Alumina Water Research Articles

Numerical analysis of unsteady free convection of Al2O3 inside a tubular reactor under the influences of exothermic reaction, and inclined MHD as an application to chemical reactor

This paper delves into the numerical investigation of aluminum oxide–water nanofluid thermal and dynamic performances under the influences of magnetic field application and chemical reaction, utilizing the Finite Element Method within a circular enclosure containing three inner tubes, as an application to the heat exchanging phenomenon between the reactive shell of the cavity and the surface of the triple tubes. Various governing parameters were studied for their interaction on the nanofluid flow and heat transmission rate within the proposed geometry, including the Rayleigh parameter (103≤Ra≤105), Hartmann parameter (0≤Ha≤61), nanoparticles concentration (0≤∅≤6×10-2), magnetic rotational angle (0o≤γ≤90o), and Frank-Kamenetskii parameter (0≤Fk≤3). The results indicated that raising Ra from 103 to 105 results in expediting the nanofluid velocity by 10.62 % and 100 % respectively as well as raising the total heat transfer efficiency. The nanofluid speed was also increased by 28.57 % when Fk has to further increase to a value of 3. When there was no exothermic activity present, the rate of heat transmission was at its lowest, and it was greater when the Fk value was 3. Similarly, there were discernible impacts in various areas of the geometry as the Ha number intensified and the Nuavg decreased. Improvements in local and mean Nusselt parameters are observed when the concentration of nanoparticles is increased, suggesting better heat transfer, achieving an increase by 7 % in the average Nusselt number. This research emphasizes the importance of nanoparticle concentration in raising the medium’s rates of heat transmission, contributing to advancements in energy storage development.

Advances in nanofluids for tubular heat exchangers: Thermal performance, environmental effects, economics and outlook

Heat transfer deterioration in thermal systems significantly limits the efficiency and practicality of these systems. This review explores state-of-the-art studies on the use of nanofluids (NFs) in various tubular heat exchangers (HEXs), addressing their influence on overcoming the limitations. It discusses the fundamentals of HEXs and NFs, including design criteria, heat transfer mechanisms and thermal transport properties. This work compiles effective thermal conductivity and viscosity correlations under diverse conditions and evaluates NF performance in reactor, flat and helical coiled tube, twisted tube, U-tube and finned tube-based HEXs. Results revealed substantial improvements in system efficiency, with SiC–MWCNT/water NFs achieving 99.9 % absorbance in solar collectors and Ag–rGO/water and Ag–ZnO/silicon oil NFs enhancing efficiency by 210 % and 240 %, respectively. Water–alumina NFs increased convective heat transfer rates and friction factors in flat tube HEXs by 123.6 % and 210 %, respectively. Helical coil exchangers exhibited a pressure drop of 47.35 % with MWCNT/water NFs and a 69.62 % rise in heat transfer coefficient with polyaniline–water NFs. This review suggests that optimising HEX efficiency depends on the strategic use of NFs and finned-tube designs. It also highlights the significance of selecting suitable source materials for NFs, the corresponding health risks, disposal and waste management. Economic viability depends on using optimal flow parameters, including temperature, concentration of nanoparticles, system compactness and installation and running costs. Finally, this review concludes with insights into existing challenges and prospects in thermohydraulic, environmental and economic aspects, pointing to future developments in engineered fluids and their commercial applications.

Transient flow and heat transfer characteristics of single-phase nanofluid past a stretching sheet under the influence of thermal radiation and heat source

This work aims to investigate the unsteady hydromagnetic free convective flow of a viscous, electrically incompressible fluid influenced by an inclined magnetic field, radiation, and heat source. Specifically, it explores the behavior of water-based nanofluids under these conditions. The Newton-Raphson shooting technique combines the 4th-order Runge-Kutta approach to obtain dimensionless and accurate solutions to the governing equations. The study assesses flow characteristics and heat transfer properties over various parameter values. The outcomes are visualized through graphical representations of velocity, temperature, skin friction coefficient, and the local Nusselt number. The present study examines the impact of copper (Cu), silver (Ag), alumina (Al2O3), and titanium dioxide (TiO2) nanoparticles in water as the base fluid on the percentage increase in skin friction and Nusselt number under various physical conditions. Suction increases skin friction by 10–15 % and the Nusselt number by a similar margin, whereas injection can reduce these metrics. Radiation enhances heat transfer, resulting in a 5–10 % increase in skin friction and a 10–15 % rise in the Nusselt number, with nanoparticles like Ag showing the most substantial effects due to their superior thermal properties.

