Water Nanofluid Flow Research Articles

Entropy generation of turbulent Cu–water nanofluid flow in a heat exchanger tube fitted with perforated conical rings

Entropy generation analysis for the Cu–water nanofluid flow through a heat exchanger tube equipped with perforated conical rings is numerically investigated. Frictional and thermal entropy generation rates are defined as functions of velocity and temperature gradients. Governing equations are solved by using finite volume method, and Reynolds number is in the range of 5000–15,000. The effects of geometrical and physical parameters such as Reynolds number, number of holes and nanoparticles volume fraction on the thermal and viscous entropy generation rates and Bejan number are investigated. The results indicate that the thermal irreversibility is dominant in most part of the tube. But it decreases with increasing the nanoparticle volume fraction. Frictional entropy generation reduces with increasing the number of holes from 4 to 10. This is because of stronger velocity gradient near the perforated holes. Bejan number decreases with augment of Reynolds number.

Simulation of exergy loss of nanomaterial through a solar heat exchanger with insertion of multi-channel twisted tape

Turbulent flow of nanofluid inside a solar collector has been presented in the current research. Turbulence mixing has been increased with insertion of new turbolentor. Heat transfer and exergy behavior within the test tube equipped with multi-channel twisted tape elements. Al2O3–water nanofluid flows inside the pipe. Absorber plates are made of aluminum. The scrutinized parameters in current paper are number of revolution (N), diameter ratio (D*), Reynolds number (Re), number of channel (n). Better convection heat transfer can be observed for greater values of diameter ratio. Exergy drop declines with increasing scrutinized parameters due to giving strongly swirling flows with rise of them.

A Numerical Simulation of Silver–Water Nanofluid Flow with Impacts of Newtonian Heating and Homogeneous–Heterogeneous Reactions Past a Nonlinear Stretched Cylinder

The aim of the present study is to address the impacts of Newtonian heating and homogeneous–heterogeneous (h-h) reactions on the flow of Ag–H2O nanofluid over a cylinder which is stretched in a nonlinear way. The additional effects of magnetohydrodynamics (MHD) and nonlinear thermal radiation are also added features of the problem under consideration. The Shooting technique is betrothed to obtain the numerical solution of the problem which is comprised of highly nonlinear system ordinary differential equations. The sketches of different parameters versus the involved distributions are given with requisite deliberations. The obtained numerical results are matched with an earlier published work and an excellent agreement exists between both. From our obtained results, it is gathered that the temperature profile is enriched with augmented values radiation and curvature parameters. Additionally, the concentration field is a declining function of the strength of h-h reactions.

An experimental study on MWCNT–water nanofluids flow and heat transfer in double-pipe heat exchanger using porous media

This paper presents the results of an experimental investigation on the heat transfer characteristics of multi-walled carbon nanotube aqueous nanofluids inside a countercurrent double-pipe heat exchanger using porous media. Aluminum porous media (e = 67%) were used because of the construction of the medium, with porous plate media at the center of the inner tube and with three porous plates on the walls of the inner tube. The effects of operating parameters including flow rate (4600 < Re < 7600), mass fractions of nanofluids (0.04–0.25 mass%), and inlet temperature of nanofluids (Tin = 50 °C) on the heat transfer coefficient were investigated. The results indicate that imposing the plate porous media increases the heat transfer coefficient significantly, and the highest increase in the heat transfer coefficient is 35% which is obtained in the test of the lowest mass fraction (0.04 mass%) with three-plate porous media in the experiment range. As the mass fractions increased, the value of heat transfer enhancement assisted by porous media gradually decreased. Also the lower range 100 (L h−1) of the volume flow rate has a powerful enhancement on the enhancement coefficient, while the higher ranges 300 (L h−1) have low influence.

Experimental investigation of TiO2–water nanofluid flow and heat transfer inside wavy mini-channel heat sinks

The present study comprises experimental investigation on heat transfer and hydrodynamic characteristics of TiO2 nanofluid as coolant in wavy channel heat sinks having three different channel configurations. The performance of TiO2 nanofluids having concentrations of 0.006, 0.008, 0.01 and 0.012 vol% is compared with that of distilled water under laminar regime at heating powers of 25 W, 35 W and 45 W. Results indicated that for all heat sinks, nanofluids showed better heat transfer characteristics than distilled water. With an increase in heating power, TiO2 nanofluid thermal performance was decreased. Using 0.012% TiO2 nanofluids, minimum wall base temperature and maximum enhancement in Nusselt number are noted as 33.85 °C and 40.57%, respectively, for heat sink with wavelength of 5 mm and amplitude of 0.5 mm corresponding to Reynolds number of 894 at heating power of 25 W. Pumping power requirement is function of flow rate and pressure drop, and its maximum value of 0.0284 W is associated with heat sink with minimum wavelength. Moreover, variation in wavelength of channel is found to have dominating effect on heat transfer performance of heat sink as compared to the width of channel.

