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Plenary Lectures

Water in confinement: Nanopore Intrusion/Extrusion Cycles and Superhydrophobicity Recovery

 Prof. C.M. Casciola

 Department of Mechanical and Aerospace Engineering, University of Rome La Sapienza, Italy

 The lecture will be focused on two aspects related to metastability and wetting in confined environments. The reference theory for thus problems is Classical Nucleation Theory that will be shortly reviewed as an introduction to the subject.

 Concerning intrusion/extrusion, heterogeneous systems composed of hydrophobic nanoporous materials and water are known to be able of efficiently dissipating (dampers) or storing (“molecular springs”) energy. The advanced molecular dynamics techniques available to shed light on these effects, which are often difficult to investigate via experiments, owing to the small pore dimensions, will be introduced. The focus will be on the string method in collective variables used to simulate the microscopic mechanism of water intrusion and extrusion in the pores, which are thermally activated, rare events. Three important non classical effects are addressed: the nucleation barriers are strongly reduced compared with CNT, the intrusion pressure is increased due to nanoscale confinement, and the intrusion/extrusion hysteresis is practically suppressed for pores with diameters below 1.2 nm. The frequency and size dependence of hysteresis exposed by the present simulations explains several experimental results on nanoporous materials paving the way for a better design of nanoporous materials for energy applications.

 Depending on time, the second part will deal with superhydrophobicity of textured surfaces. In many cases, the gas layer at the surface may break down with the liquid completely wetting the surface. Experiments have shown that the recovery of the “suspended” superhydrophobic state from the wet one is difficult. Self-recovery is one of the targets of research in this field as it would allow to overcome the fragility of superhydrophobicity. Theoretical investigations of surfaces with different textures will be discussed showing that self-recovery is controlled by features of the bottom surface while wetting and slip by the cavity mouth. A modular design strategy, based on an extended version of CNT, is then illustrated to combine self-recovery and functional properties. The calculations are validated against atomistic simulations, with the optimal texture showing self-recovery on atomic timescales, τ ∼ 2 ns.

 Tinti, A., Giacomello A., Grosu, Y., CMC, “Intrusion extrusion of water in hydrophobic nanopores”, PNAS 2017.

 Lisi E., Amabili, M., Meloni, S., Giacomello, A., CMC, “Self-Recovery Superhydrophobic Surfaces: Modular Design” ACSnano, just accepted 2017.

 Microdevices Exploiting Thermally-Driven Rarefied Flows

 Prof. Alina Alexeenko

 School of Aeronautics and Astronautics, Purdue University, USA

 We review several emerging applications of rarefied flows for microscale sensing, actuation, power generation and thermal management. The performance of conventional fluidic devices such as pumps, combustors and heat engines decreases at the microscale due to greater viscous and heat transfer losses. Yet the close coupling between non-equilibrium gas, liquid and solid-state transport and electromagnetic phenomena enables unconventional flow actuation and control mechanisms. We consider three distinct examples of microelectromechanical systems exploiting non-equilibrium gas-phase transport based on i) very large thermal gradients; ii) increased capillary forces; iii) high electric fields – all of which are achieved by scaling down the characteristic size of the device. The corresponding systems are applied to gas sensing in low-pressure environment, micropropulsion of smallsat and microcombustion for mobile power generation.

FABRICATION METHODS OF MICROFLUIDIC HEAT EXCHANGERS

 Prof. Giampaolo Mistura

 Physics and Astronomy Department, Padua University, Italy

 This lecture will present an overview of various methods for deposition, patterning and characterization of thin films for silicon and polymer based micro and nano components fabrication processes.

 After a photolithography introduction, the principle, the aim and the limits, this presentation will provide several techniques of conventional process manufacturing: Physical Vapor Deposition, CVD, ion implantation, wet and dry etching. We will also mention alternative methods to structure polymers devices: 3D laser lithography, nanoimprint, electroplating, copolymer self-assembly, ink jet, dry films…

 In another part, we will see the advantages of these fabrication techniques of silicon and polymer components for various applications, biology, environment and health, energy.

