Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Nicole Doughramaji - Kansas State University
Co-Author(s): Ryan Huber, Xi Chen, and Melanie M. Derby, Kansas State University, Manhattan, KS
Power plant cooling towers are responsible for significant amounts of evaporated water loss, providing an excellent opportunity for water collection. Previous research has shown that cooling tower moisture can be condensed onto flat metal surfaces and flexible meshes. Water droplets on a stationary film must coalesce until they are large enough to be accelerated down the film by gravity. The current research adds a flapping motion to the flexible film with the aim of collecting more water from a moist air stream. The flapping motion decreases the critical departure size, allowing droplets to be cleared from the film while much smaller, therefore leaving more blank spaces on the film for water to nucleate during condensation. For this research, water droplets were sprayed onto stationary and flapping perflouroalkoxy (PFA) films treated with Rain-X® and droplet departures were visualized and measured. The Rain-X® coating was used to increase the hydrophobicity of the film. The film was flapped by the rotation of an off-center mass which provided a displacement of about ± 9 mm and a flapping frequency of 11 Hz. High-speed videos were taken of the film from both the front and side in order to capture the motion of the water droplets. Videos were analyzed with ImageJ to obtain the percent area of the film which was covered by water at any given point in time. From these data, it was shown that the flapping motion cleared the film faster than a stationary film. The water droplets either moved in a sliding motion down the film, or were shaken perpendicularly off the film. Additionally, the departure size was smaller for droplets on the flapping film (1-2 mm) compared to the stationary film (3-4 mm). These preliminary results provide a foundation for further work including investigating different surfaces and flapping mechanisms. Continued research investigated water droplet removal efficiency on different surfaces such as meshes and films made of a variety of materials including aluminum, silver, and Teflon. Contact angles of these films were measured. A small motor was used to vibrate the different surfaces and subsequent behaviors were analyzed in pursuit of materials which shed water droplets with the least amount of applied power. The use of an airbrush was implemented in an attempt to more accurately simulate the sizes and positions of condensing water droplets. The airbrush was found to deposit droplets roughly 1 mm in size, which were located much closer together than water droplets previously sprayed onto the film. Due to this close proximity of the water droplets from the airbrush, it was found that less energy is required to move them down the surface. Further research is needed in this concept before it can be applied to industry. Ultimately, water collected from this system could be pumped back into the power plant, or recycled for other industrial or agricultural uses.
Funder Acknowledgement(s): This work was supported by National Science Foundation grant No. 1305059 (KS-LSAMP) and National Science Foundation CBET1603737.
Faculty Advisor: Melanie M. Derby, email@example.com
Role: A preliminary apparatus had been constructed prior to my involvement with the project. I made some mild changes to the apparatus and performed all of the testing & capturing of videos of the water droplet behavior. I also processed the videos and performed analysis to gather data from them in order to produce a variety of graphs of the data obtained. Investigations with the airbrush were also my responsibility.