Measurements of water molecule density by tunable diode laser absorption spectroscopy in dielectric barrier discharges with gas–water interface

Abstract

We measured water molecule (H 2 O) density by tunable diode-laser absorption spectroscopy (TDLAS) for applications in dielectric barrier discharges (DBDs) with a gas-water interface. First, the effects of water temperature and presence of gas flow were tested using a Petri dish filled with water and a gas injection nozzle. Second, the TDLAS system was applied to the measurements of H 2 O density in two types of DBDs; one was a normal (non-inverted) type with a dielectric-covered electrode above a water-filled counter electrode and the other was an inverted type with a water-suspending mesh electrode above a dielectric-covered counter electrode. The H 2 O density in the normal DBD was close to the density estimated from the saturated vapor pressure, whereas the density in the inverted DBD was about half of that in the former type. The difference is attributed to the upward gas flow in the latter type, that pushes the water molecules up towards the gas-water interface.

Characterization of dielectric barrier discharges with water in correlation to productions of OH and H2O2 in gas and liquid phases

“…55) A narrow electrode gap design in DBDs may also be effective for the increase of the extraction efficiency as realized using an inverted (water upside) structure. 64)…”

“…Left-side axis shows the absorbance per unit length integrated over the line profile A, which is converted into the water vapor concentration C wv (%) in atmospheric pressure gas using the calibrated value of water vapor density N w = 0.78 × 10 24 m −3 at A = 1 cm −1 m −1 . 64) It is seen that the relation of the gas flow-rate ratio to C wv is linear, but shows a finite concentration of 0.05% at no flow in the water bubbling path as residual humidity in the system. Using this relation, the experimental results shown hereafter with variation of the gas flow-rate ratio are converted into C wv in Ar gas at atmospheric pressure.…”

“…42) In the present study we used TDLAS, whose performance had been tested previously. 64) Total Ar gas flow was kept at 1 l min −1 and the flow rate ratio in each path was adjusted by a flow meter with a needle valve.…”

“…At the beginning, we apply tunable diode-laser absorption spectroscopy (TDLAS) 64) to measure the water vapor density in the reactor with a water bubbler as a function of the gas flow-rate ratio through a water bubbler to the total flow in comparison to the reactor with water electrode. Then, we estimate the production of OH radicals in both the situations, using optical emission spectroscopy (OES) at the OH(A-X) band from the excited A state and LIF spectroscopy for the measurement of OH(X) density in the ground X state.…”

Comparative study of discharge schemes for production rates and ratios of reactive oxygen and nitrogen species in plasma activated water

“…For the production of RONS, we used seven different types of discharge devices as shown in figure 1. The first scheme, shown in figure 1(a), is a normal dielectric barrier discharge (N-DBD) reactor with a pair of dielectric covered electrodes, where the upper metal-plate electrode of 40 mm square is moulded in a 3 mm thick glass plate 52 mm in diameter with a 1.8 mm bottom layer, and the lower metal-plate electrode 50 mm in diameter is covered by an 80 mm square, 1 mm thick glass plate [62,63]. The whole electrode assembly was placed in a plastic cube with 100 mm inner sides, which was equipped with quartz windows on three sides for optical measurements.…”