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Because of the low Reynolds numbers in microchannels, using of micromixers to improve the flow mixing is essential. Therefore, in this study mixing in nine different micromixer geometries, such as: simple T-shaped micromixer, micromixer with rectangular or parallelogram ribs on the walls of the mixing channel, T-shaped micromixer with two additional parallel or perpendicular inlet channels, micromixer with circular or triangular barriers in the middle of the mixing channel, rhombus micromixer with thick or thin edges, has been investigated. Sinusoidal oscillatory velocity with a phase difference of 180 degrees relative to each other has been applied to channels inlet. The governing equations have been solved numerically using the finite volume method. For all geometries time variation of mixing degree at microchannel outlet and the variation of mixing degree along the channel length have been computed. Results show that for micromixers, which divide the flow to several layers such as rhombus micromixers, mixing degree is high and the micromixers with ribs on the walls have lower mixing degrees. Also, there is an optimum frequency at constant average velocity in which the mixing degree has its highest value.

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Creep failure is one of the most common mechanisms which determine the life of mechanical components operating at high temperature. Gas turbine blades are among the components which operate at high temperature under mechanical loads. In new designs, cooling flow passes through the inner channels of the blade to decrease blade temperature. One of the main parameters of the cooling system is the coolant’s heat transfer coefficient. In this paper, the effect of wall roughness of the cooling channels and coolant’s specific humidity on the cooling heat transfer coefficient has been investigated. The blade body and cooling channels are regarded as a heat exchanger with a thermal barrier coating and convective- film cooling. For this purpose, the physical properties of the coolant have been considered as a function of temperature and humidity. Then, the influence of the channel’s roughness on the heat transfer coefficient has been investigated and an analytical method has been used to obtain the temperature distribution. The results show that in the rough channels, coolant receives more heat from the blade body and consequently decreases its temperature especially in the critical section. Also, it has been shown that with increasing humidity; the coolant temperature reduces along the blade span comparing with the case of using dry air and consequently, the blade metal temperature reduces with about 2.5 percent. It has been shown that by increasing coolant’s humidity and roughness of the channels in a reasonable range, blade’s creep lifetime can be increased by up to 3.18 times.

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Since the majority of fluids in engineering and biologic applications are non-Newtonian, the study on mixing of non-Newtonian fluids is very important. Secondary flows are used in curved micromixers to improve the mixing of fluids. In this study, a numerical study was performed on the mixing of non-Newtonian fluids in curved micromixers using Open source CFD code of OpenFOAM. The flow was assumed three-dimensional, steady and incompressible and Reynolds numbers were between 0.1-300. Also, water and CMC solution were used for simulation of Newtonian and non-Newtonian fluid flows, respectively. The effect of Reynolds number, power-law viscosity parameters and micromixer geometry on mixing index and non-dimensional pressure drop was studied and results were compared with those of the straight channel micromixer. The results showed that the mixing index decreased by decreasing the power law index. The mixing index was high for shear thinning flows in micromixers with sharp turns. Also, by increasing the Reynolds number, and therefore velocity, centrifugal force effects increased and mixing improved. Simultaneous investigation of mixing index and pressure drop showed that for low Reynolds numbers and small power law indexes micromixer-b had better performance.

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In the present work, the transient behavior of a single spool turbojet engine as a function of fuel flow rate is investigated, using fourth order nonlinear dynamic model based on the airplane longitudinal dynamics, compressor and turbine dynamics and dynamics of rotor. Taking into account the thermodynamic variables in all five components of the engine and representing desired parameters as function of time are contributions of the paper. Moreover, we use inter-component volume method in our study which results in more accurate simulations. In this method, by adding the pressure and temperature fluctuations, caused by saved mass, a more precise model is obtained. Taking advantage of this method and using the governing thermodynamic and Gas dynamic equations, the governing dynamic equations of engine are obtained. By solving the equations in MATLAB software, the influence of the fuel flow rate on the output variables is studied. It should be mentioned that fly considered horizontal and in specific height of 2500 (m) at all of the simulation period. Engine thrust is specifically considered as the desired modeling parameter. In addition, the variation in airplane velocity, as an important parameter in the internal fuel flow rate, is added to the simulations, resulting in more accuracy. Studying the dynamic behavior of the engine thrust is a pre-requisite to the design of appropriate controllers that is the next step of this research.