Cu-water Nanofluid Research Articles

Entropy Generation in MHD Natural Convection Within Curved Enclosure Filled with Cu-Water Nanofluid

Entropy Generation in MHD Natural Convection Within Curved Enclosure Filled with Cu-Water Nanofluid

Multi-layered Porous Foam Effects on Heat Transfer and Entropy Generation of Nanofluid Mixed Convection Inside a Two-Sided Lid-Driven Enclosure with Internal Heating

Mixed convection of Cu-water nanofluid inside a two-sided lid-driven enclosure with an internal heater, filled with multi-layered porous foams is studied numerically and its heat transfer and entropy generation number are evaluated. Use of multi-layered porous media instead of homogeneous ones is capable of heat transfer enhancement, by weakening flow where does not impose a pivotal role on heat transfer and amplifying the flow in regions where have more effects on the heat transfer. Eight different arrangements of porous layers are considered and the two-phase mixture model is implemented to simulate nanofluid mixed convection inside the cavity. Results are presented in terms of stream functions, isotherms, Nusselt and entropy generation number for the eight cases considering various Richardson numbers (Ri = 10−4 to 103) and nanofluid concentrations (φ = 0 to 0.04). Results indicate that using the multi-layered porous material can confine flow vortices in the vicinity of the moving walls and could enhance the heat transfer up to 17 percent (with respect to the case using homogeneous porous material with the highest permeability), such that this enhancement is more in lower Ri values (stronger convective effects). Entropy generation number also increases by nanofluid volume fraction increment and Ri decrement. Cases with a higher heat transfer rate also have the higher entropy generation number. In addition, an increase of volume fraction decreases the relative entropy generation number (S*) for low Ri number, while contrary fact observed for high Ri values.

Cu-water nanofluid flow and heat transfer in a heat exchanger tube equipped with cross-cut twisted tape

This paper presents a numerical analysis for Cu-water nanofluid flow through a circular duct inserted with cross-cut twisted tape with alternate axis (CCTA). Three dimensional (RNG) k − ϵ turbulence model is applied to simulate this problem. All simulations are performed for plain tube and nine different CCTA geometries in the range of width ratio (b/w) from 0.7 to 0.9, length ratio (s/w) from 2 to 2.5, Reynolds numbers in the range of 5000 to 15,000 and volume fraction of nanoparticles from 0 to 1.5%. The calculated results indicate that the swirl flow created by CCTA is transferred from the tube core to the near wall regions. This results in higher fluid mixing, which enhances heat transfer and friction factor near the tube wall. The results show that the heat transfer coefficient increases up to 23.20% with increasing the nanoparticle volume fraction from 0% to 1.5%. Finally, it is shown that the thermal performance increases by increasing the volume fraction of nanoparticles inside the duct.

Investigation of the Local Thermal Nonequilibrium Conditions for a Convective Heat Transfer Flow in an Inclined Square Enclosure Filled with Cu-Water Nanofluid

In this paper, the local thermal nonequilibrium conditions between the base fluid and the nanoparticles inside an inclined square enclosure have been investigated and analyzed numerically. The effects of magnetic field intensity and the geometry inclination angle on the heat exchange between base fluid and nanoparticles are also taken into account. Two opposite walls of the enclosure are insulated, and the other two walls are kept at different temperatures. A PDE solver, Comsol Multiphysics which uses the Galerkin weighted residual finite element technique, has been employed to solve the governing nonlinear dimensionless equations. Comparisons with previously published works are performed, and excellent agreement is obtained. Numerical simulations are accomplished to calculate the dimensionless temperature profiles along lines $$X=0.05$$ and $$Y=X$$ inside the enclosure. A single-phase approach with two temperature equations is applied in this work for the first time. The results indicate that the local thermal nonequilibrium conditions are highly controlled by the Nield number and the nanoparticles volume fraction. The domains at which base fluid and nanoparticles are at local thermal equilibrium or local thermal nonequilibrium have been calculated. These findings may open a door for the researchers to choose the suitable model in analyzing the dynamics of nanofluids and will be helpful in investigating the heat transfer rate based on fluid/particle interface. It will also provide the basis for the future research on the entropy generation investigation during natural convection in order to improve the energy efficiency which may be applicable for different renewable energy systems.

