Membrane distillation (MD) is an emerging technology capable of treating high-saline feeds and operating with low-grade heat energy. However, commercial implementation of MD is limited by so-called temperature polarization, which is the deviation in the temperature at the feed-membrane interface with respect to the bulk fluid. This work presents solutions to alleviate temperature polarization in MD by employing a localized heating concept to deliver heat at the vicinity of the feed-membrane interface. This can be realized in multiple ways, including Joule heating, photothermal heating, electromagnetic induction heating, and nanofluid heating. In the first experiment, a Joule heating concept was implemented and tested, and the results showed a 45% increase in permeate flux and a 57% decrease in specific energy consumption. This concept was further improved by implementing a new dead-end MD configuration, which led to a 132% increase in the gained output ratio. In addition, the accumulation of foulants on the membrane surface could be successfully controlled by intermittent flushing of feedwater. Three-dimensional CFD calculations of conjugate heat transfer revealed a more uniform heat transfer and temperature gradient across the membrane due to the increased feedwater temperature over a larger membrane area.
In another approach, a photothermal MD concept was used to heat the feed water locally. A 2-D photothermal material, MXene, recently known for its photothermal property, was used to coat commercial MD membranes. The coated membranes were evaluated under one-sun illumination to yield a permeate flux of 0.77 kg.m$^{−2}$h$^{−1}$ with a photothermal efficiency of 65.3% for a feed concentration of 0.36 g.L$^{−1}$. The system can produce around 6 liters of water per day per square meter of membrane.
An energy analysis was also performed to compare the efficiency of various energy sources. Considering the sun as a primary energy source, the performance of different heating modes was compared in terms of performance and scale-up opportunities.
Overall this work demonstrates that the application of localized heating will enable the scale-up and the use of renewable energy sources to make the MD process more efficient and sustainable. / The illustrative figure was produced by Ana Bigio, scientific illustrator, KAUST.
| Identifer | oai:union.ndltd.org:kaust.edu.sa/oai:repository.kaust.edu.sa:10754/673893 |
| Date | 12 1900 |
| Creators | Mustakeem, Mustakeem |
| Contributors | Ghaffour, NorEddine, Biological and Environmental Science and Engineering (BESE) Division, Sarathy , S. Mani, Mishra, Himanshu, Warsinger, David |
| Source Sets | King Abdullah University of Science and Technology |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Rights | 2022-12-05, At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation will become available to the public after the expiration of the embargo on 2022-12-05. |
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