Influence of flow regime on the decomposition of diluted methane in a nitrogen rotating gliding arc
J Ananthanarasimhan, Lakshminarayana Rao
Abstract
Abstract This work reports the operation of rotating gliding arc ( RGA ) reactor at a high flow rate and the effect of flow regimes on its chemical performance, which is not explored much. When the flow regime was changed from transitional to turbulent flow ( $$5\rightarrow 50~\hbox {SLPM}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>5</mml:mn> <mml:mo>→</mml:mo> <mml:mn>50</mml:mn> <mml:mspace/> <mml:mtext>SLPM</mml:mtext> </mml:mrow> </mml:math> ), operation mode transitioned from glow to spark type; the average electric field, gas temperature, and electron temperature raised ( $$106\rightarrow 156~\hbox {V}\cdot \hbox {mm}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>106</mml:mn> <mml:mo>→</mml:mo> <mml:mn>156</mml:mn> <mml:mspace/> <mml:mtext>V</mml:mtext> <mml:mo>·</mml:mo> <mml:msup> <mml:mtext>mm</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , $$3681\rightarrow 3911~\hbox {K}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>3681</mml:mn> <mml:mo>→</mml:mo> <mml:mn>3911</mml:mn> <mml:mspace/> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:math> , and $$1.62\rightarrow 2.12~\hbox {eV}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1.62</mml:mn> <mml:mo>→</mml:mo> <mml:mn>2.12</mml:mn> <mml:mspace/> <mml:mtext>eV</mml:mtext> </mml:mrow> </mml:math> ). The decomposition’s energy efficiency ( $$\eta _E$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>η</mml:mi> <mml:mi>E</mml:mi> </mml:msub> </mml:math> ) increased by a factor of 3.9 ( $$16.1\rightarrow 61.9~\hbox {g}_{{\text{CH}}_{4}}\cdot \hbox {kWh}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>16.1</mml:mn> <mml:mo>→</mml:mo> <mml:mn>61.9</mml:mn> <mml:mspace/> <mml:msub> <mml:mtext>g</mml:mtext> <mml:msub> <mml:mtext>CH</mml:mtext> <mml:mn>4</mml:mn> </mml:msub> </mml:msub> <mml:mo>·</mml:mo> <mml:msup> <mml:mtext>kWh</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ). The first three dominant methane consumption reactions ( MCR ) for both the flow regimes were induced by $$\text {H}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mtext>H</mml:mtext> </mml:math> , CH, and $$\text {CH}_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>CH</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> </mml:math> (key-species), yet differed by their contribution values. The MCR rate increased by 80–148% [induced by e and singlet— $$\text {N}_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>N</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> ], and decreased by 34–93% [CH, $$\text {CH}_3$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>CH</mml:mtext> <mml:mn>3</mml:mn> </mml:msub> </mml:math> , triplet— $$\text {N}_2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>N</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> ], due to turbulence. The electron-impact processes generated atleast 50% more of key-species and metastables for every 100 eV of input energy, explaining the increased $$\eta _E$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>η</mml:mi> <mml:mi>E</mml:mi> </mml:msub> </mml:math> at turbulent flow. So, flow regime influences the plasma chemistry and characteristics through flow rate. The reported RGA reactor is promising to mitigate the fugitive hydrocarbon emissions energy efficiently at a large scale, requiring some optimization to improve conversion.