Showing papers on "Film temperature published in 2015"

Cattaneo-Christov heat flux model for rotating flow and heat transfer of upper-convected Maxwell fluid

Abstract: In this paper Cattaneo-Christov heat flux model is used to investigate the rotating flow of viscoelastic fluid bounded by a stretching surface. This model is a modified version of the classical Fourier’s law that takes into account the interesting aspect of thermal relaxation time. The boundary layer equations are first modeled and then reduced to self-similar forms via similarity approach. Both analytical and numerical solutions are obtained and found in excellent agreement. Our computations reveal that velocity is inversely proportional to the viscoelastic fluid parameter. Further fluid temperature has inverse relationship with the relaxation time for heat flux and with the Prandtl number. Present consideration even in the case of Newtonian fluid does not yet exist in the literature.

Study of Natural Convection MHD Nanofluid by Means of Single and Multi-Walled Carbon Nanotubes Suspended in a Salt-Water Solution

Abstract: The natural convection boundary layer flow along a vertical cone with variable wall temperature under the presence of magnetohydrodynamics is investigated. The mathematical model based on nanolayer single and multi-wall carbon nanotubes in salt-water solutions and interfacial layers is considered. The nonlinear partial differential equations are analytically solved by means of Mathematica package BVPh 2.0 based on the homotopy analysis method. Flow behavior under altering involving physical parameters such as: Eckert number, Prandtl number, power law index, and nanoparticle volume fraction on the velocity and the temperature profiles is discussed and explained through graphs and tables. The values of Skin friction and Nusselt number are computed and examined.

Two-Phase Simulation of Nanofluid Flow and Heat Transfer in an Annulus in the Presence of an Axial Magnetic Field

Abstract: In this study, the effects of magnetic field on nanofluid flow, heat, and mass transfer between two horizontal coaxial cylinders are studied using a two-phase model. The effect of viscous dissipation is also taken into account. 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 subject to the associated boundary conditions are solved numerically using the fourth-order Runge–Kutta method. The effects of Hartmann number, Reynolds number, Schmidt number, Brownian parameter, thermophoresis parameter, Eckert number, and aspect ratio on flow, heat, and mass transfer are examined. Results show that the Nusselt number has a direct relationship with the aspect ratio and Hartmann number but it has a reverse relationship with the Reynolds number, Schmidt number, Brownian parameter, thermophoresis parameter, and Eckert number.

Effects of buoyancy and thermal radiation on MHD flow over a stretching porous sheet using homotopy analysis method

Abstract: This paper investigates the theoretical influence of buoyancy and thermal radiation on MHD flow over a stretching porous sheet The model which constituted highly nonlinear governing equations is transformed using similarity solution and then solved using homotopy analysis method (HAM) The analysis is carried out up to the 5th order of approximation and the influences of different physical parameters such as Prandtl number, Grashof number, suction/injection parameter, thermal radiation parameter and heat generation/absorption coefficient and also Hartman number on dimensionless velocity, temperature and the rate of heat transfer are investigated and discussed quantitatively with the aid of graphs Numerical results obtained are compared with the previous results published in the literature and are found to be in good agreement It was found that when the buoyancy parameter and the fluid velocity increase, the thermal boundary layer decreases In case of the thermal radiation, increasing the thermal radiation parameter produces significant increases in the thermal conditions of the fluid temperature which cause more fluid in the boundary layer due to buoyancy effect, causing the velocity in the fluid to increase The hydrodynamic boundary layer and thermal boundary layer thickness increase as a result of increase in radiation

Studying the Effect of Indentation on Flow Parameters and Slow Heat Transfer of Water-Silver Nano-Fluid with Varying Volume Fraction in a Rectangular Two-Dimensional Micro Channel

Abstract: The purpose of this study is to investigate the influence of indentations on the parameters of fluid flow and heat of water-silver nanofluid in a rectangular two-dimensional micro channel. It includes heat transfer water silver nano fluid in an indented micro channel under the constant temperature. The system is numerically modeled, by Finite Volume Method. After solving the governing equations for U, V and θ, other useful quantities such as Nusselt number and friction factor can be determined. The hot fluid inlet exits after cooling by the cold walls of the micro channel. Calculations are done for the two ranges of Reynolds number (Re). It was observed that at times the fluid has more indentations; it has a greater temperature drop that is at the output cross section of the micro channel. With increasing Reynolds number (Re), number of the indentations and the increasing volume fraction of the nanoparticles, greater temperature drop occurs. The presence of indentation in the micro channel increases the speed and the dimensionless temperature at the center line. Finally, the results are provided in the form of the contour of flow and isothermal lines, the coefficient of friction, Nusselt number, temperature and velocity profiles in different micro channel sections. The results of the numerical simulation indicate that the heat transfer rate is significantly affected by the solid volume fraction and Reynolds number.

