I attended the following seminar yesterday (see below). It was very interesting. I think this area will make a major impact in industry. A similar seminar will be held next week.
Prof. Kripa Varanasi, an assistant professor of mechanical engineering at MIT, hosted the seminar. I think his research program in related areas will do very well!
SPEAKER
Prof. Neelesh Patankar
Department of Mechanical Engineering
Northwestern University
TITLE
Fundamentals of roughness–induced superhydrophobicity
ABSTRACT
Roughness–induced superhydrophobicity has attracted global interest due to its broad technological relevance. Numerous applications in wide ranging areas such as fluidic networks, heat exchangers, energy, textile, aviation, desalination, etc., are being considered by researchers worldwide. The signature configuration for superhydrophobicity has been “bead-like” drops on rough surfaces that roll-off easily. This becomes possible if the liquid does not impale the roughness grooves, i.e., the surface is liquid-hating, and if the contact angle hysteresis is low. Finding the appropriate surface roughness is therefore necessary. Our work in this area has been focused on the theory underlying this phenomenon. In this talk I will present a thermodynamic framework to enable a systematic analysis of this problem. This framework will be used to address the following issues: i) What types of roughness are ideal for superhydrophobicity? ii) How to analyze the energy barrier between the two most common wetting configurations – the Cassie-Baxter state and the Wenzel state? iii) How to minimize contact angle hysteresis? With regards to the third issue, it has been speculated in literature that the Cassie-Baxter formula, to predict the apparent contact angles of drops on rough surfaces, may not be practically meaningful due to hysteresis. This issue will be discussed with particular emphasis on eliminating misconceptions about the theory underlying these formulas. In the last part of the talk I will discuss a new approach based on vapor stabilizing surfaces. The design of roughness–based superhydrophobic surfaces has traditionally relied upon or assumed the presence of air pockets in roughness grooves. Now consider applications such as low drag surfaces for liquid flow, either in enclosed fluidic networks or on immersed bodies. In these cases, even if air is initially present, it could dissolve out of the roughness grooves. To address this issue surface roughness could be designed such that a liquid in contact with it will vaporize in roughness grooves by way of capillary evaporation. The vapor pockets formed from the liquid itself can serve to self–lubricate the liquid flow thus leading to ultra–low drag substrates. The same mechanism of stabilizing the vapor phase can lead to effective nucleation sites for nucleate boiling leading to the inception of boiling at dramatically low superheats. Thus, a more “robust” approach based on vapor stabilizing surfaces is recommended.
BIOGRAPHY
Neelesh A. Patankar is Associate Professor of Mechanical Engineering at Northwestern University. He received his BS (B.Tech.) in Mechanical Engineering from the Indian Institute of Technology, Bombay (1993) and his doctorate in Mechanical Engineering from the University of Pennsylvania (1997). He joined the Department of Mechanical Engineering at Northwestern University in 2000 following a post-doctoral position in the laboratory of Prof. D. D. Joseph. Neelesh specializing in fast and efficient algorithms for fully resolved simulation of immersed bodies in fluids. He also specializes in theory underlying roughness-induced superhydrophobicity. Neelesh has received the NSF CAREER award and the International Conference on Multiphase Flow's Junior Award that is given once in three years. He is currently one of fifteen academicians selected to the Defense Science Study Group. He is on the editorial boards of the Journal of Computational Physics and the ASME Journal of Fluids Engineering.
Prof. Neelesh Patankar
Department of Mechanical Engineering
Northwestern University
TITLE
Fundamentals of roughness–induced superhydrophobicity
ABSTRACT
Roughness–induced superhydrophobicity has attracted global interest due to its broad technological relevance. Numerous applications in wide ranging areas such as fluidic networks, heat exchangers, energy, textile, aviation, desalination, etc., are being considered by researchers worldwide. The signature configuration for superhydrophobicity has been “bead-like” drops on rough surfaces that roll-off easily. This becomes possible if the liquid does not impale the roughness grooves, i.e., the surface is liquid-hating, and if the contact angle hysteresis is low. Finding the appropriate surface roughness is therefore necessary. Our work in this area has been focused on the theory underlying this phenomenon. In this talk I will present a thermodynamic framework to enable a systematic analysis of this problem. This framework will be used to address the following issues: i) What types of roughness are ideal for superhydrophobicity? ii) How to analyze the energy barrier between the two most common wetting configurations – the Cassie-Baxter state and the Wenzel state? iii) How to minimize contact angle hysteresis? With regards to the third issue, it has been speculated in literature that the Cassie-Baxter formula, to predict the apparent contact angles of drops on rough surfaces, may not be practically meaningful due to hysteresis. This issue will be discussed with particular emphasis on eliminating misconceptions about the theory underlying these formulas. In the last part of the talk I will discuss a new approach based on vapor stabilizing surfaces. The design of roughness–based superhydrophobic surfaces has traditionally relied upon or assumed the presence of air pockets in roughness grooves. Now consider applications such as low drag surfaces for liquid flow, either in enclosed fluidic networks or on immersed bodies. In these cases, even if air is initially present, it could dissolve out of the roughness grooves. To address this issue surface roughness could be designed such that a liquid in contact with it will vaporize in roughness grooves by way of capillary evaporation. The vapor pockets formed from the liquid itself can serve to self–lubricate the liquid flow thus leading to ultra–low drag substrates. The same mechanism of stabilizing the vapor phase can lead to effective nucleation sites for nucleate boiling leading to the inception of boiling at dramatically low superheats. Thus, a more “robust” approach based on vapor stabilizing surfaces is recommended.
BIOGRAPHY
Neelesh A. Patankar is Associate Professor of Mechanical Engineering at Northwestern University. He received his BS (B.Tech.) in Mechanical Engineering from the Indian Institute of Technology, Bombay (1993) and his doctorate in Mechanical Engineering from the University of Pennsylvania (1997). He joined the Department of Mechanical Engineering at Northwestern University in 2000 following a post-doctoral position in the laboratory of Prof. D. D. Joseph. Neelesh specializing in fast and efficient algorithms for fully resolved simulation of immersed bodies in fluids. He also specializes in theory underlying roughness-induced superhydrophobicity. Neelesh has received the NSF CAREER award and the International Conference on Multiphase Flow's Junior Award that is given once in three years. He is currently one of fifteen academicians selected to the Defense Science Study Group. He is on the editorial boards of the Journal of Computational Physics and the ASME Journal of Fluids Engineering.
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