EAS PhD Program (CSE Option / MNE) PhD Proposal Defense by Mr. Wen Jin
When: Monday,
August 28, 2017
11:00 AM
-
1:00 PM
Where: Textiles Building 101E
Description: Engineering and Applied Science PhD Program (CSE Option / Mechanical Engineering) PhD PROPOSAL DEFENSE by Mr. Wen Jin
DATE:
August 28, 2017
TIME:
11:00 a.m. 1:00 p.m.
LOCATION:
Textile Building, Room 101E
TOPIC:
Computational Investigation of the Impingement of Water Droplets on Freezing Superhydrophobic Surfaces
ABSTRACT:
Wind provides a clean and renewable source of energy that has great potential, particularly in the cold climate areas. However, in cold climates, ice formation on wind turbine blades is common and becomes a serious challenge. Ice formation can reduce the aerodynamic performance of wind turbines by increasing drag and causing flow separation. Also, heavy ice buildup on the blades may unbalance the turbine and cause catastrophic failures. Most importantly, ice layers formed on rotating blades can detach with significant momentum and cause fatal accidents or damage nearby facilities. Recently, several laboratory experiments show that water droplets impacting freezing superhydrophobic surfaces (SHS) can bounce off the surface before any ice is formed. The SHS are hydrophobic surfaces that are enhanced by adding micro-textures, such as posts or pillars, on the surface and/or by chemical hydrophobic coatings. Although the efficacy of SHS in preventing ice formation during the impact of millimeter-size water droplets has been established by various laboratory studies, further investigation is needed to determine whether such surfaces can prevent ice formation on wind turbine blades under real-world conditions, where micron-size droplets impact the surface at high speeds. This work presents computational simulations of the impingement of micron-size water droplets on freezing SHS at various Weber numbers, droplet initial temperatures, and surface temperatures. The simulation results are from an in-house volume-of-fluid based, free-surface flow solver with phase change. While the surface has been assumed smooth in these simulations, the effects of the surface micro-textures on the contact angle and thermal contact resistance were taken into account. The first objective was to investigate the conditions under which the droplets bounce off the surface or stick to the surface and freeze. The transition between the bouncing and sticking regimes is determined. Then, analyzing the timescales for droplet freezing and drop-surface contact, a theoretical model was developed for predicting the above transition. The predictions of the theoretical model are compared against the transition conditions observed in the computational simulations and experiments. Next, it is proposed to enhance the flow solver to include the surface micro-textures, which requires a robust numerical method for capturing the contact line pinning on complex surface textures in 3D. The proposed numerical method for contact line pinning and the preliminary 2D results are presented. The enhanced flow solver will enable a detailed investigation of the effects of surface texture geometry and the air entrapment under the droplet and between surface textures. The study will lead to design of textured super-ice-phobic surfaces that are specially engineered for the flow fields around wind turbine blades.
ADVISOR:
Dr. Mehdi Raessi
COMMITTEE MEMBERS:
Dr. Sankha Bhowmick, Dr. Gaurav Khanna, Dr. Jun Li
Open to the public. All MNE and EAS students are encouraged to attend.
For more information, please contact Dr. Raessi (mraessi@umassd.edu, 508-999-8496).
Thank you,
Sue Cunha, Administrative Assistant
Department of Mechanical Engineering
College of Engineering
University of Massachusetts Dartmouth
285 Old Westport Road
Dartmouth, MA 02747-2300
Science & Engineering Building, Room 116E
508-999-8492/Telephone
508-999-8881/Fax
scunha@umassd.edu
DATE:
August 28, 2017
TIME:
11:00 a.m. 1:00 p.m.
LOCATION:
Textile Building, Room 101E
TOPIC:
Computational Investigation of the Impingement of Water Droplets on Freezing Superhydrophobic Surfaces
ABSTRACT:
Wind provides a clean and renewable source of energy that has great potential, particularly in the cold climate areas. However, in cold climates, ice formation on wind turbine blades is common and becomes a serious challenge. Ice formation can reduce the aerodynamic performance of wind turbines by increasing drag and causing flow separation. Also, heavy ice buildup on the blades may unbalance the turbine and cause catastrophic failures. Most importantly, ice layers formed on rotating blades can detach with significant momentum and cause fatal accidents or damage nearby facilities. Recently, several laboratory experiments show that water droplets impacting freezing superhydrophobic surfaces (SHS) can bounce off the surface before any ice is formed. The SHS are hydrophobic surfaces that are enhanced by adding micro-textures, such as posts or pillars, on the surface and/or by chemical hydrophobic coatings. Although the efficacy of SHS in preventing ice formation during the impact of millimeter-size water droplets has been established by various laboratory studies, further investigation is needed to determine whether such surfaces can prevent ice formation on wind turbine blades under real-world conditions, where micron-size droplets impact the surface at high speeds. This work presents computational simulations of the impingement of micron-size water droplets on freezing SHS at various Weber numbers, droplet initial temperatures, and surface temperatures. The simulation results are from an in-house volume-of-fluid based, free-surface flow solver with phase change. While the surface has been assumed smooth in these simulations, the effects of the surface micro-textures on the contact angle and thermal contact resistance were taken into account. The first objective was to investigate the conditions under which the droplets bounce off the surface or stick to the surface and freeze. The transition between the bouncing and sticking regimes is determined. Then, analyzing the timescales for droplet freezing and drop-surface contact, a theoretical model was developed for predicting the above transition. The predictions of the theoretical model are compared against the transition conditions observed in the computational simulations and experiments. Next, it is proposed to enhance the flow solver to include the surface micro-textures, which requires a robust numerical method for capturing the contact line pinning on complex surface textures in 3D. The proposed numerical method for contact line pinning and the preliminary 2D results are presented. The enhanced flow solver will enable a detailed investigation of the effects of surface texture geometry and the air entrapment under the droplet and between surface textures. The study will lead to design of textured super-ice-phobic surfaces that are specially engineered for the flow fields around wind turbine blades.
ADVISOR:
Dr. Mehdi Raessi
COMMITTEE MEMBERS:
Dr. Sankha Bhowmick, Dr. Gaurav Khanna, Dr. Jun Li
Open to the public. All MNE and EAS students are encouraged to attend.
For more information, please contact Dr. Raessi (mraessi@umassd.edu, 508-999-8496).
Thank you,
Sue Cunha, Administrative Assistant
Department of Mechanical Engineering
College of Engineering
University of Massachusetts Dartmouth
285 Old Westport Road
Dartmouth, MA 02747-2300
Science & Engineering Building, Room 116E
508-999-8492/Telephone
508-999-8881/Fax
scunha@umassd.edu
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