Carbon Nanotubes Water Nanofluid Research Articles

MHD natural convection in a square enclosure using carbon nanotubewater nanofluid with two isothermal fins

MHD natural convection in a square enclosure using carbon nanotubewater nanofluid with two isothermal fins

Numerical Study of a Phase Change Material Energy Storage Tank Working with Carbon Nanotube–Water Nanofluid under Ha’il City Climatic Conditions

A numerical investigation of a phase change material (PCM) energy storage tank working with carbon nanotube (CNT)–water nanofluid is performed. The study was conducted under actual climatic conditions of the Ha’il region (Saudi Arabia). Two configurations related to the absence or presence of conductive baffles are studied. The tank is filled by encapsulated paraffin wax as the PCM, and CNT–water nanofluid flows through the capsules. The main goal is to increase the temperature of the PCM to 70 °C in order to store the thermal energy, which can then be used during the night and cloudy weather. Numerical computations are made using the finite element method (FEM) based on actual measured weather conditions. Climate conditions were collected from a weather station located on the roof of the engineering college’s building at the University of Ha’il. The collected data served as input to the numerical model, and the simulations were performed for three months (December, March, and July). The solid CNT volume fraction range was (0 ≤ ϕ ≤ 0.05) and the nanofluid volume flow rate ranged was (0.5 L/min ≤ V ≤ 3 L/min). For both considered cases (with and without baffles), it was found that the use of CNT–nanofluid led to a reduction in the charging time and enhanced its performance. An increase in the volumetric flow rate was found to accelerate the melting process. The best performances of the storage tank occurred during July due to the highest solar irradiation. Furthermore, it was found that the use of baffles had no beneficial effects on the melting process.

Impact of a hot constructal tree-shaped fin on the convection flow of single wall carbon nanotube water nanofluid inside a sinusoidal enclosure

Heat transfer due to natural convection in different types of fins embedded closed enclosures are widely used in various fields including petrochemicals, solar collectors, heat exchangers, gas turbines, semiconductor devices, automobile radiators, etc. Herein, the natural convection flow of a water-based single-wall carbon nanotube (SWCNT) nanofluid inside a novel sinusoidal closed geometry is investigated. The horizontal bottom and top boundaries of the enclosure are presumed to be hot and thermally adiabatic, respectively. The left and right vertical sinusoidal boundaries are assumed to be cold. A hot constructal tree-shaped fin is placed at the center of the hot bottom wall. The impact of the simple constructal heated tree-shaped fin on steady, two-dimensional, laminar, and incompressible flow of the water-based SWCNT nanofluid inside the sinusoidal enclosure is analyzed. The mathematical formulation of water-based SWCNT nanofluid flow inside the enclosure is formulated using the Navier–Stokes equations under the Boussinesq approximation. A modified effective thermal conductivity model of carbon nanotubes including the radius of water molecules and carbon nanotubes is employed. Galerkin finite element simulations are conducted to study the flow and heat transfer characteristics via stream function, isotherms, local Nusselt number, and averaged Nusselt number graphs. The combined effect of the amplitude of the sinusoidal wall (A = 0.1, 0.15, and 0.2) with the Rayleigh number (Ra = 104–106), nanotube volume fraction (φ = 0.01–0.05), and the thickness of the tree-shaped fin (B = 0.02–0.06) are comprehensively studied. The temperature gradient decreases with increasing nanotube volume fraction and the sinusoidal wall amplitude, while it increases above the fin with the thickness of the tree-shaped fin. Moreover, the averaged Nusselt number increases with the thickness of the tree-shaped fin by 14.72%, 16.74%, and 19.6% for A = 0.1, 0.15, and 0.2 along the fin, respectively. The averaged Nusselt number along the fin is an increasing function of the Rayleigh number, nanotube volume fraction, thickness of the tree-shaped fin, and amplitude of waviness. Additionally, a novel correlation for the averaged Nusselt number along the fin is derived.

