Showing papers on "Film temperature published in 2018"

Finite element computation of multi-physical micropolar transport phenomena from an inclined moving plate in porous media

Abstract: Non-Newtonian flows arise in numerous industrial transport processes including materials fabrication systems. Micropolar theory offers an excellent mechanism for exploring the fluid dynamics of new non-Newtonian materials which possess internal microstructure. Magnetic fields may also be used for controlling electrically-conducting polymeric flows. To explore numerical simulation of transport in rheological materials processing, in the current paper, a finite element computational solution is presented for magnetohydrodynamic, incompressible, dissipative, radiative and chemically-reacting micropolar fluid flow, heat and mass transfer adjacent to an inclined porous plate embedded in a saturated homogenous porous medium. Heat generation/absorption effects are included. Rosseland’s diffusion approximation is used to describe the radiative heat flux in the energy equation. A Darcy model is employed to simulate drag effects in the porous medium. The governing transport equations are rendered into non-dimensional form under the assumption of low Reynolds number and also low magnetic Reynolds number. Using a Galerkin formulation with a weighted residual scheme, finite element solutions are presented to the boundary value problem. The influence of plate inclination, Eringen coupling number, radiation-conduction number, heat absorption/generation parameter, chemical reaction parameter, plate moving velocity parameter, magnetic parameter, thermal Grashof number, species (solutal) Grashof number, permeability parameter, Eckert number on linear velocity, micro-rotation, temperature and concentration profiles. Furthermore, the influence of selected thermo-physical parameters on friction factor, surface heat transfer and mass transfer rate is also tabulated. The finite element solutions are verified with solutions from several limiting cases in the literature. Interesting features in the flow are identified and interpreted.

An experimental comparison of SiO 2 /water nanofluid heat transfer in square and circular cross-sectional channels

Abstract: In this paper, with the aim of enhancing the thermal conductivity of the fluid, a nanofluid is prepared based on SiO2. A series of experimental tests were carried out for both laminar and forced convection regimes in a horizontal tube with two different geometric shapes (circular and square cross section) subjected to constant wall heat flux (4735 W m−2). A comparative study has been done to investigate the effect of the geometry on the convective heat transfer. Moreover, the effect of the volume concentration on the behavior of the nanofluid and the base fluid was evaluated by comparing various volume concentrations (0.05, 0.07 and 0.2%). The experiments were done under two different conditions: constant Reynolds number and constant mass flow rate. It was found that the circular-shaped channel could be better for heat transfer purposes at the same flow rate, while the square-shaped channel has a higher heat transfer coefficient at the same Reynolds number. The slope of the lines for the square cross section is more than that for circular cross sections which result in a steeper increase in average heat transfer coefficient versus Reynolds number in the square-shaped channel. The increase of the Reynolds number may decrease the dead zones in the square channel that causes the double enhancement of the average heat transfer coefficient.

Numerical exploration of thermal radiation and Biot number effects on the flow of a non-Newtonian MHD Williamson fluid over a vertical convective surface

Abstract: A theoretical and computational study of the magnetohydrodynamic flow and free convection heat transfer in an electroconductive polymer on the external surface of a vertical plate under radial magnetic field is presented. The Biot number effects are considered at the vertical plate surface via modified boundary conditions. The Williamson viscoelastic model is employed which is representative of certain industrial polymers. The nondimensional, transformed boundary layer equations for momentum and energy are solved with the second-order accurate implicit Keller box finite difference method under appropriate boundary conditions. Validation of the numerical solutions is achieved via benchmarking with earlier published results. The influence of Weissenberg number (ratio of the relaxation time of the fluid and time scale of the flow), magnetic body force parameter, stream-wise variable, and Prandtl number on thermo fluid characteristics are studied graphically and via tables. A weak elevation in temperature accompanies increasing Weissenberg number, whereas a significant acceleration in the flow is computed near the vertical plate surface with increasing Weissenberg number. Nusselt number is reduced with increasing Weissenberg number. Skin friction and Nusselt number are both reduced with increasing magnetic field effect. The model is relevant to the simulation of magnetic polymer materials processing.

Exact analysis of heat convection of viscoelastic FENE-P fluids through isothermal slits and tubes

Abstract: In this article, two exact analytical solutions for heat convection in viscoelastic fluid flow through isothermal tubes and slits are presented for the first time. Herein, a Peterlin type of finitely extensible nonlinear elastic (FENE-P) model is used as the nonlinear constitutive equation for the viscoelastic fluid. Due to the eigenvalue form of the heat transfer equation, the modal analysis technique has been used to determine the physical temperature distributions. The closed form solution for the temperature profile is obtained in terms of a Heun Tri-confluent function for slit flow and then the Frobenius method is used to evaluate the temperature distribution for the tube flow. Based on these solutions, the effects of extensibility parameter and Deborah number on thermal convection in FENE-P fluid flow have been studied in detail. The fractional correlations for reduced Nusselt number in terms of material modulus are also derived. Here, it is shown that by increasing the Deborah number from 0 to 100, the Nusselt number is enhanced by 8.5 and 13.5% for slit and tube flow, respectively.

