Analytic solution of generalized three-dimensional flow and heat transfer over a stretching plane wall

This communication aims to investigate the incompressible generalized three-dimensional viscous flow with heat transfer analysis in the presence of viscous dissipation. The flow is generated due to uniform stretching of the plane wall. Complete analytic solutions for velocity and temperature are obtained by homotopy analysis method (HAM). Graphs are plotted to discuss the effects of different parameters.     

On the transition for a generalized Couette flow of a reactive third-grade fluid with viscous dissipation

We study the thermal transition of a reactive flow of a third-grade fluid with viscous heating and chemical reaction between two horizontal flat plates, where the top is moving with a uniform speed and the bottom plate is fixed in the presence of imposed pressure gradient. This study is a natural continuation of earlier work on rectilinear shear flows. The governing equations are non-dimensionalized and the resulting system of equations are not coupled. An approximate explicit solution is found for the flow velocity using homotopy-perturbation technique and the range of validity is determined. After the velocity is known, the heat transport may be analyzed. It is found that the temperature solution depends on the non-Newtonian material parameter of the fluid, Λ, viscous heating parameter, Γ, and an exponent, m. Attention is focused upon the disappearance of criticality of the solution set {β, δ, θ_max} for various values of Λ, Γ and m, and the numerical computations are presented graphically to show salient features of the solution set.     

Couette flow with frictional heating in a fluid with temperature and pressure dependent viscosity

This study investigates the effects of variable viscosity and frictional heating on the laminar flow in a horizontal channel having a wall at rest and a moving wall subjected to a prescribed shear stress. The wall at rest is thermally insulated, while the moving wall is kept at a uniform temperature. This investigation concerns fluids whose viscosity depends exponentially on the pressure and temperature. An appropriate approximation is introduced to analyze the interplay between the dependence of viscosity on the pressure and temperature and the viscous dissipation. It is shown that the nonlinear term in the equation for the balance of energy representing the frictional heating may lead to the existence of dual solutions of the boundary value problem for fixed values of the material parameters that characterize the fluid. The results obtained are compared with those predicted by the generalization of the Oberbeck-Boussinesq approximation for a fluid with pressure and temperature dependent viscosity. It is found that the results for the approximation carried out in this paper and those that stem from the Oberbeck-Boussinesq approximation are markedly different.     

Viscous-dissipation effects on the heat transfer in a Poiseuille flow

In this study, laminar heat-convection in a Poiseuille flow of a Newtonian fluid with constant properties is analyzed by taking the viscous dissipation into account. At first, both hydrodynamically and thermally fully-developed flow case is investigated. Then, consideration is given to thermally-developed laminar forced-convection. The axial heat-conduction in the fluid is neglected. Two different thermal boundary-conditions are considered: the constant heat-flux and the constant wall-temperature. Both the hot-wall and the cold-wall cases are considered. In the literature, the viscous-dissipation effect is commonly represented by the Brinkman number. Several different definitions of the Brinkman number arise depending on the thermal boundary conditions. Either for the thermally fully-developed case or the thermally-developing case (the Graetz problem), temperature distributions and the Nusselt numbers are analytically determined as functions of the Brinkman number.     

Homotopy Perturbation Method for Thermal Stresses in an Annular Fin with Variable Thermal Conductivity

An approximate analytical solution method for thermal stresses in an annular fin with variable thermal conductivity is presented. Homotopy perturbation method (HPM) is employed to estimate the non-dimensional temperature field by solving nonlinear heat conduction equation. The closed-form solutions for the thermal stresses are formulated using the classical thermoelasticity theory coupled with HPM solution for temperature field. The plane state of stress conditions are considered in this study. The effects of thermal parameters such as variable thermal conductivity parameter (β), thermogeometric parameter (K), and the non-dimensional coefficient of thermal expansion (χ) on the temperature field and stress field are studied. The results for temperature field and stress field obtained from HPM-based solution are found to be in very close agreement with the results available in literature. Furthermore, the HPM solution is found to be very efficient and handles nonlinear heat transfer equation with greater convenience.     

Effect of water on the thermal stability of alpha-aluminum hydride

Water can significantly enhance the thermal spontaneous combustion and explosion hazard of alpha-aluminum hydride (α-AlH₃). Thermal analysis suggested that, as the water content increased from 10% to 40%, the total reaction heat was increased by 68.3%. α-AlH₃ with different water contents (10%–40%) underwent hydrolysis reaction and oxidation reaction with the activation energy of 57.9–68.7 kJ/mol and 88.3–107.6 kJ/mol, respectively. As the heating rate increased from 0.2 to 2 °C/min, the onset temperature, the peak temperature, and the maximum heat flow of the exothermic reaction were increased. As the storage temperature increased from 45 to 65 °C, the time to maximum reaction rate decreased from 5.16 to 0.84 h. Combining the results of SEM, XRD, XPS and thermal analysis, the reaction mechanism of α-AlH₃ and water under isothermal and non-isothermal conditions was revealed.     

