Sharif Digital Repository

In the present study, the axisymmetric liquid gas/air diffusion flame in the presence of fuel concentration oscillations and velocity perturbations has been investigated experimentally. Several industrial combustions take a place by diffusion mechanism which necessitate scientists to make far better understanding of diffusion flames. In order to study diffusion flames, the instrument with two separated lines of fuel and air has been developed. Nitrogen is used for fuel dilution oscillatory with pulse of 1, 2, and 4 Hz frequencies. The pulse duration effects on flame structure are also studied. The flame shape has been captured by high speed camera and the results are processed by image... 

Recent developments in improving lighting efficiency and cost reduction of LED’s have caused them to be a suitable alternative for the current lighting systems. In this thesis a novel off-line structure is proposed to drive LED’s. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn’t use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) flyback converter in order to have power factor correction (PFC), a buck converter is added to the third winding of the flyback transformer in order to create two paths for the electrical power. DC... 

LED Drivers with near 1 power factor, Because of using electrolytic capacitors (to become flicker-free) have lifetime drawbacks. This research will focus on solutions to use magnetic energy storage instead of electrolytic capacitors (used for energy storage) to solve lifetime drawbacks and decrease output light flicker. Calculations show that magnetic energy density using iron powder cores are lower than electrolytic capacitors, also a little lower than ceramic capacitors, but obviously higher than film capacitors. After calculations, conventional isolated and non-isolated LED drivers will be reviewed and new non-isolated off-line 230v with 10w output power LED driver with magnetic energy...