Visual experimental study of nanofluids application to promote CO_(2) absorption in a bubble column

The addition of dispersed-phase nanoparticles in the liquid phase can enhance the gas-liquid transfer process as the suspended nanoparticles affect the transfer process inside the fluid through microdisturbance or micro-convection effects.In this article,a high-speed digital camera was used to visualize the bubble behavior of CO_(2) in pure water and nanofluids to examine the effects of CO_(2) gas flow rate,nanoparticle solid content and type on the bubble behavior in the fluids.The CO_(2) absorption performance in three water-based nanofluids were compared in a bubbler.And the mass transfer characteristics during CO_(2) bubble absorption and the reasons for the enhanced gas-liquid mass transfer effect of nanoparticles were analyzed.The results showed that the presence of nanoparticles affected the formation process of bubbles in the fluid,shortened the bubble detachment time,reduced the detachment diameter,effectively increased the gas-liquid contact area,and improved the bubbles detachment frequency.The system with MCM-41 corresponded to a higher overall mass transfer coefficient.Uncalined MCM-41 contained surfactant that enhanced foaming behavior in water.This prevented the transfer of CO_(2) to some extent,and the CO_(2) absorption by uncalined MCM-41/H_(2)O was 5.34%higher than that by pure water.Compared with SiO_(2) nanoparticles with the same particle size and the same composition,MCM-41 had a higher adsorption capacity and better hydrophilicity due to its larger specific surface area and rich porous structure,which was more favorable to accelerate the collision between nanoparticles and CO_(2) bubbles to cause micro-convection.Under the condition of 0.1%(mass)solid content,the enhancement of CO_(2) absorption process by MCM-41 nanoparticles was more significant and improved by 16.9%compared with pure water.

A Novel Numerical Method for Simulating Boiling Heat Transfer of Nanofluids

In this paper,a new approach called the Eulerian species method was proposed for simulating the convective and/or boiling heat transfer of nanofluids.The movement of nanoparticles in nanofluids is tracked by the species transport equation,and the boiling process of nanofluids is computed by the Eulerian multiphase method coupled with the RPI boiling model.The validity of the species transport equation for simulating nanoparticles movement was verified by conducting a simulation of nanofluids convective heat transfer.Simulation results of boiling heat transfer of nanofluids were obtained by using the commercial CFD software ANSYS Fluent and compared with experimental data and results from another numerical method(Eulerian three-phase model).Good agreement with experimental data was achieved,and it was proved the Eulerian species method is better than the Eulerian three-phase model since it can give better simulation results with higher accuracy but needs fewer computation resources.

Heat-Generating Effects Involving Multiple Nanofluids in a Hybrid Convective Boundary Layer Flow on the Sloping Plate in a Porous Medium

The hybrid convective boundary layer circulation involving multiple nanofluids via a medium with pores is approaching a sloping plate. An investigation regarding the heat-generating effects upon the examined nanofluid flows has been carried out through computational analysis. A mathematical framework employing governing differential equations that are partial has been implemented to produce an ensemble of ordinary differential equations, which happen to be nonlinear that incorporate nanofluid flows by utilizing acceptable transformations. Through the combination of the Nachtsheim-Swigert shooting method and the Runge-Kutta method, the group of resulting non-dimensionalized equations is solved computationally. In a few special, confined cases, the corresponding numeric output is thereafter satisfactorily matched with the existing available research. The consequences of heat generation regarding local skin friction coefficient and rate of heat in conjunction with mass transfer have been investigated, evaluated, and reported on the basis of multiple nanofluid flows.

Exact solutions for magnetohydrodynamic nanofluids flow and heat transfer over a permeable axisymmetric radially stretching/shrinking sheet

We report on the magnetohydrodynamic impact on the axisymmetric flow of Al_(2)O_(3)/Cu nanoparticles suspended in H_(2)O past a stretched/shrinked sheet.With the use of partial differential equations and the corresponding thermophysical characteristics of nanoparticles,the physical flow process is illustrated.The resultant nonlinear system of partial differential equations is converted into a system of ordinary differential equations using the suitable similarity transformations.The transformed differential equations are solved analytically.Impacts of the magnetic parameter,solid volume fraction and stretching/shrinking parameter on momentum and temperature distribution have been analyzed and interpreted graphically.The skin friction and Nusselt number were also evaluated.In addition,existence of dual solution was deduced for the shrinking sheet and unique solution for the stretching one.Further,Al_(2)O_(3)/H_(2)O nanofluid flow has better thermal conductivity on comparing with Cu/H_(2)O nanofluid.Furthermore,it was found that the first solutions of the stream are stable and physically realizable,whereas those of the second ones are unstable.