Review on Thermal Performance of Nanofluids With and Without Magnetic Fields in Heat Exchange Devices

Addition of nanoparticles into a fluid can improve the heat transfer performance of the base fluid in heat exchangers. In this work, the preparation method and process of nanofluids are introduced, and thermal properties of nanofluids, such as thermal conductivity and viscosity, are discussed deeply. This paper summarizes various theoretical models of thermal conductivity and viscosity of nanofluids. A comprehensive literature survey on applications and limitations of nanofluids has been compiled. This paper also aims to review the natural and forced convective heat transfer characteristics of nanofluids with and without magnetic fields. The discussion for the natural convective heat transfer of nanofluids focuses on the heat transfer performance of non-conventional enclosures and electric heaters. The effects on heat transfer due to variations of heated walls are also investigated. Specific applications of nanofluids in a tube with trapezoidal ribs, double-tube heat exchangers, and plate heat exchangers have been reviewed and presented in a discussion about forced convective heat transfer. The previous results show that the inlet temperature of nanofluids obviously affects the heat transfer characteristics of double-tube heat exchangers, whereas a multi-walled carbon nanotube–water nanofluid shows significant advantages in plate heat exchangers. Finally, this paper studies natural convective heat transfer of magnetic fluids in a square cavity and forced convection heat transfer in a straight tube and a corrugated structure under the action of magnetic fields. It is found that the heat transfer performance of an Fe3O4–water nanofluid is enhanced when a magnetic field is applied to the corrugated plate heat exchangers, and the pressure drop can be reduced by around 10%. It is recommended that natural convection of magnetic fluids needs to be investigated experimentally in a real cavity and a corrugated channel under the influence of a magnetic field. In addition, studies of alternating magnetic field are recommended to reveal any improvements of thermal performance of magnetic fluids in heat exchange devices. This review puts forward an effective solution for improvement of the thermal performance of heat transfer equipment and serves as a basic reference for applications of nanofluids in heat transfer fields.

Analysis of Unsteady Magnetohydrodynamic 3-D Rotating Flow and Transfer of Heat in Carbon Nanotube-Water Nanofluid: An Engineering Application

We have analysed unsteady Magnetohydrodynamic (MHD) 3-D rotating flow of Carbon Nanotube (CNT) water nanofluid past a stretching surface dealing with thermal radiation mechanism of heat transfer and heat source/sink. The mathematical model consists of a system of non-linear coupled Partial Differential Equations (PDEs). Numerical solution is obtained and discussed in detail. The influence of flow dominant parameters on the temperature profiles and flow-field are also discussed in detail using tables and graphs. Results are justified by previously published results in the limiting sense. Various crucial results are obtained, for example, unsteadiness parameter accelerates the fluid velocities in both directions near the sheet and reverse behaviour is noticed away from the sheet. However, fluid rotation causes reduction in primary velocity but it tends to accelerate secondary velocity near the sheet. Insertion of nanoparticle volume fraction intensifies fluid velocity and attenuates fluid temperature. We also found that multi-Walled Carbon Nanotubes (MWCNTs) offer more resistance for primary skin friction and less resistance for secondary skin friction when compared with Single-Walled Carbon Nanotubes (SWCNTs).

Three-Dimensional Study of Magnetohydrodynamic Natural Convection, Entropy Generation, and Electromagnetic Variables in a Nanofluid Filled Enclosure Equipped with Inclined Fins.

This article provides a numerical study on carbon nanotube–water nanofluid convection in a three-dimensional cavity under a magnetic field effect. Two walls are kept at a hot temperature, and the upper and lower horizontal walls are considered adiabatic. As a new configuration, the beneficial effect of using a nanofluid is coupled with the incorporation of cold V-shape obstacle placed in the cubic cavity; in addition, an external magnetic field is applied toward the horizontal x-axis direction. The finite element method based on the Galerkin’s Weighted Residual technique is used to solve the three-dimensional governing equations. In this paper, the ranges of the parameters used are the Hartmann number, varied from 0 to 100, Rayleigh number from 103 to 105, nanofluid volume fraction between 0% and 4.5%, and the body V-shaped opening angle varied from 0 to 80°. The effect of the obstacle shape and the added nanoparticle concentration on the flow behaviors, the different instabilities generated, and the heat transfer exchanged were exposed. An enhancement in heat transfer was recorded by increasing the obstacle opening angle and the volume fraction of the carbon nanotubes. Special attention has also been devoted to the calculation of the different kinds of entropy generations.

