pressure drop is higher in the trapezoidal cross-section over the square and semicircle cross section. This is due to increase in friction loss of trapezoidal cross section. The results indicate that trapezoidal cross-section oblique finned micro-channel is more suitable for heat transfer in the electronic cooling application. [ABSTRACT FROM AUTHOR]

The heat transfer performance of a system can be improved using a combination of passive methods, namely nanofluids and various types of tube geometries. These methods can help enhance the heat transfer coefficient and consequently reduce the weight of the system. In this paper, the effect of tube geometry and nanofluids towards the heat transfer performance in the numerical system is reviewed. The forced convective heat transfer performance, friction factor and wall shear stress are studied for nanofluid flow in different tube geometries. The thermo-physical properties such as density, specific heat, viscosity and thermal conductivity are reviewed for the determination of nanofluid heat transfer numerically. Various researchers had measured and modelled for the determination of thermal conductivity and viscosity of nanofluids. However, the density and specific heat of nanofluids can be estimated with the mixture relations. The different tube geometries in simulation work are analyzed namely circular tube, circular tube with insert, flat tube and horizontal tube. It was observed that the circular tube with insert provides the highest heat transfer coefficient and wall shear stress. Meanwhile, the flat tube has greater heat transfer coefficient with a higher friction factor compared to the circular tube. [ABSTRACT FROM AUTHOR]

The hybrid nanofluid has been thriving among researchers due to its potential to improve heat transfer performance. Therefore, various studies on heat transfer properties need to be carried out to provide a better understanding on hybrid nanofluid performance. In this paper, the experimental work is focused on the thermal conductivity and dynamic viscosity of TiO 2 -SiO 2 nanofluids in a mixture of water and ethylene glycol (EG) with volume ratio of 60:40. The stable suspension of TiO 2 -SiO 2 prepared at volume concentrations of 0.5 to 3.0%. The measurements of thermal conductivity and dynamic viscosity were performed at a temperature range of 30 to 80 °C by using KD2 Pro Thermal Properties Analyser and Brookfield LVDV III Ultra Rheometer, respectively. The thermal conductivity of TiO 2 -SiO 2 nanofluids was improved by increasing the volume concentration and temperature with 22.8% maximum enhancement. Besides, the viscosity of TiO 2 -SiO 2 nanofluids showed evidence of being influenced by nanofluid concentration and temperature. Additionally, the TiO 2 -SiO 2 nanofluids behaved as a Newtonian fluid for volume concentration up to 3.0%. The properties enhancement ratio suggested that TiO 2 -SiO 2 nanofluids will aid in heat transfer for concentrations of more than 1.5% and within the range of the temperature studied. A new correlation for thermal conductivity and dynamic viscosity of TiO 2 -SiO 2 nanofluids were developed and found to be precise. [ABSTRACT FROM AUTHOR]

The flow of 2-D cross fluid model with mass and heat transmission over a linearly stretched sheet is analyzed in this paper. Furthermore, we have expanded our study by considering the effects of MHD flow, stagnation point, double stratification, heat generation, radiation effect, nanofluid flow, activation energy and mass diffusion. This type of study has not being investigated previously in literature. The flow generating PDEs are altered into ODEs by deploying suitable transformations. The effects of the parameters involved, namely the Weissenberg number, magnetic field coefficient, Brownian motion coefficient, radiation parameter, Damkohler number, thermophoresis coefficient, Schmidt number, activation energy, heat generation parameter and temperature difference coefficient on the velocity, concentration and energy fields are thoroughly scrutinized. The problem is solved through numerical technique (BVP4c) on MATLAB. The outcomes reveal that the velocity curve upsurges for rising Weissenberg number and decreases due to magnetic parameter. The heat field improves for increasing behavior of the Brownian motion, thermophoresis, heat generation, thermal conductivity and radiation coefficient whereas reverse results are obtained due to Prandtl number and stratification parameter. The concentration improves due to thermophoresis parameter and diffusivity coefficient while reverse outcomes are noticed due to Schmidt number, Damkohler number, temperature difference parameter and Brownian motion parameter. [ABSTRACT FROM AUTHOR]

