Enhancement of energy conversion efficiency with distances between bubble plumes in nonlinear stratification

Abstract

About 40% of the total water resources used in Korea is taken from man-made reservoirs. However, thermal induced stratification divides water body and it prevents a vertical circulation. This causes serious problems for drinking water supply, which include decreasing aesthetic value along with eutrophication, unpleasant odor and color and clogging of filters in water treatment plants. To overcome these problems, air diffusing systems are widely adopted. It is reportedly used due to its effectiveness, inexpensiveness, and simplicity to agitate aquatic environment of the hypolimnion to be mixed with epilimnion. The circulation causes decreasing of temperature of the surface water and phytoplankton activities. However, because there is little research about bubble plumes`` design guide, this research was investigated. Firstly, Bubble plume``s dynamics and dimensional analysis was performed. Secondly, energy conversion efficiency with bubble plumes`` configuration and water depth in various non-linear stratification condition was evaluated. Finally we could get design criteria from experimental results as following. 1. When the water volume is fixed, diffuser configuration and stratification condition were changed. Then, the energy conversion efficiency at the SIL = 15~30% was relatively higher than equivalent configuration by 5~33%. 2. When the stratification condition is fixed, diffuser configuration and water volume were changed. Then, the highest energy conversion efficiency was at S/H = 0.75. It was almost every experimental conditions. It means that the critical factor in designing air diffusing system is water depth. From above results, we can hope more energy efficiency when we apply it to real design. However, it is very important to do experiment in pilot scale and elucidate the patterns about bubble plume dynamics and energy efficiency. After completing it, we can give a more powerful design guide for air diffusing system.