Influence of humidity on ozone concentration in negative corona discharge fed by oxygen

The ozone generation in negative DC corona discharge fed by pure oxygen has been investigated. The gas was flowing through the reactor at flow rate of 100cm/min. The influence of discharge power and humidity on the ozone concentration was studied. We have investigated the effect of large values of humidity on ozone concentration before and after the critical value of Becker parameter. Furthermore, the influence of the humidity on the current-voltage characteristics was studied too. The ozone concentration was measured by UV transmittance measurements. Introduction Corona discharge has been proven to be a reliable ion source for charging objects, such as particles or surfaces in electrostatic precipitators, photocopiers, and laser printers [1]. The production of ozone in the corona discharge is attributed to a series of gasphase reactions driven by the energetic electrons created in the thin corona plasma layer [2], [3]. Numerous experimental studies by many researchers have examined the dependence of ozone production on the discharge polarity, current level, discharge electrode size, feed gas temperature, velocity, and relative humidity to seek methods to reduce the ozone production [4]–[10]. Experiments indicated that the electrical characteristics of negative coronas change with relative humidity [5] and the production of ozone decreases with increasing humidity [5], [9]. The underlying reasons for the reduction of ozone in the presence of water vapour are not clear. Experimental apparatus The experimental apparatus is shown in Figure 1. Discharge tube containing coaxial cylindrical electrode systems (a stainless steel inner electrode of diameter 125 μm and a brass outer electrode of diameter 16 mm) was used in these experiments. The active part length of the discharge tube was 6.5 cm. A regulator of humidity was placed between the discharge tubes and the oxygen-fed bottle. A DC corona discharge was generated in the discharge tubes. The same gas was closed in the comparative cell of the Shimadzu UV spectrometer, which was used to measure the optical transmittance of the gas contained in the discharge. The transmittance was recorded simultaneously with discharge voltage and current. In order to identify ozone produced in the discharge the UV spectrum of the discharge was monitored and ozone identified through the characteristic Hartley Band (centred at 254nm), ozone concentrations can then be derived using the well known Beer-Lambert formula. The ozone concentration was measured as a function of Beckers’s parameter for different levels of humidity. The flow rate of the gas was maintained by mass flow controller at the level 100 cm/min. A Glassman high voltage power supply unit was used to provide power to the discharge electrodes. The discharge current and the voltage applied to the electrodes were monitored by two multimeters and recorded by computer. The current-voltage characteristics (CV) were measured. For each voltage value the transmittance of UV light (T) was registered. The experiments were carried out at atmospheric pressure. The O2 of technical purity has been used in the experiments.