No abstract is provided for this article.
A numerical technique is applied to study the efficacy of integrating twisted tapes to the collector of Photovoltaic/Thermal (PV/T) units on the system performance when the tubes with different cross-sections are used. Hence, computational fluid dynamics is employed to evaluate PV/T systems with and without twisted tapes when using cylindrical, rectangular, and triangular patterns for the tube cross-section. The effect of employing twisted tapes with various pitch-to-width ratios ( Y D ) of 3, 4 and 5 is evaluated. The impact of the total inlet mass flow rate ranging from 25 to 150 L h r is also studied. To analyze the system performance the evaluation of energy and exergy is performed. The results demonstrated that the triangular pattern is the optimum pattern for the tube cross-section without twisted tapes. However, inserting a twisted tape makes the cylindrical tube superior to other designs from electrical and thermal aspects. A collector employing a cylindrical tube with and without a twisted tape could increase the module's electrical efficiency by 7.2 and 9%, respectively. Also, it was observed that integrating twisted tape with the lowest value of pitch-to-width ratio could decrease the surface temperature by 3.2 and 17.55 K compared to the systems with cylindrical tubes and PV alone.
Nanofluid forced convective heat transfer in a porous semi-annulus is studied in presence of uniform magnetic field. Various shapes of nanoparticles are considered. Brownian motion impact on viscosity of nanofluid is taken into account. Governing equations are presented in vorticity stream function formulation. Control volume based finite element method (CVFEM) is utilized to obtain the results. At first, the best shape of nanoparticles is selected and then influences of nanofluid volume fraction, Darcy, Reynolds and Hartmann numbers are presented. Results showed that velocity of nanofluid enhances with increase of Darcy and Reynolds numbers. Platelet shape has the highest rate of heat transfer. Nusselt number enhances with increase of nanofluid volume fraction, Darcy, and Reynolds number while it reduces with increase of Lorentz forces.
In this paper, the problem of laminar Magnetohydrodynamic nanofluid flow in a porous channel is investigated. Optimal Homotopy Asymptotic Method (OHAM) is used to solve this problem.In order to consume CPU time, Galerkin method is used to minimize the residual. This investigation compared with numerical method (four-order Rung-kutte method) and found to be in excellent agreement. The base fluid in the channel is water containing copper as nanoparticle. The effective thermal conductivity and viscosity of nanofluid are calculated by the Maxwell–Garnetts (MG) and Brinkman models, respectively. The influence of the three dimensionless numbers: the nanofluid volume fraction, Hartmann number and the Reynolds number are examined. The results indicate that velocity boundary layer thickness decreases with increase of Reynolds number and nanoparticle volume fraction and it increases as Hartmann number increases.
No abstract is provided for this article.
The use of additives in the base fluid like water or ethylene glycol is one of the techniques applied to augment the heat transfer. Recently innovative nanometer sized particles had been dispersed in the base fluid in heat transfer fluids. The fluids containing the solid nanometer size particle dispersion are called “nanofluids.” Two main categories were discussed in detail: the single-phase modeling in which the combination of nanoparticle and base fluid is considered as a single-phase mixture with steady properties and the two-phase modeling in which the nanoparticle properties and behaviors are considered separately from the base fluid properties and behaviors. Moreover, nanofluid flow and heat transfer can be studied in the presence of thermal radiation, electric field, magnetic field, and porous media. Furthermore, several numerical and semianalytical methods can be used to simulate nanofluid hydrothermal behavior. In this chapter, definition of nanofluid and its application have been presented.
In the current attempt, we applied a magnetic field to expedite solidification and we also tried to report entropy generation of nanoparticle-enhanced phase change material (NEPCM). Second law analysis should be involved for designing efficient heat storage units. Nanoparticles can be dispersed in pure PCM (water) to enhance conductive heat transfer. Governing equations formulated considering Darcy law for porous terms and single phase model for nanofluid properties are solved by means of the finite element method. Results are depicted as entropy generation components and solid fraction contours. Results reveal that applying a magnetic field has a favorable effect on the discharging rate of solid fraction. The augmentation in Hartmann number corresponds to a lower time for the process of solidification.
This paper deals with heat and mass transfer in unsteady two-dimensional MHD squeezing flow of Eyring-Powell fluid between two parallel infinite plates. Heat generation/absorption, thermal radiation and Joule heating influences are taken into consideration. The governing nonlinear PDEs are converted to nonlinear ODEs using similarity transformations. Analytical solution for the velocity, temperature and concentration distribution has been obtained by means of Differential Transformation Method (DTM).The comparisons between the results of DTM and numerical method (Runge-Kutta Fehlbrg), proved high precision of DTM. The effects of various parameters, including squeeze number, radiation parameter, heat generation/absorption parameter and Hartmann number on the flow field, skin friction coefficient and heat transfer have been studied. The achieved results reveal that Lorentz force generated by magnetic field parameter (Ha), reduces velocity distribution. Also, it is found that the temperature profile reduces with the increase of radiation parameter (R).