Theory & Design Session

Lattice Boltzmann method for gas non-equilibrium flows - a conservative discrete velocity method

 Prof. Yonghao Zhang

 James Weir Fluids Laboratory, University of Strathclyde, Glasgow, UK

 In addition to traditional applications in aerospace and vacuum technology, the recently emerged micro/nano-flow technologies and shale gas extraction demand computationally efficient simulation tools that can capture non-equilibrium flow phenomena. I will introduce the conservative discrete velocity method, i.e. high-order lattice Boltzmann method (LBM), for modelling gas flows beyond the Navier-Stokes hydrodynamics, which can accurately recover steady and transient solutions of the kinetic equation in the slip-flow and early transition regimes with a moderate discrete velocity set. The focus will be on the link between LBM with the discrete velocity method (DVM). I will present our recent results on the computational accuracy and efficiency of the LBM and DVM simulations. Finally, I will discuss how to improve parallel computational efficiency using hybrid parallelisation approach.

Heat and mass flow at molecular scales

 Dr. ir. Silvia V. Gaastra-Nedea and Dr. ir. Arjan J.H. Frijns

 Energy Technology group, Dept. of Mechanical Engineering, Eindhoven University of Technology, the Netherlands

 Microfluidic systems become more and more important in engineering, since their low costs, low weights, high efficiency and flexibility enable to realize applications such as lab-on-chip, micro-cooling, environmental sensors, e.g. realized in systems-in-foil. For designing such microfluidic systems, a good physical understanding of the phenomena is needed and proper (numerical) models are required. In micro- and nanofluidic devices, length scales can be reached where a continuum approach starts to fail (e.g. due to rarefaction effects): the local properties cannot be averaged out anymore and individual particle properties have to be taken into account, boundary effects and surface and interface forces become dominant. Molecular dynamics simulations become then very useful tools helping to understand these effects and offering insight on the molecular properties of the micro/nano-fluidic systems.

 In this course we will start at the basis: the interactions that take place at a molecular level. We start with mono-atomic gases and show how to extend the models for more complex molecules and molecular structures. We will show that these small interactions sometimes can have major influences on macroscopic level, e.g. slip velocities, temperature jumps in the interfaces and heat fluxes.

Experiments & Microfabrication Session

 Microfluidic Temperature Measurement Techniques

Dr. David Newport

 School of Engineering, Bernal Institute, Faculty of Science & Engineering, University of Limerick, Ireland

 This talk will present an overview of the state-of-the-art in microfluidic temperature measurement techniques.  Temperature at a local level in a micro-scale fluidic system remains a challenging topic for liquids, and even more so for gases.  This presentation will provide insight into the key issues facing local fluid measurement at the micro-scale and outline the latest developments in this research field.  Topics covered will include micro-scale probes and scanning approaches, non-invasive techniques such as liquid crystal, fluorescent, infra-red and raman techniques.

Mass flow measurement

 Dr. Pierre Perrier

 Institut Universitaire des Systèmes Thermiques Industriels, Aix-Marseille University, France

 I will present the mass flow measurement by pressure variation in a tank or two tanks. I will show that this technique can be applied in a very general way to several types of experiment in microfluidics or in porous media. I will try to show you the use of instastionnary systems (thermal creep for example).

 I will end with a presentation of the use of this technique for particular cases which allows the extraction of the accomodation coefficient and the permitivity of a porous system.

 Bibliography

 Pong, K. and Ho, C., Liu, J. and Tai, Y., Non-linear pressure distribution in uniform microchannels, Application of microfabrication to fluid mechanics 1994 ASME FED Volume 97 Pages 51-56

 B T Porodnov, P E Suetin, S F Borisov, and V D Akinshin., Experimental investigation of rarefied gas flow in different channels, J. Fluid Mech., 64(3) :417–437, 1974.

 S K Loyalka., Kinetic theory of thermal transpiration and mechanocaloric effects, J. Chem. Phys., II :4054, 1975.

 E B Arkilic, K S Breuer, and M A Schmidt, Mass flow and tangential momentum accomodation in silicon micromachined channels.
Journal of fluid mechanics, 437 :29–43, 2001.

 J Pitakarnnop, Analyse expérimentale et simulation numérique des écoulements raréfiés de gaz simples et de mélanges gazeux dans des microcanaux. Technical report, Toulouse University, PHD Thesis, 2009.


 T Ewart, P Perrier, I A Graur, and J G Méolans., Mass flow rate measurements in gas micro flows, Experiments in Fluids, 41(3) :487–498, 2006.

 T Ewart, P Perrier, I A Graur, and J G Méolans, Mass flow rate measurements in microchannel, from hydrodynamic to near free molecular regimes.
Journal of fluid mechanics, 584 :337–356, 2007.

