Significance
Chemical and petro-chemical engineering, cooling of power electronic devices, air conditioning and refrigeration are among the many phenomena in our daily activities that utilize boiling. In the past fifty years, the boiling phenomenon has been studied far and wide. Most of the studies undertaken have, however, concentrated on parameters such as dimension, configuration, heat flux, type of working fluid and the topography of the surface. More so, majority of the researchers have focused on the use of enhanced surfaces in boiling by preparing mechanically deformed structures, sintered wires porous, materials and complex geometries. The importance of surface condition on nucleate boiling cannot be ignored. Fortunately, recent advances in nanotechnology have led to the conceptualization of efforts aimed at enhancing boiling heat transfer by using nanostructured surfaces such as deposited nanoparticles, nanowires, carbon nanotubes and metal oxide structures. Flow boiling enhancement using structured surfaces in micro-channels is a promising method to achieve high heat removal rates. Regardless, there are few studies focusing on boiling heat transfer in high aspect ratio micro-channels.
Researchers (Abdolali K Sadaghiani, Sorour Semsari Parapari, and Professor Mehmet Keskinoz from Sabanci University, Nawzat S. Saadi and Professor Tansel Karabacak from University of Arkansas at Little Rock) led by professor Ali Kosar from the Center of Excellence for Functional Surfaces and Interfaces for Nano diagnostics (EFSUN) and Sabanci University Nanotechnology and Applications Center (SUNUM) at Sabanci University in Turkey, investigated the effect of surface structure size (size scale: micro and nano) on boiling heat transfer characteristics of samples with different surface morphology. The researchers aimed at conducting flow experiments on samples of different surface morphologies: micro and nano structured, in a high aspect ratio micro channel. A new flow map have developed demonstrating the differences in flow morphologies due to structure size. Their work is now published in the research journal, Applied Thermal Engineering.
The research team undertook the experimental procedure where they investigated heat removal capacity of nano-structured, micro structured and micro-nano structured surfaces. They then employed thermal and high speed camera systems to clarify the differences in heat transfer mechanisms. The team then obtained heat transfer coefficients along with associated boiling images. Eventually, based on the visualization study results, two flow maps were constructed for a rectangular microchannel with micro and nano scale structures on copper surfaces.
From the experiment undertaken, the authors of the paper observed that the surface morphology remarkably changed boiling heat transfer mechanisms. According to the obtained thermal images, bubble departure frequency increased with surface structures, and the surface temperature distribution was more uniform for surfaces with nano scale structures (nano-structured and micro-nano-structured) compared to other surfaces (untreated, micro-structured).
In their study, copper surfaces have been used as the test samples. From the results obtained, it has been found that structured surfaces have a better heat removal capacity in comparison to the bare surface. This is good evidence that micro-structured, nano-structured and micro-nano-structured plates can be implemented in innumerable cooling applications to achieve higher energy efficiency. More so, according to the observations higher heat transfer coefficients are obtained from nano scale structured surfaces in comparison to the micro scale structured sample. Therefore, these promising results obtained in Ali Koşar lab reveal the potential of micro and nano scale structured surfaces application that will help achieve improved energy efficiency for electronics cooling systems.
About the author
Abdolali K Sadaghiani received his M.Sc. degree in Mechatronics Engineering from Sabanci University, Istanbul, in 2015. Currently, he is pursuing his Ph.D. under the supervision of Prof. Ali Koşar at Sabanci University. His research focuses on numerical and experimental studies of multiphase flows in microchannels. His research interests lie in microscale heat and mass transfer, phase change, microfabrication, and microfluidics. He received several awards including Sedat Simavi Foundation Natural Sciences Award (2016), and Best Paper Award in ASME IMECE 2014 – MEMS Track (2014).
About the author
Nawzat Saadi received his BS degree in 2003 from physics department at Duhok University, Iraq. In 2008, Nawzat get his MSc in the field of computational physics from Physics department at Duhok University. Currently, he is a PhD student at University of Arkansas at Little Rock (UALR) Department of Applied Science and works in Dr.Tansel Karabacak group. He is primarily interested in metal oxide nanostructures fabrication and material with special wettability for oil-water separation applications. He is the author and co-author of several peer-reviewed journal papers and conference proceedings, several pending patents.
