Defect and Diffusion Forum Vols. 312-315

Abstract: The microstructure and thermal diffusivity of as-cast AM60, AE63, AJ63 and AXJ620 alloys were investigated over the temperature range 20–300°C. The microstructure of as-cast AM60 magnesium alloy consists of dendrites of α-Mg solid solution and divorced eutectic containing “islands” of α-Mg and Mg17Al12 phase. In regions adjacent with divorced eutectic, the supersaturation aluminum solute in the α-Mg matrix is observed. The addition of rare earth, calcium and strontium caused the decrease of the volume fraction of Mg17Al12 compound and aluminum content in α-Mg solid solution. Moreover, the intermetallic compounds such as: Al11RE3, Al4Sr, Al3Mg13Sr, Al2Ca are observed in the interdendritic regions. The thermal diffusivity of AM60 magnesium alloy increases with increasing temperature up to 150°C, above this temperature the increase is less marked. The change in the slope of the temperature variation of the thermal diffusivity is caused by a precipitation of Mg17Al12 phase in the supersaturation of α-Mg areas neighboring the divorced eutectic α-Mg+Mg17Al12. The addition of rare earth, calcium and strontium caused the increase of the thermal diffusivity and thermal conductivity due to the decreasing of aluminum content in α-Mg matrix.

Abstract: The aim of this study is to investigate the structural changes of Al doped ZnO thin films with gamma transmission technique with Cs-137 gamma radioisotope source. Gamma transmittance and gamma absorption coefficient, (1/mm) were investigated with the increase Al (at.%) concentration. Hence it can be possible to assess the density for Al doped ZnO thin films.

Abstract: The changes on energy band gap at induced ZnO nanocrystallite thin film have investigated with the increase of absorbed dose. Irradiated ZnO nanocrystallite thin film exhibiting different absorption edges could adjust the transmittance of energetic electromagnetic radiation. The variations on absorption edge due to energy band gap were controlled by the absorbed dose.

Abstract: In this study, the drying behaviour of single layer apple slices of 5mm thickness in a microwave dryer was investigated experimentally for four different microwave power levels (90 W, 180 W, 360 W and 600 W) and suitability of drying models available in the literature in simulating the drying behaviour of apple slices was determined by statistical analysis. The performance of these models was determined by comparing the coefficients of determination (R), reduced chi-squares (χ2) and root mean square errors (RMSE) of the models. The results show that drying time and energy consumption decreases considerably with increasing microwave power. The results also show that, among of the models proposed, the Verma et al. model gives the best fit with experimental data for all drying conditions considered. In order to determine the colour change of apple, a colour meter was also used in this study and found that L* and a* values were not significantly different from the values of the fresh apples.

Abstract: Drying behavior of polyester based yarn bobbins (67% polyester, 33% viscose) was simulated for different drying air temperatures by a simultaneous heat and mass transfer model. In the model, it was assumed that mass transfer is occurred by the diffusion mechanism. In the study, firstly drying behavior of polyester bobbins for different drying air temperatures has been determined experimentally. The experiments were conducted on an experimental hot-air bobbin dryer designed and manufactured based on hot-air bobbin dryers used in textile industry. In the experimental setup, temperatures of different points of the bobbins were measured by thermocouples placed inside the bobbins and weight of the bobbins during the drying period were determined by a load cell. Then moisture ratio and temperature values of the model have been fitted to the experimental ones. The fit was performed by selecting the values for the diffusion coefficient and the thermal diffusivity in the model in such a way that these values make the sum of the squared differences between the experimental and the model results for moisture ratio and temperature minimum. The results show that there is a good agreement between the model results and the experimental ones. The results also show that temperature has a significant effect on mass transfer and temperature dependence of the diffusion coefficient may be explained by an Arrhenius type relation.

Abstract: In this study, the drying process of cotton bobbins for different drying air temperatures has been simulated by a simultaneous heat and mass transfer model. In the model, the mass transfer is assumed to be controlled by diffusion. In order to make the simulation, firstly, drying behavior of cotton bobbins for different drying air temperatures has been determined on an experimental bobbin dryer setup which was designed and manufactured based on hot-air bobbin dryers used in textile industry. In the experimental setup, temperatures of different points in cotton bobbins were measured by thermocouples placed inside the bobbins, and weights of the bobbins during the drying period were determined by means of a load cell. Then, moisture ratio and temperature values of the model have been fitted to the experimental ones. The fit was performed by selecting the values for the diffusion coefficient and the thermal diffusivity in the model in such a way that these values make the sum of the squared differences between the experimental and the model results for moisture ratio and temperature minimum. Results show that there is a good agreement between the model results and the experimental measurements. The results also show that temperature has a significant effect on mass transfer and the temperature dependence of the diffusion coefficient may be expressed by an Arrhenius type relation.

Abstract: Rough rice has high moisture content at harvest, and if their moisture content is not reduced to about 12% on the dry basis they decay due to infestation and mold growth. Drying process is generally performed by heating ambient air and then sending it by forced convection over the rough rice to be dried. The aim in heating air to a certain temperature is to reduce the relative humidity of the air, which has a positive effect on the drying potential. In this study, drying behavior of single layer rough rice for different drying air temperature was simulated by means of a liquid diffusion model numerically by finite element modeling and simulation software. The results show that temperature is an effective factor on the drying rate. The results also show that as drying proceeds, a moisture gradient develops within the grain. This slows down the drying rate considerably. Therefore, it can be concluded that performing drying with an intermittent period instead of continuous drying will cause a considerable energy-saving.

Abstract: Airborne pathogens can spread within an aircraft cabin from sneezing, coughing or breathing of a sick passenger. This paper reports a 3D numerical study on the transport of airborne pathogens inside Boeing 767 cabin. After cough or sneeze of an infected passenger, the entire unsteady pathogen dispersion process is simulated. Effects under study include the direction of coughing on the pathogens propagation and the spreading times from infected to hosts passengers.

Abstract: A 3-D numerical study is performed to investigate the effects of periodicity (geometry) on flow of fluid and on flow of solid/fluid suspensions in packing arrangements of fixed beds of spheres. The porosity is fixed at 0.58 and the following packing arrangements are studied: simple cubic, face-centered cubic, hexagonal, rhomboedric hexagonal and tetragonal. Simulations are carried out at Reynolds numbers ranging from 0.1 and 50, and using solid suspensions with different sizes (0.2, 2 and 10 micron) and densities (200 and 2000 kg/m3). The effect of the periodicity on fluid flow characteristics (permeability and inertia parameter) and on the penetration efficiency of solid suspensions within the packed beds is analyzed and quantified.

Abstract: AZ91 Mg alloy was subjected to the micro arc oxidation process by using different processing parameters. Following oxidation, surface topography and qualitative phase analysis were made by tabletop digital microscopy and X-ray diffraction (XRD) analysis. In order to evaluate the relative corrosion resistance of the samples that were oxidized in different parameters, the samples were immersed in a corrosive solution for 6 days and the weight losses before and after the corrosion tests were compared. Relative corrosion resistance of the samples was evaluated on the basis of surface topography.