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Due to simplicity of design and manufacture, self-starting characteristics and operating independently of wind direction, Savonius wind rotors have been considered by many scientists. In the present study, the effects of the primary and secondary overlap ratios on the performance of Savonius wind rotors have been investigated, by means of numerical simulation and wind tunnel tests. Eight different rotor structures were analyzed numerically; three of them were also studied by experimental methods. The effects of the primary and secondary overlap ratios, Reynolds number and the number of the blades on the power and torque coefficients were examined. For all investigated rotors, the maximum value of the power coefficient occurred at a tip speed ratio between 0.8 – 1.0 (blade tip speeds close to the wind speed). Additionally, the maximum power coefficient was found at a dimensionless primary overlap ratio of 0.2; however, increasing or decreasing the secondary overlap ratio caused a reduction in the maximum value of the power coefficient. Also, it was shown that an increase in Reynolds number resulted in the increase of the maximum and average values of power coefficient. Moreover, although adding more blades could produce a more uniform torque, it causes the maximum value of the power coefficient to decrease. By increasing the positive secondary overlap ratio, torque coefficient was increased while the negative overlap ratio reduced the torque coefficient.

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A thermoacoustic refrigerator is a device that transfers heat from a low temperature reservoir to a high temperature reservoir by utilizing acoustic wave. Due to using no moving parts, no exotic and poisonous materials, Thermoacoustic refrigerators have been considered by many researchers. In this paper, the OpenFOAM package is used to simulate a thermoacoustic refrigerator. The unsteady compressible Navier-Stokes equations and equation of state are solved with PIMPLE algorithm. The effects of driver pressure ratio, frequency and heat exchangers temperature differencing for air and helium have been studied. Length of heat exchangers and stack remains constant throughout the analysis process. The results are shown that the coefficient of performance (COP) is decreased and cooling power is increased due to rise of driver pressure ratio. Helium cooling power is greater than air, but their COP is equal because of its need greater input power. The cooling power for both air and helium are increased with enhance of temperature difference of heat exchangers. Also, COP of air refrigerator is decreased, but COP of helium refrigerator is increased. The longer device length, smaller COP and cooling power are the resultants of driver’s frequency reducing. When frequency is increased, the length of cold heat exchanger will be greater than gas particle displacement of air. Therefore, cold heat exchanger absorbs heat from the air instead of heat transfer to it and COP will be zero.

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Flatbreads have a small thickness and flat surface and, unlike bulk breads, are only used in few countries such as Iran. Given the lack of research on this type of bread, the objective of this study was to numerically and experimentally investigate the porosity and surface brightness of flatbreads baked under different ascending step heat flux profiles. In order to investigate the effect of different heat flux profiles on the baking process of porous flatbread, the required breads were baked in a laboratory-scale device and the equations of heat and mass transfer, porosity, and brightness were numerically modeled using the finite difference method in MATLAB. The results showed were suggestive of the good consistency between the experimental and numerical values. A total of 3 ascending step heat flux profiles with different time steps was experimentally and numerically investigated. The results also showed that the porosity of the bread baked under an ascending heat flux profile with 4 steps was more regular and that the average diameter and area of porosities obtained from the SEM imaging were higher in this profile compared to the other profiles. Moreover, based on the experimental and numerical results, the surface bright parameter (L*) was within the appropriate range for the breads baked under the ascending heat flux profile with 4 steps.