Analytical and Numerical Investigation of Fe3O4–Water Nanofluid Flow over a Moveable Plane in a Parallel Stream with High Suction

In the current framework, a model is constituted to explore the impacts of high suction and partial slip on Fe3O4–water nanoliquid flow over a porous moveable surface in a parallel free stream. The mechanisms of heat transfer are also modeled in the existence of Newtonian heating effect. The obtaining PDEs are transformed into a non-linear ODE system employing appropriate boundary conditions to diverse physical parameters. The governing ODE system is solved using a singular perturbation technique that results in an analytical asymptotic solution as a function of the physical parameters. The obtained solution allows us to carry out an analytical parametric study to investigate the impact of the physical parameters on the nonlinear attitude of the system. The precision of the proposed method is verified by comparisons between the numerical and analytical results. The results confirm that the proposed technique yields a good approximation to the solution as well as the solution calculation has no CPU time-consuming or round off error. Numerical solutions are computed and clarified in graphs for the model embedded parameters. Moreover, profiles of the skin friction coefficient and the heat transfer rate are also portrayed and deliberated. The data manifests that both solid volume fraction and slip impact significantly alter the flow profiles. Moreover, an upward trend in temperature is anticipated for enhancing Newtonian heating strength. Additionally, it was found that both the nanofluid velocity and temperature distributions are decelerated when the solid volume fraction and suction parameters increase. Furthermore, a rise in slip parameter causes an increment in velocity profiles, and a rise in Biot number causes an increment in the temperature profiles.

Numerical investigation on fluid dynamic and thermal behavior of a non-Newtonian Al2O3–water nanofluid flow in a confined impinging slot jet

A numerical investigation of hydrodynamic and heat transfer behaviors for Al2O3–water nanofluids for laminar confined slot jet impingement is presented. This study has been conducted by considering the nanofluid as Newtonian as well as non-Newtonian for a wide range of solid volume fraction (0 ≤ φ ≤ 5%) and Reynolds number range of (25–300). A single-phase fluid approach was used to model the nanofluid and the Ostwald–de Waele model described the non-Newtonian shear thinning nanofluid behavior has been adopted. A comparison with Newtonian and non-Newtonian nanofluid in terms of heat transfer coefficient, Nusselt number, streamlines and isotherms contours has been performed for the same Reynolds number, jet inlet velocity and the same aspect ratio H/W. It has been observed that the rate of heat transfer increases with Reynolds number and solid volume fraction of the nanofluid. Noting that the local Nusselt number is much higher for non-Newtonian nanofluid than Newtonian flow in the entire target surface with a particular enhancement located at the jet axis where a relative increase of 9.8% is evaluated for φ = 5% and Re = 300. However, the pumping power results showed a steep increase with the volume fraction for a Newtonian nanofluid case. In fact, the required PP is 1.32, 1.53, 1.99, 2.11 and 4 times greater than the values calculated in case of pure water at φ = 1, 2, 3, 4 and 5 respectively. At the same value of volume fraction φ, it is noted that the pumping power for a non-Newtonian nanofluid is many times higher than PP required in Newtonian nanofluid case, especially at Re ≤ 200. Lastly, the correlations for stagnation point and average Nusselt number are provided for Newtonian and non-Newtonian nanofluid.

Modeling of irreversibility factors for nanofluid flow in different channels regarding nanoparticle arrangement

Irreversibility factors for the TiO2–water nanofluid flow are evaluated through entropy generation rates caused by friction and heat transfer by taking into account nanoparticle migration. Effects of three factors of viscosity gradient, non-uniform shear rate and Brownian diffusion are considered. The investigations are performed in both conventional channels and minichannels since the channel size has the considerable effects of on entropy generation. Influence of particle migration on the irreversibility factors is more noticeable in smaller channels such that with considering particle migration, the maximum thermal entropy generation rate increases about 51% for 0.2 mm channel, while this increment is almost 16% for 1 mm channel. Unlike results are obtained for conventional channels and minichannels, such that total entropy generation intensifies in minichannels and reduces in conventional channels by particle concentration increment. Friction is main factor in entropy generation for minichannels, while heat transfer demonstrates a higher contribution in conventional channels. The optimal channel size where minimum entropy generation occurs is obtained which is dependent on Reynolds number. Therefore, for lower Reynolds number, optimal case occurs at smaller channel size. Furthermore, diagrams of total entropy generation show minimum (optimal) point for 3 mm channel, while they demonstrate the constant trends for other channels.

