In this thesis, development process of de-icing and anti-icing solutions and their flow instability characteristics are presented. In the beginning, the chemical additives in the solutions and their effects on the most critical physical properties of the solutions were investigated. Firstly, chemical additives were added to glycol and water mixtures at different weight ratios one by one in order to see their individual effects. Then, the changes in physical properties were observed when the chemicals were added to water-glycol mixture together. After that, study was focused on effect of polymer which makes the solution pseudoplastic. Further investigations on viscosity behavior of the solution at different pH values, glycol and water mixtures and surfactant weight ratios, which is used for surface tension reduction, were performed. For the investigation of flow instability characteristics of the solutions&rsquo / flows, linear stability analysis for two-layer flows is a basic tool. Firstly, the effects of main parameters on the stability of two-layer flows were observed with a parametric study. Then, the commercially available and developed de-icing and anti-icing solutions were compared according to the characteristics of unstable waves. According to the results, unstable waves on developed de-icing fluids are observed at a lower critical wind speed compared to the commercially available de-icing solution. Moreover, it flows off the wing faster due to a higher value of critical wave speed. Developed anti-icing solution has similar wave characteristics compared to commercially available anti-icing solution, except critical wave speed, which is significantly lower. However, this problem can be overcome by decreasing the viscosity of developed anti-icing solution at very low shear rates.

This thesis is done within the master program in energy systems engineering at Uppsala University and in cooperation with OX2. The aim was to compare the operation and performance of three different de- and anti-icing systems for wind turbines during the winter 2014/2015. The systems evaluated were de-icing with heating resistances, de-icing with warm air and anti-icing with heating resistances. Inconsistency in the operation of the wind turbines and the systems as well as lack of information made it hard to compare the efficiencies of the systems. The systems showed tendencies to improve the production. Especially examples during single ice events where the systems increased the power output were found, but the examples also showed possible improvements regarding the size of the systems and the duration of the de-or anti-icing cycles. Based on the approximated gain in production, during the studied time period, none of the systems could be determined to be profitable. The gain in production does however not have to be especially large for the systems to become profitable, and the results could be very different in a year with more ice, higher electricity prices or a more consistent operation of the systems. Important characteristics of the systems were found to be the duration of a cycle, the energy required for the operation of the system and the trigger-point for activation of the system. Additional benefits like for instance decreased loads, risk for standstill and ice throws could also be provided by the system.

No description available.

In this thesis, commercially available anti-icing fluids were tested. A methodology of assessment was designed for the effect of anti-icing fluids on the rapidity of ice growth and its development over time. These tests were conducted on a device constructed for the purpose of the thesis. The solutions were tested for their effect on the ice adhesion to a contact wire. The effect of the solutions on the tribological behaviour of the collector strip and contact wire was described. The experiments were supplemented by mensuration of the size of the contact angle of the solutions on the copper surface. However, these fluids anti-icing effect is relatively short-term. On the contrary, the thesis shows that even a small amount of anti-icing solution on the surface of the contact wire can help to significantly lower the ice adhesion.

