Optical diagnostics of electrical discharge water spray reactors for chemical synthesis

We have previously developed a low power (250 - 500 mW) pulsed gliding arc discharge reactor that utilizes water sprayed as a fine aerosol into an argon carrier gas to produce molecular hydrogen (H₂) and hydrogen peroxide (H₂O₂) with very high energy yields of H₂O₂ in the range of 80 g/kwh. Optical emissions spectroscopy in the range of 230 to 1000 nm is used in the present study to assess the formation of intermediate radicals in the plasma region of the reactor and to determine the effects of water flow rate. Peak intensities for H_β (656 nm), OH (309 nm), argon (750 nm), and O (777, 844 nm) were found between 2.5 mm and 5 mm down the length of the reactor from the point of initial discharge formation to dissipation of the arc. The H_α line (486 nm) had a minimum intensity between 5 and 7.5 mm. Water flow had a smaller effect on radical intensity and generally showed larger variations near the point of discharge initiation.