Darcy–Forchheimer modelling on unsteady MHD convection flow of a hybrid nanofluids (CNTs–Al2O3/H2O) over a stretching sheet

AbstractThe present article provides a detailed analysis of the Darcy–Forchheimer flow of hybrid nanofluid past a porous stretching sheet. The carbon nanotubes and Al2O3 (aluminium oxide) are used to synthesize hybrid nanofluid. The nanoparticles of carbon nanotubes have attained fame to enhance the thermo‐physical features of fluid particles. The inclusion of nanoparticles of multi‐wall carbon nanotube (MWCNTs)/single‐wall carbon nanotubes (SWCNTs) and alumina in water past a stretching sheet by the magnetic field, thermal radiation, heat dissipation as well as slip conditions is computationally explored. The hybrid nanofluid flow experiences the unsteady non‐Darcy relation across two‐dimensional stretchable surface. At first, the governing partial differential equations of the projected modelling are in non‐dimensional and to attain the ordinary differential equations via the appropriate dimensionless similarity transformations and are then computationally explored by bvp4c MATLAB solver. The pertinent parameters of the associated model are demonstrated by the graphical profiles and tables. Furthermore, magnetic parameter, porosity parameter and inertia coefficient parameter tend to retards the flow pattern of hybrid nanofluid. The SWCNTs‐alumina/water experiences more resistive force as compared to the MWCNTs‐alumina/water. Higher values of Forchheimer parameter retards velocity profile as MWCNTs‐alumina/water flow overshoots SWCNTs‐/alumina water. The enhancement of volume fraction of MWCNTs and SWCNTs enhanced the rate of heat transfer throughout the fluid region.

A Novel Cooling System by Surface Corrugation and Nanofluid Utilization for the Performance Improvement of Photovoltaic Module Coupled with Thermoelectric Generator and Efficient Computations by Using Artificial Neural Network-Based Hybrid Scheme

For a photovoltaic module coupled with thermoelectric generator, a unique wavy cooling channel is proposed, and its performance is numerically assessed by using three-dimensional computations. The cooling channel uses nanofluid of alumina–water with various shaped nanoparticles (spherical, cylindrical and brick). Numerical simulations are performed for a range of parameters for the corrugation amplitude (0≤Amp≤0.1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0 \\le \ ext {Amp} \\le 0.1$$\\end{document}), wave frequency (2≤Nf≤16\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2 \\le \ ext {Nf} \\le 16$$\\end{document}), nanoparticle loading quantity (0≤SVF≤0.03\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0 \\le \ ext {SVF} \\le 0.03$$\\end{document}), and nanoparticle shape (spherical, brick, and cylindrical). We analyze the photovoltaic module’s average temperature and temperature uniformity for a variety of parameter variations. When nanofluid and greater channel corrugation amplitudes are utilized, the average panel surface temperature is decreased more. A wavy shape of the cooling channel at the maximum corrugation amplitude yields a cell temperature reduction of 1.88 o\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\ ext {o}$$\\end{document}C, while frequency has little impact on average cell temperature and its uniformity. The best-performing particles are those with cylindrical shapes, and the drop-in average photovoltaic temperature with solid volume fraction is essentially linear. As utilizing cylindrical-shaped particles, the average temperature of corrugated cooling channels decreases by around 1.9 o\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\ ext {o}$$\\end{document}C as compared to flat cooling channels with base fluid at the greatest solid volume fraction. As compared to un-cooled photovoltaic, cell temperature drops by around 43.2 o\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\ ext {o}$$\\end{document}C when employing thermoelectric generator. However, temperature drop value of 59.8 o\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\ ext {o}$$\\end{document}C can be obtained by using thermoelectric generator and nano-enhanced wavy cooling channel utilizing cylindrical-shaped nanoparticles. An hybrid computational strategy for the fully coupled system of photovoltaic with cooling system is provided, which reduces the computational time by a factor of 75.