The thermal control subject of heat transference encompasses the generation, use, conversion, and transportation of thermal energy. Heat transference is critical in engineering and industrial industries such as food processing, food additive manufacturing, electronic cooling, microturbines, and so on. Because of the intriguing possibilities in sectors such as polymer manufacture, paper production, crystal glass manufacturing, and so on, academics all over the globe have attempted to investigate the influence of heat transmission on fluid past an expanding surface. We constructed a symmetric system relating extended Burgers' nanofluid (BNF) with Fourier's and Fick's laws in a symmetric stretchy slip as part of our investigation. The Cattaneo-Christov mass and heat diffusions principle has been considered. The Buongiorno occurrence is also utilized for the symmetric flowing of nanofluids (NFs) in the generalized Burger's fluid, according to the Cattaneo-Christov connection (CCC). For the numerical solution, using the similarity transformations, the control system that regulates partial differential equations (PDE) was turned into ordinary differential equations (ODE). Using the COMSOL program, the Galerkin finite element method (G-FEM) is utilized to generate mathematical results for non-linear equations. We observed greater temperature and concentration for Fourier-Fick's conditions as compared to revised Fourier-Fick's scenarios. The heat field is raised to produce the calculations of the current Biot quantity and generalized BNF factor. To receive results in the form of figures and tables, the parameter values must be between 0.1 ≤ β 1 ≤ 0.5, 0.2 ≤ β 2 ≤ 0.4, 0.2 ≤ β 3 ≤ 0.4, 0.2 ≤ β 4 ≤ 0.4, 0.1 ≤ M ≤ 1.2, 0.1 ≤ Nr ≤ 0.9, 0.1 ≤ λ ≤ 0.5, 0.2 ≤ K ≤ 1.6, 0.1 ≤ Rd ≤ 1, 0.1 ≤ λ T ≤ 0.3, 0.1 ≤ δ 1 ≤ 0.3, 0.1 ≤ E ≤ 1 and 0.1 ≤ Le ≤ 0.9. The G-FEM investigation of Burgers' nanofluid (BNF) in the presence of heat source, thermal radiative heat flux and Cattaneo-Christov mass and heat flux has not been investigated yet in the available literature. [ABSTRACT FROM AUTHOR]

The investigation of Maxwell fluid in rotating disk systems has been increased due to the many engineering applications in rotating objects. Maxwell fluids are incredibly significant in metal spinning, drilling muds, optical fibers, plastic polymers, hot rolling paper manufacture, and several more. The present analysis discovers the dynamics of MHD rotational stagnation point flow of Maxwell nanofluid of temperature-dependent viscosity towards a radially stretching rotating disk. Energy and concentration conservation laws are based upon the cross-diffusion effects (Soret- Dufour effects). Additionally, activation energy defined by the Arrhenius theory is utilized to visualize heat and mass transport behavior. By utilizing a similarity framework, the governing flow equations of partial derivative form are remodeled into the non-linear equations of ordinary derivative form. A Maple software built-in numerical algorithm BVP Midrich is executed for the integrating solution of the fundamental ODEs. From the current analysis, it is concluded that when the viscosity change in relation to temperature is of greater magnitude than the velocity of Maxwell nanofluid is decreased in all three directions. Additionally, an increment in activation energy E leads to an increment in Maxwell fluid concentration, and the higher reaction rate parameter R c minimizes the same. [ABSTRACT FROM AUTHOR]

The current paper applied dissipative particle dynamics (DPD) approach to investigate heat transfer within nanofluids. The DPD approach was applied to study natural convection in a differential heated enclosure by considering the viscosity and the thermal conductivity of the nanofluid to be dual function of temperature and volume fraction of nanoparticles. Experimental data for viscosity and thermal conductivity are incorporated in the current DPD model to mimic energy transport within nanofluids. This incorporation is done through the modification of the dissipative weighting function that appears in the dissipative force vector and the dissipative heat flux. For the entire range of Rayleigh number considered in this study, it was found that the DPD results show a deterioration in heat transfer in the enclosure due to the presence of nanoparticles for φ > 4%. However, some slight enhancement is shown to take place for small volume fraction of nanoparticles, φ ≤ 4%. The DPD results experienced some degree of compressibility at high values of Rayleigh number Ra ≥ 10 5 . [ABSTRACT FROM AUTHOR]

