As the ozone cell produces ozone, the amount of oxygen molecules interact with the plasma depending on the flow rate of feed gas. Oxygen molecules with high-energy electrons (radicals) in the corona have a longer contact time with low-flow oxygen molecules, while yielded ozone slowly escapes the ozone cell with low flow rates. The result is a high concentration of ozone in the ozone cell. With increasing flow rate, the concentration of ozone decreases (88 g/m3 at 3 L/min to 29 g/m3 at 20 L/min) (Figure 1).
How Feed Gas Effects Ozone Concentration and Ozone Output
High ozone concentrations facilitate ozone solubility in water. Adding ozone to water, for example, increases its concentration by 5 times (from 10-50 mg/L) while concentration of ozone increases by 25-125 g/m3. As a result, high ozone concentrations are desired for water disinfection. Ozone generator output is also affected by flow rate, which is also significant.
Ozone generator output is low when flow rate is low. Oxygen volume cannot enter the ozone cell and take part in the reaction at low flow rates. The volume of oxygen in an ozone cell will never change (flow rate is very low). Oxygen is consumed by the reaction that produces ozone inside the cell. Oxygen deficiency in the cell therefore limits ozone production.
The increase in oxygen in an ozone cell that occurs when feed gas is pumped into it (raising the flow rate) results in an increase in ozone output. Additionally, when flow rate reaches a certain high value, ozone output may become saturated, or may even slightly decrease. Because the thermal and flow velocity of the molecules in the ozone cell are negligible in comparison to the speed of the electron passing through them (*10-15 s), the molecules can be considered immobile in the ozone cell.
Therefore, there is no effect on ozone production due to this motion. Bernoulli’s principle describes the increase in speed and fall in pressure as a fluid flows down a tube (the ozone cell is formed from a tube similar to a venturi tube).
Because of this, the density of the gas (oxygen) inside ozone cells decreases, so the possibility of the oxygen molecules bombarding radicals in the corona media is reduced, resulting in a decrease in the production of ozone. In this way, ozone output, at first, will increase as flow rates increase, but then will become saturated or even decrease at a certain flow rate as illustrated in the Figure 1 given below.
A high output as well as a high ozone concentration are necessary from application’s point of view. In particular, using high ozone concentrations for water disinfection is important since higher concentrations of ozone are less soluble in water.
Figure 1: Ozone production (g/hr) & concentration (g/cubic meter) vs feed gas as flow rate of oxygen. The oxygen concentration here is ~ 98% and the ambient temperature is ~ 24 oC.
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