Cutting-Edge Machine Learning Techniques for Accurate Prediction of Agglomeration Size in Water–Alumina Nanofluids

Cutting-Edge Machine Learning Techniques for Accurate Prediction of Agglomeration Size in Water–Alumina Nanofluids

Unsteady magnetohydrodynamic tri-hybrid nanofluid flow past a moving wedge with viscous dissipation and Joule heating

This study aims to boost thermal convection through careful selection and adjustment of nanomaterial volumes, focusing on the unsteady magnetohydrodynamic flow past a moving wedge with viscous dissipation and Ohmic heating in a ternary nanofluid of alumina (Al2O3), copper oxide (CuO), and copper (Cu) in water. Employing mathematical modeling and numerical analysis via MATLAB's BVP4C, it explores how discharge concentration influences flow characteristics and identifies critical conditions for single or dual solutions. Key parameters such as motion and wedge parameters, Eckert number, magnetic strength, and nanoparticle volume ratios were scrutinized for their impact on fluid dynamics and heat transfer. Results show enhanced convective thermal transfer with increased nanoparticle hybridity and volume fraction, alongside suction/injection parameter (S), unsteadiness parameter (A), Eckert number (Ec), and magnetic parameter (M), albeit decreasing with wedge angle adjustments. Stability analysis revealed the stability of the initial solution vs the instability of the secondary. Introducing a novel time variable, τ=cAt(1−ct), this research demonstrates that at λ=−4.7(a leftward wedge) with a 0.04 nanoparticle volume fraction, ternary and hybrid nanofluids significantly outperform mono nanofluid, achieving thermal efficiency gains of 25.6% and 7.5%, respectively. This foundation underscores the potential of optimized nanofluid mixtures for advanced heat transfer applications.

Numerical analysis of unsteady free convection under the combined influence of inclined magnetohydrodynamic and exothermic chemical reaction in an enclosure filled with nanofluid

Unsteady study of the natural convection of aluminum oxide-water nanofluid within a trapezoidal geometry containing a circular cylinder located at its center. Finite Element method has been considered for the numerical analysis. The proposed investigation handled the impact of Rayleigh number (103–105), chemical reaction parameter (0–4), aluminum oxide nanoparticles volume fraction (0–0.06), magnetic field (0–63) and its inclination angle (0°–90°), and circular obstacle diameter (0.3–0.7) effects on time-dependent natural convection of Al2O3–H2O nanofluid. On the other hand, the value of Prandtl number has kept constant at (Pr = 6.2). Since the nanofluid mobility at φ = 0.02, Ha = 3, and Fk = 1 significantly improved, the heat transfer rate achieved its maximum intensity at Ra = 105. Research also reveals a little effect on heat transfer by increasing the fraction of nanoparticles. Additionally, as Ha intensifies from 0 to 63, a final change in the mean Nusselt number of 28.65 % is displayed. Finally, as the magnetic field angle of rotation is diminished, more enhancement in heat transmission is achieved. This research provides insights into the intricate relationship between natural convection and exothermic reaction under the influences of various conditions. This can illustrate the flow and thermal behaviors of nanofluid in such non-uniform shapes in many engineering applications.

Energy management of a concentrated photovoltaic−thermal unit utilizing nanofluid jet impingement in existence of thermoelectric module

To generate a concentrated photovoltaic–thermal (CPVT) unit system, linear Fresnel concentrators have been attached to a PV unit and a thermoelectric generator (TEG) has been combined in this work to boost productivity. In the presence of concentrators, the temperature of the silicon layer increases. While electrical output is enhanced for the CPVT unit, the non-uniform isotherms can decrease the lifetime of the panel, so confined jets of alumina–water nanofluid have been applied for cooling. To validate the numerical code, previous papers were examined and good accommodations were reported. Various values of the inlet temperature (T in) and velocity (V in) of jets have been analysed. The impacts of installing concentrators on overall performance and CO2 mitigation have been investigated. An increase in V in leads to an incremental increase in thermal performance of about 4.2% and thermal uniformity is enhanced by about 13.91%. The thermal power of the system is enhanced by about 2.19 times as a result of adding concentrators. Also, the PV power is enhanced by 86.22% in the presence of the reflectors. With the increase in T in, the thermal and electrical performance decrease by about 19.95% and 5.24%, respectively. Installing concentrators enhances the overall performance by about 6.55%. After 10 years, the amount of CO2 mitigation for the CPVT-TEG system reaches 148.28 ton.