Lattice Boltzmann Method (LBM) is utilized to simulate the magnetohydrodynamic (MHD) nanofluid forced convective heat transfer inside a porous three dimensional enclosure with hot cubic obstacle. Impact of Hartmann number H a , Darcy number D a and Reynolds number Re on nanofluid treatment were depicted. Al2O3- H 2 O nanofluid has been utilized considering single phase model. Results are demonstrated in forms of isokinetic, isotherms, streamlines, Nusselt number and velocity contours. Results show that temperature boundary layer becomes thinner with augment of D a and Re . Convective heat transfer reduces with rise of Hartmann number while it improves with rise of Darcy number.
Thermoelectric generators (TEGs) harness temperature gradients to produce electrical power, providing a sustainable and eco-friendly energy solution. This research conducts a 3D numerical analysis to investigate the effects of three fin configurations—plate fins, plate fins with pin fins, and separated plate fins with pin fins—and three cooling fluids: air, water, and a nanofluid based on water mixed with multi-walled carbon nanotubes and silicon carbide (MWCNT/SiC). This article offers a new technique by combining new fin configurations and a nanofluid cooling to enhance thermoelectric generator (TEG) performance. The numerical simulations have been performed using the finite element method, and the results revealed that air as a cooling fluid significantly decreases the TEG's power output compared to water or MWCNT/SiC nanofluid. Specifically, the open-circuit voltage (VOC) with air cooling is approximately 99 % lower than that achieved with water or nanofluid. Additionally, incorporating nanofluid increases power generation by an average of 2.6 %. Among the fin configurations, plate fins with pin fins achieve the highest electrical potential, outperforming separated plate fins with pin fins and standard plate fins by 4 % and 6.9 %, respectively. These results underscore the serious role of efficient thermal management in optimizing TEG power. The study highlights the combined impact of fin design and cooling fluid selection in enhancing TEG efficiency, contributing appreciated insights for advancing solar energy applications.
Influence of external magnetic source on Fe3O4-water heat transfer in a cavity with circular hot cylinder is studied. New numerical method is chosen namely CVFEM. Influences of Rayleigh, Hartmann numbers and volume fraction of Fe3O4 on hydrothermal characteristics are presented. Results illustrate that Lorentz forces cause the nanofluid velocity to reduce and augment the thermal boundary layer thickness. The heat transfer improvement enhances with augment of Lorentz forces. Nusselt number augments with rise of buoyancy forces but it reduces with augment of Lorentz forces.
In this study, micropolar fluid flow in a channel subject to a chemical reaction is investigated analytically using homotopy perturbation method (HPM). The concept of homotopy perturbation method is briefly introduced and employed to derive solutions of nonlinear equations. The obtained results from HPM are compared with those of obtained from numerical method (four-order Runge–Kutta method) to verify the accuracy of the proposed method. The results reveal that the HPM can achieve suitable results in predicting the solution of such problems. The effects of significant parameters such as Reynolds number, micro rotation/angular velocity and Peclet number on the flow, heat transfer and concentration characteristics are discussed. For both suction and injection it can be found that Reynolds number and Peclet number have direct relationship with Nusselt number and Sherwood number.
No abstract is provided for this article.
No abstract is provided for this article.
In this paper, the effect of a magnetic field on natural convection in a half-annulus enclosure with one wall under constant heat flux using control volume based finite element method. The fluid in the enclosure is a water-based nanofluid containing Cu nanoparticles. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. Numerical simulations were performed for different governing parameters namely the Hartmann number, Rayleigh number and inclination angle of enclosure. The results indicate that Hartmann number and the inclination angle of the enclosure can be control parameters at different Rayleigh number. In presence of magnetic field velocity field retarded and hence convection and Nusselt number decreases.
Control of heat transfer in many energy systems is crucial due to the increase in energy prices. In recent years nanofluid technology has been proposed and experimentally or numerically studied by some researchers to control heat transfer in a process. There are two models for simulating nanofluid flow and heat transfer: single phase and two phase. In the single-phase model, nanoparticles are in thermal equilibrium and there are no slip velocities between the nanoparticles and fluid molecules; thus they have a uniform mixture of nanoparticles. In the two-phase model the nanoparticles cannot accompany fluid molecules because of some slip mechanisms such as Brownian motion and thermophoresis, so the volume fraction of nanofluid may no longer be uniform and there may be a variable concentration of nanoparticles in a mixture. In this chapter the governing equations of these models are presented and solved via the control volume finite element method.
