Water-based Copper Research Articles

Impact of the Brownian motion and thermophoretic diffusion during the radiative MHD hybrid nanofluid flow past a stretching sheet

The article aims to analyze the effects of thermophoretic and Brownian motion on steady three-dimensional magnetohydrodynamics with fully developed natural convective hybrid nanofluid flow past a bidirectionally extending sheet. We assumed the water-based copper and aluminum nanoparticles suspension under the influence of the rotational effect, nonlinear chemical reaction, thermal radiations, viscous dissipation, and heat source. The flow field is modeled with the help of the basic equations. Furthermore, the problem is reduced to ordinary differential equations (ODEs) with the similarity variables. The reduced system of ODEs is solved with the semianalytical method (homotopy analysis method). The results for the state variables are displayed through graphs tables for various pertinent parameters. The thermal profile falls with the higher values of the Brownian and thermophoresis parameters, while the concentration profile shows an opposite trend with the increasing values of the Brownian parameter. Also, the slip parameter decreases both the thermal and concentration profiles as well as the surface drag. The velocity profiles along both directions fall with the higher magnetic strength and porosity parameters. The heat source and radiations parameter enhances the thermal profile with increasing values. The study also recommends the opposite trends for the axial and transverse velocities with increasing value of the stretching ratio factor. The proposed method convergence is present through [Formula: see text] curves for the regions [Formula: see text] [Formula: see text] [Formula: see text] and [Formula: see text] The skin friction and Nusselt number are displayed through tables numerically for various values of volume fraction and other important parameters.

Acoustothermal dynamic characteristics of water-based copper nanofluids on a vibrating nanosurface

The high-frequency vibration is a potential method to induce evaporation and boiling of nanofilm by acoustothermal effect. Here, we investigate the acoustothermal dynamic characteristics of water-based copper nanofluids on a vibrating nanosurface using molecular dynamics simulation. Regimes of the evaporation, nucleate boiling and film boiling can be classified at different amplitudes (A) and frequencies (f). Under the same vibration condition, the introduction of the nanoparticle is conducive to the evaporation and boiling outcome, which becomes superior with the increase of the nanoparticle diameter. Change rules of acoustothermal atomization modes depend on A and f, which are similar for basefluid and nanofluids. There is a negative linear relationship between the nonevaporating layer height and Af3/2 when Af3/2 is smaller than the turning point. Underlying reasons for the enhancement of the evaporation and boiling by adding the nanoparticle rest with the irregular Brownian motion and spinning motion of the nanoparticle, which intensifies disturbance in the water nanofilm. Moreover, a layer of water molecules is absorbed around the nanoparticle to ameliorate heat transfer and thus facilitates the evaporation and boiling of the water nanofilm on a vibrating nanosurface.

The feasibility of using magnetic refrigeration cycles in the thermal management of rechargeable batteries in electric cars

This is the first study that intends to check the feasibility of using a magnetic refrigerator (MR) in the thermal management of rechargeable batteries instead of other conventional passive/active cooling techniques. A mathematical model has been generated to study the cooling performance of the proposed system at different conditions, including synchronized and asynchronized cooling at different discharge rates and ambient temperatures, in addition to exploring the effect of using water-based copper (Cu) nanofluid as a heat transfer fluid in a spherical packed bed active magnetic regenerator on the cooling performance. The proposed system can maintain the maximum temperature of the battery pack to less than 35 °C with high coefficients of performance (COPs) [between 4.8 and 9.7] during synchronized and asynchronized cooling at an ambient temperature of 25 °C and different discharge rates. The system can operate with COP higher than 1 at an ambient temperature up to 40 °C during 0.5 discharge rate, and up to 38 °C ambient temperature during 1 discharge rate. The MR can work with COP of 5.3 compared to 3.82 for vapor compression refrigeration system (VCRS) if the two systems meet a 3-kW cooling load. The study reveals that MR outperforms many active cooling techniques especially when appropriately integrated with the thermal management of the vehicle cabin.