The aim of current paper consists in the fabrication, characterization and preparation of water based on SiC nanofluids and the experimental investigation of their thermo-physical properties. Thermal conductivity, viscosity and surface tension of SiC/water nanofluids were measured for two two weight concentrations of nanoparticles 0.5 and 1.0 wt% respectively, within the range 20 °C to 50 °C. Concerning the thermal-properties of studied nanofluids, the experimental results show that the thermal conductivity increases with the increasing both of the weight concentration of the nanoparticles and temperature. Also, the dynamic viscosity of the SiC/water nanofluids increases with increasing nanoparticles concentration and decreases with the increasing temperature. Furthermore, the surface tension of studied nanofluids increases with the increase of the weight concentrations of the nanoparticles, but the results show that at a concentration of the nanoparticles of 0.5 wt%, the surface tension was lower than the surface tension of the water, while at 1.0 wt% nanoparticles, the surface tension of the nanofluids was close to the surface tension of the water. Measurements were compared with experimental data available in literature and theoretical models. Finally, SiC/water nanofluids were used as working fluid inside of the two-phase closed thermosyphon in order to study of the heat transfer from point of view both of operating temperature and the nanoparticles concentration. [ABSTRACT FROM AUTHOR]

The natural convection heat transfer and entropy generation of Al 2 O 3 -water nanofluid, in a square cavity with inclination angle θ and the presence of a constant axial magnetic field B 0 are examined in this paper. The governing equations are solved numerically by finite volume method. Also an effective parameters analysis was performed by using of the Response Surface Methodology (RSM). The effects of the Rayleigh number (10 3 , 10 4 , 10 5 and 10 6 ), Hartmann number (0, 10, 30 and 50) and also inclination angles (0°, 30°, 60° and 90°) are investigated. It is observed that the mean Nusselt number and the total entropy generation increase when the Rayleigh number increases. It is also found that, regardless of the Ha parameter, by increasing of the inclination angles, the mean Nusselt number and entropy generation rate increase until inclination angle 30° and then they decrease. Also, for low Ra numbers, by increasing the Ha parameter, the mean Nusselt number increases until Ha = 10 and then decreases. The analysis showed that the sensitivity of the Nusselt number and the entropy generation to Ha parameter was too small, and as a result it was negligible. Also, the sensitivity of the mean Nusselt number and the entropy generation to inclination angle, θ, increases by increasing of this angle. It is also observed that the mean Nusselt number and the entropy generation were more sensitive to the inclination angle θ than the Ha parameter. [ABSTRACT FROM AUTHOR]

This paper presents numerical analysis on microchannel laminar heat transfer and fluid flow of nanoencapsulated phase change materials (NEPCM) - water slurry as coolant, with two different melting ranges, 5 °C and 20 °C. In this study n-Octadecane for NEPCM and water is used as base fluid. With the purpose of evaluating best thermal performance, NEPCM–water slurry was compared to Cu-water nanofluid. The diameter ratio of the micro-tube was D i / D o = 0.3/0.5 mm with a tube length L = 100 mm with fixed heat transfer rate Q = 2 W. NEPCM-water slurry and Cu-water nanofluid were considered with various volume concentrations ϕ = 1,3 and 5% and diameter of the particles d p = 36 nm. Two different approaches were used concerning fixed Re and pumping power Π, in terms of average heat transfer coefficient and maximum temperature of the substrate. The results revealed that NEPCM-water slurry, with melting range of 5 °C, presents better thermal performances than base fluid and NEPCM with melting range of 20 °C. Besides, Cu-water nanofluid has much higher heat transfer coefficient ( h ave ) and lower maximum temperature of substrate ( t max ) for all values of volume concentrations, in cases of both comparison criteria ( Re or Π). [ABSTRACT FROM AUTHOR]

Wavy plate-fins (WPFs) are commonly used in plate-fin heat exchangers in order to improve the performance and reduce the size. The purpose of this paper is to investigate the influences of using three passive heat transfer enhancement (HTE) techniques, namely perforations, winglets, and nanofluids, on heat transfer and flow specifications of the WPFs. The waviness aspect ratios are 0.33, 0.42, and 51, the diameter of the perforation is 5 mm, the width/height of the winglets is 5 mm, and Reynolds number changes from 3900 to 11,400. It is detected that due to the efficient mixing of the working fluid by the winglets, the heat transfer performance of the winged WPFs is always significantly superior to that of the other WPFs; at the same time, the friction factor of the winged WPFs is very high. Hence, an overall performance factor is defined to compare different HTE techniques at the same operating conditions. The maximum performance factor of 1.26 is obtained for the winged WPF compared to the typical WPF at the lowest Reynolds number and the highest waviness aspect ratio. Therefore, the winged WPF can be used as a high-quality interrupted surface in the fabrication of plate-fin heat exchangers. [ABSTRACT FROM AUTHOR]