Mechanism of Thermally Radiative Prandtl Nanofluids and Double-Diffusive Convection in Tapered Channel on Peristaltic Flow with Viscous Dissipation and Induced Magnetic Field

The application of mathematical modeling to biological fluids is of utmost importance, as it has diverse applicationsin medicine. The peristaltic mechanism plays a crucial role in understanding numerous biological flows. In thispaper, we present a theoretical investigation of the double diffusion convection in the peristaltic transport of aPrandtl nanofluid through an asymmetric tapered channel under the combined action of thermal radiation andan induced magnetic field. The equations for the current flow scenario are developed, incorporating relevantassumptions, and considering the effect of viscous dissipation. The impact of thermal radiation and doublediffusion on public health is of particular interest. For instance, infrared radiation techniques have been used totreat various skin-related diseases and can also be employed as a measure of thermotherapy for some bones toenhance blood circulation, with radiation increasing blood flow by approximately 80%. To solve the governingequations, we employ a numerical method with the aid of symbolic software such as Mathematica and MATLAB.The velocity, magnetic force function, pressure rise, temperature, solute (species) concentration, and nanoparticlevolume fraction profiles are analytically derived and graphically displayed. The results outcomes are compared withthe findings of limiting situations for verification.

Performance Simulation of a Double Tube Heat Exchanger Based on Different Nanofluids by Aspen Plus

A heat exchanger’s performance depends heavily on the operating fluid’s transfer of heat capacity and thermal conductivity.Adding nanoparticles of high thermal conductivity materials is a significant way to enhance the heat transfer fluid’s thermal conductivity.This research used engine oil containing alumina(Al_(2)O_(3))nanoparticles and copper oxide(CuO)to test whether or not the heat exchanger’s efficiency could be improved.To establish the most effective elements for heat transfer enhancement,the heat exchangers thermal performance was tested at 0.05%and 0.1%concentrations for Al_(2)O_(3)and CuO nanoparticles.The simulation results showed that the percentage increase in Nusselt number(Nu)for nanofluid at 0.05%particle concentration compared to pure oil was 9.71%for CuO nanofluids and 6.7%for Al_(2)O_(3)nanofluids.At 0.1%concentration,the enhancement percentage in Nu was approximately 23%for CuO and 18.67%for Al_(2)O_(3)nanofluids,respectively.At a concentration of 0.1%,CuO nanofluid increased the LMTD and overall heat transfer coefficient(U)by 7.24 and 5.91%respectively.Both the overall heat transfer coefficient(U)and the heat transfer coefficient(hn)for CuO nanofluid at a concentration of 0.1%increased by 5.91%and 10.68%,respectively.The effectiveness(εn)of a heat exchanger was increased by roughly 4.09%with the use of CuO nanofluid in comparison to Al_(2)O_(3)at a concentration of 0.1%.The amount of exergy destruction in DTHX goes down as Re and volume fractions go up.Moreover,at 0.05%and 0.1%nanoparticle concentrations,the percentage increase in dimensionless exergy is 10.55%and 13.08%,respectively.Finally,adding the CuO and Al_(2)O_(3)nanoparticles improved the thermal conductivity of the main fluid(oil),resulting in a considerable increase in the thermal performance and rate of heat transfer of a heat exchanger.

Improving Heat Transfer in Parabolic Trough Solar Collectors by Magnetic Nanofluids

A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.

Experimental study on preparation of nanoparticle-surfactant nanofluids and their effects on coal surface wettability

To improve the efficiency of coal seam water injection,the influence of nanofluids on coal surface wettability was studied based on the nano drag reduction and injection enhancement technology in the field of tertiary oil recovery.The composition optimization and performance evaluation of nanofluids with nano-silica and sodium lauryl sulfate as the main components were carried out,and the effects of the nanofluid with the optimal ratio on coal wettability were studied through spontaneous upward imbibition experiments.The results show that the composite nanofluid has a lower surface tension,and the lowest value of the interfacial tension is 15.79 m N/m.Therefore,the composite nanofluid can enhance the wettability of coal.However,its effects on coal samples with different metamorphic degrees is different,that is,low rank coal is the largest,middle rank coal is the second,and high rank coal is the least.In addition,a functional relationship between time and imbibition height is found for pulverized coal with different particle sizes.When the particle size of pulverized coal is 60–80 mesh,the wettability of nanofluid to coal is best.The findings in this paper provide a new perspective for improving the water injection efficiency for coal seams with low permeability.

