Defect and Diffusion Forum Vol. 336

Abstract: The presented work is devoted to the investigation of the influence of single wall carbon nanotubes (SWCNT) on the thermal and mechanical properties of rubber blends. The materials under investigation were rubber blends filled by carbon black (CB-labelled as standard or S) or a mixture of CB with single wall carbon nanotubes (0.6 wt.% of SWCNT). The thermal parameters of the rubber samples were measured on the basis of an exponential model of a cooling body (developed in a lumped capacity model). From the measured cooling curve of the sample after its deformation, the specific heat capacity c_p [J/kg/, thermal diffusivity α [m²/ and thermal conductivity k [W/m/K] were measured. The increase of α and k was observed for rubber blends filled with a mixture of CB and SWCNT. The complex thermo mechanical analyzer (CTMA) was used for determination of thermal and mechanical parameters. The static Youngs modulus shows an immense increase after SWCNT addition. The dynamic Youngs modulus also shows an increase after SWCNT introduction. A simultaneous tgδ decrease caused by SWCNT presence is observed in this case.

Abstract: In this paper, we study the oxidation process during the heating of a titanium metallic surface by a Nd-YAG fiber pulsed laser beam under air environment. For this, we adopted an approach that considers a three-dimensional heat diffusion model coupled with an oxidation parabolic law (oxidation kinetics). The heat diffusion equation solved numerically, gives the temperature field. The oxide film growth is simulated by implementing a dynamic mesh technique. We developed computational procedures UDFs (User Defined Function) running interactively with the Fluent fluid dynamics software [ that implements the finite volume method. These UDFs are developed to insert the oxidation law, the temperature field, the specific boundary conditions and the mesh deformation into the calculation.

Abstract: In the modeling of thermal recovery processes of heavy oil, it is important to know the oil primary relative permeability in the reservoir; moreover we have to be aware of effects of the temperature on oil relative permeability as well. In this study, a sand pack of quartz (SiO₂) has been used to simulate and make a porous medium. Quartz is naturally water wet. During experiments there was no change in the pore volume of the media at different temperatures because of the low expansion coefficient of quartz. The fluid used in experiments is engine oil 50. Glass pipes with length of 91cm and diameter of 2.6cm have been used in the experiments. At first, columns have been filled with sand, which sand grains had different diameters, then carbon dioxide was injected to the columns to deplete the air in the pores , then the porous media have been saturated with water to calculate the porosity using the scale model. In addition according to Darcys law in steady state, the absolute permeability was calculated. In the next step, oil was injected to columns until the water saturation reached connate water saturation and finally, water injection was begun to get residual oil saturation (S_or). Experiments results showed that increase of temperature increases the oil relative permeability, note that wetability was constant. Increasing the temperature decreases the oil viscosity then this reduction causes the fluid to move easier and its velocity increases as well.

Abstract: In addition to emission level reduction, combustion process optimization by modifications of pyrolysis boilers is aimed at fuel cost decrease. Knowledge of fuel composition and fuel combustion properties is important to the optimum and economical combustion process. The levels of emissions caused by the process can be reduced by several designs and operational modifications. This paper deals with modifications of combustion equipment in order to reduce harmful flue gas emissions in a boiler MA 23. The hot water boiler MA 23 belongs to gasification boilers for dry lump wood combustion; it is intended primarily for the heating of family houses, cottages, small office buildings and other small buildings and has the maximum required heat output of 23 kW. The boiler was tested in several modes, based on the requirements of the standard EN 303-5 dealing with emission limits. A basic requirement was the implementation of technical measures described in the paper and a proposal of method of regulation of flue gas volumetric flow rate and of installation in order to keep emission levels below the required limit.

Abstract: Liquid crystal thermography with steady-state experimental method is used to investigate the effectiveness of two-row, cross-injection film cooling on a concave or convex surface. One leg of vortices of a delta wing is used to realize the interaction mechanism between the vortex generated by the cross-injection coolant and the secondary vortex of the main flow. The secondary flow generated by the delta-wing vortex generator produces upwash or downwash motion when sweeping over the film injection holes. In the experiments, the cooling hole diameter, hole-to-hole distances, and an included angle of 120 degrees are fixed, while the main flow Reynolds number, sense of mainstream vortex, and the coolant-to-main flow blowing ratio are varied. Because the cross-injection coolant generates a counter-clockwise vortex (viewed from upstream), results show that when the mainstream vortex has a sense of rotation opposite to that of the cross-injection vortex (i.e. an upwash mainstream vortex), the effectiveness is increased. On the other hand, same sense of rotation in both vortices (i.e. a downwash mainstream vortex) decreases the effectiveness. Both the convex and concave curvatures hamper the attachment of cross-injection coolant to the surface, resulting in a reduction in film cooling effectiveness. The effect is more influential for the concave surface.

Abstract: In this research, the thermal conductivity of aluminum (Al) in macro scale was investigated by the molecular dynamics simulation technique. We used FORTRAN programming in the simulations and used a fixed number of atoms, N, confined to a fixed pressure, P, and maintained at a constant preset temperature, T, i.e. the NPT ensemble. The Sutton-Chen many-body potential was used to calculate energy and force. The temperature and pressure of the system were controlled by Nosé-Hoover thermostat and Berendsen barostat respectively. We could solve the equations of motion using the Velocity Verlet algorithm. We calculated the thermal conductivity of Al in the macro scale using the Green-Kubo method. Moreover, we have studied the effect of increasing temperature on the value of the thermal conductivity of Al. The obtained results showed that the computed thermal conductivities are in good agreement with experimental data.

Abstract: The mixed convection boundary layer of a viscoelastic fluid past a sphere with constant temperature is discussed. The boundary layer equations are an order higher than those for the Newtonian (viscous) fluid and the adherence boundary conditions are insufficient to determine the solution of these equations completely. The governing non-similar partial differential equations are first transformed into dimensionless forms and then solved numerically using the Keller-box method by augmenting an extra boundary condition at infinity. Numerical results are presented for different values of the viscoelastic and mixed convection parameters K and , respectively. It is found that for cases of cooling sphere and heating sphere, the boundary layer separates from the sphere. To the best of our knowledge, this important classical problem has not been studied before for the case of a viscoelastic fluid. Thus, the results are original and new for this type of fluids.

Abstract: In thermodynamics, the heat storage coefficient (HSC) β of a material is defined as the square root of the product of the material's thermal conductivity and its volumetric heat capacity. A material's HSC is a measure of its ability to exchange thermal energy with its surroundings. A resistor model has been proposed by us in the following manner. In the case of soil materials, the solid particles are surrounded by fluid, or in the case of vacuum, by empty space. The HSC of such an unconsolidated system will depend on the conditions of porous media: porosity, temperature, HSC of different phases and the structure of the aggregate. The present model also yields values in good agreement with experimental results of other workers.

Abstract: Several methods for numerical solution of heat transfer process have been developed exploiting various discretization techniques. Among these, the Alternating Direction Implicit Methods have the advantage of being unconditionally stable and only need to solve a sequence of tridiagonal linear systems. In this work, it is used in the heat transfer simulation in one quarter of the hollow circular cylinder in an unsteady state, considering the pre-set inner radius and different discretizations of the mesh. The temperature profiles are presented and the error analysis is carried out.