Ice repellency can be achieved on various hydrophilic and hydrophobic surfaces, although a surface that repels ice under all environmental scenarios remains elusive. Different strategies are reviewed with a focus on the recent development of superhydrophobic and lubricant-infused surfaces.

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Design of anti-icing surfaces: smooth, textured or slippery?

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy sources like wind energy is indigenous and can help in reducing the dependency on fossil fuels. Wind is the indirect form of solar energy and is always being replenished by the sun. Wind is caused by differential heating of the earth's surface by the sun. It has been estimated that roughly 10 million MW of energy are continuously available in the earth's wind. Wind energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. This paper reviews the wind resources assessment models, site selection models and aerodynamic models including wake effect. The different existing performance and reliability evaluation models, various problems related to wind turbine components (blade, gearbox, generator and transformer) and grid for wind energy system have been discussed. This paper also reviews different techniques and loads for design, control systems and economics of wind energy conversion system.

A review of wind energy technologies

Extensive terahertz laser vibration-rotation-tunneling spectra and mid-IR laser spectra have been compiled for several isotopomers of small (dimer through hexamer) water clusters These data, in conjunction with new theoretical advances, quantify the structures, force fields, dipole moments, and hydrogen bond rearrangement dynamics in these clusters This new information permits us to systematically untangle the intricacies associated with cooperative hydrogen bonding and promises to lead to a more complete molecular description of the liquid and solid phases of water, including an accurate universal force field

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Water clusters: Untangling the mysteries of the liquid, one molecule at a time

The generation of polymer brushes by surface-initiated controlled radical polymerization (SI-CRP) techniques has become a powerful approach to tailor the chemical and physical properties of interfaces and has given rise to great advances in surface and interface engineering. Polymer brushes are defined as thin polymer films in which the individual polymer chains are tethered by one chain end to a solid interface. Significant advances have been made over the past years in the field of polymer brushes. This includes novel developments in SI-CRP, as well as the emergence of novel applications such as catalysis, electronics, nanomaterial synthesis and biosensing. Additionally, polymer brushes prepared via SI-CRP have been utilized to modify the surface of novel substrates such as natural fibers, polymer nanofibers, mesoporous materials, graphene, viruses and protein nanoparticles. The last years have also seen exciting advances in the chemical and physical characterization of polymer brushes, as well as an ev...

Surface-Initiated Controlled Radical Polymerization: State-of-the-Art, Opportunities, and Challenges in Surface and Interface Engineering with Polymer Brushes

Anti-icing and de-icing techniques for wind turbines: Critical review

Ice accretion on structures is discussed with an emphasis on estimating structural design iceloads and solving operational icing problems. Basic principles of modelling of icing caused by freezing precipitation, cloud droplets and wet snow, as well as simulation of icicle growth, are presented. Theoretical models of atmospheric ice accretion are critically reviewed, particularly with respect to the simulation of the relevant physical processes. The reasons for the difficulties in simulating some icing phenomena accurately are analysed and proposals for further improvements in the models are made.

Models for the growth of rime, glaze, icicles and wet snow on structures

A time-dependent numerical model of ice accretion on wires, such as overhead conductors, is presented. Simulations of atmospheric icing are made with the model in order to examine the dependence of the accreted ice amount on atmospheric conditions. The results show that in wet growth (glaze formation) under constant atmospheric conditions, the growth rate increases with time until the process changes to dry growth. In dry growth (rime formation) the growth rate typically increases with time at the beginning of the icing process, but later decreases with time when the ice deposit has grown bigger. The effect of air temperature on the ice load turns out to be rather small for the first 24 hours of icing in typical dry growth conditions, but it is important for long-term icing. The ultimate ice load may either increase or decrease with decreasing air temperature, depending on the other atmospheric conditions and on the duration of icing. These results largely explain the difficulties encountered in ...

Modeling of Ice Accretion on Wires

In this paper concepts and models for theoretically estimating ice adhesion are presented. The effects of temperature, ice salinity and properties of the substrate material on ice adhesion are explained by these theoretical concepts. Major problems caused by ice adhesion are outlined and the applications of the theory in combating ice adhesion are discussed. Measurement methods of ice adhesion are described and results of ice adhesion for various material surfaces are reviewed and interpreted in view of the theory. Prospects for reducing ice adhesion to solve practical problems are discussed and the methods of anti-icing and de-icing are summarized.

Ice Adhesion —Theory, Measurements and Countermeasures

A numerical model that simulatesice accretion amounts and ice shapes on wind turbine blades is presented. The model simulates both rime icing due to fog droplets and glaze icing due to precipitation at all angles of droplet attack experienced by wind turbine blades. Icing can be simulated by the model also when the blade is heated. The sensitivity of ice accretions to meteorological variables is studied and predictions of the model are compared to data from icing wind tunnel experiments and from a field study of natural wind turbine icing. Applications of the model in the design of blade heating elementsfor anti-icing of wind turbines are described.

Modelling and Prevention of Ice Accretion on Wind Turbines

Friction has been widely used as a measure of slipperiness. However, controversies around friction measurements remain. The purposes of this paper are to summarize understanding about friction measurement related to slipperiness assessment of shoe and floor interface and to define test conditions based on biomechanical observations. In addition, friction mechanisms at shoe and floor interface on dry, liquid and solid contaminated, and on icy surfaces are discussed. It is concluded that static friction measurement, by the traditional use of a drag-type device, is only suitable for dry and clean surfaces, and dynamic and transition friction methods are needed to properly estimate the potential risk on contaminated surfaces. Furthermore, at least some of the conditions at the shoe/floor interface during actual slip accidents should be replicated as test conditions for friction measurements, such as sliding speed, contact pressure and normal force build-up rate.

Lasse Makkonen

Papers

Models for the growth of rime, glaze, icicles and wet snow on structures

Modeling of Ice Accretion on Wires

Ice Adhesion —Theory, Measurements and Countermeasures

Modelling and Prevention of Ice Accretion on Wind Turbines

The role of friction in the measurement of slipperiness, Part 1: Friction mechanisms and definition of test conditions