Thermal Analysis of MHD Non-Newtonian Nanofluids over a Porous Media

In the present research,Tiwari and Das model are used for the impact of a magnetic field on non-Newtonian nanofluid flow in the presence of injection and suction.The PDEs are converted into ordinary differential equations(ODEs)using the similarity method.The obtained ordinary differential equations are solved numerically using shooting method along with RK-4.Part of the present study uses nanoparticles(NPs)like TiO_(2) andAl_(2)O_(3) and sodium carboxymethyl cellulose(CMC/water)is considered as a base fluid(BF).This study is conducted to find the influence of nanoparticles,Prandtl number,and magnetic field on velocity and temperature profile,however,the Nusselt number and coefficient of skin friction parameters are also presented in detail with the variation of nanoparticles and parameters.The obtained results of the present study are presented usingMATLAB.In addition to these,some simulations of partial differential equations are also shown using software for graphing surface plots of velocity profile and streamlines along with surface plots and isothermal contours of the temperature profile.

Turbulent boundary layers and hydrodynamic flow analysis of nanofluids over a plate

A numerical analysis of the log-law behavior for the turbulent boundary layer of a wall-bounded flow is performed over a flat plate immersed in three nanofluids(Zn O-water,SiO_(2)-water,TiO_(2)-water).Numerical simulations using CFD code are employed to investigate the boundary layer and the hydrodynamic flow.To validate the current numerical model,measurement points from published works were used,and the compared results were in good compliance.Simulations were carried out for the velocity series of 0.04,0.4 and 4 m/s and nanoparticle concentrations0.1% and 5%.The influence of nanoparticles’ concentration on velocity,temperature profiles,wall shear stress,and turbulent intensity was investigated.The obtained results showed that the viscous sub-layer,the buffer layer,and the loglaw layer along the potential-flow layer could be analyzed based on their curving quality in the regions which have just a single wall distance.It was seen that the viscous sub-layer is the biggest area in comparison with other areas.Alternatively,the section where the temperature changes considerably correspond to the thermal boundary layer’s thickness goes a downward trend when the velocity decreases.The thermal boundary layer gets deep away from the leading edge.However,a rise in the volume fraction of nanoparticles indicated a minor impact on the shear stress developed in the wall.In all cases,the thickness of the boundary layer undergoes a downward trend as the velocity increases,whereas increasing the nanoparticle concentrations would enhance the thickness.More precisely,the log layer is closed with log law,and it is minimal between Y^(+)=50 and Y^(+)=95.The temperature for nanoparticle concentration φ=5%is higher than that for φ=0.1%,in boundary layers,for all studied nanofluids.However,it is established that the behavior is inverted from the value of Y^(+)=1 and the temperature for φ =0.1% is more important than the case of φ =5%.For turbulence intensity peak,this peak exists at Y^(+)=100 for v=4 m/s,Y^(+)=10 for v=0.4 m/s and Y^(+)=8 for v=0.04 m/s.

Influence factors on thermal conductivity of ammonia-water nanofluids

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

A new model to predict the densities of nanofluids using statistical mechanics and artificial intelligent plus principal component analysis

In this work, some thermodynamic properties of nanofluids such as Sb_2O_5;SnO_2/(EG + H_2O), ZnO/(EG + H_2O),Al_2O_3/(EG + H_2O), ZnO/(PEG + H_2O), ZnO/PEG, and TiO_2/EG were estimated from the extended Tao–Mason equation of state, together with the Pak and Cho equation in various temperature, pressure, and volume fractions.The equations of state using minimum input data and density at room temperature as scaling constants, were developed to estimated densities of the above mentioned nanofluids. Furthermore, the artificial neural network plus principal component analysis(PCA) technique(with 20 neuron in hidden layer) was performed over the whole range of available conditions. The AADs of the calculated molar densities of all nanofluids using the EOS and ANN at various temperatures and volume fractions are 1.11% and 0.48%, respectively. In addition, the heat capacity and isentropic compressibility of the above mentioned nanofluids are predicted using obtained densities of EOS with the Pak and Cho equation.

