Daniel Attinger

Bio: Daniel Attinger is an academic researcher from Iowa State University. The author has contributed to research in topics: Wetting & Drop (liquid). The author has an hindex of 27, co-authored 116 publications receiving 3591 citations. Previous affiliations of Daniel Attinger include Stony Brook University & École Polytechnique Fédérale de Lausanne.

Do surfaces with mixed hydrophilic and hydrophobic areas enhance pool boiling

Abstract: We demonstrate that smooth and flat surfaces combining hydrophilic and hydrophobic patterns improve pool boiling performance. Compared to a hydrophilic surface with 7° wetting angle, the measured critical heat flux and heat transfer coefficients of the enhanced surfaces are, up to respectively, 65% and 100% higher. Different networks combining hydrophilic and hydrophobic regions are characterized. While all tested networks enhance the heat transfer coefficient, large enhancements of critical heat flux are typically found for hydrophilic networks featuring hydrophobic islands. Hydrophilic networks indeed are shown to prevent the formation of an insulating vapor layer. © 2010 American Institute of Physics. doi:10.1063/1.3485057 Boiling is an efficient process to transfer large amounts of heat at a prescribed temperature because of the large latent heat of vaporization. The term flow boiling describes the boiling of liquids forced to move along hot surfaces, while in pool boiling, the topic handled in this paper, the liquid is stagnant and in contact with a hot solid surface. 1 Besides the common experience of boiling water in an electric kettle, pool boiling has applications in metallurgy, high performance heat exchangers, and immersion cooling of electronics. Pool boiling performance is measured with two parameters, the heat transfer coefficient HTC and the critical heat flux CHF. The CHF is measured by increasing the surface temperature until a transition from high HTC to very low HTC occurs. This signifies the formation of a vapor film insulating the liquid from the heated surface, a phenomenon called dry out. Several characteristics determine the performance of a boiling surface. Nucleation sites in appropriate number and dimensions need to be provided such as cavities, rough areas, or hydrophobic islands. 2 As of today, the performance of boiling surfaces has been increased by using wicking structures to prevent dry out, 3 by increasing the surface area with fins or fluidized bed, 3‐6 and by enhancing the wettability of the surface. 5‐10 The latter strategy is justified by experiments of Wang and Dhir, 11 showing that the CHF was

Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram.

Abstract: The shape of deposits obtained from drying drops containing colloidal particles matters for technologies such as inkjet printing, microelectronics, and bioassay manufacturing. In this work, the formation of deposits during the drying of nanoliter drops containing colloidal particles is investigated experimentally with microscopy and profilometry, and theoretically with an in-house finite-element code. The system studied involves aqueous drops containing titania nanoparticles evaporating on a glass substrate. Deposit shapes from spotted drops at different pH values are measured using a laser profilometer. Our results show that the pH of the solution influences the dried deposit pattern, which can be ring-like or more uniform. The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and van der Waals forces modify the particle deposition process. Also, a phase diagram is proposed to describe how the shape of a colloidal deposit results from the compet...

Self-assembly of colloidal particles from evaporating droplets: role of DLVO interactions and proposition of a phase diagram

Abstract: The shape of deposits obtained from drying drops containing colloidal particles matters for technologies such as inkjet printing, microelectronics and bioassay manufacturing. In this work, the formation of deposits during the drying of nanoliter drops containing colloidal particles is investigated experimentally with microscopy and profilometry, and theoretically with an inhouse finite-element code. The system studied involves aqueous drops containing titania nanoparticles evaporating on a glass substrate. Deposit shapes from spotted drops at different pH values are measured using a laser profilometer. Our results show that the pH of the solution influences the dried deposit pattern, which can be ring-like or more uniform. The transition between these patterns is explained by considering how DLVO interactions such as the electrostatic and van der Waals forces modify the particle deposition process. Also a phase diagram is proposed to describe how the shape of a colloidal deposit results from the competition between three flow patterns: a radial flow driven by evaporation at the wetting line, a Marangoni recirculating flow driven by surface tension gradients, and the transport of particles towards the substrate driven by DLVO interactions. This phase diagram explains three types of deposits commonly observed experimentally, such as a peripheral ring, a small central bump, or a uniform layer. Simulations and experiments are found in very good agreement.

Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study

Abstract: An efficient way to precisely pattern particles on solid surfaces is to dispense and evaporate colloidal drops, as for bioassays The dried deposits often exhibit complex structures exemplified by the coffee ring pattern, where most particles have accumulated at the periphery of the deposit In this work, the formation of deposits during the drying of nanoliter colloidal drops on a flat substrate is investigated numerically and experimentally A finite-element numerical model is developed that solves the Navier–Stokes, heat and mass transport equations in a Lagrangian framework The diffusion of vapor in the atmosphere is solved numerically, providing an exact boundary condition for the evaporative flux at the droplet–air interface Laplace stresses and thermal Marangoni stresses are accounted for The particle concentration is tracked by solving a continuum advection–diffusion equation Wetting line motion and the interaction of the free surface of the drop with the growing deposit are modeled based on criteria on wetting angles Numerical results for evaporation times and flow field are in very good agreement with published experimental and theoretical results We also performed transient visualization experiments of water and isopropanol drops loaded with polystyrene microspheres evaporating on glass and polydimethylsiloxane substrates, respectively Measured evaporation times, deposit shapes and sizes and flow fields are in very good agreement with the numerical results Different flow patterns caused by the competition of Marangoni loops and radial flow are shown to determine the deposit shape to be either a ring-like pattern or a homogeneous bump

Introduction to the Finite Element Method

Abstract: This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Atomization and Sprays

Abstract: Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Drop Impact on a Solid Surface

Abstract: A drop hitting a solid surface can deposit, bounce, or splash. Splashing arises from the breakup of a fine liquid sheet that is ejected radially along the substrate. Bouncing and deposition depend crucially on the wetting properties of the substrate. In this review, we focus on recent experimental and theoretical studies, which aim at unraveling the underlying physics, characterized by the delicate interplay of not only liquid inertia, viscosity, and surface tension, but also the surrounding gas. The gas cushions the initial contact; it is entrapped in a central microbubble on the substrate; and it promotes the so-called corona splash, by lifting the lamella away from the solid. Particular attention is paid to the influence of surface roughness, natural or engineered to enhance repellency, relevant in many applications.