Effects of overdischarge on performance and thermal stability of a Li-ion cell

Overdischarge effects on cycle-life and thermal stability of a commercially available Li-ion cell (rated at 780 mA h) were investigated. Cells were overdischarged and kept at 2.0, 1.5, 1.0, 0.5 or 0.0 V for 72 h (3 days) and then cycled five times (discharge to 3.0 V at 0.4 A and charged to 4.2 V at 0.8 A). This process was repeated five times. The cells overdischarged between 2.0 and 0.5 V experienced irreversible capacity losses of 2–16%. The same cells lost between 8 and 26% more capacity after they were cycled 100 times between 4.2 and 3.0 V at 0.8 A. Behavior of the cells overdischarged to 0.0 V was unpredictable. Some cells lost nearly 65% of their initial capacities after 15 days of being kept at 0.0 V, and others failed in different stages of overdischarging to 0.0 V. Overdischarging to 0.5 V had minimal effects on thermal stability, overcharge performance and a.c. impedance, but led to considerable swelling of the cells. Overdischarge to 0.0 V caused cell thickness and a.c. impedance to increase by 70 and 250% of their initial values, respectively. This article addresses concerns that overdischarging of Li-ion cells below 1.5 V may cause capacity losses and/or thermal stability changes which could impact tolerance to abuse conditions.     

Effect of hydrochloric acid on the thermal stability of alpha-aluminum hydride

Hydrochloric acid (HCl solution) can reduce the thermal stability of alpha-aluminum hydride (α-AlH₃). Thermal analysis suggested that, as the acid content of α-AlH₃-HCl solution mixtures increased from 0% to 40.4%, the overall reaction heat (ΔH) was increased by 142.3%. The activation energy (E_a) of the reaction between α-AlH₃ and the acid was 50.7–58.8 kJ/mol, and that of the oxidation reaction was 98.7–141.8 kJ/mol. The initiation of the reaction between α-AlH₃ and acid required low energy. As the heating rate increased, the onset temperature and the maximum heat flow of the exothermic reactions increased. At constant temperature, the reaction rate increased rapidly and then decreased slowly. As the constant temperature increased from 70 to 85 °C, the time to reach the maximum reaction rate was reduced by 89.9%. Combining with the SEM, XRD, and XPS analysis, the reaction mechanism of α-AlH₃ and hydrochloric acid was revealed in depth.     

Effect of the viscosity on the thermal transfer at early time to an impulsively started translating droplet

We study the effect of viscosity on the thermal transfer at the interface associated with a spherical liquid droplet impulsively started at constant velocity in another liquid of large extent at rest. Exact solutions for the thermal distributions are derived at short moving time. From algebraic and numerical considerations we show that viscous effects on the thermal transfer at the interface are negligible by comparison with the inviscid solutions. On the contrary, they predominantly occur on both side of it, in the two adjacent boundary layers, with a spreading effect with time.     

Influence of thermal ageing on the stability of polymer bulk heterojunction solar cells

A new approach is presented in order to improve the thermal stability of polymer: [6-6]-phenyl C₆₁ butyric acid methyl ester (PCBM) bulk heterojunction solar cells. The central idea in this approach is the use of a polymer with high glass transition temperature (T_g), well above the normal operating temperatures of the devices. In this paper, a PPV-derivative with a T_g of 150 °C was used as an electron donor and the thermal stability of the obtained solar cells was compared with solar cells based on the reference material poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with a T_g of 45 °C. The use of the material with higher glass transition temperature resulted in a significant improvement of the thermal stability of the photovoltaic parameters. Furthermore, a systematic transmission electron microscope (TEM) study demonstrates that the better thermal stability of performance coincides with a more stable active layer morphology. Both improvements are attributed to the reduced free movement of the electron donor material (PCBM) within the active layer of the solar cell.     