In this paper, the performance of ethylene glycol and water based TiO 2 nanofluids as an automobile radiator coolant is determined experimentally. Forced convective heat transfer coefficient of TiO 2 nanofluids has been measured and compared with the data of base fluid in an automobile radiator. Nanofluids were prepared taking 40% ethylene glycol and 60% water with volume concentrations of 0.1%, 0.3% and 0.5% of TiO 2 nano powder. All the experiments were conducted in the range of Reynolds numbers from 4000 to 15,000. In all the experiments the nanofluids made to flow through the radiator tubes with elliptical cross section and airflows with constant speed in the crosswise direction in between the tubes of a tube bundle. Results demonstrate that increasing the fluid circulation rate can improve the heat transfer performance while the fluid inlet temperature to the radiator has little or no effect. Nanofluids investigated in the present work with low concentrations enhanced the heat transfer rate up to 37% in comparison with base fluid. The results of the investigation are presented graphically in terms of non-dimensional heat transfer coefficient as a function of volume concentration, temperature and flow rate. [ABSTRACT FROM AUTHOR]

Heat transfer characteristics of Fe 2 O 3 /water and Fe 2 O 3 /EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe 2 O 3 nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe 2 O 3 nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow. [ABSTRACT FROM AUTHOR]

The significance of the present work is that it is very useful in different fields of bio-engineering and engineering including magnetic drug targeting systems, magnetic hyperthymia, directing of magnetic drugs and etc. This paper explored the mechanical features of the magnetic dipole, activation energy and chemical reaction over the MHD flow of two-dimensional non-Newtonian Williamson Ferro-nanofluid under the stretched surface. The main aim of using the magnetic dipole effect in this problem is to control the momentum and thermal boundary layer thickness with the combining impact of nanofluid. As a result, the current approach is extremely valuable for controlling the thickness of thermal and momentum boundary layers. The thermal radiation and heat source/sink impacts are included in the heat equation for the calculation of heat transmission phenomena. The role of the gyrotactic microorganisms is discussed in the present analysis. The influence of Brownian motion and thermophoresis are also examined. The present mechanical system is formulated in the form of the higher-order PDEs and these nonlinear PDEs are relocated into the nonlinear higher-order ODEs by using the suitable similarity transformations. In the methodology section, for the solution of these highly nonlinear ODEs, the homotopic analysis scheme is employed. The effects of distinct flow parameters on the velocity, temperature, concentration and motile gyrotactic microorganism of the Williamson nanoliquid are scrutinized and discoursed in a graphical form. The following are some key outcomes from this analysis, it is predicted that the speed of the nanoliquid particles is lesser for nanoparticle volume fraction. Also, it is examined that the activation energy boosted the nanofluid concentration. Computation for streamline is performed in the present study. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, swirling flow boiling of a dilute nanofluid (water and 0.1 vol% Fe 3 O 4 ) in an annulus with a twisted fin on the outside of the inner wall in the presence of transverse magnetic gradient has been numerically investigated, using a two fluid model and a control volume technique. The results indicate that, in the boiling of swirling flow, the rate of the heat transfer increases. This phenomenon can be attributed to the effect of centrifugal force on the liquid phase flow and also reduction of the conductive sub-layer thickness that exists on the heated wall. The effects of improved surface wettability induced by nanoparticle deposition during the boiling process are accounted. The results demonstrate that the modified liquid property due to the existence of nanoparticles in the liquid has a negligible effect on the boiling heat transfer performance with dilute nanofluids while the improved surface wettability plays an important role and leads to reduction of the void fraction and consequently, an increase of critical heat flux. Applying a transverse magnetic field causes augmentation of the centrifugal force and results in increased flow turbulence. Furthermore, in the presence of the magnetic field due to magnetic force, the bubble departure diameter is reduced and bubble detachment occurs faster. Therefore, the critical heat flux will be increased. Swirling flow boiling in the presence of magnetic field is strongly suggested in devices requiring high heat transfer rates. [ABSTRACT FROM AUTHOR]

