| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 106 === There are two approaches frequently used to enhance the permeate mass flux in membrane distillation (MD). One is the special channel design to create turbulence earlier. The other is the irradiation of ultrasound. The focus of the recent study is about the physical mechanism and enhancement on MD for one of those, so it is necessary to explore what will be going on if we combine both of them in the system.
The effects of permeate flux enhancement for direct contact membrane distillation (DCMD) of pure water in the straight channel and zigzag channel with 28kHz ultrasound irradiation at a power in the range of 0-108W were tested. The Reynolds number of feed side varies in a range of 1110-5180, the velocity of permeate side and the temperature difference of both sides is fixed at 0.06m/s and 15℃ in the system. The results show that the permeation fluxes of both without ultrasound irradiation increase with increasing of Reynolds number but smaller rise under higher Reynolds number. The enhancement of zigzag channel in contrast to straight channel could reach 7.6%.
With ultrasound irradiation, the permeation fluxes of both are not sensitive to ultrasound under higher Reynolds number. The maximum enhancement in contrast to the flux without ultrasound is 24.9% for straight channel with Reynolds number of 2035 and 17.4% for zigzag channel with Reynolds number of 1110. The turbulent internal flows under lower Reynolds number may suppress the effects of ultrasound. Nevertheless, there is a maximum permeation flux for enhancing MD with ultrasound for any channel design which is only dependent on the Reynolds number. The peak of maximum flux appears if the Reynolds number is closed to the critical Reynolds number.
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