Estimation of heat transfer coefficient and friction factor with showering of aluminum nitride and alumina water based hybrid nanofluid in a tube with twisted tape insert

Twisted tape is one of the active thermal proficiency boosting technology which has been deeply examined because to consistent efficiency findings and easy implementations. Thermo-hydraulic effectiveness of tubes fitted with twisted tapes is becoming highly significant. Although twisted tapes can cause swirls and disturb boundary layers, this is the most widely used method for improving convection. In the present attempt, to enhance the heat transfer twisted tape is inserted in tube. In the current modern research, the effect of twisted tape, on the enhancement of thermal transport, Nusselt number and friction factor performance of AIN–Al2O3/water hybrid nanofluid is evaluating utilizing CFD and ANSYS-FLUENT software. the consequence of twisted pitch 44 mm, 66 mm, 88 mm, 100 mm and Reynolds numbers 800, 1200, 1600 and 2000 on Nusselt number, heat transfer coefficient and friction coefficient have been computed numerically with 0.01 to 0.04 volume friction of nanopowders. The commercial ANSYS-FLUENT code was used in this analysis utilizing the SIMPLE method for pressure–velocity coupling. The K-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K - \\omega$$\\end{document} model and Navier Stokes equations are integrating utilizing finite volume method in ANSYS-FLUENT. It was observed that inserting the twisted tape in tube significantly improves the thermal conductivity as well as friction factor compared with the simple tube without turbulator.

Dual Stratification on the Double Diffusive Magnetohydrodynamics Flow of Nanofluids with Dissipation Effects-Revised Buongiorno Model

We analyze the effects of double stratification and dissipation on the hydro magnetic free convection flow of nanofluids over a vertical plate in this work. Considered two different kinds of nanofluids, such as copper and alumina–water nanofluids. By employing the similarity transformation, partial differential equations are converted into non-linear ordinary differential equations, which can be numerically computed with MATLAB. In practical situations where the heat and mass transfer mechanisms run simultaneously, the analysis of natural convection in the influence of double stratification is a fundamentally interesting and important problem, because of its broad range of engineering applications. These applications include the rejection of heat into the environment, such as lakes, rivers, and seas; the storage of thermal energy, such as solar ponds; and the transmission of heat from thermal sources, such as the condensers of power plants. To highlight the impact of double stratification and dissipation on the hydromagnetic free convective flow of nanofluid over a vertical plate, a wide variety of parameter values are used. The numerical outcomes for the different parameters of velocity, temperature, volume fraction, and concentration are obtained and displayed graphically. The skin friction coefficient and reduced Nusselt number are also determined numerically and tabulated.

A simple and efficient hydratable alumina gel‐casting method for the fabrication of high‐porosity mullite ceramics

AbstractIn this study, we have developed a method for the preparation of porous alumina‐containing ceramics by inorganic gel‐casting of hydratable alumina system. The gelation behavior of hydratable alumina in water and the high‐temperature phase evolution of alumina gels were clarified. In addition, extremely high‐porosity mullite ceramics were prepared using the hydratable alumina gel‐casting method combined with carbon fibers as the pore‐forming agent method. The as‐prepared mullite ceramics have a pore size of less than 10 μm, controllable high porosity of 90.6%–78.1%, a lightweight of 0.30–0.70 g cm−3, high compression strength of 1.41 ± 0.21–16.30 ± 0.20 MPa, low dielectric constants at 30 GHz of 1.34–1.79, the dielectric loss tangent of less than 3 × 10−3, and low thermal conductivities of 0.083–0.305 W/(m K). Lightweight, high strength, excellent dielectric properties, and outstanding thermal insulation indicate the potential of porous mullite ceramics for use in radar radomes or windows.

Studying Alumina–Water Nanofluid Two-Phase Heat Transfer in a Novel E-Shaped Porous Cavity via Introducing New Thermal Conductivity Correlation

Investigating natural convection heat transfer of nanofluids in various geometries has garnered significant attention due to its potential applications across several disciplines. This study presents a numerical simulation of the natural convection heat transfer and entropy generation process in an E-shaped porous cavity filled with nanofluids, implementing Buongiorno’s simulation model. Analyzing the behavior of individual nanoparticles, or even the entire nanofluid system at the molecular level, can be extremely computationally intensive. Symmetry is a fundamental concept in science that can help reduce this computational burden considerably. In this study, nanofluids are frequently conceived of as a combination of water and Al2O3 nanoparticles at a concentration of up to 4% by volume. A unique correlation was proposed to model the effective thermal conductivity of nanofluids. The average Nusselt number, entropy production, and Rayleigh number have been illustrated to exhibit a decreasing trend when the volume concentration of nanoparticles inside the porous cavity rises; the 4% vol. water–alumina NFs yield 17.35% less average Nu number compared to the base water.

