In this study, heat and mass transfer characteristic of unsteady nanofluid flow between parallel plates is investigated. The important effect of Brownian motion and thermophoresis has been included in the model of nanofluid. The governing equations are solved via differential transformation method. The validity of this method was verified by comparison previous work which is done for viscous fluid. The analytical investigation is carried out for different governing parameters namely: the squeeze number, Hartmann number, Schmidt number, Brownian motion parameter, thermophoretic parameter, and Eckert number. The results indicate that skin friction coefficient has direct relationship with Hartmann number and squeeze number. Also it can be found that Nusselt number increases with increase of Hartmann number, Eckert number, and Schmidt number but it is decreases with augment of squeeze number.
Magnetohydrodynamic ferrofluid radiation and free convection heat transfer is investigated numerically using Control Volume based Finite Element Method (CVFEM). Nanofluid viscosity is a function of magnetic field strength. Roles of Radiation parameter ( Rd ) , inclination angle ( ξ ) , Fe3O4-water volume fraction ( ϕ ) , Hartmann ( Ha ) and Rayleigh ( Ra ) numbers are illustrated. A formula for average Nusselt number is derived. Results proved that Nusselt number augments for larger buoyancy forces and radiation parameter. Nusselt number decays through rise of Lorentz forces. Rate of heat transfer augments when inclination angle is increased.
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Magnetohydrodynamic nanofluid flow between two parallel vertical permeable sheets is investigated. Buongiorno model is selected for nanofluid simulation. Joule heating and viscous dissipation impacts are taken into account. Differential Transform Method (DTM) is utilized to solve the final formulae which are obtained via similarity transformation. Roles of Prandtl and Hartmann numbers, Eckert number, suction parameter, Buoyancy ratio, Schmidt number, thermophoretic and Brownian motion parameters are presented. Results illustrated that shear stress enhances with rise of Eckert number but it reduces with rise of Lorentz forces. Temperature gradient on left sheet augments with enhances of Lorentz forces but it decreases with rise of Brownian motion.
In this study, natural convection in a concentric annulus between a cold outer square and heated inner circular cylinders in presence of static radial magnetic field is investigated numerically using the lattice Boltzmann method. The inner and outer cylinders are maintained at constant uniform temperatures and it is assumed that all walls are insulating the magnetic field. The numerical investigation is carried out for different governing parameters namely; the Hartmann number, nanoparticles volume fraction and Rayleigh number. The effective thermal conductivity and viscosity of nanofluids are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. Also, the multi-distribution-function (MDF) model is used for simulating the effect of uniform magnetic field. The results reveal that the average Nusselt number is an increasing function of nanoparticle volume fraction as well as the Rayleigh number, while it is a decreasing function of the Hartmann number.
Hydromagnetic flow between two horizontal plates in a rotating system, where the lower plate is a stretching sheet and the upper is a porous solid plate, is analyzed. Heat transfer in an electrically conducting fluid bonded by two parallel plates is studied in the presence of viscous dissipation. The equations of conservation of mass and momentum and energy are reduced to a nonlinear ordinary differential equations system. Homotopy perturbation method is used to get complete analytic solution for velocity and temperature profiles. Results show an acceptable agreement between this method results and numerical solution. Also the effects of different parameters are discussed through graphs.
In this research, nanofluid magnetohydrodynamic forced convection through a permeable enclosure with moving wall is demonstrated. Brownian motion influence on nanofluid treatment is considered. CVFEM is employed to model this problem. Graphs are shown for different nanofluid volume fraction ( ϕ ) , Reynolds number ( Re ) , Hartmann number ( H a ) and Darcy number ( D a ) . Results demonstrate that convective heat transfer improves with augment of Darcy and Reynolds numbers while it decreases with enhance of Ha.
In this study, effect of thermal radiation on magnetohydrodynamics nanofluid flow between two horizontal rotating plates is studied. The significant effects of Brownian motion and thermophoresis have been included in the model of nanofluid. By using the appropriate transformation for the velocity, temperature and concentration, the basic equations governing the flow, heat and mass transfer are reduced to a set of ordinary differential equations. These equations, subjected to the associated boundary conditions are solved numerically using the fourth-order Runge–Kutta method. The effects of Reynolds number, magnetic parameter, rotation parameter, Schmidt number, thermophoretic parameter, Brownian parameter and radiation parameter on heat and mass characteristics are examined. Results show that Nusselt number has direct relationship with radiation parameter and Reynolds number while it has reverse relationship with other active parameters. It can also be found that concentration boundary layer thickness decreases with the increase of radiation parameter.
Commercial photovoltaic (PV) systems have a relatively low energy conversion efficiency (15∼20%) and this low efficiency reduces by an increase in the working temperature. A higher operating temperature can also reduce the working life of PVs. Therefore, researchers are trying new technologies and also combining them with heat recovery units to elevate the overall productivity of such systems and prevent performance loss and possible damages. The performance loss problem is more considerable in concentrated photovoltaic systems (CPV) and extra consideration is required for them under a higher level of radiation. The present review remarks on the advances obtained in cooling techniques for PVs and especially for CPVs. The current findings showed that various operation and environmental factors could be important in the selection of suitable heat recovery or cooling systems. In this regard, the applied passive and active cooling methods on the front and back surfaces of PVs under different working conditions are categorized here with a broad discussion concerning the advantages, disadvantages, and advances. It is expected that based on the findings, relying on the needs and conditions, the appropriate cooling unit is selected.
In this research, combined turbulator was proposed to achieve good thermal performance. Steady turbulent flow of copper oxide nanofluid with homogeneous model was simulated involving k-ɛ model. Among various geometric parameters, height of turbulator (b) has been selected and its variation as well as Reynolds number was demonstrated in outputs. Exergy loss as well as flow and heat transfer was analyzed. Augmenting b is capable of increasing heat transfer. More disturbances can be seen with augmenting inlet velocity. Exergy loss is inversely proportional to increase of pumping power.
Economic reasons (material and energy saving) leads to make efforts for making more efficient heat exchange. The heat transfer enhancement techniques are widely used in many applications in the heating process to make possible reduction in weight and size or enhance the performance of heat exchangers. These techniques are classified as active and passive techniques. The active technique required external power while the passive technique does not need any external power. The passive techniques are valuable compared with the active techniques because the swirl inserts manufacturing process is simple and can be easily employed in an existing heat exchanger. Insertion of swirl flow devices enhance the convective heat transfer by making swirl into the bulk flow and disrupting the boundary layer at the tube surface due to repeated changes in the surface geometry. An effort has been made in this paper to carry out an extensive literature review of various turbulators (coiled tubes, extended surfaces (fin, louvered strip, winglet), rough surfaces (Corrugated tube, Rib) and swirl flow devices such as twisted tape, conical ring, snail entry turbulator, vortex rings, coiled wire) for enhancing heat transfer in heat exchangers. It can be concluded that wire coil gives better overall performance if the pressure drop penalty is considered. The use of coiled square wire turbulators leads to a considerable increase in heat transfer and friction loss over those of a smooth wall tube.
