Prof. Zan Wu
Lund University, Sweden
Speech Title: Experiments and Modelling of Pool Boiling Heat Transfer on Micro/nanostructured Surfaces
Biography: Zan Wu has been an Associated Professor (universitetslektor) since 2018.02 at the Department of Energy Sciences, Lund University, Sweden. He received his B.S. and Ph.D. from Zhejiang University, Hangzhou, China in 2008 and 2013, respectively. He worked as a postdoctoral fellow, a senior researcher, and then he was promoted as tenured Associate Professor in 2018, all at Lund University. He is currently the head of the heat transfer laboratory. He is leading projects granted by various funding agencies, especially the Swedish Research Council.
His research interests are mainly multiphase flow, heat transfer enhancement by micro/nanostructures, boiling and condensation, microreactors, microfluidics and nanofluidics, and renewable energy. These basic research topics can easily find their applications, for example, in heat exchangers (evaporators and condensers) and heat pipes, electronics cooling, MEMS, chemical reactors, biomedical engineering and food engineering. Although Zan’s research works are mainly experimental, he has interests in both experimental and numerical works. He has co-authored more than 130 papers in journals and conferences. He currently serves as associate editor of the Heat Transfer Engineering journal.
Abstract: Boiling heat transfer enhancement is an evergreen and important topic of big relevance in existing, future and renewable energy systems as well as for energy conversation, specifically, in applications like steam power plants, thermal desalination, HVAC (heating, ventilation and air conditioning), electronics cooling, oil, gas and chemical processing systems, waste heat recovery and renewable energy systems. These industrial applications rely on boiling to efficiently transfer large heat fluxes across system boundaries. In practical applications, it is desirable to increase the heat transfer coefficient (HTC) and the critical heat flux (CHF). Surface modification at micro/nanoscale can be recognized as the next-generation heat transfer technology, upgrading boiling heat transfer significantly to improve energy efficiency and enable energy savings/recovery of vast amounts of low-grade energy. Therefore, boiling heat transfer enhancement by surface micro/nanostructures has been a hot topic during the past decade.
This work aims to present the boiling heat transfer performance of various micro/nanostructured surfaces via different techniques such as electrostatic deposition, electrophoretic deposition and electrochemical deposition. Hybrid micro/nanostructured surfaces were experimentally investigated as well. Water, pentane and dielectric well-wetting liquids such as HFE-7200 and Novec-649 were tested as working fluids. Bubble dynamics were visualized simultaneously. The results showed that the HTC was enhanced by up to 600% and the CHF was enhanced by up to 100%. A mechanistic heat transfer model was proposed for micro/nanostructured porous surfaces, including not only the heat fluxes from microlayer evaporation and transient conduction but also the heat flux from micro-convection due to liquid agitation and entrainment by growing and departing bubbles. The mechanistic heat transfer model can predict experimental pool boiling curves relatively well, especially for the isolated bubble regime where most bubbles are isolated and bubble coalescence is not intensive. Besides, a discussion regarding the CHF enhancement mechanisms of micro/nanostructured surfaces was also given, based on force analysis and possible contribution of wickability.