393 publications from this institution
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Forced convection heat transfer in Fe3O4-ethylene glycol nanofluid in a two-dimensional enclosure with Coulomb force is analyzed. Viscosity of the nanofluid is considered to be a function of the supplied voltage. The lid wall is taken into account as positive electrode. Control volume based finite element method (CVFEM) is used to obtain the flow and heat transfer characteristics. The effects of the Reynolds number (Re), the volume fraction of Fe3O4 (ϕ) and the supplied voltage (Δφ) are presented through graphs and tables, and are discussed. The numerical results show that the isotherms become dense on the lid wall with increasing values of Re and Δφ. However, the electric field is more effective at lower values of Re. Furthermore, the effect of electro-hydrodynamics is to increase the convention currents and the supplied voltage increases the temperature gradient. In the absence of electric field, we observe two vortexes in the streamlines and they rotate in the opposite directions. The upper one is counter clock wise vortex and it diminishes in the presence of Coulomb force. Also the Coulomb force helps in generating the thermal plume over the lid wall. As the Reynolds number increases, the strength of the vortexes increases. Furthermore, thermal plume is generated in the absence of an electric field. Isotherms are disturbed with an increase in the Coulomb force. Results indicate that the Coulomb force makes the upper vortex to disappear.
The goal of this research is to demonstrate the influence of variable magnetic field on ferrofluid flow in a porous cavity. Shape factor impact on nanofluid properties is taken into consideration. Final equations are derived via vorticity stream function formulation. Then they are solved via CVFEM. Graphs are shown for different values of radiation parameter, Darcy number, Fe3O4-water volume fraction, Rayleigh and Hartmann numbers. Results prove that Nusselt number reduces with increase of Lorentz forces. In order to reach highest Nusselt number, Platelet shaped nanoparticles should be used.
No abstract is provided for this article.
In the present study, the discharging process of Latent Heat Thermal Energy Storage System (LHTESS) containing Phase Change Material (PCM) is investigated numerically. These systems are used to establish balance between energy supply and demand. Conventional PCMs have high latent heat but low thermal conductivity. This feature weakens heat transfer mechanisms of LHTESS during charging and discharging processes. In this paper, a novel fin configuration is optimized by multi-objective Response Surface Method (RSM) based on discharging process of LHTESS, and then this fin configuration is applied to LHTESS. Comparison between full discharging time by applying this fin array and LHTESS with other fin structures is carried out. Then nanoparticles is dispersed into the PCM to enhance heat transfer during solidification process and comparison between adding nanoparticles to LHTESS and immersing fin is carried out. Standard Galerkin Finite Element Method is used to provide numerical simulation of solidification phenomenon in the present study and Adaptive Grid Refinement is employed to solve the governing equations. Since immersing fin into the LHTESS reduces the amount of PCM mass and as a result, reduces the value of maximum energy storage capacity, in this work, the parameter of energy storage capacity is studied quantitatively and employed as the objective of optimization in order to consider these changes in LHTESS. Finally the results indicate that considering this parameter and optimizing the LHTESS shape based on the interaction of this parameter and solidification acceleration leads to efficient design. This is proposed as the novelty of present study. Other major results indicate that immersing fin in LHTESS enhances solidification rate significantly higher than nanoparticles dispersion.
Thermal radiation impact on magnetic nanofluid heat transfer in a curved cavity is studied. Impact of external magnetic source is taken into account. Innovative numerical method is chosen namely CVFEM. Impacts of radiation parameter ( Rd ) , Rayleigh ( Ra ) , Hartmann ( Ha ) numbers and volume fraction of Fe3O4 ( ϕ ) on hydrothermal treatment are examined. Results indicate that temperature gradient enhances with augment of Ra , ϕ , but it reduces with rise of Rd , Ha . Lorentz forces cause the nanofluid velocity to reduce and augment the thermal boundary layer thickness. Impact of radiation becomes stronger for higher buoyancy forces.
No abstract is provided for this article.
In this research, effect of Lorentz force on nanofluid natural convection inside a porous cavity is reported. Simulations have been done via Lattice Boltzmann Method. KKL model is employed to add Brownian motion effect on nanofluid properties. Impacts of Darcy number (Da), Rayleigh number (Ra), nanofluid volume fraction (ϕ) and Hartmann number (Ha) on heat transfer treatment are demonstrated. Outputs demonstrate that temperature gradient reduces with increase of Hartmann number but it enhances with augment of Darcy number.