Semi-analytical solution of nanofluid flow with convective and radiative heat transfer

The application of nanofluids has exploded in recent decades to improve the local number, mean Nusselt number, and rate of heat transfer. However, boundary layer equations of nanofluid across a flat plate with radiation have not been studied, and therefore this paper studies them mathematically for the first time. For water-based copper and aluminum oxide nanofluids, a similarity solution is presented in this study, and the subsequent system of the ordinary differential equation (ODE) is numerically solved by the Runge–Kutta method in MATLAB. Two different hydraulic boundary conditions are used in the simulations. In the first, the flow across a moving plate and the direction of the flow are analyzed, while in the second, the flow over a nonlinearly moving plate in a still fluid is investigated. The nanoparticle’s boundary layer thickness is found less than the thermal and hydraulics boundary layers. The local Nusselt number and friction factor of both the nanofluids are calculated and compared with the base fluid. The results demonstrate that the friction coefficient is high and the Nusselt number is low for nanoparticles with a high volume fraction. It also revealed that the friction factor for water–aluminum oxide is 16% greater than that for the water–CuO whereas the local Nusselt number for water–aluminum oxide is only 5% more than that for the water–CuO.

Numerical simulation and intelligent prediction of thermal transport of a water-based copper oxide nanofluid in a lid-driven trapezoidal cavity

This article investigates the fluid dynamics and heat transfer properties in a trapezoidal enclosure containing a heated cylindrical object. It involves the interaction of multiple physical processes such as the magnetic field, thermal radiation, porous materials, and aqueous copper oxide nanoparticles. The governing partial differential equations are analyzed numerically through the continuous Galerkin finite element algorithm. The analysis takes into account various physical parameter factors, including the Richardson number (0–5), the Hartmann number (5−40), the Darcy number (0.001−0.1), thermal radiation parameter (0.5−2), and nanoparticle volume concentration (0.01−0.1). The physical mechanism of thermal and mass transfer in the enclosure caused by various factors is fully explored. In addition, the multiple expression programming (MEP) technique is implemented to report a comparative analysis of flow profiles and thermal distribution. The findings demonstrated that at low Ri, the primary flow within the cavity is driven by the shear friction generated by the moving walls. The growing importance of radiative heat transfer reduces the effectiveness of convective heat transfer, resulting in a decline in the average Nusselt number with R. The heat transfer rate rises up to 27.7% as ϕ augments; however, its value declines by 9.37% against Ha. The expected results obtained by the MEP approach are very consistent with the numerical ones. There is no doubt that the new MEP concept provides a valuable tool for researchers to predict the heat transfer behavior of any data set in cavities of different shapes. It is expected to provide new idea for the development of efficient cooling systems and the improvement of energy efficiency in various engineering applications.

Heat transport phenomenon of the MHD water-based hybrid nanofluid flow over a rotating disk with velocity slips

The present investigation computes the heat transport phenomenon of the magnetohydrodynamic (MHD) flow of CuO-Ag/H2O hybrid nanofluid over a spinning disc. The authors are confident that there is very less analysis covering the fluid flow containing silver and copper oxide nanoparticles over a rotating disk. Therefore, the authors are interested to consider the water-based nanoliquid flow over a spinning disk. Furthermore, the velocity slip and thermal convective conditions are taken into consideration. The formulation of the problem is made in the form of PDEs and is then converted into the nonlinear ODEs by employing suitable similarity transformations. The homotopic analysis approach is applied for the semi-analytical solution of these resulting equations. The convergence of homotopic approach has also revealed with the help of figure. The performance of the hybrid nanofluid flow velocities and temperature has been shown in a graphical form against distinct flow parameters. Also, the numerical results of skin friction coefficient and Nusselt number have been calculated in a tabular form. The outcomes of the current problem show that the increase in the skin friction of the water-based copper oxide nanofluid is greater than the water-based silver nanofluid at 4% of the nanoparticle volume fraction. Also, the skin friction of the hybrid nanofluid is increased by 8% compared to the silver nanofluid at 4% of the nanoparticle volume fraction. Furthermore, the heat transfer rate of the water-based copper oxide nanofluid is greater than the water-based silver nanofluid at 4% of the nanoparticle volume fraction. Also, the heat transfer rate of the hybrid nanofluid is 52% greater than that of silver nanofluid at 4% of the nanoparticle volume fraction. It is found that the Nusselt number of the hybrid nanofluid is highly affected by the embedded parameters as compared to nanofluids.