Dual exact solutions of graphene–water nanofluid flow over stretching/shrinking sheet with suction/injection and heat source/sink: Critical values and regions with stability

Boundary layer flow of an electrically conducting fluid past a stretching/shrinking sheet inserted in graphene–water nanofluid was investigated. The detailed exact analytical solutions for the flow and heat have been extracted. A theoretical analysis was implemented to explore the regions of non–existence and existence of unique and dual solutions by providing the critical values. In addition, the asymptotic formulas for large first/second slips valid for a stretching/shrinking type, has been deduced. The profiles and distributions of the stream function, velocity, temperature, reduced skin friction coefficient and reduced Nusselt number were examined and discussed via the obtained closed forms. With no restrictions, it was proved that the unique solutions were detected for the flow of all considered parameters over the stretching sheet. However, to obtain the dimensionless temperature solutions, a very sensitive condition on the heat source/sink parameter has to be considered. Whilst in the case of flow over the shrinking sheet, solutions turn out to be unique or dual for some combinations of the parameters. Moreover, two sensitive conditions have to be simultaneously achieved to get the dual solutions depending mainly on the magnetic and thermal radiation parameters. Further, even in the weakness of magnetic field, the dual solutions were obtained for both suction and injection cases. Furthermore, it was proved in detail that the first solutions of the stream function and temperature are stable and physically realizable, whereas those of the second ones are highly–unstable. This means that, while two solutions exist mathematically, only the first one is to be physically considered. It was also concluded that graphene nanoparticles can be used as a heater on increasing the solid volume fraction, injection, thermal radiation and Eckert number. On the other hand, they act as a cooler with an increase of magnetic field, suction, first velocity slip, second velocity slip and heat source/sink. Additionally, the asymptotic formulas and behavior of the stream function and temperature for both sheets were introduced.

Three dimensional CuO–Water nanofluid flow considering Brownian motion in presence of radiation

In this investigation, three dimensional CuO–Water nanofluid flow between two horizontal parallel plates through porous medium in a rotating system is scrutinized. Micro mixing in suspensions is taken into account while calculating viscosity. The problem under consideration gives rise to set of nonlinear partial differential equations. Using proper change of variables, these give rise to set of ordinary differential equations. This cannot be solved using analytical methods, so Mathematica is employed for obtaining solution using HAM. To avail insight of the physics of the problem, the effects of pertinent parameters are discussed. Nanofluid temperature can be increased by increasing either of Radiation parameter, Magnetic parameter, Rotation parameter, Thermophoretic parameter or Brownian parameter. It is observed that skin friction can be reduced by reducing Reynolds number and rotation parameter. Also it can be established that Nusselt number and Sherwood number can be decreased by increasing values of Thermophoretic parameter, Schmidt number, Brownian parameter or rotation parameter.

Analytical and Numerical Investigations of Unsteady Graphene Oxide Nanofluid Flow Between Two Parallel Plates

In this research, different analytical methods were applied to characterize thermal behavior of unsteady graphene oxide–water nanofluid flow between two parallel moving plates. First of all, partial differential equations (PDEs) were transformed to a system of nonlinear ordinary differential equations (ODEs) using similarity solution. Then, collocation method (CM), least square method (LSM) and Galerkin method (GM) were used to solve the system of ODEs and determine velocity and temperature distribution functions. In addition, effects of moving parameter, concentration, Eckert and Prandtl numbers on nanofluid velocity and temperature profiles were examined. Next, using numerical solution of the obtained system of differential equations, the results obtained from the analytical solutions were validated with that of the numerical solution. The validation results indicated high and appropriate accuracy of the analytical solutions compared to the numerical one.