Numerical study of MHD natural heat transfer of non-Newtonian, carbon nanotube-water nanofluid inside an internally finned annulus

Numerical study of MHD natural heat transfer of non-Newtonian, carbon nanotube-water nanofluid inside an internally finned annulus

Nanofluid jet impingement heating of a cooled surface with a constant heat flux in the presence of porous layer

PurposeThe purpose of this study is to numerically investigate the confined single-walled carbon nanotube-water nanofluid jet impingement heating of a cooled surface with a uniform heat flux in the presence of a porous layer. The analysis of the convective heat transfer mechanism is introduced considering the buoyancy force effect under local thermal non-equilibrium conditions.Design/methodology/approachThe governing equations for the nanofluid and solid phase are discretized by the finite volume method and the SIMPLE algorithm is used to solve these equations.FindingsIt is observed that there is an increase in a local variation of temperature along the upper wall with increasing Reynolds, Darcy and Grashof numbers. For given parameters, the optimum values of thermal conductivity ratio and porous layer thickness leading to better heating on the upper wall are found as Kr = 1.0 and S = 0.5, respectively. The maximum and minimum values of temperature on the upper wall are obtained in the case of higher nanoparticle volume fraction at Re = 100, however, the temperature values get higher along the upper wall with increasing nanoparticle volume fraction at Re = 300.Originality/valueThe effects of various parameters, such as Reynolds number, Darcy number and Grashof number, on thermal behavior and nanofluid flow are examined to determine the desirable heating conditions for the upper wall. This paper provides a solution to problems such as icing on the surface with a suitable thermal design and optimum geometric configuration.

Transient Free Convective Flow of CNT Water Nanofluid with Heat Transfer from a Moving Cylinder

Background: In this paper, transient two-dimensional laminar boundary layer viscous incompressible free convective flow of water based nanofluid with carbon nanotubes (CNTs) past a moving vertical cylinder with variable surface temperature is studied numerically in the presence of thermal radiation and heat generation. Methods: The prevailing partial differential equations which model the flow with initial and boundary conditions are solved by implicit finite difference method of Crank Nicolson type, which is unconditionally stable and convergent. Results: Influence of Grashof number (Gr), nanoparticle volume fraction (φ), heat generation parameter (Q), temperature exponent (m), radiation parameter (N) and time (t) on velocity and temperature profiles are sketched graphically and elaborated comprehensively. Conclusion: Analysis of Nusselt number and Skin friction coefficient is also discussed numerically for both single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

Numerical simulation of three-dimensional thermo-solutal convection of micropolar multi-walled carbon nanotubes water nanofluid stabilized by lignin and sodium polycarboxylate

A computational analysis has been performed in this study to solve three-dimensional thermo-solutal natural convection in a differentially heated cubical enclosure filled with micropolar CNT/water nanofluid stabilized by two types of surfactants lignin and sodium polycarboxylate. The work is carried out for different pertinent parameters as Rayleigh number (104 \(\le\) Ra \(\le\) 106), micropolar parameter (0 \(\le\) K \(\le\) 10), buoyancy ratio (−1 \(\le\) N \(\le\) 0) and nanoparticles’s volume fraction (0.0055% \(\le \varphi \le\) 0.557%). It is observed that the heat and mass transfer rates are lower for a micropolar nanofluid model when compared to the pure nanofluid model. In fact, the enhancement of micropolar parameter results a decrease in average Nusselt and Sherwood numbers. The use of lignin as a surfactant ameliorates heat and mass transfer rate and nanofluid flow better than the use of sodium polycarboxylate as a surfactant. The nanoparticles volume fraction can be used as a control element for heat rate and fluid flow. Thus, for a nanoparticles volume concentration less than the critical value, the flow intensity is ameliorated and is deteriorated when it exceeds this value.