Significance of Nanoparticle Radius and Gravity Modulation on Dynamics of Nanofluid over Stretched Surface via Finite Element Simulation: The Case of Water-Based Copper Nanoparticles

This communication studies the importance of varying the radius Dp of Copper nanoparticles for microgravity-modulated mixed convection in micropolar nanofluid flux under an inclined surface subject magnetic field and heat source. In the current era, extremely pervasive modernized technical implementations have drawn attention to free convection governed by g-jitter force connected with microgravity. Therefore, fixed inter-spacing of nanoparticles and effects of g-jitter on the inclined surface are taken into consideration. A mathematical formulation based on conservation principles was non-dimensionalized by enforcement of similarity transformation, yielding a related set of ODEs. The convective non-linearity and coupling, an FE discretization, was implemented and executed on the Matlab platform. The numerical process’ credibility was ensured for its acceptable adoption with the defined outcomes. Then, the computational endeavor was continued to elucidate the impacts of various inputs of Dp, the amplitude of modulation ϵ, material parameter β, mixed convection parameter λ, inclination angle γ, and magnetic parameter M. The enlarging size of nanoparticles accelerated the nanofluid flow due to the depreciation of viscosity and receded the fluid temperature by reducing the surface area for heat transportation. The modulated Nusselt number, couple stress, and skin friction coefficient are significantly affected by the variation of Dp, M, β, λ, and ϵ. These results would benefit experts dealing with upper space transportation and materials’ performance, such as the effectualness of chemical catalytic reactors and crystals.

Viscosity Analysis of Water-based Copper Oxide Nanofluids

In this paper, the effects of weight concentration of nanoparticles and temperature on the viscosity of water-based copper oxide nanofluids have been studied experimentally using analysis of variance (ANOVA)-based two-factor three-level (23) factorial design. The results show that a maximum increase of 23.12% in viscosity is observed at 30°C temperature as the weight concentration of nanoparticles increases from 0.03 to 0.3wt.%. Whereas the temperature increases from 30 to 60°C, the viscosity decreases up to 46.19% in the case of 0.3wt.% nanofluid. Temperature is found to be more dominant than the concentration of nanoparticles. The optimum value of viscosity (0.513 mPa.s) is found at concentrations of 0.1wt.% and 60°C temperature with an 18.72% enhancement in viscosity as compared to the base fluid. The experimental and model values of viscosity have been compared with the predictions of the proposed equation for viscosity. The experimentally measured results are found near the proposed results whereas the model underestimates the viscosity in the case of all nanofluids. The maximum underestimation of 25.92 % was observed in the case of 0.3wt.% nanofluid at 60°C temperature.

Experimental Analysis of the Thermal Performance Enhancement of a Vertical Helical Coil Heat Exchanger Using Copper Oxide-Graphene (80-20%) Hybrid Nanofluid

The thermal performance enhancement of a vertical helical coil heat exchanger using distilled water-based copper oxide-graphene hybrid nanofluid has been analyzed experimentally. Accordingly, the focus of this study is the preparation of CuO-Gp (80-20%) hybrid nanoparticles-based suspensions with various mass fractions (0% ≤ wt ≤ 1%). The volume flow rate is ranged from 0.5 L·min−1 to 1.5 L·min−1 to keep the laminar flow regime (768 ≤ Re ≤ 1843) and the supplied hot fluid’s temperature was chosen to equal 50 °C. To ensure the dispersion and avoid agglomeration an ultrasound sonicator is used and the thermal conductivity is evaluated via KD2 Pro Thermal Properties Analyzer. It has been found that the increment in nanoparticles mass fraction enhances considerably the thermal conductivity and the thermal energy exchange rate. In fact, an enhancement of 23.65% in the heat transfer coefficient is obtained with wt = 0.2%, while it is as high as 79.68% for wt = 1%. Moreover, increasing Reynolds number results in a considerable augmentation of the heat transfer coefficient.