Turbulent Eulerian–Eulerian simulation and Taguchi optimization of twin oblique nanofluid jets injecting into a water cross-flow

In this work, a turbulent Eulerian–Eulerian description is utilised to simulate the injection of twin oblique jets of alumina–water nanofluid into a water cross-flow. This technique can be considered as a heat transfer enhancement strategy in cooling technologies. A Taguchi optimization study is undertaken to determine the optimal combination of the involved control factors to achieve the highest heat transfer rate and to explore the contribution ratio of each factor. Inspection of the simulation results demonstrates that about 70% of the contribution on the final response belongs to the velocity and the angle of the first jet. Meanwhile, it is elucidated that the presence of the nanoparticles in the injected jets may not alter the heat transfer rate more than 6%. This indicates that with proper selection of the velocity and the angle of the jets (especially the first one), the need to utilise nanofluids will be eliminated.

Influence of using nanofluid and phase change material on the performance of a solar thermal panel to provide the required energy of an office building in a mine

This paper examines the effect of using fins installed on tubes placed under a solar panel (SOP) numerically. The SOP is employed to generate electricity and hot water in a mine. The helical fins are mounted around the tubes under the SOP. By changing the cross-section of the fins, unsteady simulations are performed. Besides, OM37 phase change material (PCM) is utilized under the SOP and the tubes are placed inside the PCM. Alumina water nanofluid (NFD) flows inside the tubes, which are analyzed in two phases. The results show that for models M1 and M2 in 1500s, the use of tubes with a DIT of 5 mm under the SOP leads to a decrease in the SOP's average temperature of 8.58 and 8.24° respectively. The use of model M2 results in a lower outlet temperature (T-O) of the NFD when the tube DIT is 3 mm. Model M1 leads to a lower NFD T-O most of the time. Using the designed solar system can provide 56% of the hot water needed in the hot seasons and 18% of the hot water needed in the cold seasons for the building placed inside the mine.

Nanofluid flowing over a rotating disk that is stretching and permeable: An unsteady model

The model presented in this paper deals with the investigation of the unsteady laminar flow past a stretchable disk. The nanofluids Al2O3/H2O and Cu/H2O are considered for the analysis where the thermal characteristics and flow behavior of these nanofluids are compared. In addition, the system is subjected to the suction force that has significant impacts on velocity of the nanofluid flow. Further, the nanoparticle solid volume fraction is another important parameter that is discussed which has a prominent role on both profiles of the nanofluid. Furthermore, the investigated mathematical model is framed using PDEs that are transformed to ODEs using suitable transformations. The system of equations obtained in this regard is solved by employing the RKF-45 numerical method where the results are obtained in the form of graphs. Various nanofluids flow parameters arise in the study and the impact of all these parameters has been analyzed and interpreted. Some of the major outcomes are that the higher values of nanoparticle solid volume fraction enhance the temperature while it decreases velocity of the flow. The comparison of flow of the two nanofluids concluded that alumina–water nanofluid has a better velocity while the copper–water nanofluid has a better thermal conductivity.

Effects of Rough Boundaries on Rayleigh–Bénard Convection in Nanofluids

Abstract A linear stability analysis of Rayleigh–Bénard convection in a Newtonian nanofluid is carried out using most general boundary conditions. A single-phase description of nanofluids is adopted in the study. The nanofluids used for the study are water–alumina and water–copper nanofluids in order to analyze how a choice between them can be made. The values of thermophysical quantities of nanofluids are calculated using the mixture theory and phenomenological-laws. The paper applies the Maclaurin series in solving the boundary-eigenvalue-problem through a simple and innovative approach. A single-term Galerkin technique is adopted to obtain the guess value of the critical Rayleigh number and the wave number. Further, improved values of the Rayleigh number and the wave number are obtained using the solution of a system of three linear-algebraic equations. A detailed discussion is made on the effect of rough-boundaries and Robin-boundary conditions for temperature on the onset of convection. A comparative study between the results of two nanofluids is made and the destabilizing effect of nanoparticles in the Newtonian carrier-fluid on the onset of convection is studied.