Magneto-natural convection in square cavities with a source-sink pair on different walls

Abstract: Magnetohydrodynamic natural convection fluid flow and heat transfer in a square enclosure with a pair of source and sink on its walls, filled with liquid Gallium fluid with Prandtl number of 002 has been investigated numerically The heat source and heat sink are maintained at a constant temperature Th and Tc, respectively with Th >T c By variation of relative location of the heat source and sink on the walls of the enclosure, five different cases are generated The governing equations written in terms of the primitive variables are solved numerically using the finite volume method and the SIMPLER algorithm Using the developed code, a parametric study is performed, and the effects of the Rayleigh number, the Hartman number, and the locations of the source and sink on the fluid flow and heat transfer inside the enclosure are investigated The results show that the flow and temperature distributions inside the enclosure are affected by the strength of the magnetic field, the Rayleigh number, and the relative location of the heat source and sink The magnetic field decreases the rate of heat transfer, suppresses the convection heat transfer, and tends to slows down the flow velocity in the cavity Moreover in some cases the magnetic field changes the flow pattern inside the enclosure

A note on convective heat transfer of an MHD Jeffrey fluid over a stretching sheet

Abstract: This article focuses on the exact solution regarding convective heat transfer of a magnetohydrodynamic (MHD) Jeffrey fluid over a stretching sheet. The effects of joule and viscous dissipation, internal heat source/sink and thermal radiation on the heat transfer characteristics are taken in account in the presence of a transverse magnetic field for two types of boundary heating process namely prescribed power law surface temperature (PST) and prescribed heat flux (PHF). Similarity transformations are used to reduce the governing non-linear momentum and thermal boundary layer equations into a set of ordinary differential equations. The exact solutions of the reduced ordinary differential equations are developed in the form of confluent hypergeometric function. The influence of the pertinent parameters on the temperature profile is examined. In addition the results for the wall temperature gradient are also discussed in detail.

Numerical investigation on heat and mass transfer effect of micropolar fluid over a stretching sheet through porous media

Abstract: The present paper deals with the study of unsteady heat and mass transfer characteristics of a viscous incompressible electrically conducting micropolar fluid. The flow past over a stretching sheet through a porous medium in the presence of viscous dissipation. A uniform magnetic field is applied transversely to the direction of the flow. Similarity transformations are used to convert the governing time dependent non-linear boundary layer equations into a system of non-linear ordinary differential equations that are solved numerically by Runge–Kutta fourth order method with a shooting technique. The influence of unsteady parameter ( A ), Eckert number ( E c ), porous parameter ( K p ), Prandtl number ( P r ), Schmidt number ( S c ) on velocity, temperature and concentration profiles are shown graphically. The buoyancy force retards the fluid near the velocity boundary layer in case of opposing flow and is favorable for assisting flow. In case of assisting flow, the absence of porous matrix enhances the flow. The impact of physical parameters on skin friction co-efficient, wall couple stress and the local Nusselt number and Sherwood number are shown in tabular form.

Effect of inclined magnetic field in flow of third grade fluid with variable thermal conductivity

Abstract: This paper examines effects of inclined magnetic field and heat transfer in the flow of a third-grade fluid by an exponentially stretching surface. Formulation and analysis are given with heat source and sink. Thermal conductivity is taken temperature dependent. The governing boundary layer equations and boundary conditions are simplified through appropriate transformations. Resulting equations are solved for the approximate solutions. Convergence of governed problems is explicitly discussed. Influences of various dimensionless parameters such as on the flow and thermal fields are discussed. Local skin friction coefficient and the local Nusselt number are analyzed through tabulated values.

