[show abstract][hide abstract] ABSTRACT: Force convective heat transfer of alumina/water nanofluid inside a cooled parallel-plate channel in the creeping flow regime and the presence of heat generation is investigated theoretically. A modified two-component four-equation non-homogeneous equilibrium model is employed for the alumina/water nanofluid that fully accounts for the effects of nanoparticles volume fraction distribution. To impose the temperature gradients across the channel, the upper wall is subjected to a prescribed wall heat flux while the bottom wall is kept adiabatic. Moreover, due to the nanoparticle migration in the fluid, the no-slip condition of the fluid–solid interface at the walls is abandoned in favor of a slip condition that appropriately represents the non-equilibrium region near the interface. The results indicated that nanoparticles move from the adiabatic wall (nanoparticles depletion) toward the cold wall (nanoparticles accumulation) and construct a non-uniform nanoparticle distribution. Moreover, the anomalous heat transfer rate occurs when the Brownian motion takes control of the nanoparticle migration (smaller nanoparticles).
[show abstract][hide abstract] ABSTRACT: Thermally fully developed mixed convection flow of nanofluids in a vertical annular pipe was investigated. Because of the non-adherence of the fluid–solid interface in the presence of nanoparticles, known as slip condition, the Navier’s slip condition was considered at the pipe walls. The Buongiorno’s model was employed for nanofluids that incorporate the effects of Brownian motion Nb and thermophoresis Nt numbers. Using the similarity variables, the governing partial differential equations were transformed into a system of ordinary ones with a constraint parameter and a solution was prepared via a reciprocal numerical algorithm. The effects of Grashof number Gr and slip parameter λ on nanoparticle volume fraction, velocity, temperature, average Nusselt number Nuavg, and pressure coefficient σ have been investigated in details. Results indicate that an increase in Gr and λ reduces the peak value of the dimensionless velocity profile in the core region of the annulus, away from the pipe walls, however, the velocity closer to the pipe walls increases. Furthermore, it was shown that nanofluids can transfer heat more efficiently in a slip condition than in a no-slip condition.
Journal of the Brazilian Society of Mechanical Sciences and Engineering 02/2014; · 0.23 Impact Factor
[show abstract][hide abstract] ABSTRACT: Unsteady two-dimensional stagnation point flow of a nanofluid over a stretching sheet is investigated numerically. In contrast to the conventional no-slip condition at the surface, Navier's slip condition has been applied. The behavior of the nanofluid was investigated for three different nanoparticles in the water-base fluid, namely copper, alumina and titania. Employing the similarity variables, the governing partial differential equations including continuity, momentum and energy have been reduced to ordinary ones and solved via Runge-Kutta-Fehlberg scheme. It was shown that a dual solution exists for negative values of the unsteadiness parameter A and, as it increases, the skin friction Cfr grows but the heat transfer rate Nur takes a decreasing trend. The results also indicated that, unlike the stretching parameter ε, increasing in the values of the slip parameter λ widen the ranges of the unsteadiness parameter A for which the solution exists. Furthermore, it was found that an increase in both ε and λ intensifies the heat transfer rate.
[show abstract][hide abstract] ABSTRACT: In this paper the process of solidification and melting of a phase change material is investigated in fin and tube heat exchanger. The shell side including around the tubes and spaces between fins is filled with the material R35 allocated to store energy of water, as heat transfer fluid, which flows inside the tubes. Experimental apparatus is used to investigate the effect of flow rate, inlet temperature and geometrical parameter (fin pitch) on charging and discharging processes of the phase change material. The shell side is a rectangular cube in which a continuous spiry tube creates a heat transfer surface. Results indicate that utilizing fins increases fin average temperature regardless of flow regime. While reduction in fin pitch doesn't affect this parameter sensibly for both regimes. By the increase of inlet temperature from Th = 50 °C to Th = 60 °C, melting time decreases more severally in comparison with the same rise from Th = 60 °C to Th = 70 °C.
International Communications in Heat and Mass Transfer 01/2014; · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this study, entropy generation minimization (EGM) was employed to optimize fluid flow and heat transfer over a moving wedge. Governing partial differential equations including continuity, momentum and energy are reduced to ordinary ones using similarity variables and solved numerically. The novelty of this study is to consider the effects of the moving wedge parameter λ, to find the stable system via entropy generation minimization (EGM) method. The results indicated that as the slope of the wedge increases, the absolute values of the optimum moving wedge parameter λo grow as well. Moreover, it was found that the minimum value of entropy generation happens for the negative values of λo which gets smaller as Falkner–Skan power law parameter m increases.