Non-wetting surfaces offer enhanced capabilities over bare metal substrates for condensation with or without phase change. This trait can be utilized to broaden strategies in combating water scarcity in water stressed areas. Slippery lubricant infused surfaces have the ability to shed water droplets with lower nucleation times, taking advantage of more of the limited amount of time available to collect dew and fog than traditional surfaces. However, existing studies focus on short durations with scant information available on the longer-term performance or durability of the materials in application environments. To address this knowledge gap, dew harvesting studies were conducted over a 96 hour period on a lubricant infused surface vis-à-vis regular surface of the same material. Three phases of performance are identified and discussed with regard to the water harvesting potential. The second part of the thesis addresses water condensation under conditions where freezing is a potential issue. Non-wetting surfaces have been shown to be a promising method of limiting the formation of ice from sessile droplets. This study explores the effect of surface roughness on the freeze time of sessile water droplets. Superhydrophobic and hydrophobic, lubricant infused, copper surfaces were created via electrodeposition and chemical etching in conjunction with chemical treatments to achieve non-wetting surfaces of varying surface textures. Freezing characteristics on the surfaces are studied experimentally and, for the first time, computationally, wherein the surface is described using a fractal surface topography. The effect of surface engineering on the freezing dynamics and comparison between the experimental and the computational studies are elucidated. / Master of Science / The use of durable, water repelling surfaces that are also thermally conductive provide an opportunity to help alleviate strain from a growing world crisis, water scarcity. Lubricant infused surfaces shed water from their surface by providing a slippery layer for the droplets to slide on, as opposed to bare metal which water tends to cling to. This behavior makes lubricant infused surfaces attractive as a water harvesting method. However, these surfaces degrade over time and must be maintained to perform at their maximum capability, collecting water for 40 minutes more than a bare surface. This thesis focuses on the performance of these surfaces over a 96-hour operating period to characterize the effect lubricant drainage has on the water collection behavior. Freezing water droplets, commonly referred to as icing, poses concerns for safety and operational ability in industries like renewable energy generation, where icing limits efficiency. Non-wetting surfaces have a unique ability to inherently slow down the phase change of a water droplet to ice due to the lower contact area of droplets resting on the surface. This thesis examines superhydrophobic and lubricant infused surfaces of varying degrees of roughness to explore the effect that the contact angle and different surface structures have on the freezing rate of water on the surface. The experimental results are compared to numerical simulations, which is useful in designing systems that would implement this passive icing mitigation technique.

No description available.

As clean energy demand is on the rise and the wind energy sector in growth, locations with the highest wind potential are becoming of higher interest for wind farm projects, but they are located in colder regions. In cold climates, ice accumulation on wind turbine blades is a serious issue, both in terms of safety and performance. To prevent this, anti-icing technologies, such as Vestas Wind Systems A/S’s, electro-thermal elements are added to wind turbine blades’ construction. This thesis project consists of developing a method to investigate the heat transfer inside and out of wind turbine blades to assess the performance of the anti-icing system and most importantly, verify if it could lead to thermal damage of the blade’s adhesive. In an integrated MATLAB code, the heating requirement is calculated and the 2D conduction modelled based on the wind conditions. The output is a temperature map of the internal structure along with the points with the highest temperature for all adhesive locations, which shows that the selected heating power provided by the heating elements compromises the integrity of the adhesive and doesn’t perform to allow the surface temperature to reach the necessary threshold the prevent icing.

Aircraft are not allowed to take off prior to cleaning of snow and ice deposits that form on their surfaces under winter conditions to refrain from compromising flight safety. Water based solutions containing mainly ethylene or propylene glycol, or both, are employed either to remove the snow/ice layers or to provide protection against deposition of these layers. The first group of solutions, i.e. de-icing fluids, are Newtonian and have generally low viscosity so that right after their application they fall off the aircraft surfaces, providing little or no further protection against precipitation. Therefore, various anti-icing solutions have then been developed to provide the prolonged protection due to their non-Newtonian and high viscosity characteristics. Although the appropriate ranges of viscosity and surface tension have been determined in a number of studies, actual compositions of these solutions are proprietary. The main objective of this study is to determine the basic interactions between the chemical species in de/anti-icing fluids and their effects on the physical properties of the solutions, especially viscosity, surface tension,freezing point and corrosive effect which enable the design of the de/anti icing fluid composition. A number of polymers and surfactants were dissolved in water-glycol solutions and used in different compositions to get the desired viscosity and surface properties. The dependence of viscosity on polymer concentration, pH of the solutions, glycol content, surfactant concentration, temperature and shear rate were investigated and reported in detail. Among various chemicals, slightly crosslinked and hydrophobically modified polyacrylic acid was utilized as a thickener, sodium oleate and tributyl amine were used as surface agents in the de/anti-icing solutions whose physical properties satisfied the desired requirements. In addition to the studies about de/anti icing solutions, synthesis of a new polymer namely poly (DADMAC-co-vinyl pyyrolidone) was made and its characterization and performance tests were performed. High swelling ratios (up to 360) were attained with 0.5 % crosslinker in 2-3 minutes. Moreover, swellings of the gels were demonstrated to be independent of pH. It was also thought that such a copolymer having anti-bacterial effect induced by DADMAC (Diallyldimethyl ammonium chloride) segments and biocompatability of NVP (N-vinyl pyyrolidone) component would be of interest in biorelated areas.