Influence of uniform magnetic field on nanofluid hydrothermal treatment in a porous enclosure is analyzed numerically using Control volume based finite element method. Influence of thermal radiation is considered in energy equation. Non-Darcy and KKL models have been utilized for porous media and nanofluid properties, respectively. Numerical approach is presented for various values of Radiation parameter, Darcy number, Hartmann number, volume fraction of nanofluid and Rayleigh number. Results indicated that heat transfer rate enhances with rise of Radiation parameter while it reduces with rise of Hartmann number. Also it can be concluded that Nusselt number has direct relationship with Darcy and Rayleigh numbers.
According to the recent researches, adding nanomaterial within the pure refrigerant can substantially enhance the heat transfer rate in phase change (boiling/condensing) flows. Therefore, for a given operating conditions, it is unclear whether the heat transfer is optimized at a certain mass fraction of nanoparticles. In the present study, an integrated analytical, and experimental approach was scrutinized to find the heat transfer optimization of flow condensation using nanorefrigerant. For the experiment, CuO nanoparticles were disperesed with varying mass fractions (0.5–3.5%) in the baseline refrigerant/oil (R600a/POE) to produce Nanorefrigerants (R600a/POE/CuO). The optimum nanomaterial concentration for maximum perfromance has been desiganted by a novel optimization method called two stage-Bayesian optimization (TS-BO), which replaces the expensive experimental process by a cheap surrogate model constructed by Kriging. It was proved that the optimum nanoparticle fraction is significantly depend on the mass velocity and vapor quality while at a fixed vapor quality, the optimum nanoparticle concentration increased with decreasing mass flux. The highest heat transfer enhancement was achieved by nanparticle concentrations of 1.5–2.2%.
There are several methods that can be used to solve the governing equations of fluid flow and heat transfer, such as the finite difference method, the finite volume method (FVM), and the finite element method (FEM). The control volume finite element method (CVFEM) comprises interesting characteristics from both the FVM and FEM. The CVFEM combines the flexibility of the FEMs to discretize complex geometry with conservative formulation of the FVMs, in which the variables can be easily interpreted physically in terms of fluxes, forces, and sources. This chapter highlights the basic concept of CVFEM. The necessary ingredients in numerical solutions are discussed.
The effects of CaSO<sub>4</sub> on CaCo<sub>3</sub> fouling had been studied in the batch tests at 60, 70 and 80°C. Calcium carbonate was the dominant salt and the total initial concentration of calcium was constant in all the runs. The solubility product and rate constants were determined. The results indicated that co-precipitation even in minute amount affect the thermodynamics, kinetics and the scale structure. Solubility and rate constants for the pure salt precipitation are not applicable to co-precipitation. Presence of CaSO<sub>4</sub> increased the solubility constant for the calcium carbonate in co-precipitation; the solubility product increased from 65% to 280% when CaSO<sub>4</sub> was added to the solution. The rate equation suggested by Nancollas and Reddy [1] was not applicable to the experimental data. The addition of CaSO<sub>4</sub> slowed down caCO<sub>3</sub> precipitation. The general observations indicated that the presence of CaSO<sub>4</sub> had weakened the CaCo<sub>3</sub> scale that is usually a very adherent scale.
Effect of typical and perforated conical ring turbulators on hydrothermal behavior of air to water double pipe heat exchanger is investigated. Two arrays (Direct conical ring (DCR) array and Reverse conical ring (RCR) array) are considered. Experimental analysis is examined for different values of open area ratio (0–0.0833), Reynolds number (6000–12,000), conical angle (0°–30°) and pitch ratio (1.83–5.83). Correlations for friction factor, Nusselt number and thermal performance factor are presented. To reach the optimal design, Non Sorting Genetic Algorithm II is applied. Pareto front of optimized solution is presented. Also the finite volume method (commercial code) is utilized for numerical section in order to show physical phenomena. Results indicate that friction factor reduces with augment of open area ratio, pitch ratio and Reynolds number. Nusselt number reduces with increase of open area ratio and pitch ratio while it augments with enhance of Reynolds number. Also it can be concluded that thermal performance rises with augment of conical angle for direct conical ring array.
