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This study experimentally investigated the effect of different molecular weights of Poly vinyl acetate (PVAc) on electrospinning ability of PVAc/DMAC sol-gels. The influences of polymer solution concentration and electrospinning process parameters (needle tip to collector distance, flow rate, and applied voltage) on the mean diameters of electrospun PVAc nanofibers were examined by design of the experiments based on the Taguchi method. Three levels were considered for each process factor as inputs for the Taguchi DoE technique. To characterize and optimize the mentioned parameters, Taguchi's L9 orthogonal design (four parameters, three levels) was used. The “smaller-the-better” approach was used to utilize the optimum production conditions based on the signal-to-noise (S/N) ratios. The results indicated that the polymer solution concentration was the most important parameter on the mean diameter of the nanofibers. The minimum nanofiber diameter at the optimum conditions was measured about 52 nm. In conclusion, the Taguchi DoE method was identified as an efficient technique to characterize and optimize the electrospinning process parameters to increase the robustness of nanofiber fabrication.

AbstractIn this study MHD flow around and through porous cylinder is numerically investigated. The governing equations are developed in polar coordinate arrangement in both porous and non-porous media on the basis of single-domain technique. The equations are solved numerically based on finite volume method over staggered grid structure. Nusselt number and drag coefficient are selected as two key parameters describing performance of this system. By applying response surface methodology the sensitivity of these parameters to main factors of the problem, including Stuart number, Darcy number and Reynolds number are quantified. RSM is also utilized to perform an optimization process to find the best condition in which the lowest drag force and highest heat transfer rate occur simultaneously. The CFD analysis is carried out for variant Reynolds numbers (10 ≤ Re≤ 40), Darcy numbers (10-6≤ Da≤ 10-2) and Stuart numbers (2 ≤ N≤ 10). Streamlines and isotherms are presented to indicate the impacts of such parameters on heat and fluid flow. It can be seen that, Drag coefficient and Nusselt number increase by augmenting magnetic field strength. Beside, Darcy number and Reynolds numbers have a direct and inverse effect on Nuaveand Cd, respectively. Results of optimization process show that Nuaveand Cdare more sensitive to Reynolds and Stuart numbers, respectively, while they less sensitive to Darcy number. Moreover, it is revealed that the optimum condition occurs at Da= 10-2, Re= 38.1 and N= 4.49.

AbstractThis paper presents analysis and optimization of turbine bade cooling systems. Since the temperature of combustion gases is very high sometimes reaching 2400 K, the turbine blade cannot sustain the resulting thermal stress. Moreover, for higher efficiency for advanced gas turbines, increase of inlet temperature is needed. Common blade cooling methods are film cooling, convection cooling, impingement cooling and combined cooling. In this paper, a numerical solution of the thermal and flow fields in film cooling technique on the AGTB expand symmetrical turbine blade was obtained and the results were validated with experimental data. Then the turbine blade geometry was changed and two combined cooling (impingement/convection cooing and impingement/film cooling) techniques were evaluated. The low Reynolds number k-ε turbulence model (AKN) was used for the turbulent flow simulations at various blowing ratios for two blade thicknesses. Comparisons of the results between the available experimental and numerical data showed that the AKN model is capable of predicting the turbulent flow and heat transfer in turbine blade cooling. Combined techniques (impingement/convection cooling and impingement/film cooling) were also carried out and more cooling effectiveness and uniform temperature distribution were found than film cooling method only.

Mathematical modelling of non-catalytic gas–solid reactions was carried out based on the grain model in terms of non-equimolar counter diffusion of gaseous phase in the solid matrix. By justifying the model parameters, the model can be used for reactions involving volume change between gaseous products and gaseous reactants. The grain model was used in the present work. The model was used for studying the reduction of chromium oxide with methane in the formation of chromium carbide. By justifying the diffusion coefficient of reactant methane through the product layer around the grains, the simulation results showed a good fit with experimental data. A MATLAB m-file has been developed to simulate the gas–solid reactions under unsteady state condition in the gas phase and by considering mass transfer resistances in gas phase outside the solid and through the product layer around the grains for different orders of reaction. Transport equations were solved numerically by using finite volume technique in the implicit form. After parameter justification, the model was used for studying effect of different parameters on the conversion of the reaction. The model shows a good fit to experimental data and can be used for studying the sensitivity analysis for such reactions.