Nanofluids have gained significant attention in recent years due their great potential for heat transfer enhancement . The heat transfer of nanofluids can be numerically studied using a single-phase or two-phase approaches. The first assumes that the fluid phase and nanoparticles are in thermal equilibrium and move with the same velocity, while the second requires more computational effort but provides the possibility of understanding the behavior of both fluid phase and solid particles in the heat transfer mechanism. This paper reviews various computational approaches to predict fluid flow and heat transfer characteristics of nanofluids. The characteristics of single-phase and two-phase (volume of fluid, mixture, Eulerian–Lagrangian and Eulerian–Eulerian) approaches have been analyzed and discussed systematically. Latest development and recent researches related to the computational nanofluids are also given. [ABSTRACT FROM AUTHOR]

Recently, nanofluids have been studied extensively by the researchers as a result of the developments in nanotechnology. It is essential for researchers to know nanofluids' physical properties in order to make calculations regarding their specific research topics. Determination of viscosity issue is an actual one due to its common usage in heat transfer and thermodynamics. In this study, graphite particles are selected to have nanofluid mixture with its base fluid of pure water. Their volumetric concentrations are varied from 0 to 2% in pure water. Once the stabilized nanofluid is prepared by a sonicator and ultrasonic bath, viscosity is measured by a viscosity meter for the temperatures ranging from 20 °C to 60 °C. Validation of the experiments have been done by means of the comparison of them with the 32 empirical correlations in the literature. Then, Artificial Neural Network (ANN) analyses have been performed in order to have better empirical correlation than those in the literature. Furthermore, detailed information on the preparation nanofluids, measurement of viscosity, a list of measured data, numerical model by Matlab software, and alteration of viscosity with temperature and concentration have been given in the paper. It was concluded that viscosity correlations in the literature can predict different types of nanofluids' viscosity although they have been derived using specific type and diameter of nano particles and their base fluids. [ABSTRACT FROM AUTHOR]

In this work, a three-dimensional analysis is used to study the heat transfer and entropy generation inside a helically coiled tube-in-tube heat exchanger in laminar flow regime using two different types of nanofluids. Overall heat transfer coefficient, effectiveness, Nusselt number, and entropy generation of helically coiled tube-in-tube heat exchanger were investigated considering the nanoparticle volume concentrations between 0 and 2.0 vol.%. The mass flow rate of the nanofluid from the inner tube was kept and the mass flow rate of the water from the annulus was set at either half, full, or double the value. The present contribution is a companion paper of Huminic and Huminic [1]. The numerical results reveal that the use of nanofluids in a helically coiled tube-in-tube heat exchanger improves the heat transfer performances. Thus, the maximum effectiveness was 91% for 2% CuO nanoparticles and 80% for 2% TiO 2 nanoparticles. Also, the increase of nanoparticles volume concentration leads to the Nusselt number increase and the reduction of the entropy generation due heat transfer effects, the viscous effects to entropy generation being negligible. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement technologies play an important role in research and industrial fields; thus, they have been widely applied to many applications as in refrigeration, automotive, aerospace, and process industry. For example, heat transfer can be passively enhanced by increasing the thermal conductivity of the working fluids, adopting nanofluids, or actively by employing impinging jets. In this paper a numerical analysis on confined impinging slot jets working with pure water or water/Al 2 O 3 based nanofluids is presented. The flow is laminar and a constant uniform temperature is applied on the target surface. The single-phase model approach has been adopted in order to describe the nanofluid behavior and different particle volume concentrations have been considered. Moreover, simulations have been performed for different geometric ratios in order to take into account the confining effects and Reynolds numbers. The behavior of the system has been analyzed in terms of average and local convective heat transfer coefficient, Nusselt number, and required pumping power profiles. Correlations for stagnation point and average Nusselt number for 100 ≤ Re ≤ 400, 0% ≤ ϕ ≤ 5% and 4 ≤ H / W ≤ 10 are provided. [ABSTRACT FROM AUTHOR]