CFD Heat Pipe Simulation of Mass Transfer in NH3-Water Nanofluid Flow

CFD Heat Pipe Simulation of Mass Transfer in NH₃-Water Nanofluid Flow

Heat transfer analysis of unsteady MHD rotating graphene oxide water nanofluid flow

In this study, the Runge Kuta numerical method (RK4), was used to find an accurate solution for the velocity and temperature fields of an unsteady flow of grapheme oxide nanofluid, in a rotating system, within a channel with lower porous wall in presence of imposed external uniform magnetic field. First of all, a local similarity solution for the transformed governing equations was achieved. The nonlinear partial differential equations (PDEs) and boundary conditions were changed to dimensionless form. Thereafter, the numerical approach was employed for obtaining the solution of resulted coupled nonlinear ordinary differential equations. The effect of various parameters including Eckert number, Magnetic parameter and etc. on temperature and velocity distributions were investigated. Finally, the entropy generation rate was calculated. To study the accuracy of solutions, RVIM –analytical method- was used for validation procedures.

Comparative analysis between 36 nm and 47 nm alumina–water nanofluid flows in the presence of Hall effect

White crystalline powder (aluminum oxide $$-\hbox {Al}_2\hbox {O}_3$$ ) and water are the products often formed after the heating of aluminum hydroxide. In this report, boundary layer flow of two different nanofluids (i.e., 36 nm $$\hbox {Al}_2\hbox {O}_3$$ -water and 47 nm $$\hbox {Al}_2\hbox {O}_3$$ -water) over an upper horizontal surface of a paraboloid of revolution under the influence of magnetic field is presented. The combined influence of magnetic field strength, electric current density, electric charge, electron collision time, and the mass of an electron in the flows are considered in the governing equations. Three-dimensional transport phenomenon was considered due to the influence of the Lorentz force $$(\vec {F})$$ along the z-direction as in the case of Hall currents. In this study, the dynamic viscosity and density of the nanofluids are assumed to vary with the volume fraction $$\phi$$ . The dimensional governing equations were non-dimensionalization and parametrization using similarity variables. The corresponding boundary value problem was transformed into initial value problem using the method of superposition and solved numerically using fourth-order Runge–Kutta method with shooting technique (RK4SM). Magnetic field parameter is seen to have dual effects on the cross-flow velocity profiles of both nanofluids. The maximum cross-flow velocity is attained within the fluid domain when 36 nm nanoparticles alumina is used. The cross-flow velocity gradient at the wall increases with magnetic field parameter (M) and also increases significantly with Hall parameter at larger values of M.

Conjugated heat transfer and entropy generation of Al2O3–water nanofluid flows over a heated wall-mounted obstacle

The present study reports numerical simulations of water-based Al2O3 nanofluid flowing in a 2D channel with a heated wall-mounted obstacle. The conjugated heat transfer problem including forced convection within the fluid and conduction inside the obstacle is numerically solved using the mixture model with temperature-dependent properties. The model has been first carefully validated against published data. Then, the fluid flow and heat transfer have been investigated for six nanoparticle volume fractions $$\varphi$$ up to $$1.8\%$$ and bulk Reynolds numbers within the range $$100 \le Re \le 1600$$ . The results show that only the Reynolds number has an influence on the hydrodynamic field, especially on the reattachment length behind the obstacle. The heat transfer rate increases with increasing nanoparticle concentrations and/or Reynolds number. The second law analysis is employed to study the heat transfer and fluid friction irreversibilities. The average entropy generation increases linearly with the Reynolds number. Increasing the nanoparticle volume fraction reduces the thermal entropy generation while the frictional one increases. Finally, the benefit of using this nanofluid is discussed regarding five merit criteria.

Experimental and Numerical Investigation of Inlet Temperature Effect on Convective Heat Transfer of γ-Al2O3/Water Nanofluid Flows in Microtubes

ABSTRACTNanofluids are the combination of a base fluid with nanoparticles with sizes of 1–100 nm. In order to increase the heat transfer performance, nanoparticles with higher thermal conductivity compared to that of base fluid are introduced into the base fluid. Main parameters affecting single-phase and two-phase heat transfer of nanofluids are shape, material type and average diameter of nanoparticles, mass fraction and stability of nanoparticles, surface roughness, and fluid inlet temperature. In this study, the effect of inlet temperature of deionized water/alumina (Al2O3) nanoparticle nanofluids was both experimentally and numerically investigated. Nanofluids with a mass fraction of 0.1% were tested inside a microtube having inner and outer diameters of 889 and 1,067 µm, respectively, for hydrodynamically developed and thermally developing laminar flows at Reynolds numbers of 650, 1,000, and 1,300. According to the obtained numerical and experimental results, the inlet temperature effect was more pronounced for the thermally developing region. The performance enhancement with nanoparticles was obtained at rather higher Reynolds numbers and near the inlet of the microtube. There was a good agreement between the experimental and numerical results so that the numerical approach could be further implemented in future studies on nanofluid flows.

