Abstract
The use of ultrasound has been considered a promising way to enhance the efficiency of permeation for membrane distillation (MD) due to effects such as ultrasonic cavitation, acoustic streaming, vibration and acoustic heating…etc. In this study, ultrasound with the irradiation power of 0.14~0.42 W/〖cm〗^2 and the frequency of 28~120kHz is applied in the system of direct contact membrane distillation (DCMD) for the feed velocity of 0.1~0.4m/s, the feed temperature of 40~60℃ and the feed salinity of 0~3.5wt%. The inlet conditions on the permeate side are fixed at 0.1 m/s and 25℃. The PTFE membrane used is of 150μm thickness and 0.22μm pore diameter. The results imply that ultrasonic cavitation and acoustic streaming are the two major enhancement mechanisms which are mainly influenced by the power and frequency of the ultrasound. The problem of membrane fouling is found to be improved by ultrasound irradiation. The enhancement of efficiency generally increases with ultrasound power and decreases with frequency and is more perceptible at relatively low flow speed, salinity and temperature on the feed side. The maximum enhancement of permeation flux with ultrasound irradiation is 10.63% for the problem of interest.