Natural convection nanofluid flow with heat transfer analysis of carbon nanotubes–water nanofluid inside a vertical truncated wavy cone

The flow of heat transfer study of carbon nanotubes (CNTs)–water nanofluid over vertical truncated wavy cone is considered. The present boundary layer power law fluid is analyzed near the truncated wavy cone. The considered cone is wavy in physical configuration and placed in a vertical direction. Moreover, nanosized particles of CNTs suspended into water (base fluid) are transporting in two directions, which are modeled by using Boussinesq's approximation. Coordinate transformation is applied in order to shift the wavy surface to a flat surface. Then governing equation dealing with the momentum of nanofluid along with thermal stratification are reduced in dimensionless form by using appropriate transformation. Results point out that the thickness of thermal boundary layer decreases by increasing the value of volume fraction of carbon nanotubes. Finally, the obtained solution is related through a graphical survey, and it is inferred that the investigation is in good accordance with the current literature.

Corrosion Behaviour of 316L Stainless Steel in CNTs-Water Nanofluid: Effect of Temperature.

The inhibition behavior of carbon nanotubes (CNTs) and Gum Arabic (GA) on the corrosion of 316L stainless steel in CNTs–water nanofluid under the effect of different temperatures was investigated by electrochemical methods and surface analysis techniques. Thereby, 316L stainless steel samples were exposed to CNTs–water nanofluid under temperatures of 22, 40, 60 and 80 °C. Two concentrations of the CNTs (0.1 and 1.0 wt.% CNTs) were homogenously dispersed in deionized water using the surfactant GA and tested using three corrosion tests conducted in series: open circuit test, polarization resistance test, and potentiodynamic scans. These tests were also conducted on the same steel but in solutions of GA-deionized water only. Tests revealed that corrosion increases with temperature and concentration of the CNTs–water nanofluids, having the highest corrosion rate of 32.66 milli-mpy (milli-mil per year) for the 1.0 wt.% CNT nanofluid at 80 °C. In addition, SEM observations showed pits formation around areas of accumulated CNTs that added extra roughness to the steel sample. The activation energy analysis and optical surface observations have revealed that CNTs can desorb at higher temperatures, which makes the surface more vulnerable to corrosion attack.

Laminar Forced Convection of Nanofluids in a Circular Tube: A New Nonhomogeneous Flow Model

Abstract In this paper, the local and average heat transfer coefficient enhancement or deterioration, and rise in pumping power in steady, laminar alumina–water, titania–water, and carbon nanotube (CNT)–water nanofluids flow in a horizontal circular tube subjected to constant heat flux at the outer wall have been investigated numerically based on a new variable property nonhomogeneous flow model which takes into account agglomeration of nanoparticles. The results have been compared with the published experimental results of Utomo et al. (Utomo, A. T. et al., 2014, “The Effect of Nanoparticles on Laminar Heat Transfer in a Horizontal Tube,” Int. J. Heat Mass Transfer, 69, pp. 77–91.) using various property models of thermal conductivity and viscosity, and for equal Reynolds number, equal inlet velocity, equal mass flowrate, and equal pumping power of nanofluid and base fluid. Stream function–vorticity–temperature formulation and finite difference method have been used. Using the same Reynolds number of nanofluid and base fluid gives much higher enhancement in average heat transfer coefficient as compared to other modes of comparison. Interestingly, the criterion of equal pumping power gives negative percent enhancement in the case of CNT–water nanofluid. The pumping power is found to rise for all three nanofluids. It is found that consideration of agglomeration of nanoparticles has produced improved accuracy in the numerical solution.

