Water Droplet Temperature Research Articles

Enhancing Icephobic Coatings: Exploring the Potential of Dopamine-Modified Epoxy Resin Inspired by Mussel Catechol Groups.

A nature-inspired approach was employed through the development of dopamine-modified epoxy coating for anti-icing applications. The strong affinity of dopamine's catechol groups for hydrogen bonding with water molecules at the ice/coating interface was utilized to induce an aqueous quasi-liquid layer (QLL) on the surface of the icephobic coatings, thereby reducing their ice adhesion strength. Epoxy resin modification was studied by attenuated total reflectance infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (NMR). The surface and mechanical properties of the prepared coatings were studied by different characterization techniques. Low-temperature ATR-FTIR was employed to study the presence of QLL on the coating's surface. Moreover, the freezing delay time and temperature of water droplets on the coatings were evaluated along with push-off and centrifuge ice adhesion strength to evaluate their icephobic properties. The surface of dopamine-modified epoxy coating presented enhanced hydrophilicity and QLL formation, addressed as the main reason for its remarkable icephobicity. The results demonstrated the potential of dopamine-modified epoxy resin as an effective binder for icephobic coatings, offering notable ice nucleation delay time (1316 s) and temperature (-19.7 °C), reduced ice adhesion strength (less than 40 kPa), and an ice adhesion reduction factor of 7.2 compared to the unmodified coating.

A numerical simulation of the distribution and the variation law of the liquid water content in icing wind tunnel

To solve the aircraft icing problem, simulation of the high-altitude clouds as the icing environment becomes necessary. Clouds always contain many micro-scale subcooled droplets. The accurate control of the icing environment simulation is challenging. To investigate the distribution and the variation law of the liquid water content in the icing wind tunnel, a simulation model of the icing wind tunnel was developed with the reprogramming software FLUENT. The model was validated with the parameters of ice shape and maximum ice thickness on the model of SC0710 airfoil with a constant cross-section at zero angle of attack. The errors of the maximum ice thickness, the maximum and mean deviation are 5.06%, 0.22 mm and 0.13 mm, respectively. Then, the influences of the parameters of water droplets at the nozzle exit and airflow were simulated and analyzed. The results indicate that increasing the initial velocity or temperature of water droplets at nozzle exit will promote the uniformity of the liquid water content (LWC) distribution and reduce the average LWC in the test section. The average LWC of the test section is significantly reduced due to a large amount of water droplets hitting the wall under the action of inertia once the medium volume diameter (MVD) exceeds 40 μm.

Icing behavior of supercooled droplets on superhydrophobic polymercoatings between lotus effect and petal effect

Abstract This paper investigated anti-icing behavior and wettability of droplets on superhydrophobic polymercoatings between lotus effect and petal effect, which were prepared on surfaces of 2021 aluminum alloy with 1H, 1H, 2H, 2H-heptafluorodecyl (FAS-17). The prepared surfaces displayed excellent hydrophobicity with contact angles of 154.9° ± 1.5°and 139.8° ± 1.3°, while rolling angles are 4° ± 1.0° (lotus effect) and 30° ± 1.5° (petal effect). Thus, the present study focused on the different characterizations and the anti-icing potential of the superhydrophobic polymersurfaces were analyzed based on three parameters including the icing delay time, the crystallization temperature of water droplets, and contact time of impinging droplets on the cold superhydrophobic polymer coatings (−15 °C). Furthermore, the anti-icing of superhydrophobic coatings between lotus effect and petal effect with freezing time and crystallization temperature experimental phenomena were consistent with the thermodynamic analysis. It is also proved that the droplets have different bounce behavior on different polymercoating surfaces by droplet impact experiment. The study offers a comprehensive perspective on polymercoatings of different wetttablility for anti-icing behavior applications.

Impingement and freezing of a supercooled large droplet on an ice surface

In the present study, we carried out an experimental investigation of the impinging and freezing processes of a supercooled large water droplet on an ice surface. One high speed camera was used to measure the dynamic motions of the water droplet while two charge coupled device (CCD) cameras were adopted to obtain the images of the freezing process and the freezing morphologies, respectively. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were carefully evaluated. The results showed that the subcooling degree of the water droplet had an apparent influence not only on the spreading process but on the freezing morphology as well. When the subcooling temperature of the water droplet was high (e.g., Tw = –3.0 °C), a triangle cross-section profile formed. However, once the subcooling temperature of the water droplet was relatively low (e.g., Tw = –9.0 °C), the final ice morphology consisted of two parts: one part was a cone-like bead in the center while the other part was an ice ring at the periphery. Moreover, at the same water droplet temperature, raising the ice surface temperature led to an increase in the maximum spreading factor.