Hydrogen production on nano Al2O3 surface by water splitting using gamma radiation

AbstractOBJECTIVESDue to changes in climate and the estimation of fossil fuel exploitation in the future, there is a great demand for green energy. Therefore, hydrogen production was studied by water splitting using Al2O3 nanoparticles as a radiation catalyst with gamma rays irradiationEXPERIMENTALThe effects of different particle sizes, surface area, amounts of radiation catalyst and the time of gamma rays irradiation were studied. The kinetics of hydrogen generated by the water decomposition of the water system with Al2O3 nanoparticles were also studied. It was determined that the hydrogen produced by water splitting with smaller‐sized nanoparticles was 1.4–1.6 times greater than the large‐sized catalysts.RESULTS AND DISCUSSIONThe best conditions were 5 nm particle size, 250 mm2/g surface area, 0.25 g amount and 10 h time (5.97 molecules/100 eV). The equivalent dispersal of radiation nanocatalyst (alumina) in water and greatly more sorption of water on the catalyst surface caused more effective radiolysis. The mechanism of water splitting and radiolysis was also established.CONCLUSIONThe reported method may be used in the future for hydrogen production on an industrial scale. © 2023 Society of Chemical Industry (SCI).

The Effect of Threaded Rod Inserts and Aluminum Oxide–Water Based Nanofluids on Performance of a U-Bend Double Pipe Heat Exchanger

Double pipe heat exchangers, owing to their simplicity in construction and ease of maintenance, are being widely used in refineries, food processing units and pharma industries. However, they have a limitation that they can only operate at low heat loads. In order to make them suitable for higher loads, it is essentially required to enhance the rate of heat transfer. In this work, an attempt is made to this end using a combination of threaded rods and water-based aluminum oxide nanofluids. Experimental investigations were carried on a counter-flow double pipe return bend heat exchanger (DPHE) using water-aluminum oxide (Al2O3) nanofluids with threaded rod inserts. The volume concentration of Al2O3 nanofluid added in water was 0.03% and 0.05%. The entire analysis was carried out under turbulent flow regime by varying the mass flow rates of cold water from 3 to 15 LPM in steps of 2 LPM, with the hot water flow rate being fixed at 6 LPM. The Reynolds number range considered was from 3000 to 30000. From the obtained results, it was found that the maximum enhancement in the Nusselt number and friction factor for 0.05% concentration of the nanofluid and threaded rod inserts respectively is 89.95% and 32.46% more than the plain tube. The maximum thermal performance factor was found to be 1.75 for the combination of 0.05% nanofluid and inserts.

Insight into Unsteady Separated Stagnation Point Flow of Hybrid Nanofluids Subjected to an Electro-Magnetohydrodynamics Riga Plate

The main objective of this work is to analyze and compare the numerical solutions of an unsteady separated stagnation point flow due to a Riga plate using copper–alumina/water and graphene–alumina/water hybrid nanofluids. The Riga plate generates electro-magnetohydrodynamics (EMHD) which is expected to delay the boundary layer separation. The flow and energy equations are mathematically developed based on the boundary layer assumptions. These equations are then simplified with the aid of the similarity variables. The numerical results are generated by the bvp4c function and then presented in graphs and tables. The limitation of this model is the use of a Riga plate as the testing surface and water as the base fluid. The results may differ if another wall surfaces or base fluids are considered. Another limitation is the Takabi and Salehi’s correlation of hybrid nanofluid is used for the computational part. The findings reveal that dual solutions exist where the first solution is stable using the validation from stability analysis. Graphene–alumina/water has the maximum skin friction coefficient while copper–alumina/water has the maximum thermal coefficient for larger acceleration parameter. Besides, the single nanofluids (copper–water, graphene–water and alumina–water) are also tested and compared with the hybrid nanofluids. Surprisingly, graphene–water has the maximum skin friction coefficient while alumina–water has the maximum heat transfer rate. The findings are only conclusive and limited to the comparison between graphene–alumina and copper–alumina with water base fluid. The result may differ if another base fluid is used. Hence, future study is necessary to investigate the thermal progress of these hybrid nanofluids.