Reduce Ice Accumulation Research Articles

Prediction of Icing on Wind Turbines Based on SCADA Data via Temporal Convolutional Network

Icing on the blades of wind turbines during winter seasons causes a reduction in power and revenue losses. The prediction of icing before it occurs has the potential to enable mitigating actions to reduce ice accumulation. This paper presents a framework for the prediction of icing on wind turbines based on Supervisory Control and Data Acquisition (SCADA) data without requiring the installation of any additional icing sensors on the turbines. A Temporal Convolutional Network is considered as the model to predict icing from the SCADA data time series. All aspects of the icing prediction framework are described, including the necessary data preprocessing, the labeling of SCADA data for icing conditions, the selection of informative icing features or variables in SCADA data, and the design of a Temporal Convolutional Network as the prediction model. Two performance metrics to evaluate the prediction outcome are presented. Using SCADA data from an actual wind turbine, the model achieves an average prediction accuracy of 77.6% for future times of up to 48 h.

Experimental investigation of surface wettability induced runback water flow and heat transfer behavior

Aircraft icing is a serious threat to flight safety, therefore, active anti-icing systems are widely utilized in the aviation industry. In order to reduce the energy consumption of anti-icing systems, passive anti-icing methods combined with superhydrophobic surfaces are of interest. However, the passive protection of superhydrophobic surfaces is not as effective as expected when applied to aircraft anti-icing, which involves high speed and high humidity condition. The flow and heat transfer of runback water is an issue of fundamental importance for understanding of the aircraft anti-icing processes. In order to understand the mechanism of passive anti-icing on superhydrophobic surface, this study experimentally investigated the runback water flow and heat transfer behavior on airfoil with different surface wettabilities in a straight-flow spray wind tunnel. It was found that the runback water film was more likely to break up and form the rivulets when the wettability is more hydrophobic, with the breakup location closing to the leading edge, and the wetted surface area became smaller, therefore reducing ice accumulation. The water droplets on superhydrophobic surface shed away easily to make the surface have no runback water, which enables low energy consumption for the dry anti-icing method. The coupled analysis of the flow and heat transfer behavior indicated that surface wettability altered the runback water patterns, leading to changes in the convective heat transfer coefficient and heat transfer area, ultimately affecting the overall heat transfer process. In addition, the droplet erosion resistance of superhydrophobic surfaces prepared by two methods were tested and compared in this study.

Transparent hierarchical micro-nano structure PTFE-SiO2 nanocomposite thin film with superhydrophobic, self-cleaning and anti-icing properties

Superhydrophobic surfaces are often recommended for anti-icing applications due to their high ability to repel water and reduce ice accumulation and adhesion. In this study, PTFE-SiO2 thin films with different concentrations of silica (0, 1, 2 and 5 g/l) were deposited on the glass substrate by a sol-gel dip coating method. Water contact angle on the samples were measured by a water contact analyzer. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and field emission scanning electron microscopy (FE-SEM) techniques were used to investigate the chemical bonds formed on the film surface and film surface morphology. The thermal stability of the films was evaluated at different temperatures (from 200 to 500 °C). Also, the stability of the film under ultraviolet radiation was investigated under UV light irradiation. Also, the anti-icing properties of the films were investigated using both simulated static and dynamic methods. Self-cleaning properties of the film were evaluated using iron oxide powder. The water contact angle on the sample with PTFE film without silica nanoparticles is equal to 146°. The water contact angle on the film surface remains constant with increasing amount of the silica nanoparticles from 0 to 1 g/l. By increasing the amount of the silica nanoparticles to 2 g/l d, the contact angle increases to 155°. With increasing the silica nanoparticles amount to 5 g/l, water contact angle decreases. So, PTFE-SiO2 thin film with 2 g/l SiO2 was selected as an optimal thin film. The results of the thermal stability and UV irradiation tests showed that the films were stable up to 400 °C and 16 days of UV radiation, respectively. Indeed, the optimal thin film showed anti-icing and self-cleaning properties.

