Experimental Investigation of Condensation and Freezing Phenomenon on Hydrophilic and Hydrophobic Titanium Nanopillared Glass Surfaces

Abstract

Atmospheric condensation is very important for multiple practical applications such as heat transfer, thermal management, aerospace, and condensate harvesting. Water droplets heterogeneously nucleate on the surfaces when the temperature is below the dew point temperature. The nucleation energy barrier for a condensed droplet varies significantly with the humidity content in the operating environment. The freezing of this condensate is also dependent on the operating conditions and surface properties. This article presents an experimental study of condensation and freezing from humid air with the objective of understanding how the surface morphology and chemistry determines the droplet shape and wetting state. Hexagonal close-packed arrays of titanium (Ti) pillars are patterned using microsphere photolithography (MPL). The Ti nanostructured surface was tested with and without a Teflon^© coating to reveal the condensate harvesting, passive freezing, and dropwise condensation applications, respectively. Condensation and freezing tests were conducted in the presence of non-condensable gases (air) with different relative humidity (RH) levels to control the nucleation site density. The experiments showed that droplet growth occurs in the following stages: initial nucleation, direct growth, and coalescence events. By pinning droplets, coalescence is suppressed for the Ti nanopillared surface altering the size distribution of droplets and significantly accelerating the freezing process.

Acknowledgments

The authors would also like to thank Dr. Steven Eckels and Matt Campbell for the use of their environmental chambers.

Additional information

Funding

This material is based upon work supported by the National Science Foundation under Grants No. 1604183 and 1653792.

Notes on contributors

Mohammad Rejaul Haque

Mohammad Rejaul Haque is currently working as a faculty member in the Mechanical and Production Engineering Department of Ahsanullah University of Science & Technology. He received his Ph.D. in Mechanical Engineering at Mechanical and Nuclear Engineering Department of Kansas State University (KSU), USA in 2019. His main research investigated the droplet growth on nanopillared surface, frost formation, condensation heat transfer, numerical heat transfer, and compact heat exchangers. Prior to joining KSU, He earned his B.Sc. and M.Sc. degree in mechanical engineering from Bangladesh University of Engineering and Technology.

Chen Zhu

Chen Zhu is a Ph.D. student in Aerospace and Mechanical Engineering Department, University of Notre Dame (Indiana, USA). His research interests are focused on nanoscale fabrication and optics particularly toward controlling heat transfer. Prior to joining Notre Dame, he earned his B.S. from Wuhan University (2013) and Master’s Degree (2016) from USTC in China.

Chuang Qu

Chuang Qu received his B.E. and M.E. in Thermal and Power Engineering from Dalian University of Technology, China in 2012 and 2014, respectively, and Ph.D. in Mechanical Engineering from Missouri University and Science and Technology in 2019. He is currently a Postdoctoral Associate in the Department of Speed School Electrical & Computer Engineering at the University of Louisville for the Kentucky Multi-Scale Manufacturing and Nano Integration Node (KY MMNIN). His research focuses on bottom-up manufacturing techniques, including thin film depositions, additive manufacturing, and self-assembly.

Edward C. Kinzel

Edward Kinzel received his B.S., M.S. and Ph.D. in Mechanical Engineering from Purdue in 2003, 2005, and 2010, respectively. He is currently an Associate Professor in the Aerospace and Mechanical Engineering Department, University of Notre Dame. His research focuses on practical nanofabrication of frequency selective surfaces/ metasurfaces, additive manufacturing, and applying infrared radiation /optical antennas as sensing elements as well as for energy harvesting. He is a member of ASME, SPIE, and IEEE.

Amy Rachel Betz

Amy Rachel Betz received her bachelor's degree in mechanical engineering from George Washington University and her master's and doctoral degrees from Columbia University. She is an Associate Professor in the Mechanical and Nuclear Engineering Department at Kansas State University. Her research investigates multiphase processes such as boiling, condensation, and frost formation. She is passionate about research, education, and mentoring. She is also committed to creating a more inclusive engineering culture.