[show abstract][hide abstract] ABSTRACT: Unsteady motion of a rigid spherical particle in a quiescent shear-thinning power-law fluid was investigated analytically. The accurate series solution was found by coupling the homotopy-perturbation method (HPM) and the variational iteration method (VIM). The results were compared with those obtained from VIM and the established finite difference scheme. It was shown that both methods (VIM and HPM–VIM) gave accurate results; however, the amount of calculations required for HPM–VIM was significantly reduced. In addition to improved efficiency, it was revealed that HPM–VIM leads to completely reliable and precise results. The terminal settling velocity—that is the velocity at which the net forces on a falling particle eliminate—for three different spherical particles (made of plastic, glass and steel) and three flow behavior index n, in two sets of power-law non-Newtonian fluids was investigated, based on the series solution. Analytical results obtained indicated that the time of reaching the terminal velocity in a falling procedure is significantly declined with growing the particle size. Further, with approaching flow behavior to Newtonian behavior from shear-thinning properties of flow (n → 1), the transient time to achieving the terminal settling velocity is decreased.
Journal of Molecular Liquids 01/2014; · 1.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: The present study is a theoretical investigation of the laminar flow and convective heat transfer of water/alumina nanofluid inside a parallel-plate channel in the presence of a uniform magnetic field. A modified two-component, four-equation, nonhomogeneous equilibrium model was employed for the alumina/water nanofluid, which fully accounted for the effect of the nanoparticle volume fraction distribution. The no-slip condition of the fluid–solid interface is abandoned in favor of a slip condition which appropriately represents the non-equilibrium region near the interface at micro/nano channels. The results obtained indicated that nanoparticles move from the heated walls (nanoparticles depletion) toward the core region of the channel (nanoparticles accumulation) and construct a non-uniform nanoparticles distribution. Moreover, in the presence of the magnetic field, the near wall velocity gradients increase, enhancing the slip velocity and thus the heat transfer rate and pressure drop increase.
Journal of Magnetism and Magnetic Materials 01/2014; 362:172–179. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this study MHD effect on natural convection heat transfer in an enclosure filled with nanofluid is investigated. The transport equations used in the analysis took into account the effect of Brownian motion and thermophoresis parameters. The Navier Stokes equations in their vorticity-stream function form are used to simulate the flow pattern, isotherms and concentration. The governing equations are solved via Control Volume based Finite Element Method. The inner and outer circular walls are maintained at constant temperatures while two other walls are thermally insulated. The heat transfer between cold and hot regions of the enclosure cannot be well understood by using isotherm patterns so heatline visualization technique is used to find the direction and intensity of heat transfer in a domain. Effect of Hartmann number (Ha = 0, 30, 60 and 100), buoyancy ratio number (Nr = 0.1–4) and Lewis number (Le = 2, 4, 6 and 8) on streamline, isotherm, isoconcentration and heatline are examined. Also a correlation for Nusselt number corresponding to active parameters is presented. The results indicate that Nusselt number is an increasing function of buoyancy ratio number but it is a decreasing function of Lewis number and Hartmann number. Also it can be concluded that as buoyancy ratio number increases the effects of other active parameters are more pronounced.
[show abstract][hide abstract] ABSTRACT: This paper deals with the mixed convective heat transfer of nanofluids through a concentric vertical annulus. Because of the non-adherence of the fluid-solid interface in the presence of nanoparticle migrations, known as slip condition, the Navier’s slip boundary condition was considered at the pipe walls. The employed model for nanofluid includes the modified two-component four-equation non-homogeneous equilibrium model that fully accounts for the effects of nanoparticles volume fraction distribution. Assuming the fully developed flow and heat transfer, the basic partial differential equations including continuity, momentum, and energy equations have been reduced to two-point ordinary boundary value differential equations and solved numerically. Two cases including constant heat flux at the outer wall and insulated inner wall (Case A) and constant heat flux at the inner wall with insulated outer wall (Case B) have been considered. Results indicate that the buoyancy has negative effects on the efficiency of the system; however, slip velocity at the surface enhances both the heat transfer rate and the efficiency.