On the dynamics of contact line freezing of water droplets on superhydrophobic carbon soot coatings

Despite the opportunity to manipulate the water freezing via superhydrophobic materials, their commercial use for passive icing protection is still questioned, since the combined effect of surface morphology, air cushion arrangement, roughness, chemistry and film thickness on the icephobic properties of a given non-wettable solid remains unexplored. This article addresses the existing research gaps by studying the ice nucleation dynamics at the contact line of various superhydrophobic soot-based surfaces, potentially applicable in cryobiology for enhancing the existing cryopreservation technologies. We examine the freezing time and freezing temperature of water droplets settled on three groups of soot coatings with divergent morphochemical features, adjusted by modifying the samples with alcohol, fluorocarbon and/or silver hydrogen fluoride. Our results demonstrate the appearance of a new “contour” freezing mode, where the droplet shell crystallizes simultaneously with the contact interface, whilst the soot's chemical bonds along with some of its physical characteristics govern the ice formation.

The Inhibition of Icing and Frosting on Glass Surfaces by the Coating of Polyethylene Glycol and Polypeptide Mimicking Antifreeze Protein.

The development of anti-icing, anti-frosting transparent plates is important for many reasons, such as poor visibility through the ice-covered windshields of vehicles. We have fabricated new glass surfaces coated with polypeptides which mimic a part of winter flounder antifreeze protein. We adopted glutaraldehyde and polyethylene glycol as linkers between these polypeptides and silane coupling agents applied to the glass surfaces. We have measured the contact angle, the temperature of water droplets on the cooling surfaces, and the frost weight. In addition, we have conducted surface roughness observation and surface elemental analysis. It was found that peaks in the height profile, obtained with the atomic force microscope for the polypeptide-coated surface with polyethylene glycol, were much higher than those for the surface without the polypeptide. This shows the adhesion of many polypeptide aggregates to the polyethylene glycol locally. The average supercooling temperature of the droplet for the polypeptide-coated surface with the polyethylene glycol was lower than for the polypeptide-coated surface with glutaraldehyde and the polyethylene-glycol-coated surface without the polypeptide. In addition, the average weight of frost cover on the specimen was lowest for the polypeptide-coated surface with the polyethylene glycol. These results argue for the effects of combined polyethylene glycol and polypeptide aggregates on the locations of ice nuclei and condensation droplets. Thus, this polypeptide-coating with the polyethylene glycol is a potential contender to improve the anti-icing and anti-frosting of glasses.

The influence of surface structuring on evaporation of sessile drops of water

The paper presents the results of experimental studies of the evaporation of sessile water droplets on smooth and structured surfaces of Teflon fluoropolymer. Using high-speed microphotographs, data were obtained on the change in the contact angle and the diameter of the contact spot of water droplets during evaporation on smooth and structured surfaces. Using the method of infrared thermography, the dynamics of changes in the average temperature of water droplets during evaporation was investigated. The results show that the structure of the surface has a decisive influence on the change in the geometric parameters and temperature of the sessile water droplets.

Droplet on oil impregnated surface: Temperature and velocity fields

The water droplet dynamics on silicon oil impregnated polydimethylsiloxane (PDMS) replicated and inclined surface is considered and the droplet sliding velocity incorporating force and energy balance is formulated. Since silicon oil film is kept at 308 K and water droplet temperature is initially at 300 K, the droplet heat transfer due to temperature disturbance is examined during droplet sliding. Velocity and temperature fields are computed using the experimental conditions. The droplet sliding velocity resulted from the analytical formulation is compared with the high-speed camera data. In addition, the predictions of the droplet surface temperature are validated with the thermal camera data. The findings reveal that the droplet sliding velocity obtained from the analytical formulation is in agreement with the high-speed camera data. The predictions of droplet temperature also agree well with the thermal camera data. Droplet heat transfer results in two contour rotating circulating structures in the droplet, which contribute to convection heat transfer in the droplet fluid. Silicon oil cloaking on water droplet surface alters the heating rates and flow structure in the droplet. As the distance along the silicon oil surface increases, a unique circulation structure is developed inside the droplet, which enhances the Nusselt and the Bond numbers. Formation of a single circulation is attributed to increased silicon oil ridge height in the frontal region of the droplet.