Ice accretion on various surfaces can cause destructive effect of our lives, from cars, aircrafts, to infrastructure, power line, cooling and transportation systems. There are plenty of methods to overcome the icing problems including electrical, thermal and mechanical process to remove already accumulated ice on the surfaces and to reduce the risk of further operation. But all these process required substantial amount of energy and high cost of operation. To save the global energy and to improvement the safety issue in many infrastructure and transportation systems we have to introduce some passive anti-icing coating known as ice-phobic coating to reduce the ice-formation and ice adhesion onto the surface. Ice-phobic coatings mostly devoted to utilizing lotus-leaf-inspired superhydrophobic coatings. These surfaces show promising behavior due to the low contact area between the impacting water droplets and the surface. In this present study we investigate systematically the influence of chemical composition and functionality as well as structure of surfaces on wetting properties and later on icing behavior of surfaces. Robust anti-icing coating has been prepared by using modified silica particles as a particles film. Polymer brushes were synthesized on flat, particle surfaces by using Surface initiated ATRP. We have also investigated the effect of anti-icing behavior on the surfaces by varying surface chemistry and textures by using different sizes of particles. This approach is based on the reducing ice accumulation on the surfaces by reducing contact angle hysteresis. This is achieved by introducing nano to micro structured rough surfaces with varying surface chemistry on different substrates. Freezing and melting dynamics of water has been investigated on different surfaces by water vapour condensation in a high humidity (80%) condition ranging from super hydrophilic to super hydrophobic surfaces below the freezing point of water. Kinetics of frost formation and ice adhesion strength measurements were also performed for all samples. All these experiments were carried out in a custom humidity and temperature controlled chamber. We prepared a superhydrophobic surface by using Poly dimethyl siloxane (PDMS) modified fumed silica which display very low ice-adhesion strength almost 10 times lower than the unmodified surface. Also it has self-cleaning behavior after melting of ice since whole ice layer was folded out from the surface to remove the ice during melting. Systematic investigation of the effect of three parameters as surface energy, surface textures (structure, geometry and roughness) and mechanical properties of polymers (soft and stiff) on icing behavior has also been reported.

<p>Ice forming on wind turbine blades can cause loading imbalance and reduce power production of the turbine. Heating systems that prevent or remove ice on wind turbine blades are one of the more promising solutions to mitigate ice accretion. Methods to apply heat include direct application through electro-thermal resistance heaters mounted on the external surface of the blade or by indirect heating by forcing hot air through a channel along the leading edge of the blade. Heating systems for aircraft blades have become standardized and in some cases compulsory on aircraft to preserve human life; however, the technology is not directly transferable to the blades on wind turbines. The relative power of the anti-icing or de-icing system is critical to providing a cost benefit of having the system.</p> <p>This thesis investigates the heat transfer involved for electro-thermal and hot air heating strategies. An appropriate range of operating conditions and blade constructions are considered in order to characterize the effectiveness of both systems. A numerical model is developed to solve the one dimensional, differential heat transfer equations. The heater power required to prevent ice accumulation (anti-icing) on wind turbine blades is determined for electro-thermal heating. Anti-icing with hot air is shown to be unrealistic for a practical range of operating conditions.</p> <p>The low conductivity of the blade core creates a bottleneck for the de-icing system. It is shown that alternative core materials (Nomex/aluminum honeycomb) can reduce this effect. Electro-thermal and hot air de-icing each have their advantages and cannot be equally compared. In this thesis the suitability of each system has been analysed for a range of operating conditions and wind turbine constructions; the designer can then implement the most suitable strategy for their individual application.</p> / Master of Applied Science (MASc)