Defect and Diffusion Forum Vol. 354

Abstract: The structure and properties of multi-rod Cu-Nb composites with the true strain of 10.2 and 12.5 have been studied by TEM, SEM and microhardness measurements. The non-uniform distribution of Nb ribbons throughout the composite cross sections was revealed, at higher strain their structure being more dispersed. In both wires the Cu/Nb interfaces are partly coherent, and the Nb lattice is more distorted at interfaces than in the bulk. The behavior at heating was studied in the temperature range of 300-800^оС. In the range of 600-800^oC complete coagulation of Nb filaments accompanied with drastic microhardness drop is observed. The thermal stability of Cu-Nb nanocomposites is higher than that of Nb and Cu nanostructured by SPD.

Abstract: A three dimensional conductive field is analyzed and solved numerically by means of a commercial code. The investigated work-pieces are made up of a simple brick-type solid. A laser source with combined donut-Gaussian distributions is considered moving with a constant velocity along motion direction. The solid dimension along the motion direction is assumed to be infinite or semi-infinite, while finite width (2l_y) and thickness (s) are considered. Thermal properties are considered temperature dependent and the materials are considered isotropic. Surface heat losses toward the ambient are taken into account. Several Reynolds numbers of the impinging jet, Biot and Peclet numbers are considered with negligible radiative heat losses. Results are presented in terms of temperatures field and profile to evaluate the effect of impinging jet.

Abstract: The thermo-physical behavior of open-celled metal foams depends on their microscopic structure. Various ideal periodic isotropic structures of tetrakaidecahedron shapes with constant cross section of the ligament having circular, square, diamond, hexagon and star strut shapes with various orientations are studied. We have proposed a generalized analytical model in order to obtain geometrical parameters correctly and various relationships between different geometrical parameters and porosities (60-95%) are presented. We have also studied the flow parameters namely permeability and inertia coefficient for different strut shapes and various Reynolds number (0.00001<Re<3000). The range of solid to fluid phase conductivity ratios (λ_s/λ_f) studied is from 10 to 30000 for different porosities in local thermal equilibrium condition and an analytical correlation is proposed comprising geometrical parameters of foam structure.

Abstract: Synthesising zinc oxide nanoparticles (ZnO-NPs) to get certain characteristics to be applied in Enhanced Oil Recovery (EOR) is still challenging to date. In this work, the importance of high surface area of ZnO nanoparticles as EOR agent was highlighted. A simulation on density of state (DOS), band structure and adsorption energy of hydrogen and nitrogen gases on the surface of ZnO was carried out; it is observed that from the band structure of the band gap value for ZnO is 0.808ev. For the ZnO, Zn 4s states contribute to conduction band and O 2p states contribute to valence band. ZnO-NPs were synthesised using the sol-gel method by dissolving zinc nitrate hexahydrate in nitric acid and varying the stirring time (1 and 24h) and sintering time (30 and 40 min). A microwave oven was used for annealing ZnO without insulating the samples in any casket. The results show that 30 and 40 min of annealing and stirring for 1 & 24 h influenced the morphology and size of ZnO-NPs. These parameters could be tailored to generate a range of nanoparticle morphology (flask and/with agglomerated nanoparticles in a corn shape) obtained by Field Emission Scanning Electron Microscope (FESEM) and hexagonal crystal, determined by X-ray diffractometer (XRD), with the mean size of 70.5 & 74.9 nm and a main growth at the peak (101). The prepared sample via stirring for 24h and sintering for 40 min was chosen to prepare ZnO nanofluid because it has the highest surface area (BET) among the rest of samples, 0.23 m²/g. 10% of Original Oil In Place (OOIP) was recovered successfully to prove that ZnO is a good candidate to be applied in some chemical reactions. Moreover, it was found that ZnO is a promising catalyst for ammonia synthesis based on the adsorption energy of hydrogen and nitrogen gases (-1.05 and-1.60 kcal/mol respectively).

Abstract: New applications for carbon nanotubes (CNTs) are emerging every day. CNTs are mostly used as the reinforcing phase in polymer composites. Recently, their application in improving the conductivity of these composites has attracted a lot of researchers. Considering helping to have a more realistic view of their reinforcing ability, this paper investigates the effect of nanotubes arbitrary orientations on the reinforced composite thermal conductivity. Two cases, i.e. the case when all the fibers are aligned and the case when the fibers are distributed with arbitrary orientations have been studied. Also, the effect of volume fraction value on the reinforcing capability of the inclusions is investigated. It is shown that the fibers orientation has an unfavorable effect on the composites conductivity and decreases it in comparison with the case when all the fibers are aligned and parallel to the heat flux. Furthermore, increasing the volume fraction also increases the thermal conductivity.

Abstract: This article presents a thermo-mechanical approach to investigate heat transfer between solid and fluid phases in a model gasifier. A two-temperature equation approach is applied in addition to a macroscopic model for laminar flow through a porous moving bed. Transport equations are discretized using the control-volume method and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effects on inter-phase heat transfer due to variation of medium permeability, thermal conductivity and thermal capacity are analyzed. Results indicate that for smaller medium permeabilities, as well as for higher solid-to-fluid thermal capacity and thermal conductivity ratios, enhancement of heat transfer between phases is observed.

Abstract: This paper shows the use of the Lattice Boltzmann Method (LBM) for the simulation of the diffusion equation in complex heterogeneous media. The theoretical background of the method for both homogeneous and heterogeneous media is developed. A simple method to determine the safe use conditions of the LBM is proposed, accompanied by a practical example. The range of interest and condition of non-negativity of the equilibrium distributions are identified for a broad range of diffusive properties ratios.