Experimental investigation of the impact and freezing processes of a hot water droplet on an ice surface

Water droplet freezing on an ice surface is a common phenomenon and poses hazards to a lot of applications, including wind turbines, aircraft, and power transmission lines. Since the water droplet temperature is critical, many studies have been carried out to understand the influence of the water droplet temperature on both the impact and freezing processes of droplets on different surfaces. However, the past research studies mainly focused on supercooled water droplets, not on hot water droplets. For applications such as hot-water ice-drilling, the understanding of freezing of hot water droplets on an ice surface is necessary. In the present study, we report the detailed dynamic motions of a hot water droplet impacting on an ice surface. The impact and freezing processes of the hot water droplet on the ice surface are recorded by two cameras. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were experimentally investigated. The results showed that, at the same ice surface temperature, the increase of the water droplet temperature resulted in the increase of the maximum spreading factor, the reduction of the height of the ice bead, and the slight increase of the freezing time. In addition, during the droplet spreading process, the experimental results of the normalized contact diameter fitted well with the exponential model and the water droplet temperature was found to have an apparent influence on the lamella thickness.

The effects of initial water-droplet temperature on performance of heat exchange device attached to a diffuser

Abstracts Firstly, the calculation models of motion, heat and mass transfer between water-droplet and exhaust airflow in a device are established under the conditions of summer, winter, respectively, and are solved by the fourth-order Runge–Kutta method, secondly. Furthermore, the data of numerical calculations are analyzed to discuss that the initial droplet temperature affects upon the final water temperature, airflow temperature and specific humidity, device efficiency. The results are shown that: (1) when the absolute value of difference temperature between water-airflow in summer is equal to that in winter, the heat transfer in summer is more effective; for examples, when this difference is 18 °C, the efficiency in summer is 80.42%, corresponding to 54.93% in winter; (2) in winter, the heat transfer is mainly concentrated in the bottom of this device, on the contrary, it is at the top in summer; (3) with the initial droplet temperature increasing, the proportion of latent heat transfer increases, and the device performance is improved.

Investigation of droplet behaviors for spray cooling using level set method

The droplet dynamics and heat removal is one of the popular research streams in spray cooling applications. The increase in the water droplet temperature as a result of its impact on the hot solid surface would determine the efficiency of the heat removal that is crucial in some sensitive applications such as spray cooling in depressurization systems in commercial nuclear power plants. Computer modelling of the underlying mechanism of the liquid droplet interaction with the hot solid surface would be necessary. The accuracy and the reliability of these models are important in simulating the multiphysics phenomena such as droplet dynamics and heat removal. In present work, the level set method coupled with heat transfer was used to simulate the water droplet impact on an isothermal solid surface. The changes in the temperature of water droplet were found to be highly dependent upon its size and the impingement speed. Topological variations in the droplet shape as a result of its impact onto the solid wall would cause abrupt changes in the temperature of the water droplet. In addition, the droplet detachment, coalescence and flattening were found to strongly influence the temperature of the droplet which would evidently affect the heat removal efficiency in the spray cooling systems employed in the commercial nuclear power plants. Furthermore, we demonstrated that the level set method had the ability to produce more accurate estimations of the water droplet dynamics when compared to the Volume-Of-Fluid (VOF) method in simulating the droplet behavior.

Impacts on the solidification of water on plate surface for cold energy storage using ice slurry

Ice slurry has been widely used for thermal energy storage system due to its high cold energy storage capacity. To effectively improve the efficiency of ice slurry generator, it is essential to have a deeper understanding about the solidification mechanism on the plate surface of ice generator, which is affected by many factors, such as the roughness of surface and the apparent contact angle. This work studies the impacts of roughness and inhibitor concentration on the freezing temperature, subcooling and the heterogeneous nucleation energy at the surface of aluminum, copper and Teflon plates. Results show that both the roughness and the inhibitor concentration can clearly affect the freezing temperature of water droplet and the heterogeneous nucleation energy. In general, the freezing temperature rises and the subcooling and the heterogeneous nucleation energy drop as the surface roughness increases for all studied materials; and the heterogeneous nucleation energy also increases with the increase of inhibitor concentration. Since the heterogeneous nucleation energy is mainly determined by the substance and the roughness, while not by the surface material, it is important to increase the roughness in order to reduce subcooling and save energy, especially for copper and aluminum.