Upward Flow Boiling to DI-Water and Cuo Nanofluids Inside the Concentric Annuli

Abstract: In this work, flow boiling heat transfer coefficients of deionized water and copper oxide water-based nanofluids at different operating conditions have been experimentally measured and compared. The liquid flowed in an annular space. According to the experiments, two distinguished heat transfer regions with two different mechanisms can be seen namely forced convective and nucleate boiling regions. Results demonstrated that with increasing the applied heat flux, flow boiling heat transfer coefficient increases for both of test fluids at both heat transfer regions. In addition to, by increasing the flow rate of fluid, the heat transfer coefficient dramatically increases at both regions. Influence of inlet temperature of fluid to the annulus as a complicated parameter has been investigated and briefly discussed. Results showed that inlet temperature of fluid displaces the boundary between forced convection and nucleate boiling areas such that with increasing the inlet temperature, nucleation mechanism become dominant mechanism at lower heat fluxes. Furthermore, higher heat transfer coefficient can be obtained due to interactions of bubbles and local agitations. Also, Chen type model was modified in terms of thermo-physical properties and examined to experimental data. Results showed that experimental data are in a good agreement with those of obtained by the correlation with deviation up to 30%.

Atomic Degradation and Wear of Thin Carbon Films Under High-Speed Sliding Contact Using Molecular Dynamics Simulation

Abstract: The thermomechanical contact behavior and the resulting change in atomic structure of diamond-like carbon (DLC) film were investigated through molecular dynamics simulation. Under the high-speed sliding contact between a diamond asperity and an amorphous DLC film, the atomic stress, temperature rise, and atom coordination number were measured with the elapsed contact time. It was observed that the increase in atomic stress caused higher kinetic energy on the carbon atoms, which accordingly led to the increase in the DLC film temperature. Examining the change in atom coordination number for the carbon atoms in the DLC film, it could be found that the number of sp 2 bonds (i.e., three-fold structure) increased with the contact time, which supported the graphitization process on the DLC film. During the sliding contact, some of the carbon atoms were debonded from the diamond asperity, which were rebonded (or transferred) onto the DLC film surface right after. From the analysis of atomic structural change, it could be concluded that this rebonding process was relying on covalent bonding rather than van der Waals interaction.

Study of magnetic and heat transfer on the peristaltic transport of a fractional second grade fluid in a vertical tube

Abstract: Performance tests were carried out for a microchannel printed circuit heat exchanger (PCHE), which was fabricated with micro photo-etching and diffusion bonding technologies. The microchannel PCHE was tested for Reynolds numbers in the range of 100‒850 varying the hot-side inlet temperature between 40 °C–50 °C while keeping the cold-side temperature fixed at 20 °C. It was found that the average heat transfer rate and heat transfer performance of the countercurrrent configuration were 6.8% and 10%‒15% higher, respectively, than those of the parallel flow. The average heat transfer rate, heat transfer performance and pressure drop increased with increasing Reynolds number in all experiments. Increasing inlet temperature did not affect the heat transfer performance while it slightly decreased the pressure drop in the experimental range considered. Empirical correlations have been developed for the heat transfer coefficient and pressure drop factor as functions of the Reynolds number.

Heat Transfer and Pressure Drop Characteristics in Straight Microchannel of Printed Circuit Heat Exchangers

Abstract: Performance tests were carried out for a microchannel printed circuit heat exchanger (PCHE), which was fabricated with micro photo-etching and diffusion bonding technologies. The microchannel PCHE was tested for Reynolds numbers in the range of 100‒850 varying the hot-side inlet temperature between 40 °C–50 °C while keeping the cold-side temperature fixed at 20 °C. It was found that the average heat transfer rate and heat transfer performance of the countercurrrent configuration were 6.8% and 10%‒15% higher, respectively, than those of the parallel flow. The average heat transfer rate, heat transfer performance and pressure drop increased with increasing Reynolds number in all experiments. Increasing inlet temperature did not affect the heat transfer performance while it slightly decreased the pressure drop in the experimental range considered. Empirical correlations have been developed for the heat transfer coefficient and pressure drop factor as functions of the Reynolds number.

A molecular dynamics simulation on the convective heat transfer in nanochannels

Abstract: The understanding of the flow and heat transfer processes for fluid through micro- and nanochannels becomes imperative due to its wide application in micro- and nano-fluidic devices. In this paper, the method to simulate the convective heat transfer process in molecular dynamics is improved based on a previous study. With this method, we simulate a warm dense fluid flowing through a cold parallel-plate nanochannel with constant wall temperature. The characteristics of the velocity and temperature fields are analysed. The temperature difference between the bulk average temperature of fluid and the wall temperature decreases in an exponential form along the flow direction. The Nusselt number for the laminar flow in parallel-plate nanochannel is smaller than its corresponding value at macroscale. It could be attributed to the temperature jump at the fluid–wall interface, which decreases the temperature gradient near the wall. The results also reveal that the heat transfer coefficient is related to the surfac...