Effect of microbubble generator operating parameters on oxygen transfer efficiency in water

Abstract

This study utilized multistage orifice microbubble generator to investigate dissolved oxygen (DO) formation characteristics and to increase its efficiency, by considering saturator pressure, water supply, and gas flow rates as the main operating factors. The effect of changing the parameters was described in terms of dissolution performance using volumetric mass transfer rate, which is very important element for aerator design and scale-up. Pressure values from 1 to 6 atm were taken for the analysis. To improve the oxygen transfer efficiency of the multistage orifice, the internal supply line was controlled to circulate the bubbles water up to 300% cycling. The volumetric mass transfer coefficient was limited below 0.01 per min for air; however, the value varied from 0.10 to 0.13 per min for oxygen at 4.5 L/min flow rate, showing increasing pattern with pressure. The transfer characteristic was doubled, with circulating ratio applied, because circulation could multiply the number of microbubbles. Examining the various operating conditions within the range set for the cost to generate 1 kg of DO, under gas injection velocity of 1.27 m/s, higher liquid pressurization showed lower cost per production in case of oxygen than air. Thus, natural water bottom area environment can be economically improved using oxygen microbubbles, considering the excessive dissolution.

Keywords:

• Microbubble
• Dissolved oxygen
• Operating parameters
• Mass transfer
• Cost-benefit

Acknowledgement

This work is supported by the Korea Institute of Civil Engineering and Building Technology, KICT, of Korean Government number 2015-0113.

Notes

Presented at CEST2015—14th International Conference on Environmental Science and Technology, Rhodes, Greece, 3–5 September 2015