In order to meet the increased water demand triggered by population explosion, rapid industrialization, agriculture development, and tourism, many water-stressed regions are augmenting their water supply with desalinated water. Further, in some areas such as Qatar and Kuwait, 100% of domestic and industrial water demand is supplied through desalination implying development of desalination beyond a marginal or supplemental water resource. This has led to the development of various desalination techniques which can mainly be divided into four major categories as mechanical, chemical, thermal, and electrical desalination systems. Thermal desalination systems have been identified as one of the potential strategy to clean high salinity water in large volume, and when utilizing industrial waste or solar heat could serve as a sustainable and clean approach. In thermal desalination processes such as multi-effect distillation (MED), vapor compression (VC), and humidification-dehumidification (HDH), saline water is atomized for higher evaporation rate and subsequently condensed to collect the fresh water. However, atomization using conventional atomizers faces serious technical problem of scale formation/fouling. Further, in the conventional atomizers saline water passes through a small orifice and small fouling can easily clog the atomizers. Therefore, to minimize such fouling, the existing desalination techniques operate in a limited range of pressure and temperature. This is also highlighted by Adel M. Abdel Dayem in his study named “Pioneer Solar Water Desalination System: Experimental Testing and Numerical Simulation”, where he had to limit the operating temperature of atomizer below 70℃ to avoid scaling and clogging in the atomizer. Such fouling in the system significantly affects the productivity as well as the maintenance cost of the process. Therefore, there is a need to develop a robust atomization technique to make thermal desalination processes more flexible to accommodate the increasing global water demand.

In this regard, we propose a novel perforated plate atomizer which significantly reduces the scaling of the nozzle tip. In contrast to the conventional atomizer, perforated plate atomizer avoids saline water passing through any small orifice. A thin film of saline water is maintained on the top of a perforated plate with the help of primary and secondary manifolds, while air jet flows perpendicular to the saline thin film and atomizes it. Primary manifold is used to stabilize the saline water flow to the secondary manifolds, which maintain a thin annular saline water film around the air holes. An in-house experimental facility of perforated plate atomizer was developed and tested for different geometries and operating conditions including air and water temperatures, water salinity, air-to-water ratio and mass flow rates. Maximum salinity of 10% was tested during the experiments and no fouling was observed for three hours of operation. High speed imaging (5000 fps) was performed to characterize the atomized droplets in terms of droplet size, distribution, and uniformity. A shadow box fosters the atomizer assembly, which minimizes the interference of the ambient light and allowed to capture high quality videos. Analysis of the high speed videos reveled droplets as small as 100 µm was achieved within the tested conditions. Further, it was observed that the spray was fairly uniformly distributed.  The results demonstrate the capabilities of newly proposed perforated plate atomizer to completely avoid the flow of saline water through small orifice, and thus, reducing the chances of clogging. Accordingly, the existing desalination systems with the perforated plate atomizer could operate for a larger range of operating temperatures with reduced scaling. Such improved performance will reduce the maintenance cost, making system economically viable and sustainable. Future work will focus on developing design guides to obtain specific spray characteristics to optimize desalination.


Perforated Plate Atomizer: A Novel Approach to Improve Desalination System Efficiency

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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