The mechanisms of heat transfer enhancement are used in many industrial applications. Several techniques have been promoted to enhance heat transfer rate and to decrease the size and cost of equipment especially the heat exchangers. In this paper, heat transfer coefficient and pressure drop for Al 2 O 3 /water nanofluid flow inside circumferential ribbed tubes with different rib dimensions have been experimentally and numerically studies. The nanoparticle size was set equal to 13 nm and the volume fractions from 0% to 3% were considered. The ribbed copper tubes tested in this investigation with inner diameter of 14.9 mm have the ranges: circumferential depth from 0.5 mm to 1.0 mm and axial pitch distance from 5 mm to 15 mm. The inlet temperature of turbulent nanofluid was 25 °C and the constant wall heat flux was 5,000 W/m 2 . Comparison of numerical data of ribbed tubes with plain tube shown that the heat transfer coefficient from 92% to 621% and friction factor from 25% to 241% compared to those obtained in smooth tube depending on the circumferential geometric parameters, mass velocity and thermal conductivity of the working fluid. [ABSTRACT FROM AUTHOR]

This paper focuses on designing an artificial neural network which can predict thermal conductivity and dynamic viscosity of ferromagnetic nanofluids from input experimental data including temperature, diameter of particles, and solid volume fraction. The experimental data were extracted and they were used as learning dataset to train the neural network. To find a proper architecture for network, an iteration method was used. Based on the results, there was no over-fitting in designed neural network and the neural network was able to track the data. ANN outputs showed that the maximum errors in predicting thermal conductivity and dynamic viscosity are 2% and 2.5%, respectively. Based on the ANN outputs, two sets of correlations for estimating the thermal conductivity and dynamic viscosity were presented. The comparisons between experimental data and the proposed correlations showed that the presented correlations were in an excellent agreement with experimental data. [ABSTRACT FROM AUTHOR]

In this paper, a numerical investigation on heat transfer performance and flow fields of different nanofluids flows through elliptic annulus in a laminar and turbulent flow regimes. The three-dimensional continuity, Navier–Stokes and energy equations are solved by using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of laminar and turbulent flow on heat transfer characteristics. This study evaluates the effects of four different types of nanoparticles, Al 2 O 3 , CuO, SiO 2 and ZnO, with different volume fractions (0.5–4%) and diameters (25–80 nm) under constant heat flux boundary condition using water as a base fluid were used. The Reynolds number of laminar flow was in the range of 200 ≤ Re ≤ 1500, while for turbulent flow it was in the range of 4000 ≤ Re ≤ 10,000. The results have shown that SiO 2 –water nanofluid has the highest Nusselt number, followed by ZnO–water, CuO–water, Al 2 O 3 –water, and lastly pure water. The Nusselt number for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nusselt number increases with Reynolds number. It is found that the glycerine–SiO 2 shows the best heat transfer enhancement compared with other tested base fluids. [ABSTRACT FROM AUTHOR]

In practice, nanofluids' thermal conductivity and viscosity are the most important parameters in engineering applications. Viscosity affects pumping performance. Theoretical viscosity correlations are widely used in numerical studies. However, existing correlations show an underestimation of the actual viscosity compared to the measurement results. Although many nanofluid viscosity correlations have been developed, there is no generally accepted correlation. This paper reviews the theoretical, numerical, and experimental viscosity correlations and proposes a new correlation based on an analysis of approximately 1200 experimental and 4000 theoretical data tested for about 50 types of nanofluids in the temperature range 273–333 K and particle diameters 2–300 nm. The studied volume fraction range for the nanofluids was up to 10%. Existing correlations take into account the impact of up to two to three parameters The new viscosity correlation is proposed to predict the effective viscosity of nanofluids based on regression analysis of theoretical and experimental viscosity results, and it considers several factors that significantly affect the effective viscosity of nanofluids, such as nanoparticle diameter, density, temperature, types of nanoparticles, and base fluid. [ABSTRACT FROM AUTHOR]

This paper presents novel treatments for the Ellis non-Newtonian nanofluids flow over a rotating cone in the presence of motile oxytactic microorganisms. These treatments are depending on solutions of the stress tensor equations at specific values of the power-law index α (α = 0,0.5,1, 2) and introducing the stress as expressions in terms of the velocity gradients. Here, four systems of the governing equations for each value of α are presented and the non-similar forms for these systems are obtained. An efficient finite difference method based on the Blottner technique is applied to solve the converted systems. Various important impacts are examined in these simulations such as, magnetic field, non-linear radiation, viscous dissipation, heat generation and Joule heating. Wide ranges of the non-similar parameters are considered, namely, 0 ≤ ξ ≤ 10, 0 ≤ η ≤ 35. The major results revealed that, the skin friction gets higher values at the Ellis case α = 2 while the Newtonian nanofluids α = 1 gives the highest heat transfer rate. Both the velocity and temperature gradients are diminishing as the bioconvection Rayleigh number is enhanced. [ABSTRACT FROM AUTHOR]