MHD stagnation point flow of a water-based copper nanofluid past a flat plate with solar radiation effect

Due to many biological and technical applications, including microelectronics, heat exchangers, cancer therapy, process industries, solar collectors and power production, researchers have been more interested in the mechanism of heat transfer involving nanomaterials. A contemporary method to increase the thermal conductivity of various cooling fluids is the use of nanomaterials. Many researches suggest that the thermal conductivity of nanoliquids; solid nanoparticles combined with a base fluid, is expressively greater than that of conventional fluids. This work presents the theoretical investigation of magnetohydrodynamic stagnation point flow of non-Newtonian nanofluid flow past flat plate. The applications of solar radiation towards water-based copper nanoparticles are highlighted in this study. The system of PDEs is transmuted into the system of ODEs by mean of suitable similarity variable. Analytical solution of the present analysis has been performed with the help of HAM technique. The impacts of physical factors on the flow profiles, skin friction coefficient, heat, and mass transfer rates are calculated. It is significant to note that the default concentration is weighted by 4% throughout this analysis. Also in this analysis, we examined the temperature and heat transfer rate for the presence and absence of solar radiation. It is found that the greater nanoparticles volume fraction of the water-based copper nanoparticles has accelerated the flow profiles for the absence of magnetic field. However, for the presence of strong magnetic field, the velocity, and temperature of the water-based copper nanoparticles have significantly reduced. Due to the incidence of Lorentz force, the velocity of the water-based copper nanoparticles has deteriorated, while the temperature profile has augmented. It is found that the solar radiation has always dominant impression on temperature of the water based copper nanoparticles.

Dynamics of inter-particle spacing, nanoparticle radius, inclined magnetic field and nonlinear thermal radiation on the water-based copper nanofluid flow past a convectively heated stretching surface with mass flux condition: A strong suction case

Scientists and researchers have recently been very interested in copper nanoparticles due to their potential modern uses, such as high temperature superconductors, gas sensors, catalytic processes, and solar cells, as well as their usage in wound dressings and biocidal properties. Therefore, in this analysis, the authors have investigated the applications of an inclined magnetic field, radius of nanoparticles, nonlinear thermal radiation, and inter-particle spacing on the two-dimensional flow of an electrically conducting water-based copper nanofluid over a stretching surface using a porous medium. Furthermore, the effects of chemical reaction, exponential heating, thermophoresis and Brownian motion are also taken into account. The nanofluid flow is considered under strong suction, convective, and mass flux conditions. The present model is solved by means of HAM. Convergence of HAM is shown with the help of Figure. The current findings are contrasted with previously reported findings to confirm that the current model is accurate. The outcomes of this study showed that the surface drag gets higher with the increasing angle of inclination. A maximum impact of angle of inclination on the surface drag is found, when α = π/2. Also, it is found that the impact of angle of inclination is greater when the inter-particle spacing is small. While on the other hand, exploring the role of radius of nanoparticle, a higher impact is found when radius of nanoparticle is higher. The velocity profiles are highly affected by the embedded parameters when the inter-particle spacing is small as compared to large inter-particle spacing. The temperature profiles are highly affected by the embedded parameters in the case of nonlinear thermal radiation as compared to linear thermal radiation.

Hydromagnetic CuO-H2O nanofluid transportation through irreversibility analysis

The current investigation aimed for the exploration of steady-state, incompressible flow and energy transportation of water-based copper oxide nanofluid past a linear stretching sheet through suction/injection possessions. Furthermore, the impact of magnetohydrodynamic, radiation, and entropy generation are taken in the problem development. The nonlinear equations are reframed into single independent variable equations by the implication of appropriate similarity transformations. The Fehlberg scheme is developed for the numerical computations of re-structured non-linear expressions. The variations of influential constraints on the dimensionless physical quantities are investigated and reported in detail. The prominent features of the investigation include the higher velocity and weaker temperature is achieved against the incrementing stretching constraint values. The irreversibility ratio is reduced against the emerging stretching strength constraint. The Bejan number is decaying against the higher magnetic constraint. The blowing and suction have opposite impacts on the skin-friction factors.

Experimental study on the influence of a conical cavity’s inclination angle and aspect ratio on thermal behavior of a cone cooled with nanofluid saturated porous media

ABSTRACT An experimental setup has been developed to measure the thermal state of a conical antenna cooled by means of porous media saturated with water-based copper nanofluid. Thermal conductivity of the used porous materials varies between 4 and 41.2 times that of the water which constitutes the base fluid of the nanofluid whose volume fraction ranges from 0% (pure water) to 5%. The antenna is placed in the center of a coaxial concentric cavity of the same shape. Aspect ratio of the enclosure varies between 0.2 and 0.6. Its base is inclined with respect to the horizontal plane with an angle ranging between 0° and 180° corresponding to a horizontal circular base with the top of the cone oriented upwards and downwards, respectively. Measurements validate the calculations obtained in a recent numerical approach based on the finite volume method. They confirm that the Maxwell and Brinkman models remain valid for the ranges of the Rayleigh number considered here and Water based-Copper nanofluid volume fraction (0–5%). This work also confirms the effectiveness of porous materials saturated with nanofluids to ensure the thermoregulation of electronic equipment dissipating a large amount of thermal power.