Analysis of Heat Transfer of Cu-Water Nanofluid Flow Past a Moving Wedge

In this paper, heat transfer of a steady, two-dimensional, incompressible Cu-water nanofluid flow over a moving wedge in the presence of thermal radiation effect are investigated. Gyarmati's variational principle developed on the thermodynamic theory of irreversible processes is employed to solve the problem numerically. The governing boundary layer equations are approximated as simple polynomial functions, and the functional of the variational principle is constructed. The Euler-Langrange equations are reduced to simple polynomial equations in terms of boundary layer thicknesses. The velocity and temperature profiles as well as skin friction and heat transfer are analyzed for various parameters. The obtained numerical solutions are compared with the previously published results and are found to be in good agreement.

Heat transfer and entropy generation of the nanofluid flow inside sinusoidal wavy channels

Corrugating channel walls is a way to enhance heat transfer in heat exchangers. In the current investigation, the entropy generation minimization approach has been employed to optimize heat transfer and fluid flow within a wavy channel. A numerical method has been built to compute entropy generation rate in a sinusoidal wavy-wall channel with copper-water (Cu-water) nanofluid flow. The governing equations have been discretized using finite volume method for a two-dimensional steady flow. The effects of geometrical and flow parameters, including nanoparticles volume fraction (0.01 < ϕ < 0.05), Richardson number (0.1 < Ri < 10), wave amplitude ratio (0.1 < α < 0.3) and wave length ratio (1 < λ < 3), have been investigated. Results reveal that increasing nanoparticle volume fraction within investigated Richardson number will increase Nusselt number. In addition, the maximum entropy generation rate declines as Richarson number increases. The optimal wave amplitude ratio (corresponding to lowest entropy generation), for wave length ratios of λ = 1 and λ = 2, found to be α = 0.2. Also, for wave length ratio of λ = 3, the minimum entropy generation approximately occurs at α = 0.1.

An analytical study of the periodic laminar forced convection of non-Newtonian nanofluid flow inside an elliptical duct

In this study, an analytical solution was obtained for a laminar forced convection of non-Newtonian nanofluid flowing inside an elliptical duct, with inlet temperature varying periodically with the time. The solution was obtained using the Generalized Integral Transform Technique (GITT). The thermal behavior of Cu-water non-Newtonian nanofluid, described by the power-law model was investigated. Also, an accurate correlation was established to estimate the thermal length required to achieve 99% of the amplitude attenuation. The results show a significant effect of aspect ratio β/α and fluid behavior index on the temperature amplitude reduction. For instance, an elliptical duct with β/α = 0.25 reduces the thermal length Lth more than 50% compared with circular duct. Adding nanoparticles until 5% increases the heat transfer coefficient up to 27% for the cylindrical tube. Besides, the heat transfer coefficient is improved over 42% relatively to the cylindrical configuration by reducing the aspect ratio to 0.25. Therefore, adding 5% of nanoparticles both using an elliptical duct with β/α = 0.25, improves the mean heat transfer coefficient around 83% compared to the flow of water base fluid inside a cylindrical duct.

Effect of the Wick and the Working Medium on the Thermal Resistance of FPHP

This paper introduces a novel micro-deep, triangle-grooved wick, and compares the performance of the flat plate heat pipe (FPHP) with various types of wicks, including foam metal copper wick, sintered copper powder wick, copper mesh wick, micro-deep rectangle-grooved wick, and micro-deep triangle-grooved wick. Test results verified the feasibility of the nanofluids applied to FPHP. Tested working fluids included deionized water, Cu-water nanofluids, carbon-coated copper nanofluids and multi-walled carbon nanotube (MWCNT) nanofluids. These nanofluids were applied on foam metal FPHP and the results were compared. The results indicated that the metal foam wick is better than the other heat pipe wicks, in the contrast experiment, when the heating power is 100w, the thermal resistance is 0.1238 ℃/K. The thermal resistance of micro-deep triangle-grooved wick FPHP is 15% lower than the micro-deep rectangle-grooved wick FPHP; The optimal filled ratio of 40% can make flat heat pipe have good performance; With the increase of mass fraction of nanofluid, the thermal resistance decreased first and then increased, the best mass fraction is 0.5%, the thermal conductivity of carbon-coated copper nanofluids FPHP is optimal, the average thermal resistance is 0.1369 ℃/K, and is 17% and 9% lower than the multi-walled carbon nanofluids and copper FPHP, and is 46% lower than the deionized water FPHP; The gravitational stability of the heat pipe is verified by the experiments.