Hard Quasicrystalline Coatings Deposited by HVOF Thermal Spray to Reduce Ice Accretion in Aero-Structures Components

Weather hazards, in particular icing conditions, are an important contributing factor in aviation accidents and incidents worldwide. Many different anti-icing strategies are currently being explored to find suitable long-lasting solutions, such as surface engineering, which can contribute to reduce ice accumulation. Quasicrystals (QCs) are metallic materials, but with similar properties to those of ceramic materials, such as low thermal and electrical conductivities, and high hardness. In particular, QCs that have low surface energy are commercially used as coatings to replace polytetrafluoroethylene (PTFE), also known as Teflon, on frying pans, as they do not scratch easily. PTFE exhibits excellent anti-wetting and anti-icing properties and therefore QCs appear as good candidates to be employed as ice-phobic coatings. Al-based QCs have been applied by High Velocity Oxyfuel (HVOF) thermal spray on typically used aeronautic materials, such as Ti and Al alloys, as well as steels. The coatings have been characterized and evaluated, including the measurement of hardness, roughness, wetting properties, ice accretion behavior in an icing wind tunnel (IWT), and ice adhesion by a double lap shear test. The coatings were studied, both as-deposited, as well as after grinding, in order to study the effect of the surface roughness and morphology on the ice accretion and adhesion properties. The QC coating was compared with PTFE and two polyurethane (PU)-based commercial paints, one of them known to have anti-icing properties, and the results indicate an ice accretion reduction relative to these two materials, and ice adhesion lower than bare AA6061-T6, or the PU paint in the ground version of one of the two QCs. Since the QC coatings are hard (GPa Vickers hardness > 5), a durable behavior is expected.

Evaluation of atmospheric-pressure plasma parameters to achieve superhydrophobic and self-cleaning HTV silicone rubber surfaces via a single-step, eco-friendly approach

Effective self-cleaning and superhydrophobic surfaces having superb water repellency are among the most widespread alternatives for eliminating surface contamination, corrosion resistance, reducing ice accumulation, etc. to enhance the life-span of various engineered materials. In this study, we developed a simple methodology, based on an atmospheric-pressure air plasma system, as a simple, environmentally friendly and industry applicable approach for fabricating superhydrophobic surfaces. Our approach is significant as the use of an atmospheric-pressure plasma system combined with compressed air as an eco-friendly plasma gas offers great potential for the industrialization of superhydrophobic surfaces for mass production. The creation of micro- and nano-structured surface roughness on a low surface energy high temperature vulcanized (HTV) silicone rubber substrate resulted in a static water contact angle (WCA) > 160° and a contact angle hysteresis (CAH) < 3°. Scanning electron microscopy (SEM) revealed the presence of the plasma-induced coral-like micro- and nano-structures responsible for the superhydrophobicity of the surfaces. We assessed the influence of plasma operating parameters on the water repellency of silicone rubber via a design of experiment (DoE) method to determine the near-optimal operating parameters; once established, we could assess the characteristics of the surfaces. In addition to the superhydrophobic surfaces, we also fabricated another surface, named a slippery hydrophobic surface, under specific plasma operating conditions. Superhydrophobic surfaces prepared at these optimal plasma operating conditions showed favorable water repellency and self-cleaning properties under both wet and dry conditions.

Anti-icing Properties on Surfaces through a Functional Composite: Effect of Ionic Salts.

