Influence of transitional and turbulent flow on electrical, optical, morphological and chemical characteristics of a nitrogen rotating gliding arc

Abstract

Abstract The work reports the effect of flow regime on plasma characteristics of an atmospheric <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mtext>N</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> rotating gliding arc (RGA). When changed from transitional (5 SLPM) to turbulent (50 SLPM) flow, operation mode transitioned from glow to spark discharge due to frequent reignition events; the average reduced electric field ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfrac> <mml:mi>E</mml:mi> <mml:mi>N</mml:mi> </mml:mfrac> </mml:math> ) and electron temperature raised (38 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">→</mml:mo> </mml:math> 92 Td, 0.84 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">→</mml:mo> </mml:math> 2.2 eV); and gas temperature ( T g ) slightly cooled (2973 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">→</mml:mo> </mml:math> 2807 K). Molecules generated for 100 eV of energy input (G–factor) increased by a factor of 20 and 65, for the chemically active singlet and triplet metastable states of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mtext>N</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , respectively—a promising feature for chemical applications. A sudden three fold increase in the energy efficiency, achieving a destruction of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>3.0</mml:mn> <mml:mrow/> <mml:mrow/> <mml:mo>±</mml:mo> <mml:mrow/> <mml:mrow/> <mml:mn>0.2</mml:mn> </mml:math> g·kWh −1 of dilute toluene ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>112</mml:mn> <mml:mrow/> <mml:mo>±</mml:mo> <mml:mrow/> <mml:mn>10</mml:mn> </mml:math> ppmV) at highly turbulent flow corroborated the enhancement of the G–factor, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfrac> <mml:mi>E</mml:mi> <mml:mi>N</mml:mi> </mml:mfrac> </mml:math> and T g ; and indicated the sensitivity of plasma properties to the flow regime. Interestingly, for flows having Reynolds number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>⩾</mml:mo> <mml:mtext> </mml:mtext> <mml:mn>3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mn>4</mml:mn> </mml:msup> </mml:mrow> </mml:math> , the bandhead of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mtext>N</mml:mtext> <mml:mn>2</mml:mn> <mml:mo>+</mml:mo> </mml:msubsup> </mml:math> shifted from 0–0 at 391.4 nm to 3–3 at 383.3 nm attributed to higher-level perturbations, showing again the sensitivity. The smallest eddies ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>η</mml:mi> <mml:mo>≈</mml:mo> <mml:mn>6</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>μ</mml:mi> </mml:math> m) is less than the discharge diameter ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>d</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">d</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> </mml:math> 220±90 µ m), and thermal/mass Péclet number <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>&gt;</mml:mo> </mml:math> 1. The eddies of size <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>⩽</mml:mo> <mml:msub> <mml:mi>d</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">d</mml:mi> </mml:mrow> </mml:msub> </mml:math> advected the plasma species, wrinkled/distorted the discharge, and increased the reignition events, eventually affected the plasma properties including the chemical performance (energy efficiency), which is observed in this work.

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