Low-cost and high-throughput synthesis of copper nanopowder for nanofluid applications

Copper (Cu) is a low cost and efficient filler for nanofluids. However, commercially available copper nanopowders are as costly as silver. A few methods are available for synthesis of copper nanopowder in the lab, but the amount of powder produced per batch is very small, and it is impractical to produce a large volume of nanofluid using these methods. Solution based high concentration synthesis for production of copper nanopowder using batch reactor has been reported in this work. Cost of production is minimal in this method and nanoparticles are separated from the suspension by a controlled flocculation process. The proposed method relies on the higher solubility of cuprammonium complex in an aqueous medium and its chemical reduction using hydrazine hydrate. The colloid has been stabilised using sodium citrate and obtained as sub 50 nm powder re-dispersible in water and ethylene glycol (EG). Continuous synthesis of this product using a Continuous Stirred Tank Reactor (CSTR) has also been demonstrated. The quality of particles from the CSTR is similar to that of the batch method. Stable nanofluids have been prepared by re-dispersing the nanopowder in water and EG. Moderate enhancement (∼5%) in thermal conductivity for Cu-EG nanofluids and small enhancement (∼2%) for Cu-water nanofluid have been observed with 0.6 vol% of copper loading.

Effect of solid-to-fluid conductivity ratio on mixed convection and entropy generation of a nanofluid in a lid-driven enclosure with a thick wavy wall

A numerical study on the conjugate heat transfer by mixed convection of a Cu-water nanofluid and conduction in a solid region is conducted in an enclosure with a thick wavy heated wall. The upper lid of the enclosure is made to slide horizontally at a constant speed, along with that the condition of heated outer boundary of the thick bottom wall leads to a mixed convection within the enclosure. The impact of the wavy fluid-solid interface, solid-to-fluid thermal conductivity ratio and nanoparticle volume fraction on the heat transfer characteristics is analyzed for different choice of the Richardson number. The computational domain is transformed into an orthogonal co-ordinate system. The transformed governing equations along with the specified boundary conditions are solved through a finite volume method for a wide range of Richardson number, nanoparticle volume fraction, wave amplitude, wave number and wall-to-fluid conductivity ratio for different Reynolds number. Results show that the heat transfer rate increases substantially due to the inclusion of nanoparticles. Heat transfer rate varies due to the variation of the solid-to-fluid conductivity ratio, amplitude and wave number of the wavy wall. The impact of the wavy surface is stronger when the solid conductivity is in the order of the conductivity of the fluid. The Bejan number and the entropy generation are determined to analyze the thermodynamic optimization of the conjugate mixed convection.

Numerical investigation of cu-water nanofluid in a differentially heated square cavity with conducting solid square cylinder at center

Numerical investigation of cu-water nanofluid in a differentially heated square cavity with conducting solid square cylinder at center

Natural convective flow in circular and arc cavities filled with water-cu nanofluid: a comparative study

The fluid flow and heat transfer mechanism on steady state solutions obtained in circular and arc-square enclosures filled with water/Cu nanofluid as well as base fluid has been investigated numerically by Galerkin's weighted residual finite element procedure. The left and right boundaries of the cavities are, respectively, heated and cooled at constant temperatures, while their horizontal walls are adiabatic. Effects of buoyancy force (Rayleigh number) and viscous force (Prandtl number) with a wide range of Ra (103 - 106) and Pr (4.2 - 6.2) on heat transfer phenomenon inside cavities are observed. The fluid flow and temperature gradient are shown by streamlines and isotherms patterns. From the investigation, it is reported that the Rayleigh and Prandtl numbers are playing significant role in heat transfer rate. The variation in heat transfer is calculated in terms of average Nusselt number. Heat transfer rate is found to be higher for water/Cu nanofluid with 2% solid volume fraction than pure water. About 2.7% higher heat transfer rate is obtained for circular cavity than that of arc cavity using water/Cu nanofluid at Ra = 104 and Pr = 5.8.

Effect of viscous dissipation on MHD water-Cu and EG-Cu nanofluids flowing through a porous medium

This paper provides a comparative analysis of two different types of nanofluids for Stokes second problem. Additional effects of MHD, porosity and viscous dissipation are also considered. Two types of Newtonian liquids (water and ethylene glycol) are considered as base fluids with suspended nanosized Cu particles. A homogenous model of Newtonian nanofluids over a flat plate is used to describe this phenomenon with Stokes boundary conditions such that the ambient fluid is static and with uniform temperature. The problem is first written in terms of nonlinear partial differential equations with physical conditions; then after non-dimensional analysis, the Laplace transform method is used for its closed-form solution. Exact expressions are determined for the dimensionless temperature, velocity field, Nusselt number and skin friction coefficient and arranged in terms of exponential and complementary error functions satisfying the governing equations and boundary conditions. They are also reduced to the known solutions of Stokes second problem for Cu-water nanofluids. Results are computed using Maple software. The results showed that both skin friction and rate of heat transfer increase with increasing solid volume fraction of nanoparticles. MHD and porosity had an opposite effect on velocity for both types of nanofluids. The dimensionless temperature increases by increasing the Eckert and Hartmann numbers.