This study reports the potential of a unique functional composite for anti-icing applications. To date, various ionic salt formulations have been applied to prevent ice accumulation on surfaces. However, salt can be removed by external factors and large amounts must be used to attain anti-icing properties. Incorporating hydrophilic salts into hydrophobic mediums and controlled release of specific agents can provide effective solution to reduce ice accumulation on surfaces. Here, we developed functional polymer composites with salt pockets of altered ionic salts consisting of potassium formate (KCOOH), sodium chloride (NaCl), or magnesium chloride (MgCl2). We dissolved ionic salts in hydrophilic gel domains and dispersed in a hydrophobic styrene–butadiene–styrene polymer matrix. Na+ and Cl– ions delayed ice formation by 42.6 min at −2 °C compared to that for unmodified surfaces. Functional composites prepared with the NaCl ionic salt exhibited better anti-icing behavior at −2 °C because of their high concentration compared to that of the composites prepared with KCOOH and MgCl2 ionic salts. We also characterized the release of ionic salts from composite-modified hydrophobic medium separately up to 118 days. Furthermore, we monitored freezing of water on composite-incorporated or composite-coated hydrophobic surfaces in a camera-integrated cold chamber with a uniform temperature (−2 °C). The results demonstrated significant increases in the delay of freezing on composite-incorporated or composite-coated surfaces compared to that on controls. We observed altered effects of each ionic salt on the mechanical, morphological, and functional properties of the composite-incorporated or composite-coated hydrophobic surfaces. Our results suggested that the efficiency of a polymer composite to promote anti-icing behavior on a surface is directly related to the type and concentration of the particular ionic salt incorporation into the composite. This approach is promising and demonstrates significant potential of the ionic salt embedded within polymer composite-modified hydrophobic surfaces to attain delayed icing function.

Anti-icing properties of superhydrophobic ZnO/PDMS composite coating

We present the excellent anti-icing performance for a superhydrophobic coating surface based on ZnO/polydimethylsiloxane (ZnO/PDMS) composite. The superhydrophobic ZnO/PDMS coating surface was prepared by a facile solution mixing, drop coating, room-temperature curing and surface abrading procedure. The superhydrophobic ZnO/PDMS composite coating possesses a water contact angle of 159.5° and a water sliding angle of 8.3° at room temperature (5 °C). The anti-icing properties of the superhydrophobic coating were investigated by continuously dropping cold-water droplets (about 0 °C) onto the pre-cooled surface using a home-made apparatus. The sample was placed at different tilting angle (0° and 10°) and pre-cooled to various temperatures (−5, −10 and −15 °C) prior to measure. The pure Al surface was also studied for comparison. It was found that icing accretion on the surface could be reduced apparently because the water droplets merged together and slid away from the superhydrophobic surface at all of the measuring temperatures when the surface is horizontally placed. In addition, water droplet slid away completely from the superhydrophobic surface at −5 and −10 °C when the surface is tilted at 10°, which demonstrates its excellent anti-icing properties at these temperatures. When the temperature decreased to −15 °C, though ice accretion on the tilted superhydrophobic coating surface could not be avoided absolutely, the amount of ice formed on the surface is very small, which indicated that the coating surface with superhydrophobicity could significantly reduce ice accumulation on the surface at very low temperature (−15 °C). Importantly, the sample is also stable against repeated icing/deicing cycles. More meaningfully, once the superhydrophobic surface is damaged, it can be repaired easily and rapidly.

Reducing ice accumulation and adhesion by using a flexible micro-rod film

Ice accumulation and adhesion on solid surfaces can cause various problems in aircrafts, power lines, roads, ships, wind turbines, oil platforms, and telecommunication systems. A feasible strategy to combat icing is to cover the surface by using a flexible hydrophobic film. In this study, ice accumulation and adhesion were reduced by using a flexible PDMS micro-rod film. A simulative closed-loop ice wind tunnel and an ice adhesion measurement apparatus were custom built to investigate the relationship between PMDS micro-rod geometry and ice accumulation and adhesion. Our experiments show that decreasing the micro-rod space on the flexible PDMS film will increase the contact angle and decrease the contact angle hysteresis of the surface, thus reducing ice accumulation and adhesion. Wettability change is interpreted by a speculative and qualitative model of intruding depth variation. The reduction in ice accumulation is attributed to ice nucleation delay because of the increased energy barrier in the heterogeneous nucleation. The reduction in ice adhesion is explained by the reduced ice–solid contact area and mechanical interlock. Results indicate that the flexible micro-rod film has great potential in future anti-icing applications.