The Effect of Navier Slip and Skin Friction on Nanofluid Flow in a Porous Pipe

The flow of nanofluids through a porous medium is considered the optimum method for convective heat transfer. In this study, nanofluid flow in a porous pipe with Navier slip is investigated. Two water-based nanofluids, Copper (Cu) and alumina (Al2O3), were considered. The governing equation is presented and non-dimensionalization has been done for momentum and energy equations, initial and boundary conditions, skin friction, and Nusselt number. The governing system was simplified to ordinary differential equations, which were numerically solved and a mathematical model of nanofluid flow was formulated. The results, with regard to variations in various parameters such as temperature, velocity, skin friction, and Nusselt number, are presented graphically and discussed. It was found that the velocity during the flow decreases with the increase of the Navier slip.

The ciliated flow of water-based graphene oxide and copper nanoparticles (GO-Cu/H2O) in a complex permeable tube with entropy generation phenomenon

In recent years, thermal enhancement using the suspension of hybrid nanofluid has become useful to improve the heat transportation phenomenon in various engineering and industrial processes. The current investigation presents the thermal impacts of hybrid nanofluid with applications of ciliated motion through a cylindrical tube. The concentration of graphene oxide and copper nanoparticles is used in current formulations. Additionally, the physical influences of porosity parameters on the rheology and the heat analysis are examined. The rheological equations are modeled using cylindrical polar coordinates in the laboratory frame. The problem is simplified using two distinct assumptions: the lubrication theory and the long-wavelength estimate. The solutions of rheological equations are attained analytically using the integration technique. The obtained expressions for velocity profile, pressure gradient, temperature profile, and entropy production are described through graphs for numerous embedded parameters. The boundary layer (BL) occurrences are predicted in the axial velocity under higher porosity impacts. The transportation of the hybrid fluid is controlled with the help of the ciliated length. The present research is useful in the chemical processes of thermo-fluidic micro-pumps and devices of nanomaterials.

Finite element simulation on the convective double diffusive water-based copper oxide nanofluid flow in a square cavity having vertical wavy surfaces in presence of hydro-magnetic field

We explored natural convection of copper oxide-water nanofluid flow within a square domain having two wavy vertical surfaces in existence of the hydro-magnetic field using non-uniform dynamic model. Two vertical surfaces on the left and right are regarded as connecting outlets through which heat can pass and considered as the colder walls, the bottom surface is regarded as a uniform heat source, and the upper boundary line is regarded as an insulating surface through which heat cannot pass. The Galerkin's extension in the finite element analysis has been incorporated to design, transform, and solve the nanofluid equations. The results reveal that when the thermal Rayleigh number upturns, the amplitude of the velocity, streamlining, isotherms efficacy, and uniformity of the isoconcentration labeling increase for a nanofluid with reduced nanoparticle volume percentage. As the magnetic pitch intensifies, the flow strength drops, and effective flow occurs in the vertical magnetic field. Flow convolution develops as more waves are formed on a vertical surface. The average heat transmission rose by 158% as the Rayleigh number grew from 104 to 106. The mean heat transmission increases by 10.18% when the nanoparticle volume segment is increased from 0.025 to 0.05. The heat transmission rate is higher on the vessel's non-wave vertical surface. Heat transfer is reduced by 16.98% when the wave number is augmented to 2 and increased by 3.62% when the wave number is risen from 2 to 4.

Thermal state of a conical antenna cooled by means of nanofluid saturated porous media

Thermal state of a conical antenna used for big data transfer was determined in this work. Its cooling is provided through porous media saturated with water-based copper nanofluid (NF) whose volume fraction varies in the 0% (pure water) [Formula: see text] range. Otherwise, the ratio between the thermal conductivity of the highly porous material and that of the fluid base (water) varies between 4 and 41.2. The solution is obtained by means of 3D numerical approach based on the volume control method using the SIMPLE algorithm in the large [Formula: see text]–[Formula: see text] Rayleigh number range. The average temperature of the antenna can be determined with the correlation proposed in this work for any combination of the thermal conductivity ratio, volume fraction and Rayleigh number. This new and original correlation makes it possible to determine the optimal values of these three influencing parameters to ensure the correct antenna’s operation.

