Intake direction is one of the most important factors which have significant effect on vortex formation at intakes. Due to the importance of withdrawal direction to vortex formation, the present study examined the effect of different intake angles on strength of vortices and critical submergence. Experiments were performed on dual and single intakes with three withdrawal directions (with angles of 0°, 45° and 90°). To calculate the strength of formed vortices, the tangential velocity component of vortices was measured using an ADV. Results showed that, by varying the intake angle from vertical to horizontal, strength of vortices decreased by 31% and 35% for single and dual intakes, respectively. An empirical relationship between the circulation number and Froude number for various submergence depths was developed for each withdrawal direction of the dual intakes. Furthermore, the critical submergence of single and dual intakes was investigated and results indicated that the critical submergence is considerably affected by changing the withdrawal directions.

Non-thermal plasma (NTP) has been introduced over the last few years as a promising after- treatment system for nitrogen oxides and particulate matter removal from diesel exhaust. NTP technology has not been commercialised as yet, due to its high rate of energy consumption. Therefore, it is important to seek out new methods to improve NTP performance. Residence time is a crucial parameter in engine exhaust emissions treatment. In this paper, different electrode shapes are analysed and the corresponding residence time and NO_x removal efficiency are studied. An axisymmetric laminar model is used for obtaining residence time distribution numerically using FLUENT software. If the mean residence time in a NTP plasma reactor increases, there will be a corresponding increase in the reaction time and consequently the pollutant removal efficiency increases. Three different screw thread electrodes and a rod electrode are examined. The results show the advantage of screw thread electrodes in comparison with the rod electrode. Furthermore, between the screw thread electrodes, the electrode with the thread width of 1 mm has the highest NO_x removal due to higher residence time and a greater number of micro-discharges. The results show that the residence time of the screw thread electrode with a thread width of 1 mm is 21% more than for the rod electrode.