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Experimental evaluation of overall convection heat transfer coefficient of a rectangular bar in the vicinity of a flat plate is investigated. A quad of rectangular shape and later a quad with the cause of optimal heat transfer are placed at the near and the inside of a turbulent boundary layer over a flat plate. The overall convection heat transfer coefficient of the flat plate are measured and compared to the case similar to a single flat plate. A low speed wind tunnel is employed to maintain main flow field at the requested speed and special electrical circuit is prepared to provide heat and measure heat losses from the flat plate. Conclusion is made that when the obstacle closes to the flat plate, the total convective heat transfer coefficient increases to a maximum and then reduces again by moving towards the plate. Distance from the flat in which the maximum heat transfer coefficient occurs is reported.

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In previous studies, there is no comprehensive experimental study that has evaluated dissimilarity between heat transfer and momentum transfer for all the interactions between effective variables. On the other hand, when a rectangular cylinder is located near a flat plate, skin friction coefficient and heat transfer coefficient are effected some variables that change in an extensive range. Therefore, testing all possible combinations of effective variables will not be reasonable. In this paper, maximum and minimum of skin friction coefficients and heat transfer coefficients were determined using robust Taguchi design. Design of experiments method was applied for decreasing the number of experiments without losing the required information in the first step. Then, experiments were performed in a wind tunnel, the maximum speed of which was 13 m/s. Finally, skin friction coefficient and heat transfer coefficient were optimized using Taguchi method and Minitab software. Results showed that dissimilarity between heat transfer and momentum transfer has occurred for all the possible combinations of the effective variables. Additionally, the gap height between the rectangular cylinder and flat plate was the most effective variable on generating the dissimilarity.

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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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One of the disadvantages of drag driven vertical axis wind turbines, is low aerodynamic performance of the turbine which is mainly due to adverse torque of the returning blade. A recently introduced design suggests using opening/closing blades for the rotor to eliminate the negative torque of the returning blade. In this study, the aerodynamic performance of the newly proposed turbine has been investigated experimentally and numerically. The experimental measurements are performed in a subsonic open-jet type wind tunnel facility. However, the numerical simulations are performed using the Ansys-Fluent commercial software, using the Multiple Reference Frame model (MRF). The effects of the number of blades (3, 4 and 6-bladed), end plates and turbulence intensity on the torque and power coefficients are examined in details, in several Reynolds numbers. Results show that the new rotor has no negative torque in one complete revolution and the 3-bladed rotor has the best aerodynamic performance, in a manner that, it reaches a maximum power coefficient of 0.21 at TSR=0.5. Although increasing the number of blades decreases the output torque oscillations, it also decreases the average power coefficient of the rotor. Results also show that, Reynolds number does not have significant effects on the average power coefficients of the rotors, in the studied range of Reynolds numbers, 7.7×104 ≤ Re ≤ 1.2×105.