Thermal conductivity of confined-water in graphene nanochannels

Significance 

Nanoconfined fluids exhibit specific characteristics different from bulk fluids that make them attractive for numerous applications in various fields. With the rapid development of advanced nanoscience and nanotechnology, significant improvement has been achieved in the study of nanoconfined fluids over recent decades. One key area of concern has been the transport properties of nanoconfined fluids, which has enabled in-depth scientific research on their flow dynamics and heat transfer. Nevertheless, despite extensive research, the underlying mechanism explaining the difference in the physical behavior between the bulk fluids and nanoconfined fluids has not been fully clarified. In recent research, nanoconfined water in graphene channels was reported to exhibit distinct characteristics desirable for water purification applications. This revelation opened doors for intensive studies on the transport properties of water confined in graphene nanochannels.

To this account, Professor Chengzhen Sun and Runfeng Zhou (PhD candidate) from Xi’an Jiaotong University together with Dr. Zhixiang Zhao from Xi’an Polytechnic University investigated the nanoscale effect of the thermal conductivity of water confined in graphene nanochannels based on equilibrium molecular dynamic (EMD) simulations with employing Greek-Kubo formula. Also, they studied and compared the thermal conductivities in the x-, y-, and z-directions. The main aim was to illustrate the anisotropic and size-dependent transport properties of nanoconfined water in graphene channels from the physical insights. Their research work is currently published in the research journal, International Journal of Heat and Mass Transfer.

According to the results, the thermal conductivity of nanoconfined water exhibited obvious anisotropy; that is, the perpendicular thermal conductivity (thermal conductivity in the z-direction) was lower than the longitudinal thermal conductivity (average thermal conductivity in the x- and y-directions). This was attributed to the partial trapping of the water molecules in the potential wells near the graphene walls, which inhibited the molecular collision in the z-direction while enhancing it in the x- and y-directions. Consequently, channel height exhibited remarkable effects on thermal conductivity. For instance, the perpendicular thermal conductivity decreased with an increase in the channel height while the perpendicular conductivity increased with an increase in the channel height. Furthermore, increasing the channel height resulted in an overall weakening of the contributions of the trapped water molecules in both the perpendicular and longitudinal directions, such that the thermal conductivity in the x-, y- and z-directions approach the bulk values.

In summary, the study investigated the thermal conductivity of confined-water in graphene nanochannels using EMD simulations with the Green-Kubo formula. Based on the analysis of the size-dependence of thermal conductivity, the authors reported that the thermal conductivity in the nanoconfined water is rather anisotropic. Parameters such as the channel height exhibited a remarkable influence on thermal conductivities in both x-, y- and z-directions. Overall, the study successfully identified the anisotropy and size dependence of thermal conductivity of confined water in graphene nanochannels and also clarified the underlying mechanism from the thermodynamics perspective. In a statement to Advances in Engineering, the authors said their findings would advance further research on the mass and energy transport of nanoconfined fluids that would benefit its various applications.

Thermal conductivity of confined-water in graphene nanochannels - Advances in Engineering

About the author

Chengzhen Sun received the B.Eng. degree in thermal engineering from Xi’an Jiaotong University, Xi’an, China, in 2008 and the Ph.D. degree in engineering thermophysics from Xi’an Jiaotong University, Xi’an, China, in 2014. As a Ph.D student, he studied at the Department of Mechanical Engineering in MIT as a visiting student from 2012 to 2013. He started his academic career as a Lecturer at Xi’an Jiaotong University, China in 2014 and then worked as an Associate Professor in 2017. Currently, his researches focus on mass and energy transport of nanoconfined fluids, especially on the mass transport in two-dimensional nanopores and gas/oil/water multiphase flow in nanoslits to develop the high-efficiency membrane separation technology and enhanced oil recovery technology.

He published more than 35 peer-reviewed SCI-indexed papers in the journals of Acs nano (1), J Phys Chem Lett (3), Phys Chem Chem Phys (4), Science Bulletin (2), Langmuir (1), Chem Eng Sci (3) etc. His papers have received citations up to 850 times in the journal of Nature and others, among them 2 papers were indexed as highly-cited papers. He was invited to publish book chapter, review paper, perspective, highlight and present 2 keynote lectures in international conferences. He was honored as the Best Doctoral Thesis in Shaanxi Province, Annual Best Paper in Science Bulletin and others. He was invited to serve as the leading editor of a special issue “Nanoconfined fluids in energy applications” in the SCI-indexed journal of Frontiers in Energy Research.

About the author

Zhixiang Zhao received the B.Eng. degree in thermal engineering from Xi’an Jiaotong University, Xi’an, China, in 2008 and the Ph.D. degree in power engineering and engineering thermophysics from Xi’an Jiaotong University, Xi’an, China, in 2015. During the Ph.D study, his researches focused on multiple flow pattern and heat and mass transfer with phase change. He was employed by Huawei Technologies Co., Ltd. to research and develop precision air-conditioner since receiving his doctorate until 2018. During his career as an engineer in Huawei, he led and participated a number of product developments and was honored as the Hope Star of Huawei in 2017.

He began his academic career once again as an associate professor at Xi’an Polytechnic University in 2019. Currently, his research interest is transport properties of nanoconfined fluids. He published more than 10 peer-reviewed SCI papers in the journals of J Phys Chem Lett (1), Int J Heat Mass Tran (2), Exp Therm Sci (1) etc.

About the author

Runfeng Zhou received his B.Eng. degree in new energy science and engineering from Xi’an Jiaotong University, Xi’an, China, in 2019 and presently pursuing his Ph.D. degree in engineering thermophysics from Xi’an Jiaotong University. He combines theory and simulations to explore the underlying mechanisms of nanoconfined fluids at the molecular level. He has participated in several projects funded by National Natural Science Foundation of China and published 4 peer-reviewed SCI-indexed papers in the journals of J Phys Chem Lett (1), Int J Heat Mass Tran (1) etc. He was honored as the National Scholarship of China, Alumni Scholarship, Outstanding Postgraduate Cadre and Outstanding Youth League Member.

Reference

Zhao, Z., Sun, C., & Zhou, R. (2020). Thermal conductivity of confined-water in graphene nanochannels. International Journal of Heat and Mass Transfer, 152, 119502.

Go To International Journal of Heat and Mass Transfer

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