Experimental study on thermo-hydraulic performances of nanofluids flowing through a corrugated tube filled with copper foam in heat exchange systems

Thermo-hydraulic characteristics of TiO_2-water nanofluids in thin-wall stainless steel test tubes(corrugated tube and circular tube) filled with copper foam(40 PPI) are experimentally investigated and compared with those in test tubes without copper foam. The effects of nanoparticle mass concentration on flow and heat transfer performances are investigated. In addition, the mutual restriction relationships between Reynolds number(Re), Nusselt number(Nu) and resistance coefficient(f) are discussed respectively. Also, the comprehensive coefficient of performance(CCP) between heat transfer and pressure drop is evaluated. The results show that core-enhancement region for heat transfer using experimental tubes filled with copper foam is notably different from that of tubes without copper foam. There is a corresponding Reynolds number(about Re = 2400) for the maximum CCP of each condition. And the heat transfer can be enhanced dramatically and sustained at 8000 ≤ Re ≤ 12000.

Effect of multipolar interaction on the effective thermal conductivity of nanofluids

Nanofluids or liquids with suspended nanoparticles are likely to be the future heat transfer media, as they exhibit higher thermal conductivity than those of liquids. It has been proposed that nanoparticles are apt to congregate and form clusters, and hence the interaction between nanoparticles becomes important. In this paper, by taking into account the interaction between nearest-neighbour inclusions, we adopt the multiple image method to investigate the effective thermal conductivity of nanofluids. Numerical results show that then the thermal conductivity ratio between the nanoparticles and fluids is large, and the two nanoparticles are close up and even touch, and the polnt-dipole theory such as Maxwell-Garnett theory becomes rough as many-body interactions are neglected. Our theoretical results on the effective thermal conductivity of CuO/water and Al2O3/water nanofluids are in good agreement with experimental data.

Hybrid Effects of Thermal and Concentration Convection on Peristaltic Flow of Fourth Grade Nanofluids in an Inclined Tapered Channel: Applications of Double-Diffusivity

This article brings into focus the hybrid effects of thermal and concentration convection on peristaltic pumping of fourth grade nanofluids in an inclined tapered channel.First,the brief mathematical modelling of the fourth grade nanofluids is provided along with thermal and concentration convection.The Lubrication method is used to simplify the partial differential equations which are tremendously nonlinear.Further,analytical technique is applied to solve the differential equations that are strongly nonlinear in nature,and exact solutions of temperature,volume fraction of nanoparticles,and concentration are studied.Numerical and graphical findings manifest the influence of various physical flow-quantity parameters.It is observed that the nanoparticle fraction decreases because of the increasing values of Brownian motion parameter and Dufour parameter,whereas the behaviour of nanoparticle fraction is quite opposite for thermophoresis parameter.It is also noted that the temperature profile decreases with increasing Brownian motion parameter values and rises with Dufour parameter values.Moreover,the concentration profile ascends with increasing thermophoresis parameter and Soret parameter values.

Experimental Study on Enhancement of Bubble Absorption of Gaseous CO2 with Nanofluids in Ammonia

In order to study the effects of nanoparticles on the CO_2 absorption in ammonia,nanofluids with different ammonia concentration and different nanoparticle solid loading were prepared by a two-step method.The nanofluids-enhanced gas absorption test devices were also established. The CO_2 absorption in TiO_2,CuO,SiO_2 nanofluids,which nanoparticles solid loading were 1. 0-8. 0 g/L,was tested respectively. In comparison with the blank absorption experiment,the effects of nanoparticle solid loading,nanoparticle types,ammonia concentration on the removal efficiency and removal rate were obtained. Experimental results show that adding nanoparticles can enhance the removal efficiency and removal rate,which increase first and then decrease with the increase of nanoparticle solid loading,and there exists an optimum solid loading of TiO_2 nanoparticles. The effect of SiO_2 nanofluid is inhibitory on the reaction. The enhancement factor of CuO nanofluid is always hovering around 1,which does not show the obvious enhancement or inhibition on the reaction. The optimum solid loading decreases gradually with the increase of ammonia concentration. In addition,according to the experimental results,the mechanism of enhanced absorption was analyzed theoretically.