About the author
Sorour Semsari Parapari received her B.Sc. degree in Materials Engineering from University of Tabriz, Iran in 2009. She continued her graduate studies at Sabanci University, Turkey and obtained her M.Sc. degree in 2015 in Materials Science and Engineering. Sorour is pursuing her Ph.D. under the supervision of Prof. Mehmet Ali Gülgün at Sabanci University. She is currently working at the National Institute of Chemistry, Slovenia as a visiting student. Her primary interests are lithium ion battery materials, structure-property relationships, electron microscopy and materials characterization.
About the author
Dr. Tansel Karabacak received his BS degree in 1996 from Physics at Middle East Technical University in Turkey. He conducted his PhD studies at Rensselaer Polytechnic Institute (RPI) Department of Applied Physics in the field of growth dynamics of thin film coatings and glancing angle deposited (GLAD) nanostructures. After he received his doctoral degree in 2003 and a period of postdoctoral research at RPI, in 2006 he joined University of Arkansas at Little Rock (UALR) Department of Applied Science as a faculty member. He also became the graduate coordinator of the Applied Science PhD program at UALR. In recent years, Dr. Karabacak has been working on various projects on the properties and applications of GLAD nanostructures and physical vapor deposited thin films. He is primarily interested in alternative energy technologies including solar cells, fuel cells, and batteries. His research led to numerous awards including American Vacuum Society Graduate Research Award and University of Arkansas Excellence in Research Award, and also to several grants from NSF, NASA, and DOE. He is the author and co-author of about 130 peer-reviewed journal papers and conference proceedings, two book chapters, one patent, and several pending patents.
About the author
Dr. Mehmet Keskinoz got his M.S. and Ph.D. degrees from Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh (USA), in 1997 and 2001, respectively. In 2001, he joined to Electronics Engineering Program of Sabanci University Istanbul, Turkey where he is now an Associate Professor. His research interests include signal processing for wired and wireless communications, UWB communications, Multi-band OFDM UWB systems, Wireless Mesh Networks, magnetic and optical data storage systems, distributed detection and data fusion for wireless sensor networks, Turbo and LDPC coding, synchronization, digital watermarking. He is a recipient of Turkish NSF Research grant on distributed detection in wireless sensor networks and Career Award on wireless mesh networks in August 2005. He is a co-guest editor of IEEE Communications Magazine January 2009 Special Issue on Advances in Signal Processing for Wireless and Wired Communications. He is a member of IEEE Communication Society, IEEE Signal Processing Society and Optical Society of America.
About the author
Ali Koşar received his B.S. degree in Mechanical Engineering from Bogazici (Bosphorus) University, Istanbul, in 2001. He pursued his graduate study in the Department of Mechanical Engineering at Rensselaer Polytechnic Institute between 2001 and 2006. He joined Mechatronics Engineering Program at Sabanci University in Fall 2007. He is one of the pioneers in the design and development of new generation micro heat sinks and microfluidic devices.
His research interests lie in heat and fluid flow in micro/nano scale, boiling heat transfer, and cavitation. The results of his research have already generated more than 100 journal research articles in prestigious journals. He received many awards such as METU (Middle East Technical University) Prof. Mustafa N. Parlar Foundation Technology Award (2017), Sedat Simavi Foundation Natural Sciences Award (2016), Ten Outstanding Young Persons Turkey Award in Scientific Leadership (TOYP 2015), ASME (American Society of Mechanical Engineers) ICNMM (International Conference on Nanochannels, Microchannels and Minichannels) Outstanding Early Career Award, Japan, Sapporo (2013), Kadir Has Outstanding Young Investigator Award (March 2013), TUBITAK (The Scientific and Technological Research Council of Turkey) Incentive Award (July 2012), and Outstanding Young Researcher Award, Turkish Academy of Sciences (2011). He is currently a Professor at Sabanci University and the Co-director of Center of Excellence for Functional Surfaces and Interfaces for Nano diagnostics (EFSUN).
Reference
Abdolali Khalili Sadaghiani, Nawzat S. Saadi, Sorour Semsari Parapari, Tansel Karabacak, Mehmet Keskinoz, Ali Kosar. Boiling heat transfer performance enhancement using micro and nano structured surfaces for high heat flux electronics cooling systems. Applied Thermal Engineering volume 127 (2017) page 484–498.
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