Ice accretion on superhydrophobic insulators under freezing condition

Surface icing of insulators causes serious problems such as tower collapse and power failure. Superhydrophobic (SHP) surfaces are attractive candidates to realize anti-icing as its water repelling property. This article studies the effects of SHP coatings applied on glass and insulators under freezing conditions in an artificial climate chamber. Compared with the bare glass and RTV coated glass, the SHP surface could effectively reduce the freezing area and accumulation of ice. The bare insulators were soon covered with a thick layer of ice, whereas only isolated ice points formed on the SHP insulators. The critical droplet diameter is about 40 times smaller for the as-prepared glass surface (121.4μm at α=90°) than for the bare glass slide (4.9mm at α=90°). Therefore, the tiny water droplets on the SHP surface can easily aggregate into large droplets, and roll off before freezing, thus reducing ice accumulation. Besides, the anti-icing behavior of SHP surfaces considerably depends on the tilting angle. With a higher inclination, the water droplets are easier to roll off the surface by gravity. The anti-icing property of as-prepared samples is mainly attributed to the superhydrophobicity of the coatings, which was obtained by a simple nanoparticle filling method. The added nanoparticles can coarsen the surface and contribute to the superhydrophobicity of the coatings. Moreover, the self-cleaning property and durability of the SHP surface were analyzed by corresponding methods.

The Collision Behavior of Droplets Splitted from a Droplet that Rebounded on Super-Hydrophobic Surface

Droplet rebounding on super-hydrophobic surfaces is critical to suppress pollution flashover (i.e. enhancement of pollution flashover-voltage) and to reduce ice accumulation on insulators. This paper presents a novel way to reduce water accumulation on surface via the elastic collision between droplets splitted from a droplet that has rebounded from super-hydrophobic surface. The water-mass that contacted with surface will be reduced resultantly. The influence of hydrophobicity of the surface on contact time and spreading time of water droplets are discussed. The collision behavior between the splitted droplets is indicated by the surface charge that was induced by the rebounding droplets on super-hydrophobic surface. Experimental results show that the super-hydrophobic surface endows water droplets with shorter contact time, spreading time than those values obtained on a bare glass. Specific Web and Reynolds numbers can lead to the elastic rebounding between water droplets, delaying the water contact with the super-hydrophobic surface. The contact electrification between the rebounded droplet and the super-hydrophobic surface renders the droplet charged, thus determines the collision behavior of the splitted droplets that born from the rebounded droplet.

Large-scale cold-start simulations for automotive fuel cells

In this study, the three-dimensional transient cold-start model is applied to a real-scale polymer electrolyte fuel cell (PEFC) geometry, and transient cold-start simulations are carried out from subzero to normal temperatures. In order to reduce the computational turnaround time involved for a large numerical mesh with millions of grid points, the cold-start code is parallelized for parallel computing. The simulation results clearly show the evolution of ice, water content, temperature, and current density contours at different cold-start stages, characterizing freezing, melting, hydration, and dehydration processes. In addition, the model predictions emphasize the beneficial influence of vapor-phase diffusion from the cathode catalyst layer (CL) to the gas-diffusion layer (GDL) during cold starts, which can contribute to reducing ice accumulation in the cathode CL. As the effect of vapor-phase diffusion is substantial, more ice is accumulated in the cathode GDL than in the cathode CL. The total amount of ice accumulated inside a cell is therefore not always proportional to the amount of ice in the cathode CL, depending on the vapor-phase diffusion strength.