Effects of nanoparticles dispersion on the mixed convection of a nanofluid in a skewed enclosure

A non-homogeneous model in which the nanoparticles have relative velocity compared to the based fluid is considered to study the convective heat transfer of a Cu-water nanofluid in a differentially heated skewed enclosure. The effect of nanoparticles size, volume fraction, Brownian diffusion and thermophoretic diffusion on the mixed convection is studied and compared with the result due to the homogeneous model. The theromphysical properties of the nanofluid is considered to depend on the temperature and nanoparticle volume fraction. A pressure correction based algorithm is used to solve the transport equations.The effects of the relevant parameter such as, the size of the nanoparticles (30nm⩽dp⩽100nm), temperature difference (1K⩽ΔT⩽10K) and bulk volume fraction of the nanoparticles (0⩽ϕb⩽0.05) on mixed convection of nanofluid studied by considering the skew angle to vary between 30° and 150°. The analysis shows that the nanoparticles distribution is nonuniform inside the enclosure and this non-uniformity increases with the rise of the temperature difference. The variation of the average Nusselt number and total entropy generation with the variation of the relevant parameter is analyzed for the thermodynamic optimization. The purpose of the present study is to analyze the effects of Brownian diffusion and thermophoresis of nanoparticles on the mixed convection of a Cu-water nanofluid. The results show that the Brownian diffusion and thermophoretic diffusion has relatively negligible effects on the mixed convection for the considered range of parameter values.

Impact of wall properties on the peristaltic flow of Cu-water nano fluid in a non-uniform inclined tube

The objective of this paper is to study the influence of wall properties and Cu-water nano fluid in a non-uniform inclined tube. In this analysis, two dimensional flow of a viscous nano fluid generated by peristaltic motion is observed, thermal and velocity slip effects are also taken into account. The features of peristaltic structures are determined by the dominance of viscous effects over inertial effects using the long wave length approximation. Exact solutions have been established for both velocity and temperature profiles, which include nanoparticle effects. Graphical results are also obtained for both velocity, temperature profile and trapping phenomena is also discussed. Temperature profile decreases by increasing values of nanoparticle volume fraction. This justifies the use of the nanoparticle in different type as a coolant.

Uniform Magnetic field (UMF) Effect on the Heat Transfer of a Porous Half-Annulus Enclosure Filled by Cu-Water Nanofluid Considering Heat Generation

Background: In this work, the effect of a uniform magnetic field (UMF) on the natural convection heat transfer of Cu-water nanofluid in a porous half-annulus cavity is studied by finite element method, considering heat generation. The effects of four parameters (magnetic field angle (γ), Hartmann number (Ha), nanoparticles volume fraction (φ) and Rayleigh number (Ra)) on the local and average Nusselt numbers of outer wall have been investigated. Methods: Numerical Finite Element Method (FEM) based on FlexPDE commercial code was used to solve the described problems and the validation was also performed by Finite Difference Method (FDM) in previous studies. Results: It was found that by applying external magnetic field with a certain angle with respect to the geometry, the maximum local heat Nusselt number could shift to one side of outer wall and the shift is dependent on the angle of the imposed magnetic field. Conclusion: Our results also confirm that increasing the Hartmann number decreases the Nusselt number due to Lorentz force resulting from the presence of stronger magnetic field which slows down the fluid motion and in turn leads to a decreased heat transfer.

Mathematical model for thermal and entropy analysis of thermal solar collectors by using Maxwell nanofluids with slip conditions, thermal radiation and variable thermal conductivity

Abstract In the present research a simplified mathematical model for the solar thermal collectors is considered in the form of non-uniform unsteady stretching surface. The non-Newtonian Maxwell nanofluid model is utilized for the working fluid along with slip and convective boundary conditions and comprehensive analysis of entropy generation in the system is also observed. The effect of thermal radiation and variable thermal conductivity are also included in the present model. The mathematical formulation is carried out through a boundary layer approach and the numerical computations are carried out for Cu-water and TiO2-water nanofluids. Results are presented for the velocity, temperature and entropy generation profiles, skin friction coefficient and Nusselt number. The discussion is concluded on the effect of various governing parameters on the motion, temperature variation, entropy generation, velocity gradient and the rate of heat transfer at the boundary.