Thermal characteristics of forced convection in combined pressure and shear-driven flow of a non-Newtonian third-grade fluid through parallel plates

Heat transfer in a non-Newtonian third-grade fluid, flowing under the action of pressure gradient and shear, through two parallel plates, is considered. The upper plate moves with a constant velocity. Constant wall heat fluxes are applied to the plates. Effect of viscous dissipation is included, which has a major role in heat transfer of non-Newtonian fluids. The governing equations are nonlinear and are solved semi-analytically by using the least-square method (LSM). Then, using the solution for velocity in the energy equation, the solution is obtained by a direct integration process. Further, approximate analytical solutions are obtained by the perturbation method, which validates the results generated by the LSM. The effects of the third-grade fluid parameter on the velocity and temperature and also on the physical quantity, such as Nusselt's number, are discussed. Further, viscous dissipation effects on the temperature distribution have been analyzed. Observations show that the movement of the upper plate results in a significant decrease in temperature near the upper plate. For the unit heat flux ratio, the temperature difference between the surface and fluid is more at the upper surface due to the enhanced convective heat transfer caused by the moving upper plate. Nusselt's number increases significantly with an increase in the heat flux ratio.     

Unsteady boundary layer flow and heat transfer past a porous stretching sheet in presence of variable viscosity and thermal diffusivity

The aim of this paper is to present the unsteady boundary layer flow and heat transfer of a fluid towards a porous stretching sheet. Fluid viscosity and thermal diffusivity are assumed to vary as linear functions of temperature. Using similarity solutions partial differential equations corresponding to the momentum and energy equations are converted into highly non-linear ordinary differential equations. Numerical solutions of these equations are obtained with the help of shooting method. It is noted that due to increase in unsteadiness parameter, fluid velocity decreases up to the crossing over point and after this point opposite behaviour is noted. The temperature decreases significantly in this case. Fluid velocity decreases with increasing temperature-dependent fluid viscosity parameter (i.e. with decreasing viscosity) up to the crossing over point but increases after that point and the temperature decreases in this case. Due to increase in thermal diffusivity parameter, temperature is found to increase.     

On inherent irreversibility in a reactive hydromagnetic channel flow

This study is devoted to investigate the inherent irreversibility and thermal stability in a reactive electrically conducting fluid flowing steadily through a channel with isothermal walls under the influence of a transversely imposed magnetic field. Using a perturbation method coupled with a special type of Hermite-Pade＂ approximation technique, the simplified governing non-linear equation is solved and the important properties of overall flow structure including velocity field, temperature field and thermal criticality conditions are derived which essentially expedite to obtain expressions for volumetric entropy generation numbers, irreversibility distribution ratio and the Bejan number in the flow field.     

Heat transfer enhancement in hydromagnetic dissipative flow past a moving wedge suspended by H2O-aluminum alloy nanoparticles in the presence of thermal radiation

This letter investigates the two dimensional magnetohydrodynamic Falkner Skan flow of water saturated with AA7072–H₂O and AA7075–H₂O nanoparticles over a moving wedge. Influence of viscous dissipation and thermal radiation is also under consideration. The model is reduced into nondimensional form by using defined self-similar transformations. Then, numerical study (Runge-Kutta numerical scheme) is carried out for solution purpose. The effects of pertinent flow parameters are discussed in the flow regimes by means of graphical aid. Graphical results for special cases (static wedge and when the movement of flow and wedge is in opposite direction) of the model are also elucidated graphically. It is noted that fluid velocity decreases for volumetric fraction and magnetic force favor the velocity. Significant effects of thermal radiation and nanoparticles volume fraction pointed for thermal filed and the influence of Eckert number is almost inconsequential. For more radiative fluid heat transfer coefficient decreases and nanoparticles volumetric fraction favor the local rate of heat transfer. In the presence of AA7075 nanoparticles, rate of heat transfer is quite rapid as compared to that of AA7072 nanoparticles. To validate the present computations, some present results are compared with already existing results in the literature and found better agreement between them. Finally, major points of the study ingrained in the last section of the letter.     

Effects of radiation and variable viscosity on a MHD free convection flow past a semi-infinite flat plate with an aligned magnetic field in the case of unsteady flow

The effect of radiation and variable viscosity on a MHD free convection flow past a semi-infinite flat plate with an aligned magnetic field has been studied in the case of unsteady flow. The plate is moved with a constant velocity, which is in the same or opposite direction to the free stream velocity. The fluid viscosity is assumed to vary as an inverse linear function of temperature. The effect of the induced magnetic field has been included in the analysis. The governing partial differential equations have been solved numerically using the finite difference method. The velocity, the x-component of the induced magnetic field and heat transfer characteristics of the flow are determined     

Study on the crystallization behaviour and thermal stability of glass-ceramics used as solid oxide fuel cell-sealing materials