Anti-icing Performance of a Superhydrophobic PDMS/Modified Nano-silica Hybrid Coating for Insulators

This paper presents a new type of poly(dimethylsiloxane)/modified nano-silica (PDMS/modified nanosilica) hybrid superhydrophobic coating to reduce ice accumulation on insulators. The PDMS/modified nano-silica hybrid coating and a room temperature vulcanized (RTV) silicone rubber coating were formed on glass insulators for ice accumulation experiments in the laboratory. The hydrophobicity of the two coatings was measured and compared. Average water contact angle on the PDMS/modified nano-silica hybrid coating reached 161°. The microstructures and functional groups on the surfaces of both coatings were investigated using field-emission scanning electron microscopy (FE–SEM) and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy, respectively. Analysis results show that both multiscale microstructure and low surface energy contributed to the superhydrophobicity of the PDMS/modified nano-silica hybrid coating. Finally, experiments on ice accumulation on insulators were carried out to investigate the anti-icing properties of the PDMS/modified nano-silica hybrid coating on insulators. Significantly smaller rate of ice accumulation was observed for the insulators treated with the PDMS/modified nano-silica hybrid coating, relative to that treated with the RTV silicone rubber coating.

On Hydrophobic and Icephobic Properties of TiO2-Doped Silicon Rubber Coatings

In the present work, flat and micro-/nano-rough water and ice-repellent coatings based on room-temperature vulcanized silicone rubber (RTV SR) incorporated with titania (TiO2) nanopowder as a dopant were prepared and investigated. Such water and ice-repellent coatings are potential candidates for protecting high-voltage equipment such as conductors and insulators. Supehydrophobic samples with contact angle (CA) >145o and contact angle hysteresis (CAH) ~5-10o were prepared by spin coating TiO2-loaded RTV SR suspensions on etched substrates. The SEM investigations of the sample surfaces revealed that the alumina filler (loaded into the as-supplied silicone rubber product) had some influence on the surface topographies of the prepared coatings. It was also found that the nanopowders used as dopants further increased the surface roughness (and correspondingly water repellency) of the coatings. While the TiO2-doped RTV SR demonstrates high CA and low CAH values, which is characteristic of the Cassie wetting regime, the wetting mode on the rough RTV SR coated sample with high CAH is expected to be a mixed Cassie-Wenzel regime. The anti-icing behaviour of the coating was studied under atmospheric icing conditions. Rough superhydrophobic coatings prepared with TiO2 nanoparticles of dielectric constant (~80) resulted in reducing the ice adhesion strength by at least ~7 times compared to a mirror-polished aluminium sample and by ~9 times compared to an as-received aluminium sample. At approximately -15 oC, water droplets were found to freeze on polished aluminium after approximately 5 s, while their freezing was delayed by as long as ~12-13 min on a superhydrophobic nanocomposite surface doped with TiO2 powder. This delay is explained by the insulating properties of the rough surface that entraps a significant amount of air into its structure. Therefore, the coatings prepared show promise for industrial applications on high-voltage equipment, including insulators, since they can reduce ice accumulation, while also reducing the risk of flashover on outdoor insulators.

Reducing Ice Accumulation on Insulators by Applying Semiconducting RTV Silicone Coating

Ice accumulation on high voltage insulators can cause accidents by flashover across the ice-covered insulators. The ice accumulation can be reduced by changing the insulator surface properties by application of a semiconducting RTV silicone coating. This method is based on the hydrophobicity and semiconductivity properties of the coating. The mechanism for reducing ice accretion is analyzed theoretically. Experimental results are presented to validate the effectiveness of the semiconducting RTV coating at reducing ice on insulator strings. The results show that the coating on the insulators delays ice formation and reduces the amount of ice.

PREDICTING AND REDUCING GLAZE ICE ACCRETION ON ELECTRIC POWER LINES WITH JOULE HEATING: THEORY AND EXPERIMENTS

An analytical model is developed for the prediction of glaze ice accretion with runback water for electric power lines including the Joule heating effect. In this model, the external air flow is coupled with the liquid film flow by slip (non-zero velocity) boundary conditions a the liquid-air interface. In this way, corrections to previous rime ice models are given in order to account for runback water and its effect on wet ice growth in freezing rain conditions with ambient temperatures slightly below 0[°C]. Also, the process of Joule heating in icing conditions is examined from a thermodynamic optimization viewpoint in a manner which permits efficient power transmission while dissipating heat in order to reduce ice accumulation. Good agreement is achieved between theoretical predictions of the glaze ice accretion and experimental results from the freezing rain simulator at the University of Manitoba.