Mixed convection in a lid-driven cavity filled with single and multiple-walled carbon nanotubes nanofluid having an inner elliptic obstacle

In this study, numerical analysis and optimization in a single and multiple walled carbon nanotube-water nanofluid filled lid driven cavity having an inner elliptic obstacle were performed by using finite element method and COBYLA optimization solver. The top wall is moving with constant speed and vertical walls are kept at constant temperatures. An optimal size of the inner elliptic obstacle was determined by using an optimization study to maximize the average heat transfer along the hot wall of the cavity. Numerical simulation was performed by for various values of Richardson numbers (between 0.05 and 50) and various solid particle volume fraction (between 0 and 0.06) for single and multiple-walled carbon nanotubes water nanofluid. A larger obstacle (higher values of radii in the major and minor axis) with lower values of Richardson number results in higher heat transfer rates. The average Nusselt number versus solid particle volume fraction shows a linear trend and the discrepancy between the average Nusselt number for the cavity with the optimized obstacle and other obstacles becomes higher with higher particle volume fraction. The average heat transfer enhances significantly which is about 120.20% for single wall carbon nanotube -water nanofluid at solid volume fraction of 0.06 when compared to pure water. The discrepancy between the average Nusselt number for single and multiple walled carbon nanotubes becomes higher for higher values of Richardson number and solid particle volume fraction. A polynomial type correlation was proposed for the average Nusselt number along the hot wall which is fifth order for Richardson number an first order for nanoparticle volume fraction.

Viscosity of carbon nanotube/water nanofluid

Special features of nanofluids as heat transfer media have made them very important. The first step for investigating nanofluids was to know the characteristics of nanofluid because they are very important for describing their behavior. Although many attempts have been made to model the thermo-physical properties of nanofluids, there is no comprehensive model to predict these properties. In this study, the viscosity of single-wall carbon nanotube–water nanofluid as most important thermo-physical property of nanofluid was investigated by equilibrium molecular dynamics simulation. In addition, the effect of volume fraction of nanoparticles and the nanofluid temperature on viscosity is studied. The viscosity variability was investigated in range of 0.125–0.734% and the temperature 25–65 °C. The results showed that viscosity increases with high volume fraction of nanoparticles and low temperature of nanofluid. Furthermore, maximum nanofluids viscosity was 320% with volume fractions of 0.73% at 25 °C.

Mixed convection due to a rotating cylinder in a 3D corrugated cavity filled with single walled CNT-water nanofluid

Analysis of mixed convection due to a rotating inner cylinder in a corrugated three-dimensional cavity filled with carbon nanotube-water nanofluid was performed. Numerical simulations were performed by using Galerkin weighted residual finite element method. The three-dimensional corrugated cavity was differentially heated form the vertical surfaces, and an inner rotating adiabatic cylinder was used. Influence of Rayleigh number (between 10 $$^4$$ and 10 $$^6$$ ), angular rotational velocity of the cylinder (between − 50 and 50 rad/s), height (between H / 10 and H / 3) and number of triangular waves (between 1 and 16) and solid nanoparticle volume fraction (between 0 and 0.04) on the convective heat transfer characteristics was analyzed. It was observed that average heat transfer augments significantly by changing the nanoparticle volume fraction and up to 128 $$\%$$ of enhancement is obtained. Depending on the rotational direction of the cylinder, average Nusselt number enhances $$68\%$$ in the three-dimensional cavity. Surface corrugation parameters are not as effective as solid particle volume fraction and angular rotational speed of the cylinder on the heat transfer enhancements. Finally, a correlation for the average Nusselt number along the cold surface was provided which is dependent upon the angular rotational speed of the cylinder and Rayleigh number.

