حسام مویدی

In this study, the effect of DBD plasma actuator on natural convection heat transfer enhancement in four vertical channels with the smooth wall, rectangular corrugation, trapezoidal corrugation and triangular corrugation has been numerically studied. In order to investigate the effect of using a plasma actuator and channel geometry, local Nusselt number, variations of average Nusselt number ratio, and performance evaluation criterion on the flow field and heat transfer are studied. The results show that increasing voltage increases the average Nusselt number for all channels. For example, in Rayleigh number 105 , by increasing voltage from 6 kV to 10 kV, the average Nusselt number ratio is 89.11, 96.47, 102.50, and 96.62% for vertical channels with smooth, rectangular corrugation wall, trapezoidal corrugation wall, and triangular corrugation wall, respectively. Also, the performance evaluation criterion in the presence of the DBD plasma actuator for all vertical channels has a value higher than 1.25 in all conditions, which indicates the effectiveness of the DBD plasma on the thermal efficiency of the natural convection heat transfer in smooth and corrugated channels

In this paper, the effect of secondary flow induced by the DBD plasma actuators on the flow and separation performance of solid particles in a cyclone is numerically investigated. The effect of the effective parameters such as the applied voltage of the DBD plasma actuator, the arrangement of plasma actuators, the velocity of the incoming flow of the cyclone, and the size of solid particles are evaluated. The results show that the separation performance of the cyclone in the presence of the DBD plasma actuators increases in all particles with different diameters between 1 and 2 mm, compared to the cyclone without the presence of plasma actuator, and the performance enhancement is higher in the particles with a larger diameter (2 mm). The arrangement of plasma actuators has a significant effect on the particle separation performance of the cyclone, and the uniform installation of plasma actuators in the entire height of the cylindrical part of the cyclone (type one arrangement) improves the particle separation performance compared to other arrangements. The results show that the use of the DBD plasma actuators inside the cyclone can increase the cyclone separation performance by 26.5% compared to the cyclone without the DBD plasma actuator.

In this paper, the effect of configurations of rotating cylinders in a vented cavity with inlet and outlet port on the flow field and heat transfer enhancement of forced convection of Al2O3/Cu-water hybrid nanofluid flow in the laminar regime is numerically investigated. In this study, the influence of parameters as configurations of cylinders (A, B, C, and D), as well as the rotational velocity of cylinders (from -10 to +10), Reynolds number (from 100 to 500), and the volume fraction of nanoparticles (from 0.5% to 3%) on the flow field and heat transfer are studied. Results indicate that the average Nusselt number and the Performance Evaluation Index for configuration D are higher than other configurations. Also, it is obvious that by increasing the rotational velocity of cylinders, Reynolds number, and the volume fraction of nanoparticles, the Performance Evaluation Index increases. Also, by rotating the cylinders in the counterclockwise rotation direction with respect to the clockwise rotation direction, the η increases about 1.30. The results show that Al2O3/Cu-water hybrid nanofluid causes heat transfer enhancement compared to the Cu-water nanofluid and it increases the Performance Evaluation Index compared to the Al2O3-water nanofluid.

In this paper, the effect of baffle on the flow field and heat transfer enhancement of forced convection of Cu-water nanofluid flow in the laminar regime over a backward facing step is numerically investigated. In this study, the influence of baffle geometrical parameters as height, width and number of baffles, as well as the Reynolds number and the volume fraction of nanoparticles on the flow filed and heat transfer are evaluated. Also, to evaluate the simultaneous of the heat transfer enhancement and pressure drop, the Performance Evaluation Index (η) is calculated. The results indicated that in presence of baffle, the η is higher than 1 for all cases, and it is clear that the presence of baffle is effective on thermal efficiency. It is obvious that by increasing the Reynolds number and decreasing the volume fraction of nanoparticles, the Performance Evaluation Index is increased. For all cases, the average Nusselt number and the Performance Evaluation Index for wb=2H are higher than other cases about 7.6% and 15% respectively. The results show that using 2 baffles must be more beneficial than other number of baffles. Finally, a correlation for the Num/Num0 as a function of Reynolds number (Re), volume fraction of nanoparticles (φ), number of baffles (N), baffle height (hb) and baffle width (wb) is presented with an average error of 2.88%.

In this paper, the effect of the secondary flow induced by the electrohydrodynamic (EHD) actuator is numerically investigated in the vorticity flux, as a criterion for the secondary flow strength, and the EHD vortices through a smooth channel. In this study, the influence of effectiveness parameters of the EHD as the Reynolds number, applied voltage and the arrangement of the emitting electrode on the vorticity flux, and also relationship between flow and heat transfer characteristics with the vorticity flux are evaluated. The results indicated that in presence of electric field, by increasing the Reynolds number, dimension of the upstream EHD-induced vortices and the vorticity flux are decreased. Also, it is obvious that by increasing the applied voltage, the dimension of the EHD-induced vortices and the vorticity flux are increased. According to numerical results, the heat transfer enhancement is completely depend on the vorticity flux. Also, by changing of the emitter arrangements, the non-dimension average vorticity flux and the average heat transfer enhancement are changed. It is shown that with decrease of the distance between emitter electrode and inlet of channel, from d=50 cm to d=10 cm, the non-dimension average vorticity flux and the average heat transfer enhancement are increased 27.9% and 17.9%, respectively.

In this work, the effect of emitter electrode arrangement on the Electrohydrodynamic effectiveness is studied using micropolar fluid model through a smooth channel. Finite volume method by the open source CFD code OpenFOAM is used to solve governing equations. The effects of longitudinal position and the gap between emitter electrode and collector electrode, as well as, longitudinal arrangements are investigated. The computed results of micropolar approach are compared with obtained from the fully turbulent k-ε model. The results of each type of the EHD flow with certain conditions show that the adequate material parameter(κ_ω⁄μ) is constant for the longitudinal electrode arrangements for single electrode and multiple electrodes because this parameter completely depends on the flow and the high magnitude of electric body force. Also, this parameter is increased with decrease of the gap between emitter electrode and collector electrode. In addition, the heat transfer enhancement and also the flow pattern has the same efficiency for both the micropolar and the k-ε models.