In this investigation, the simulation of nanoparticle convective motion in permeable space has been presented numerically in the presence of the Lorentz effect. The working fluid is a H2O-based nanofluid. The non-Darcy model was utilized to employ porous terms in momentum equations. A radiation effect has been reported for various shapes of nanoparticles. The impact of shape factor, radiation parameter, magnetic force, shape of the nanoparticles and Rayleigh number on nanofluid conduct was demonstrated. The CVFEM (control-volume finite-element method) approach was utilized. The radiative flow is considered and the impact of physical parameters on nanofluid performance was demonstrated. The results prove that higher values of shape factor lead to stronger convection. By adding Lorentz forces, conduction becomes more practical.
This article deals with the numerical simulation to examine the significant effects of MHD flow and nanoparticle migration inside a permeable space including two temperature model. For more physical situation, thermal radiation influence is considered. Viable transformation is assumed to alter the governing set of PDEs into dimensionless form. CVFEM was adopted to model this article. Impacts of radiation parameter, Rayleigh number (103 < Ra < 104), nanofluid–solid interface factor (10 < Nhs <1000), Hartmann number (0 < Ha < 20) and nanoparticles’ shape (3 < m < 5.7) on nanofluid behavior were demonstrated. Outcomes depict that stronger convection can be obtained with augmenting in shape factor. Average Nusselt number increases as enhancing the buoyancy and radiation effect whereas decreases as enhancing nanofluid–solid interface factor and Hartmann number. Comparison of the numerical outputs achieved by means of CVFEM with published data was also deliberated. It is evident that the applied approach is very accurate to investigate solution of the discussed problem.
In this paper, the effect of melting heat transfer on the nanofluid flow in the presence of Lorentz forces is reported. Two phase model is considered for the nanofluid. The Runge–Kutta method is selected to solve the ODEs, which are obtained from a similarity transformation. The roles of the Reynolds number, Schmidt number, Brownian parameter, thermophoresis parameter, Eckert number and melting parameter are illustrated graphically. The results reveal that the Nusselt number increases with an increase of the Hartmann number. The temperature gradient reduces with a rise of the melting parameter and Eckert number.
In this paper magnetohydrodynamic free convection flow of CuO–water nanofluid in a square enclosure with a rectangular heated body is investigated numerically using Lattice Boltzmann Method (LBM) scheme. The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo–Kleinstreuer–Li) correlation. The influence of pertinent parameters such as Hartmann number, nanoparticle volume fraction and Rayleigh number on the flow, heat transfer and entropy generation have been examined. The results show that the heat transfer rate and Dimensionless entropy generation number increase with increase of the Rayleigh number and nanoparticle volume fraction but it decreases with increase of the Hartmann number.
In photovoltaic (PV) solar systems, electricity can be produced from part of the sunlight and the remaining energy raises the temperature. The aim of the current investigation is to suggest a novel design for the heat transfer tube's (HTT) cross section for overcoming this challenge in photovoltaic/thermal (PVT) systems. In this numerical simulation, the range of fluid inlet velocity (Vin) was set between 0.01 and 0.18 m/s. The value of ambient temperature (Tamb) and fluid inlet temperature (Tin) is 30 °C, and solar radiation (G) has been adjusted to 800 W/m2. A comparison was made between the circular tube and the 8-lobed tube with the same hydraulic diameter, and the better performance of the 8-lobed tube was proved. To meet the increased efficiency of the PVT system, copper fins with four different arrangements were employed. The highest efficiency occurred when the fins were placed all around the inside of the HTT. To create heat transfer fluid (HTF), non-toxic graphene nanoplatelets (GNP) have been mixed with water involving two weight fractions (0.025 % and 0.1 %). Examining the effect of changing the fluid inlet velocity (Vin), it was concluded that the system's electrical performance is increased by 5.8 %, with rise of Vin, in the best case. By using the GNP nanoplatelets (0.1 %), at Re = 1611, the maximum exergy, electrical, and thermal performances of the unit were 15.32 %, 14.05 %, and 55.22 %, respectively, in the best case. In the best case, more carbon dioxide (about 7.1 Tons) can be reduced and the carbon credit is 5.5 % higher than that of base case. In addition, the payback period is less than 2 years in the best case with 18700$ profit in the 10th year.