 B T Porodnov, P E Suetin, S F Borisov, and V D Akinshin, Experimental investigation of rarefied gas flow in different channels, J. Fluid Mech., 64(3) :417–437, 1974.

Industrial & Application aspects Session

CFD based design methodologies for compact heat exchangers

 Dr. Michel Delanaye

 MITIS SA, Liège, Belgium

 The lecture will describe the methodologies developed by MITIS for design of its heat exchangers. Due to the complexity of the geometries, a hierarchical method was devised by combining detailed CFD modelling for intricate channels and reduced order modelling. The method allows the understanding and prediction of the distribution of the flow through collectors and core to assess the global performance of the system.

Developing the Next-Generation of Multiphase Thermal Systems

 Dr. Ryan Enright

 Nokia Bell Labs, Dublin, Ireland

 In the last two decades, substantial efforts have been focused on understanding how surface micro- and nanostructuring can modify the behaviour of wetting liquids to produce interesting and, potentially, very useful effects. One well-known example of surface engineering is the “Lotus-effect”, whereby the combination of intrinsic hydrophobicity and surface structuring results in superhydrophobic droplet behaviour characterized by water droplet contact angles approaching 180° and negligible contact angle hysteresis. In the thermal engineering community, surface engineering has emerged as a new paradigm in the push towards higher performance in multi-phase thermofluid systems. However, while a good deal of work has been done to show how fundamental understanding of these types of wetting interactions can be exploited for thermal applications, for researchers applying surface engineering techniques to unlock further performance enhancements and new functionalities in phase-change heat and mass transfer, the availability of multiscale, multiphase modeling techniques remains a key challenge.

 In this talk, I will present an overview of two thermal systems we have been investigating where wetting interactions dominate and that have the potential to make great gains in thermal management systems for 5G wireless, power electronics, 3D optoelectronics and space-based systems applications. Special attention will be given to the challenges associated with modeling these systems which are characterised by multiple phases and length scales. In the first example, I will discuss our recent work focused on understanding the role of surface forces in controlling the heat and mass transfer performance of jumping droplet water condensation. In the second example, I will describe a high-performance nanoporous evaporator design that operates in a new thermal regime where the solid and liquid conduction resistances are similar or smaller in comparison to that of the interphase region between the liquid and vapour.

Vacuum Pressure Sensors in the Semiconductor Industry

Dr. Martin Wüest

INFICON AG, Balzers, Liechtenstein

 Semiconductor industry products such as computers, cell phones, or memory devices are ubiquitous in today’ life. The manufacturing of semiconductors chips is an extremely complex and demanding process that involves more than 250 lithographic and chemical process steps over the course of about 2 months. In order to achieve low product cost the processes have to achieve high yields. This implies very high reproducibility of the processes and this in turn requires accurate process control. Pressure sensors are an important part in vacuum process control. However, the use of aggressive chemicals such as halogen containing substances for semiconductor etch process do not just etch the wafer, but also affect the  sensor.  It is highly demanding to design and build vacuum pressure sensors that survive semiconductor processes for a long time before they need to be replaced. After a brief introduction into the manufacturing steps used in semiconductor industry, I will give a few examples how we have improved sensor life time in harsh process environments.

Complementary Skills Session

Talks and Presentations – 10 simple steps how to ruin them efficiently

Prof. Dr.-Ing. habil. Juergen J. Brandner

 Institute of Microstructure Technology, Karlsruhe Institute of Technology, Germany

 Presenting scientific or engineering results – or even yourself at a job interview – is an essential part of academic life.

 However, most people in academia do not learn how to present in another way than “learning-by-doing”, because there’s no opportunity to learn how to present.

 Although many things can be done properly with the method “learning-by-doing”, others are just nonsense or misleading.

 The lecture will present the 10 most favorite and efficient possibilities to ruin a talk completely and, therefore, make the content not interesting at all to the audience.

Work-Life-Balance…and 10 simple, efficient steps to destroy it

 Prof. Dr.-Ing. habil. Juergen J. Brandner

 Institute of Microstructure Technology, Karlsruhe Institute of Technology, Germany

 When heading for a PhD or even going into academic career, it is quite clear that the work will dominate life to a certain extent.

 Interesting things to learn, curiosity of the researcher, nice places to go for conferences are the topics to deal with, just to name but a few.

 However, there can be a balance between work and regular life, which should be taken care of.

 The lecture will present the 10 most prominent steps to run down work-life-balance efficiently and finally destroy it.