Natural convection with water-copper nanofluid around a finned vertical cylindrical electronic component

PurposeThe purpose of this study is to quantify the free convective heat transfer around a vertical cylindrical electronic component equipped with vertical fins representing an antenna, contained in a closed cavity maintained isothermal. Its cooling is provided via a water-based copper nanofluid whose volume fraction varies between 0% and 10%. Its effective viscosity and thermal conductivity are determined with the Brinkman and Maxwell models.Design/methodology/approachThe governing equation system has been solved by means of the volume control method based on the SIMPLE algorithm.FindingsA Nusselt-Rayleigh correlation valid in the 3.32 × 105 – 6.74 × 107 Rayleigh number range is proposed. It allows the thermal sizing of the considered system used in high power electronics to ensure their correct operation in the worst conditions.Originality/valueThe proposed correlations are original and unpublished.

Computational study of three-dimensional flow and heat transfer of 25 nm Cu–H2O nanoliquid with convective thermal condition and radiative heat flux using modified Buongiorno model

The three-dimensional steady flow of an incompressible 25 nm water-based copper nanoliquid over a bi-directional elongated surface with convective thermal boundary condition is studied. This work may meet various thermal engineering applications for instance thermal energy exchangers, solar energy collectors, geophysical transports, radiators, electronic cooling devices, and nuclear reactors. Corcione's model for effective thermal conductivity and dynamic viscosity is used in conjunction with correlations based on effective medium theory for density, specific heat, and electrical conductivity. The effects of radiative heat and convective thermal energy conditions are also taken into account. Modified Buongiorno inhomogeneous model-based governing equations transmuted to nonlinear ordinary boundary value problem. The subsequent system has been deciphered using computer algebraic system software. The method used is validated against the available data and found an exceptional agreement. Two dimensional charts are designed to analyze the impact of the key parameters involved in the model. Three dimensional surface plots are plotted for the study of the Nusselt number, friction coefficients, and Sherwood number values are tabulated for several key parameters. A regression analysis is also performed for the local Nusselt number.

Numerical study on convective flow boiling of nanoliquid inside a pipe filling with aluminum metal foam by two-phase model

This study tries to employ the computational fluid dynamics (CFD) approach to investigate the influence of the simultaneous use of the metal foam (porous media) and the water-based nanofluid on the boiling flow regime. For this purpose, boiling flow heat transfer of water-based copper nanofluid inside of both simple pipe and aluminum metal foam pipe is simulated using the Eulerian two-phase CFD model. The nanofluid is supposed to flow inside the pipe with the mass flux of 1927 kg/m2s and the subcooled temperature of 10oc at atmospheric working pressure. The pipe is also under a constant wall heat flux (50–110 KW/m2). Different copper nanoparticle volume fractions (i.e., 0.5, 1, and 1.5%) are considered for this investigation. The porosity and pore density of the metal foam are 0.8 and 10 pore per inch (PPI) respectively. The heat transfer parameters of boiling flow including the wall temperature, the vapor volume fraction on the wall, the onset of the nucleate boiling (ONB), the local heat transfer coefficient, and the mean diameter of the vapor bubble are considered in this study. All heat transfer coefficients predicted by the CFD are compared with the Chen correlation. As far as the authors know, for the first time, the boiling flow of nanofluid-based water inside a metal foam pipe was simulated by the two-phase model of Eulerian. The results reveal that for the metal foam pipe, after happening of the ONB, the wall temperatures suddenly jump over the saturated temperature and the critical heat flux (CHF) happens. But no such sudden increase of the wall temperature is seen along the simple pipe before and after the ONB. Besides, the convective heat transfer coefficient in the metal foam pipe before the beginning of the boiling is more than double the boiling flow in the simple pipe. Although in metal foam pipe, once the boiling happened, the heat transfer coefficient was degraded by 50%, this value is still 25% more than the heat transfer coefficient of the boiling flow in the simple pipe. The results of this study could be practically used for boiling heat transfer analysis of heat exchangers filled by porous media and nanofluid.