A numerical and experimental study to investigate convective heat transfer and associated cutting temperature distribution in single point turning

Abstract: During the metal cutting operation, heat generation at the cutting interface and the resulting heat distribution among tool, chip, workpiece, and cutting environment has a significant impact on the overall cutting process. Tool life, rate of tool wear, and dimensional accuracy of the machined surface are linked with the heat transfer. In order to develop a precise numerical model for machining, convective heat transfer coefficient is required to simulate the effect of a coolant. Previous literature provides a large operating range of values for the convective heat transfer coefficients, with no clear indication about the selection criterion. In this study, a coupling procedure based on finite element (FE) analysis and computational fluid dynamics (CFD) has been suggested to obtain the optimum value of the convective heat transfer coefficient. In this novel methodology, first the cutting temperature was attained from the FE-based simulation using a logical arbitrary value of convective heat transfer coefficient. The FE-based temperature result was taken as a heat source point on the solid domain of the cutting insert and computational fluid dynamics modeling was executed to examine the convective heat transfer coefficient under similar condition of air interaction. The methodology provided encouraging results by reducing error from 22 to 15% between the values of experimental and simulated cutting temperatures. The methodology revealed encouraging potential to investigate convective heat transfer coefficients under different cutting environments. The incorporation of CFD modeling technique in the area of metal cutting will also benefit other peers working in the similar areas of interest.

Numerical Investigation of MHD Nanofluid Forced Convection in a Microchannel Using Lattice Boltzmann Method

Abstract: In this paper, flow and heat transfer of water–Al2O3 nanofluid in a two-dimensional microchannel that is under the influence of a uniform magnetic field is investigated. The thermal boundary conditions applied on the channel walls are constant temperature at the lower wall and insulated at the upper one. Lattice Boltzmann method is used to obtain the velocity and temperature fields. The effects of relevant parameters such as the Reynolds number (5–25), the nanoparticles volume fraction (0–4%) and the Hartmann number (0–10) are investigated on heat transfer coefficient and friction factor. The results show that the microchannel heat transfer performance is improved 19% by increasing the Reynolds number from 5 to 25. The magnetic field does not have remarkable effect on the heat transfer coefficient, but increases the friction factor up to 86%. Also, heat transfer coefficient enhances 17% by increasing the nanoparticles volume fraction up to 4%, but the rate of improvement in heat transfer coefficient decreases at higher Reynolds and Hartmann numbers.

Radiative non linear heat transfer analysis on wire coating from a bath of third-grade fluid

Abstract: Wire coating as an industrial process coats bare conducting wires for primary insulation so as to accomplish mechanical strength and provide protection for aggressive environments. In the present study, we have investigated and discussed the influence of radiative linear as well as non-linear heat transfer on wire coating with melt polymer as a coating fluid in response to a third-grade fluid model subject to Joule heating. In our analysis, we deal with (i) Reynolds model and (ii) Vogel’s model to implement the temperature-dependent viscosity. The governing equations characterizing the flow and heat transfer are solved numerically by the fourth-order Runge-Kutta method. It is heartening to note that the temperature parameter ΘR is an indicator of the small/large temperature difference between the surface and the ambient fluid, which has a remarkable effect on the heat transfer characteristics and the temperature distributions in the flow region within the die. It is visualized that an increase in ΘR and the radiation parameter R decrease the fluid temperature of the coating fluid, thereby enhancing the rate of heat transfer associated with a thinner thermal boundary layer.

Natural convection in rectangular cavities with different aspect ratios

Abstract: Natural convection in closed cavities has been extensively studied in recent decades. This spontaneous method of heat transfer has a wide range of applications in engineering. In the present work, natural convection was numerically analyzed in a rectangular cavity heated on one of the sides and cooled on the opposite side. Temperatures of the heated wall and of the cooled wall were assumed to be constant. The objective of these studies was to determine the effects of the aspect ratio and the Rayleigh number on flow behavior and heat transfer in the cavity. In the simulations, the Rayleigh number drastically influenced the flow profile and heat transfer inside de cavity, as well as the thickness of the thermal boundary layer. It was also verified that the Nusselt number is strongly dependent on the L/D (Length/Height) ratio, and that this dimensionless variable increases with the increase of the W/L. The simulation of natural convection problems in the CFD Studio satisfactorily described the studied situations.

Enhancement of Heat Transfer in Partially Heated Vertical Channel Under Mixed Convection by Using Al2O3 Nanoparticles

Abstract: Laminar mixed convection in a two-dimensional symmetrically and partially heated vertical channel is investigated. The heaters are located on both walls and uniform temperature is applied on the heated sections. The number of heaters is considered as 1, 4, 8, and 10. Aluminum oxide/water nanofluid is considered as working fluid and the inlet velocity is uniform. The continuity, momentum and energy equations with appropriate boundary conditions are solved in dimensionless form, numerically. The study is performed for Richardson number of 0.01 and 10, Reynolds number of 100 and 500, and nanofluid volume fraction of 0% and 5%. Based on the obtained velocity and temperature distributions, the local and mean Nusselt number is calculated and plotted for different cases. The variation of the mean Nusselt number with the number of the heated portions is also discussed. It is found that the addition of nanoparticles into the base fluid increases mean Nusselt number but the rate of increase depends on Reyno...

