Events

PEOPLE'S CHOICE SECOND PLACE WINNER

A Novel Film Atomizer for Zero Liquid Discharge Water Desalination  

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. However, most desalination processes and plants rely on high-grade heat or electricity to desalinate water. Therefore, at the Water & Energy Technologies Laboratory a novel low-grade solar thermal energy driven solar desalination technology is being developed. Solar heat is used to heat and accelerate air jets through a thermocompressor unit, which is used to atomize the water and humidify the air by evaporation, leaving only salt particles behind. Fresh water is subsequently extracted from the saline-free, humid air stream. 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. 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 film atomizer which significantly reduces the scaling of the nozzle tip. In contrast to the conventional atomizer, film 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 (4000 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 250 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 film 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.

This project presenter is available for live video chat on Sept. 1, 2020 from 10:15 a.m. - 12:00 p.m. PDT.