In this paper, the convective heat transfer of the heat transfer oil-copper oxide nanofluid flow in horizontal smooth and microfin tubes is investigated experimentally. Using a flow control system, the flow regime is always laminar and the wall temperature is constant by using a steam tank. Pure heat transfer oil and nanofluid with the weight concentrations of 0.5%, 1% and 1.5% are used as working fluids. The results are in good agreement with the classic correlations for the pure fluid flow. Based on the results, combination use of nanoparticles and the microfin tube leads to the heat transfer enhancement up to 230%, in comparison with the base fluid flow in the smooth tube. The results are useful in the prediction of the heat transfer rate and the pressure drop in nanofluid flows. [ABSTRACT FROM AUTHOR]

Synthesizing stable nanofluids with favourable thermal properties that can cater to practical applications is a challenge over the past few years. This paper presents the preparation and analyzes the thermal efficiency of the novel nanofluid prepared by the suspension of nanocrystalline Cr 2 AlC MAX phase powder in ethylene glycol (EG). Incorporation of h-BN , MoS 2 , Al 2 O 3 , and Cr 2 AlC showed a thermal conductivity enhancement at 303 K when compared to EG. Accurate experimental models for the thermal conductivity and the viscosity of EG + Cr 2 AlC nanofluids are estimated. The theoretical analysis of the flow profiles of EG + Cr 2 AlC/Al 2 O 3 /MoS 2 /h-BN nanofluids is carried out with Blasius and Sakiadis flow models. The Cr 2 AlC MAX phase possesses both ceramic and metal properties that help these nanofluids to show high heat transfer performance. The results show that 0.50 wt% EG + Cr 2 AlC nanofluid displays maximum improvement in heat transfer performance. There is a substantial rise in the thermal conductivity when both temperature and weight fraction increase. The simulated flow of the nanofluid past a plate indicated superior heat transfer and thermal profiles for the EG + Cr 2 AlC nanofluids. For the flow past a moving plate, the nanofluid possesses less skin friction at the plate, which is favourable for various practical applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this paper an experimental study of convective boiling heat transfer of R-600a/oil/nanoparticle mixtures is investigated. The experimental setup was prepared with a smooth horizontal tube as a test section with the length and diameter of 9.5 and 103mm, respectively, and pure R-600a was applied for evaluating the heat transfer enhancement. Six mixtures containing 1% weight fraction of R-600a/oil with different concentrations of CuO nanoparticles including 0.0, 0.5, 1.0, 1.5, 2.0 and 5.0% weight fraction of R-600a/oil/nanoparticle were used in our study. The mass velocity per cross area was considered at the range of 50–700kg/m2 s for low vapor quality (ϕ <0.25). The results showed that the convective boiling heat transfer coefficient will be increased by increasing the mass fraction of nanoparticles up to 2%, while by increasing the mass fraction of nanoparticles up to 5% the heat transfer coefficient will be reduced. [Copyright &y& Elsevier]

Abstract: The purpose of this paper was to present an inverse heat conduction method used for determining the local convective boiling heat transfer coefficient in mini-channel for pure water, copper nanofluid by using three different concentrations of nanoparticles: 5mg/L, 10mg/L and 50mg/L. Conjugated gradient method with adjoint equation is used to solve the IHCP and estimate directly the space-variable convective heat transfer coefficient. Direct estimation local convective boiling heat transfer coefficient is a nonlinear inverse heat problem. The uncertainties in the estimated in heat transfer coefficient are calculated using bias and variance errors. This method is able to estimate local convective boiling heat transfer coefficient very well. [Copyright &y& Elsevier]