Entropy generation analysis of Cu–water nanofluid flow over a moving wedge

Entropy generation analysis of Cu–water nanofluid flow over a moving wedge

Numerical Study of Mixing Thermal Conductivity Models for Nanofluid Heat Transfer Enhancement

Researchers have paid attention to nanofluid applications, since nanofluids have revealed their potentials as working fluids in many thermal systems. Numerical studies of convective heat transfer in nanofluids can be based on considering them as single- and two-phase fluids. This work is focused on improving the single-phase nanofluid model performance, since the employment of this model requires less calculation time and it is less complicated due to utilizing the mixing thermal conductivity model, which combines static and dynamic parts used in the simulation domain alternately. The in-house numerical program has been developed to analyze the effects of the grid nodes, effective viscosity model, boundary-layer thickness, and of the mixing thermal conductivity model on the nanofluid heat transfer enhancement. CuO–water, Al2O3–water, and Cu–water nanofluids are chosen, and their laminar fully developed flows through a rectangular channel are considered. The influence of the effective viscosity model on the nanofluid heat transfer enhancement is estimated through the average differences between the numerical and experimental results for the nanofluids mentioned. The nanofluid heat transfer enhancement results show that the mixing thermal conductivity model consisting of the Maxwell model as the static part and the Yu and Choi model as the dynamic part, being applied to all three nanofluids, brings the numerical results closer to the experimental ones. The average differences between those results for CuO–water, Al2O3–water, and CuO–water nanofluid flows are 3.25, 2.74, and 3.02%, respectively. The mixing thermal conductivity model has been proved to increase the accuracy of the single-phase nanofluid simulation and to reveal its potentials in the single-phase nanofluid numerical studies.

Three-dimensional convective flow of CNTs nanofluids with heat generation/absorption effect: A numerical study

Three-dimensional flow of carbon water nanofluid by nonlinear stretched sheet is studied. Nanofluid saturates the porous space. Heat transfer mechanism is examined via more suitable convective type condition and nonuniform heat generation/absorption. The solutal concentration is regulated by a simple isothermal model of homogeneous–heterogeneous reactions. The numerical solutions are obtained through shooting technique by Runge–Kutta method of order five. Both single and multiple walled carbon nanotubes as nanoparticles in the base fluid are considered. Graphical illustrations and tabulated values point out the impact of sundry variables. Both components of velocity show reverse effect for stretching rate ratio. The simulations predict that wall heat flux is inversely proportional to heat generation variable. However value of heat flux is predicted more in case of larger convecting heating strength and volume fraction of carbon nanotubes. Heat transfer coefficient is more in single walled carbon nanotubes (SWCNTs) than in multi walled carbon nanotubes (MWCNTs). Heterogeneous–homogeneous variables and Schmidt number have opposite behaviors on nanoparticle concentration distribution. Excellent agreement is shown through comparison of past and present results.

Thermal-hydraulic characteristics of nanofluid flow in corrugated ducts

This study aims are to present effects of periodic corrugations in rectangular ducts on the thermal-hydraulic behaviors of nanofluids. The applied corrugations were rectangular cavities with a constant cavity length. In this regard, three various dimensionless cavity shaped corrugation widths such as S/H = 0.1, 0.2, and 0.3 were investigated. Computations were carried out at different Reynolds numbers in the range of 500≤Re≤2000. Alternatively, for further improvement of thermal characteristics, effects of an alumina–water nanofluid flow on the aforementioned corrugated ducts were investigated using the constant nanoparticle size dp = 25 nm and various nanoparticle volume concentrations in the range of 1%≤ Φ ≤8%. The governing equations were solved numerically by means of the finite volume method. The obtained results revealed that application of periodic corrugations in ducts develops the turbulent flow all over the duct, which results in the higher flow mixing and thermal efficiency compared with the plain duct. Furthermore, rates of turbulence intensity and flow mixing change as a function of S/H. In addition, it was demonstrated that application of alumina–water flow in such corrugated ducts enhances the rate of heat transfer and thermal efficiency index compared with water flow. It is hoped that the obtained results arouse interest for thermal designer.