Defect and Diffusion Forum Vols. 312-315

Abstract: We investigate the optical properties of a weak probe field in an asymmetry semiconductor double QDs system. We apply a coupling and a probe field to the system and it is shown that in the presence of interdot tunneling, the dispersion and absorption properties of the system can be controlled by the amplitude and relative phase of applied fields. Moreover, it is demonstrated that just by changing the relative phase of applied fields, the slope of dispersion is changed from positive to negative, corresponding to the superluminal light propagation.

Abstract: Carbon nanotubes (CNTs) have been suggested to be reinforcement fillers in a variety of composite materials due to their exceptional electrical, thermal and mechanical properties. In terms of thermal properties, incorporating CNTs into a polymer matrix should increase the effective thermal conductivity of the resulting composite. However, the presence of resistance to the transfer of heat at the CNT-polymer interface, known as the Kapitza resistance, results in underperformance of CNT nanocomposites, in terms of thermal properties. In this work, we use Monte Carlo simulations to calculate the effective thermal conductivity of CNT nanocomposites taking into account the Kapitza resistance, as well as the effective thermal conductivity for different inclusion geometries (sphere, cylinder and parallelepiped). The effect of the dispersion pattern of the nano-inclusions is also investigated. Finally, comparing the calculated thermal conductivity from the simulations to experiments, the methodology can be used to calculate the Kapitza resistance of such systems.

Abstract: This paper is devoted to the study of thermal transport phenomena changes caused by natural aging of rubber blends. Thermal conductivity, diffusivity and heat capacity of rubber blends were measured and compared for the same samples before and after half of a year. Samples were stored at room temperature and daily light. In the frame of our investigations there has been observed the decrease of the thermal diffusivity as well as the thermal conductivity in the interval approximately 40-50 %. The changes of specific heat capacity after sample aging were negligible. The explanation of such behaviour we can see in the sample structure degradation caused by the environmental influence.

Abstract: The aim of this work is to present an experimental research of the shell side heat transfer coefficient and pressure drop in a plastic shell and tube heat exchanger with single segmental baffle. The tube bundle consisted of 110 U-tubes constructed of high-density polyethylene, the inside diameter was 9.2 mm, the tube pitch was 1.5 the out side diameter. The shell was constructed of polypropylene with a diameter of 315 mm. Shell side heat transfer coefficients and pressure drop were determined varying the flow rates. An experimental rig for the experimental research was designed and constructed. The overall experimental rig consisted of two operation cycles. The two fluids used in this system were hot and cold water. The experimental results were compared with theoretical predictions using the Bell-Taborek and Wills and Johnston Methods. The heat transfer coefficient predictions, for Reynolds number greater than 780, showed that the Bell-Taborek and Wills-Johnston methods are in general agreement with the experimental data with only 5% difference, Wills-Johnston overpredicts it and Bell underpredicts it, except at the lower Reynolds number than 780 where there was an average underprediction of 15%. The pressure drop predictions by Wills-Johnston and Bell-Taborek methods were generally acceptable including the inlet and outlet nozzles with the highest experimental data (Reynolds number greater than 780) within a 15% overprediction, however, at the lower data the pressure drop was overpredicted up to 2 times the measured values.

Abstract: A hydrogel kept at its equilibrium swelling state during taking the measurements controlled in a diffusion cell. The diffusion data gained from Raman spectra were analyzed to calculate the mutual diffusion coefficient in the hydrogel as semi-infinite medium. The relation between the solute concentration and Raman intensity for poly(N-isopropylacrylamide), which is characterized by the distinct peak for the isopropyl group at 2925 cm-1 was taken into account. The determination of the mutual diffusion coefficient, Dmut for hydrogels/phenol system was achieved successfully using confocal Raman spectroscopy at different solute concentrations. At 25oC, the value of the mutual diffusion coefficient is found between 5.61845x10-11 m2/s and 3.34565x10-9 m2/s for the hydrogel loaded with phenol of an initial concentration of 0.01 mM and 0.1 mM, respectively.