Non-coaxial rotating flow of viscous fluid with heat and mass transfer

Abstract: Heat and mass transfer in unsteady non-coaxial rotating flow of viscous fluid over an infinite vertical disk is investigated. The motion in the fluid is induced due to two sources. Firstly, due to the buoyancy force which is caused because of temperature and concentration gradients. Secondly, because of non-coaxial rotation of a disk such that the disk executes cosine or since oscillation in its plane and the fluid is at infinity. The problem is modeled in terms of coupled partial differential equations with some physical boundary and initial conditions. The dimensionless form of the problem is solved via Laplace transform method for exact solutions. Expressions for velocity field, temperature and concentration distributions are obtained, satisfying all the initial and boundary conditions. Skin friction, Nusselt number and Sherwood number are also evaluated. The physical significance of the mathematical results is shown in various plots and is discussed for several embedded parameters. It is found that magnitude of primary velocity is less than secondary velocity. In limiting sense, the present solutions are found identical with published results.

Experimental Study of Heat Transfer Enhancement for Fluid Flow Inside Annulus with Spiral Wires

Abstract: The evaluation of heat transfer and pressure drop in a water flow inside an annulus of a double concentric-tube heat exchanger with spiral wires inserts was carried out. Three spiral wires with a constant pitch and different wire diameter were tested for a Reynolds number from 1500 to 5500 and a Prandtl number from 5 to 8. The results obtained showed that the spiral wires increased the heat transfer and the pressure drop in comparison with a fluid flow inside a smooth annulus. From the heat transfer point of view, this increase was proportional to the wire diameter but the effect decreases when the Reynolds number increases. General empirical correlations based on dimensionless parameters to calculate the convective heat transfer coefficient and friction factor were developed with an uncertainty of ±6.1% and ±7.6%, respectively, when these estimates were compared against experimental data. The empirical correlations developed were also compared with the estimates calculated by empirical correlatio...

VO2 film temperature dynamics at low-frequency current self-oscillations

Abstract: Low-frequency (∼2 Hz) current self-oscillations were first obtained in a millimeter-sized two-terminal planar device with a vanadium dioxide (VO2) film The film temperature distribution dynamics was investigated within one oscillation period It was established that the formation and disappearance of a conductive channel occur in a film in less than 60 ms with oscillation period 560 ms The experimentally observed temperature in the channel region reached 413 K, being understated due to a low infrared microscope performance (integration time 10 ms) The VO2 film temperature distribution dynamics was simulated by solving a 2D problem of the electric current flow and heat transfer in the film The calculation showed that the thermally initiated resistance switching in the film occurs in less than 4 ms at a channel temperature reaching ∼1000 K The experimental results and simulation are consistent with the current self-oscillation mechanism based on the current pinching and dielectric relaxation in the VO2

Effect of moving walls on heat transfer and entropy generation in a nanofluid-filled enclosure

Abstract: In this work, a numerical investigation of mixed convection has been carried out in a two-sided lid-driven enclosure filled with copper–water nanofluid. Three different cases have been discussed depending on the direction of moving vertical walls to analyze the behavior of fluid flow and heat transfer in nanofluid. The buoyancy effects are incorporated using two discrete heat sources placed on the bottom wall maintaining a fixed distance from both the side walls. The stationary part of the bottom wall is kept insulated while other walls are maintained at constant low temperature. A two-dimensional computational visualization technique has been employed to demonstrate the main findings of the presented work. The effect of higher nanoparticle volume fraction (up to 20%) with variations of Reynolds number and Richardson number is studied to find the rate of heat transfer. The results are presented using streamlines, isotherms, and energy flux vectors. The thermodynamic optimization of the system is analyzed by using Nusselt number and entropy generation.

Toward calibration-free wall shear stress measurement using a dual hot-film sensor and Kelvin bridges

Abstract: Combined heat transfer and wall shear stress measurements on the inner wall of a fully developed turbulent air flow in a round pipe were presented in this paper. The heat transfer was measured using a flush-mounted dual hot-film sensor composed of a non-electric conductive membrane sandwiched in between two thin nickel films. Each of the two films was installed in a branch of a separate Kelvin bridge, and operated at a same temperature; the bottom film served as an active heat insulator so that the Joule heat from the upper film transferred only to the air. Both theoretical analysis and measurements indicated for , where was the averaged Nusselt number and was the Peclet number. A calibration-free technique for wall shear stress measurement based only on measuring the Joule heat flux was found to be feasible, providing the Peclet number was in the range of 300–2500 and the film temperature was sufficiently large.