Abstract: Nanofluid, as a kind of new engineering material consisting of nanometer-sized additives and base fluids, has attracted great attention from investigators for its superior thermal properties and many potential applications. In this review, we summarize the nanofluid preparation methods reported by different investigators in an attempt to find a suitable method for preparing stable nanofluids. Nanofluids are classified according to material type as metallic and nonmetallic nanoparticles since different nanoparticles need their own stability method. Various nanoparticle types with different basefluids are investigated. Moreover, challenges and future directions of applications of nanofluids have been reviewed and presented in this paper. The aim of this review is to summarize recent developments in research on the synthesis and characterization of stationary nanofluids and to try finding some challenging issues that need to be solved for future research. [Copyright &y& Elsevier]

Abstract: The increasing demand of nanofluids in industrial applications has led to increased attention from many researchers. In this paper, heat transfer enhancement using TiO2 and SiO2 nanopowders suspended in pure water is presented. The test setup includes a car radiator, and the effects on heat transfer enhancement under the operating conditions are analyzed under laminar flow conditions. The volume flow rate, inlet temperature and nanofluid volume concentration are in the range of 2–8 LPM, 60–80°C and 1–2% respectively. The results showed that the Nusselt number increased with volume flow rate and slightly increased with inlet temperature and nanofluid volume concentration. The regression equation for input (volume flow rate, inlet temperature and nanofluid volume concentration) and response (Nusselt number) was found. The results of the analysis indicated that significant input parameters to enhance heat transfer with car radiator. These experimental results were found to be in good agreement with other researchers' data, with a deviation of only approximately 4%. [Copyright &y& Elsevier]

Abstract: Heat transfer performance with nanofluids depends on the thermo physical properties of the suspension. Surface tension is an important property for heat transfer calculation. In this paper, various parameters that effect on the surface tension of nanofluids such as nanofluid preparation method, effect of volume fraction, temperature, and surfactants on nanofluids have been studied. Additionally, precise assessments on the theoretical correlations related to the surface tension of nanofluids have also been included. Based on the existing experimental results, surface tension augments respectively with volume fraction intensification. Surface tension of nanofluids decreases accordingly with the increase of temperature and surfactant concentration. Nevertheless, there have been some contradictory results on the effect of volume fraction and surfactant on surface tension of nanofluids. [Copyright &y& Elsevier]

Abstract: An influence of multi-walled carbon nanotube (MWCNT) based aqueous nanofluids with different concentrations on the heat transport and the relevant pressure distribution in oscillating heat pipe (OHP) has been investigated. The present paper describes the heat transfer phenomena in terms of thermal resistance, pressure and frequency of pressure fluctuation in multi-loop oscillating heat pipe (OHP) charged by aqueous nanofluids with MWCNT loadings of 0.05wt.%, 0.1wt.%, 0.2wt.% and 0.3wt.%. The multi-loop OHP with 3mm inner diameter has been conducted in the experiment at 60% filling ratio. Experimental results show that thermal characteristics are significantly inter-related with pressure distribution and strongly depend upon the number of pressure fluctuations with time. The investigation shows that the 0.2wt.% MWCNTs based aqueous nanofluids obtain maximum number of the fluctuation frequency and low thermal resistance at any evaporator power input. Based on the experimental results, we discuss the reasons for enhancement and decrement of thermal characteristics of the nanofluids. [Copyright &y& Elsevier]

Abstract: In this paper forced convection turbulent nanofluid flow is numerically investigated to analyze the effects of different types of nanoparticles with different nanoparticle parameters in a fully detached ribbed channel. The bottom wall of the channel is kept at a constant temperature while the upper wall is thermally insulated. The continuity, momentum and energy equations were discretized and solved by the Finite Volume Method (FVM). The influence of different types of nanoparticles (Al2O3, CuO, SiO2, and ZnO) with nanoparticle concentration (1% to 4%) and nanoparticle diameter (20nm to 50nm) suspended in a water as a base fluid is studied on the heat transfer enhancement, friction factor and pressure drop. The Reynolds number was in the range of 10,000 to 50,000 in a rectangular channel having mounted rectangular ribs on its bottom wall with clearance ratio of 0.1. The results indicate that the highest heat transfer enhancement is achieved with SiO2 nanofluid and the friction factor did not considerably change with using different types of nanoparticles in the base fluid. Furthermore, increment of nanoparticle concentration or Reynolds number has a positive impact on heat transfer enhancement due to the increment of the velocity and thermal conductivity of the mixture. However, a rise of nanoparticle diameter decreases the heat transfer enhancement due to stronger Brownian motion even at lower nanoparticle diameter. [Copyright &y& Elsevier]