[show abstract][hide abstract] ABSTRACT: The aim of this paper is to find a general mathematical expression for amperometric enzyme
kinetics problems. The variational iteration method coupled with Padé approximation (VIM-Padé) is used to attain a reliable mathematical expression based on the rational functions. The
accuracy of the results is shown in two cases of the electrochemical polymerization on the
electrode surfaces. The comparisons indicated that the presented mathematical expression is not
only a general model—which could be used in most amperometric enzyme kinetics problems—
but also gives more accurate results than the mathematical expressions previously developed for
Journal of electroanalytical chemistry 12/2013; In Press. · 2.67 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper, heat transfer and flow analysis for a non-Newtonian third grade nanofluid flow in porous medium of a hollow vessel in presence of magnetic field are simulated analytically and numerically. Blood is considered as the base third grade non-Newtonian fluid and gold (Au) as nanoparticles are added to it. The viscosity of nanofluid is considered a function of temperature as Vogel's model. Least Square Method (LSM), Galerkin method (GM) and fourth-order Runge-Kutta numerical method (NUM) are used to solve the present problem. The influences of the some physical parameters such as Brownian motion and thermophoresis parameters on non-dimensional velocity and temperature profiles are considered. The results show that increasing the thermophoresis parameter (Nt) caused an increase in temperature values in whole domain and an increase in nanoparticles concentration just near the inner wall of vessel. Furthermore by increasing the MHD parameter, velocity profiles decreased due to magnetic field effect.
Computer methods and programs in biomedicine 11/2013; · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: This work aims to focus on the study of natural convection heat transfer characteristics in a vertical wall embedded in a non-Darcy porous medium filled with nanofluids.
International Journal of Numerical Methods for Heat and Fluid Flow 11/2013; 23. · 1.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: Steady laminar flow of a micropolar fluid towards a stagnation point on a vertical melting surface is investigated. The external velocity is normal to the wall, and the wall temperature is assumed to vary linearly with distance from the stagnation point. The transformed nonlinear ordinary differential equations describing the flow are solved numerically by a cubic spline collocation method. The skin friction coefficient, local Nusselt number, as well as the velocity and temperature profiles for different values of the governing parameters, are presented. The effects of the melting and material parameters on the flow and heat transfer characteristics are examined thoroughly. The results show that both the material and melting parameters reduce the heat transfer rate on the fluid–solid interface.
Journal of Engineering Physics and Thermophysics 10/2013;
[show abstract][hide abstract] ABSTRACT: Combustion process for iron particles burning in the gaseous oxidizing medium is investigated using the Boubaker polynomial expansion scheme (BPES) and the differential transformation method (DTM). Effects of thermal radiation from the external surface of burning particle and alterations of density of iron particle with temperature are considered. The solutions obtained using BPES technique and DTM are compared with those of the fourth-order Runge-Kutta numerical method. Results reveal that BPES is more accurate and reliable method than DTM. Also the effects of some physical parameters that appeared in mathematical section on temperature variations of particles as a function of time are studied.
[show abstract][hide abstract] ABSTRACT: A numerical investigation is carried out to study the effect of splitter’s inclination angle behind an inclined square cylinder on the forced convection heat transfer in a plan channel using the lattice Boltzmann method (LBM). The simulations are conducted for the pertinent parameters in the following ranges: the Reynolds number Re=50–300, the gap ratio G/d = 2, and the splitter’s inclination angle θ = 0°−90°. The results show that with the increase in the angle of the splitter, the drag coefficient initially decreases and then increases. Moreover, the time-averaged Nusselt number at a certain angle increases noticeably.
Applied Mathematics and Mechanics 05/2013; 34(5). · 0.65 Impact Factor
[show abstract][hide abstract] ABSTRACT: The present article solves the couple equations of a spherical solid particle’s motion in plane coquette fluid flow by using the HPM-Padé technique which is a combination of the Homotopy Perturbation Method (HPM) and Padé approximation. The series solutions of the couple equations are developed. Generally, the truncated series solution is adequately in a small region and to overcome this limitation, the Padé techniques which have the advantage of turning the polynomial approximation into a rational function, are applied to the series solution to improve the accuracy and enlarge the convergence domain. The current results compared with those derived from HPM and the established fourth order Runge–Kutta method in order to ascertain the accuracy of the proposed method. It is found that this method can achieve more suitable results in comparison to HPM.
[show abstract][hide abstract] ABSTRACT: In the present work attempts are made to enhance the heat transfer rate in shell and coiled tube heat exchangers experimentally. Hot water flows in helical tube and cold water flows in the shell side. Tube and shell side heat transfer coefficients are determined using Wilson plots. Experimental apparatus and Taguchi method are used to investigate the effect of fluid flow and geometrical parameters on heat transfer rate. After experiments, Taguchi method is used for finding the optimum condition for the desired parameters in the range of 0.0813 < Dc < 0.116, 13 < Pc < 18, tube and shell flow rates from 1 to 4 LPM. Then the optimum condition according to the overall heat transfer coefficient for the whole heat exchanger is found. Results indicate that the higher coil diameter, coil pitch and mass flow rate in shell and tube can enhance the heat transfer rate in these types of heat exchangers. Contribution ratio obtained by Taguchi method shows that shell side flow rate, coil diameter, tube side flow rate and coil pitch are the most important design parameters in coiled heat exchangers.