Controlling the Properties of Solvent-free Fe_3O_4 Nanofluids by Corona Structure

We studied the relationship between corona structure and properties of solvent-free Fe3O4 nanofluids. We proposed a series of corona structures with different branched chains and synthesize different solvent-free nanofluids in order to show the effect of corona structure on the phase behavior, dispersion, as well as rheology properties. Results demonstrate novel liquid-like behaviors without solvent at room temperature. Fe3O4 magnetic nanoparticles content is bigger than 8% and its size is about 23 nm. For the solvent-free nanofluids,the long chain corona has the internal plasticization, which can decrease the loss modulus of system, while the short chain of corona results in the high viscosity of nanofluids. Long alkyl chains of modifiers lead to lower viscosity and better flowability of nanofluids. The rheology and viscosity of the nanofluids are correlated to the microscopic structure of the corona, which provide an in-depth insight into the preparing nanofluids with promising applications based on their tunable and controllable physical properties.

A Review of Methods Based on Nanofluids and Biomimetic Structures for the Optimization of Heat Transfer in Electronic Devices

Nowadays,the utilization rate of electronic products is increasing while showing no obvious sign of reaching a limit.To solve the associated“internal heat generation problem”,scientists have proposed two methods or strategies.The first approach consists of replacing the heat exchange medium with a nanofluid.However,the high surface energy of the nanoparticles makes them prone to accumulate along the heat transfer surface.The second method follows a different approach.It tries to modify the surface structure of the electronic components in order to reduce the fluid-dynamic drag and improve the rate of heat exchange.This article reviews these effects considering different types of nanofluid and different shapes,sizes,and arrangements of“biomimetic grooves”.The idea to use these two methods in a combined fashion(to improve heat transfer and reduce flow resistance at the same time)is also developed and discussed critically to a certain extent.

Microchannel heat sink;Nanofluids;Entropy generation;Numerical analysis;Laminar flow

Based on the Second Law of Thermodynamics, the entropy generation is studied for laminar forced convection flow of different nanoparticles(Al_2 O_3, CuO and SiO_2) mixed with water through a hexagon microchannel heat sink(HMCHS). The effects of different heat fluxes and Reynolds numbers on the entropy generation for different nanofluids, volume fractions and nanoparticles diameter are investigated. The heat flux is in the range of 125 to 500 kW·m^(-2) and the Reynolds numbers vary between 200 and 1500. The thermal, frictional and total entropy generations are calculated by integrating the volumetric rate components over the entire HMCHS. The results clearly show that the rise in the heat flux leads to an increase in the thermal entropy generation for nanofluids and pure water but they don't have any influence on the frictional entropy generation. Moreover, when the Reynolds number increases, the frictional entropy generation increases while the thermal entropy generation decreases. The results revealed that at low heat fluxes and high Reynolds numbers, pure water gives the lowest entropy generation, while at high heat flux the nanofluid has to be used in order to lower the overall irreversibility.

Preparation and stabilization mechanism of carbon dots nanofluids for drag reduction

During the development of low or ultra-low permeability oil resources,the alternative energy supply becomes a prominent issue.In recent years,carbon dots(CDs)have drawn much attention owing to their application potential in oil fields for reducing injection pressure and augmenting oil recovery.However,carbon dots characterized of small size,high surface energy are faced with several challenges,such as self-aggregation and settling.The preparation of stably dispersed carbon dots nanofluids is the key factor to guarantee its application performance in formation.In this work,we investigated the stability of hydrophilic carbon dots(HICDs)and hydrophobic carbon dots-Tween 80(HOCDs)nanofluids.The influences of carbon dots concentration,sorts and concentration of salt ions as well as temperature on the stability of CDs were studied.The results showed that HICDs are more sensitive to sort and concentration of salt ions,while HOCDs are more sensitive to temperature.In addition,the core flooding experiments demonstrated that the pressure reduction rate of HICDs and HOCDs nanofluids can be as high as 17.88%and 26.14%,respectively.Hence,the HICDs and HOCDs nanofluids show a good application potential in the reduction of injection pressure during the development of low and ultra-low permeability oil resources.