Glass ceramics are commonly used as sealing materials for planar solid oxide fuel cells (SOFCs). The major requirements of stack and module builders for these materials are the stability of the coefficient of thermal expansion (CTE), excellent bonding (sticking) behaviour and the absence of volatile ingredients, which can lead to changes of the material properties and the sealing ability.SCHOTT Electronic Packaging has developed special glasses and glass-ceramics for various solid oxide fuel cell designs and operating temperatures. The glass compositions are based on the system MgO-Al₂O₃-BaO-SiO₂-B₂O₃.In this study the evaluation of the developed materials was done by high temperature aging tests for up to 1000 h, high temperature XRD-studies and Rietveld calculations, combined with scanning-electron microscope analysis. Samples of these aged samples were chemically analysed by XRD and wet chemical methods.Results show that after thermal aging of the glasses barium silicates accompanied by barium-magnesium silicates are the major crystalline phases of the glasses. The crystal phases remain stable during high temperature aging tests, indicating a low driving force of material change. The experimental results are compared to phase diagrams by phenomenological and thermochemical considerations.     

On the effectiveness of viscous dissipation and Joule heating on steady MHD flow and heat transfer of a Bingham fluid over a porous rotating disk in the presence of Hall and ion-slip currents

The combined effects of viscous dissipation and Joule heating on steady magnetohydrodynamics (MHD) flow of an electrically conducting viscous incompressible non-Newtonian Bingham fluid over a porous rotating disk in the presence of Hall and ion-slip currents is studied. An external uniform magnetic field is applied in the z-direction and the fluid is subjected to uniform suction. Numerical solutions are obtained for the governing momentum and energy equations. Results for the details of the velocity as well as temperature are shown graphically and the numerical values of the skin friction and the rate of heat transfer are entered in tables.     

Salient features of Dufour and Soret effect in radiative MHD flow of viscous fluid by a rotating cone with entropy generation

BackgroundHere physical characteristics of convective magnetohydrodynamic flow of viscous liquid subject to a rotating cone are discussed. Dissipation, Joule heating, thermal flux and heat generation/absorption are scrutinized in energy expression. Physical aspects of diffusion-thermo and thermo diffusion effect are deliberated. Thermo-diffusion is the mechanisms of transportation in which particles are transferred in a multi-factor mixture determined by temperature gradient. Furthermore irreversibility analysis is considered.MethodNonlinear partial differential system are reduced to ordinary one with the help of similarity variables. Here we implemented ND solve technique to get numerical results for given nonlinear system.ResultsCharacteristics of influential variables for entropy optimization, velocity, concentration, Bejan number and temperature are scrutinized. Numerical outcomes of gradient of velocity and Nusselt and Sherwood numbers are examined through tabulated form. Velocity components are declined against higher velocity slip parameters. For larger estimation of heat generation and radiation parameters the temperature is upsurges. Entropy generation and Bejan number are boost up via rising values of diffusion and radiation parameters. For larger estimation of Brinkman number both Bejan number and entropy rate have opposite effect. Comparative studies of the current and previous results are discussed in tabularized form and have a good agreement.     

Experimental investigation of titanium nanofluids on the heat pipe thermal efficiency

The enhancement heat transfer of the heat transfer devices can be done by changing the fluid transport properties and flow features of working fluids. In the present study, therefore, the enhancement of heat pipe thermal efficiency with nanofluids is presented. The heat pipe is fabricated from the straight copper tube with the outer diameter and length of 15, 600 mm, respectively. The heat pipe with the de-ionic water, alcohol, and nanofluids (alcohol and nanoparticles) are tested. The titanium nanoparticles with diameter of 21 nm are used in the present study which the mixtures of alcohol and nanoparticles are prepared using an ultrasonic homogenizer. Effects of %charge amount of working fluid, heat pipe tilt angle and %nanoparticles volume concentrations on the thermal efficiency of heat pipe are considered. The nanoparticles have a significant effect on the enhancement of thermal efficiency of heat pipe. The thermal efficiency of heat pipe with the nanofluids is compared with that the based fluid.     

Natural convection flow along the vertical wavy cone in case of uniform surface heat flux where viscosity is an exponential function of temperature

The effect of temperature dependent viscosity μ(T), on steady two dimensional natural convection flow along a vertical wavy cone with uniform surface heat flux has been investigated. Viscosity is taken to be an exponential function of temperature. Using the appropriate variables the basic equations are transformed to non-dimensional boundary layer equations and then solved numerically employing implicit finite difference method. The effects of viscosity variation parameter on the velocity profile, temperature profile, velocity vector field, skin friction, average Nusselt number, streamlines and isotherm have been discussed. The results have been shown graphically by utilizing the visualizing software Techplot.