Three-dimensional investigation of the effects of external magnetic field inclination on laminar natural convection heat transfer in CNT–water nanofluid filled cavity

A finite volume-based three-dimensional numerical analysis is conducted to investigate the effects of the angle of inclination of an external magnetic force on the natural convection inside a cubical cavity filled with a carbon nano-tube (CNT)-water nanofluid. The governing equations are solved using vorticity-vector potential formalism. The vertical walls are differentially heated and the horizontal walls are assumed to be adiabatic. The effects of the Rayleigh number (103≤Ra≤105), volumetric fraction (0≤φ≤0.05) of the CNT particles, angle of inclination of the external magnetic force (0°≤α≤90°), and the Hartmann number (0≤H a≤100) are investigated. The results of a fluid flow using a single-phase model are illustrated based on the particle trajectories, velocity vectors, isosurfaces of temperature, and the Nusselt number. The heat transfer is shown to intensify with the increasing percentage of CNT particles and a larger Rayleigh number. The repelling effect of the magnetic force inhibits the heat transfer by 50% when Ha is increased from 50 to 100.

Carbon nanotube nanofluid in enhancing the efficiency of evacuated tube solar collector

Abstract The use of solar thermal collectors is one of the promising options for heating and/or cooling due to the green nature (pollution free) and abundance of the solar energy in many parts of the world. Improvement of thermal performance of solar collectors is important for better energy conversion. In this regard, many studies reported in literature tried to modify geometry of the collectors. On the other hand, nanofluids as heat transfer fluids could be a promising option for the efficiency enhancement of solar collectors. In this study, heating performance of an evacuated tube solar collector system initially operated with water is considered for improvement using nanofluid. The collector (about 20 kW heating capacity) is a part of an absorption cooling system. The aim of the present study is to analyze the effect of Single Walled Carbon Nanotube–water nanofluid on the collector performance. Thermal efficiency improvement is assessed based on comparative analyses between collector working with ordinary water and that with nanofluid. The results indicate that up to 56.7% and 66% of efficiencies are observed when the collector is operated with water and 0.2 vol% nanofluid, respectively. Therefore, nanofluids are promising to enhance the efficiencies of solar collectors.

Experimental and numerical investigation on turbulent flow of multiwall carbon nanotube-water nanofluid inside vertical coiled wire inserted tubes

In this paper, heat transfer and pressure drop behavior of MWCNT-water nanofluid turbulent flow inside vertical coiled wire inserted tubes with constant heat flux boundary condition were investigated experimentally and numerically. In the experimental section, plain and five wire coil inserted tubes were used as the test section's geometries. In the numerical section, the governing equations associated with the required boundary conditions were solved using finite volume method based on the SIMPLE technique. The standard k-e turbulence model was used in order to simulate the turbulence flow. The great agreement was found between the obtained experimental and numerical data with those predicted by the classical correlations for heat transfer and pressure drop in the plain tube. After validating the achieved data, the effects of various ranges of Reynolds number, particle weight concentration, wire diameter and coil pitch ratio on heat transfer coefficient and performance evaluation criterion (PEC) were declared. It was concluded that the Nusselt number has been increased up to 102% at the highest Reynolds number inside the coil wire WC3. Moreover, the maximum enhanced PEC was seen for the wire coil with lowest coil pitch-to-tube inner diameter ratio (p/d) and highest wire-to-tube diameter ratio (e/d).

Thermal performance analysis of a flat heat pipe working with carbon nanotube-water nanofluid for cooling of a high heat flux heater

Experimental investigation on the thermal performance of a flat heat pipe working with carbon nanotube nanofluid is conducted. It is used for cooling a heater working at high heat flux conditions up to 190 kW/m2. The heat pipe is fabricated from aluminium and is equipped with rectangular fin for efficient cooling of condenser section. Inside the heat pipe, a screen mesh was inserted as a wick structure to facilitate the capillary action of working fluid. Influence of different operating parameters such as heat flux, mass concentration of carbon nanotubes and filling ratio of working fluid on thermal performance of heat pipe and its thermal resistance are investigated. Results showed that with an increase in heat flux, the heat transfer coefficient in evaporator section of the heat pipe increases. For filling ratio, however, there is an optimum value, which was 0.8 for the test heat pipe. In addition, CNT/water enhanced the heat transfer coefficient up to 40% over the deionized water. Carbon nanotubes intensified the thermal performance of wick structure by creating a fouling layer on screen mesh structure, which changes the contact angle of liquid with the surface, intensifying the capillary forces.