RESUMO
PURPOSE: Noise pollution is a common health hazard worldwide which is emitted along with chemical air pollutants, simultaneously from many sources. Some studies have been conducted to control these pollutants, simultaneously with promising results being achieved. Dielectric beads have been used in air pollution control technologies, successfully and probable effectiveness of them in noise reduction can be promising in dual use of them in the exhausts emitting noise and air pollution, simultaneously. METHODS: In order to investigate the effectiveness of dielectric beads in noise reduction, two types of them; namely glass and ceramic beads, were placed separately inside the connecting tube of a double-expansion chamber muffler. Then the transmission loss (TL) of muffler was examined using impedance tube. A factorial design was used to evaluate and optimize the effect of noise related parameters on TL of such a system. RESULTS: Results show that the presence of dielectric beads has significant effect on TL of muffler. The maximum TL was obtained as 74.76 dB for muffler with ceramic beads, under the optimal condition of 5250 Hz and 120 dB. Measurement of TL and sound absorption coefficient (SAC) of glass and ceramic beads showed that the noise reduction in muffler with ceramic and glass beads is probably due to SAC in ceramic beads and noise reflections in glass beads, respectively. CONCLUSION: These results promise the dual use of dielectric beads in the exhausts emitting noise and air pollution simultaneously.
RESUMO
Sulfur dioxide, a noxious air pollutant, can cause health and environmental effects, and its emissions should be controlled. Nonthermal plasma is one of the most effective technologies in this area. This study evaluated the efficiency of a packed-bed plasma reactor (PBR) and in-plasma catalysis (IPC) in SO2 removal process which were finally optimized and modeled by the use of the central composite design (CCD) approach. In this study, SO2 was diluted in zero air, and the NiCeMgAl catalyst was selected as the catalyst part of the IPC. The effect of three main factors and their interaction were studied. ANOVA results revealed that the best models for SO2 removal efficiency and energy yielding were the reduced cubic models. According to the results, both PBR and IPC reactors were significantly energy efficient compared with the nonpacked plasma reactor and had high SO2 removal efficiency which was at least twice larger than that of the nonpacked one. Based on the results, the efficiency of IPC was better than in PBR, but its performance decreased over time. However, the PBR had relatively high SO2 removal efficiency and energy efficiency compared to the nonpacked reactor, and its performance remained constant over the studied time. In optimization, the maximum SO2 removal efficiency and energy efficiency were 80.69% and 1.04 gr/kWh, respectively (at 1250 ppm, 2.5 L/min, and 18 kV as the optimum condition) obtained by the IPC system which were 1.5 and 1.24 times greater than PBR, respectively. Finally, the model's predictions showed good agreement with the experiments.