Abstract: The mechanical engineering industry is always in the search of new hardfacing alloys which nowadays make it possible to solve considerable delicate problems of abrasive wear and corrosion. These alloys are heterogeneous materials and are generally composed of a ductile matrix and a significant proportion in hard phases (carbides, borides or silicides), which give a good wear resistance and corrosion. The following studies made on alloys containing Ni, rich in Silicon and tungsten. We noted that addition of these elements (Si and W) got interesting mechanical properties. The alloys that we chose for this study contain the elements C, B, Si, Cr and W with additions in Ti and Mo. The aim of this work is the characterisation of the various phases formed during solidification, to study chemical affinities in this system poly-constitutes and to make a correlation between the chemical composition, the conditions of development and the microstructures obtained.

Abstract: The desiccant wheel is the key component in a solid-desiccant system for air dehumidification. The heat and mass transfer phenomena occurring within the porous channel walls of the wheel and with the airflow are strongly coupled, and some properties of the airflow and of the desiccant medium exhibit important changes during the sorption/desorption processes. The dynamic analysis of such devices integrated in non-conventional HVAC&R systems can be easily done by a project designer using the NTU-effectiveness method, provided that appropriate correlations for two independent effectiveness parameters are available. In this work, the performance of a desiccant wheel was evaluated by numerical modelling the cyclic behaviour of a representative channel of the hygroscopic matrix. The physical model adopted takes into account the gas-side and solid-side resistances, as well as the simultaneous heat and mass transfer coupled with the water adsorption/desorption process in the channel wall domain. Two phases co-exist in equilibrium inside the desiccant porous medium, the equilibrium being characterized by sorption isotherms. The desiccant medium considered is silica gel RD. In the numerical model, the airflow is treated as a bulk flow, and its interaction with the wall channel matrix is represented by appropriate convective heat and mass transfer coefficients. Two independent effectiveness parameters were defined. A set of cases was numerically simulated and the results were analysed to assess the dependence of those effectiveness parameters on the process and regeneration airflow rates and on the channel length. As a conclusion, novel empirical correlations are here purposed.

Abstract: Thin scandium-containing layers fabricated by different methods are good systems to investigate some properties of Al-Sc intermetallic compounds (IMC). The electrochemical deposition of a thin scandium layer onto a solid metallic surface leads to complex diffusion processes, especially if the second metal forms a number of IMC with Sc. Here, we used the electromotive force (EMF) method to study thin Al-Sc films in dynamics. Also, the Al-Sc alloy layers were prepared by direct aluminium-scandium interaction. The results of SEM and EDX investigations of these alloys are also presented in this paper. Analogue coatings (like Sc on Ni, Y on Cu, Al on Ni etc.) were also considered in order to discuss the phase sequence formation.

Abstract: In the present work, the thermal diffusivity measurements of uniaxially cold pressed NiWO4 has been carried out. The measurements were performed isothermally at temperatures between 973 and 1273 K under H2 gas using the laser flash technique. The experimental thermal diffusivity values were found to increase with the reduction progress as well as with increasing temperature. The calculated activation energy was found to be higher than that for chemically controlled reaction. The difference has been attributed to factors like agglomeration of the product as well as sintering of the precursor along with the chemical reaction. In order to sort out the sintering effect on the thermal diffusivity values, complementary experiments have been done on pressed NiWO4 and Ni-W, produced by the reduction of NiWO4 at 1123K, under Argon gas. The porosity change and its effect on thermal diffusivity values have been studied.

Abstract: Sn-filled and Fe-doped CoSb3 skutterudites were synthesized by encapsulated induction melting. A single δ-phase was obtained by subsequent annealing, as confirmed by X-ray diffraction. The as-solidified ingot consisted of mixed phases of -CoSb, -CoSb2, δ-CoSb3 and elemental Sb. The phases could be transformed by annealing, and the phases of the as-solidified ingot annealed at 773 K for 24 h transformed to δ-CoSb3. The temperature dependence of the Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed p-type conduction. The electrical resistivity increased with increasing temperature, which showed that the SnzCo3FeSb12 skutterudite is highly degenerate. The thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. The thermoelectric figure of merit was enhanced by Sn filling and its optimum composition was considered to be Sn0.3Co3FeSb12.