직접접촉식 막증류 공정의 성능 향상을 위한 새로운 선회유동형 미세기포 발생기의 개발

Abstract

In this study, a novel air-assisted swirling flow-type microbubble generator was designed and fabricated to improve the transmembrane flux in the downstream of a multi-stage direct contact membrane distillation (MDCMD) seawater desalination system, and its performance was experimentally evaluated at assorted operating conditions. In order to simulate the operating conditions at the downstream of the MDCMD system, low temperature and high concentration conditions on the feed side were considered in the experiments. It was found that the formation of a gas-liquid twophase flow in the feed channel had a positive influence on the performance of the DCMD process, and in particular microbubbles with a diameter of less than 100 μm played an important role in improving its heat and mass transfer. The DCMD performance using MBG was shown to be more pronounced at lower feed temperatures and higher feed flow rates, where the enhancement in permeate flux was approximately 37%. The optimal air flow rate to achieve maximum DCMD performance was found to be about 50 cc/min, while a further increase in air flow rate induced a slug flow in the feed channel, which resulted in a decrease in the number of microbubbles and hence a decrease in DCMD performance. In addition, the process performance was evaluated using highly concentrated brine as feed solution, and the results demonstrated the applicability of MBG to practical desalination applications. Therefore, the application of MBG in the MDCMD system can provide an energy-efficient concept that can occupy less space while maintaining process performance.