Nanoparticle migration and natural convection heat transfer of Cu-water nanofluid inside a porous undulant-wall enclosure using LTNE and two-phase model

Using Buongiorno's model, the natural convection of Cu-water nanofluid flowing within a wavy wall porous enclosure at the presence of a cylindrical heater was numerically investigated. The problem is considered such that there is no local thermal equilibrium between two phases of porous media. The effects of Rayleigh number (103≤Ra≤106), the Lewis number (1≤Le≤50), Brownian motion parameter (0.1≤Nb≤0.5), the thermophoresis parameter (0.1≤Nt≤0.5), the buoyancy ratio (0.1≤Nr≤0.5), the Darcy number (10−5≤Da≤10−1), porosity (0.1≤ε≤0.9), the ratio of the thermal conductivity of the nanofluid to the solid phase (0.1≤γs≤10), coefficient of heat transfer at the interface (1≤Nhs≤1000) on hydrodynamic and thermal parameter have been studied. Streamlines, distribution of temperature and concentration of nanoparticles are presented and discussed. Increasing in the Rayleigh, the Darcy, the Lewis numbers, the thermal conductivity ratio and the Brownian parameter of the nanoparticle motions homogenizes the nanofluid. Meanwhile, the homogeneity is reduced as thermophoresis is increased. The results show that the thermal equilibrium model for porous media is applicable for the cases with large heat transfer coefficient at the interface between the solid matrix and the nanofluid. Moreover, the average Nusselt number of both porous phases' increases with the Brownian parameter, while the Nusselt number is reduced as the thermophoresis is increased.

Heat and fluid flow of water and ethylene-glycol based Cu-nanoparticles between two parallel squeezing porous disks: LSGM approach

This study is dedicated to analyze the heat transfer and flow of ethylene glycol and water based copper (Cu) nanoparticles between two squeezed parallel disks with suction/injection effects. The lower disk is assumed to be permeable. Additionally, we have considered the influence of MHD to keep the metallic particles in charge. These particles are normal to the surface and strongly effected by magnetic field. Constructed mathematical model consist of system of partial differential equations in cylindrical coordinates, based upon momentum and energy equations. The governing equations reduced to a nonlinear set of ordinary differential equations. The said set of nonlinear equations consists of squeezing number S, Hartmann number (M), nanoparticle volume fraction ϕ and suction/injection parameter (A) tackled by least square Galerkin method (LSGM). The outcomes are analyzed by means of temperature and velocity profiles for every Cu-water and Cu-ethylene glycol nanofluids. The heat transfer and flow behavior at the surface are studied via graphical plots for local Nusselt number and skin friction. It is observed that local Nusselt number achieved from Cu-water remain lesser than Cu-ethylene glycol while the behavior for skin friction coefficient is totally opposite. We support our theoretical study via a detailed evaluation of outcomes. The obtained results via least square Galerkin method (LSGM) are compared with RK (order-4) and already existing results. Moreover, graphical representation, the error, convergence and comparison analysis of outcomes endorsing that the least square method is extremely effective. The suggested method could be extended to other nonlinear problems.

Heat transfer flow of Cu-water and Al2O3-water micropolar nanofluids about a solid sphere in the presence of natural convection using Keller-box method

Natural convection boundary layer flow over a solid sphere in micropolar nanofluid with prescribed wall temperature is studied. Copper (Cu) and alumina (Al2O3) in water-based micropolar nanofluid has been considered. Tiwari and Das’s nanofluid model with realistic empirical correlations are considered to analyze the nanoparticles effects on natural convective flow. The nonlinear partial differential equations of the boundary layer are first transformed into a non-dimensional form and then solved numerically using an implicit finite difference scheme known as Keller-box method. The effects of nanoparticles volume fraction, Prandtl number, micro-rotation parameter on temperature, velocity and angular velocity are plotted and discussed. Further, numerical results for the local Nusselt number and the local skin friction coefficient are obtained. It is found that Cu has a low heat transfer rate as compare to Al2O3 water-based micropolar nanofluid with increasing micro-rotation parameter. The present results of local Nusselt number and the local skin friction for viscous fluid are found to be in good agreement with the literature.