Temperature measurement of supercooled droplet in icing phenomenon by means of dual-luminescent imaging

The collision of a supercooled water droplet with a surface result an object creates ice accretion on the surface. The icing problem in any cold environments leads to severe damages on aircrafts, and a lot of studies on prevention and prediction techniques for icing have been conducted so far. Therefore, it is very important to know the detail of freezing mechanism of supercooled water droplets to improve the anti-and de-icing devices and icing simulation codes. The icing mechanism of a single supercooled water droplet impacting on an object surface would give us great insights for the purpose. In the present study, we develop a dual-luminescent imaging technique to measure the time-resolved temperature of a supercooled water droplet impacting on the surface under different temperature conditions. We apply this technique to measure the exact temperature of a water droplet, and to discuss the detail of the freezing process.

Energy and Second Law of Thermodynamics Analysis of Shower Cooling Tower with Variation in Inlet Air Temperature

A shower cooling tower (SCT) operates without fill because of salt decomposition on the fill that leads to deterioration of conventional cooling tower performance. This study presents a two-dimensional mathematical model for energy and exergy analysis of multi-diameter droplets and air interaction along with the height of the forced draft SCT, to predict the exit condition of water droplet for industrial application. Different inlet air dry bulb temperatures (DBT) were used for the study and the model was validated with experimental results. At the inlet of the tower, ten different diameters of water droplets simultaneously were used at a given time for analysis and the droplet diameter model based on Rosin Rammler distribution. The result showed that thermal efficiency and second law efficiency relatively increased along the height of SCT with increase of the inlet air temperature. It was confirmed that maximum reduction in water droplet temperature along the height of SCT was achieved by minimum inlet air DBT. It was also noticed that exergy supplied by water was more than exergy absorbed by air and maximum destruction of total exergy took place at the beginning of air-water interaction.

マイクロガスタービン圧縮機環境下の一様流中における水滴の蒸発効果

A model has been developed to investigate the evaporation behavior of water droplets in a uniform duct flow under gas turbine environments. It is assumed that the change of water droplet temperature is caused by convective heat transfer through droplet surface. The temperature of a water droplet has been calculated by treating the droplet as a lumped mass with a representative temperature uniformly distributed in the droplet. The proposed model consists of two steps. The 1st step is the heat transfer calculation between a water droplet and surrounding air flow and the 2nd step is the calculation to take the latent heat of vaporization into consideration. The evaporation rate is calculated based upon mass transfer between water droplet and surrounding air flow.

The effect of gas and water droplet temperature on characteristics of water-droplet deformation at moderate velocities of droplet movement

An experimental study has been performed on the effect of the temperature of gas and water droplets (3–6 mm in size) on deformation of water droplets that move with a moderate velocity (up to 5 m/s). A high-speed videocamera (recording at up to 105 fps) and a cross-correlation videocomplex were used. The droplet temperature varied in the range of 285–360 K. For gaseous mediums, air at a temperature of 280–300 K and condensed substance combustion products at a temperature about 1100 K were used. Typical deformation cycles were found. Their length, duration, and amplitude were calculated. The time a shape of droplet transforms into a new shape and the time the droplets retain their shape as they move through a gas medium have been determined. Approximating correlations for the basic characteristic of deformation under various heating or cooling conditions in a water droplet–gas system were derived.

Exploring an approximation for the homogeneous freezing temperature of water droplets

Abstract. In this work, based on the well-known formulae of classical nucleation theory (CNT), the temperature TNc = 1 at which the mean number of critical embryos inside a droplet is unity is derived from the Boltzmann distribution function and explored as an approximation for homogeneous freezing temperature of water droplets. Without including the information of the applied cooling rate γcooling and the number of observed droplets Ntotal_droplets in the calculation, the approximation TNc = 1 is able to reproduce the dependence of homogeneous freezing temperature on drop size V and water activity aw of aqueous drops observed in a wide range of experimental studies for droplet diameter > 10 µm and aw > 0.85, suggesting the effect of γcooling and Ntotal_droplets may be secondary compared to the effect of V and aw on homogeneous freezing temperatures in these size and water activity ranges under realistic atmospheric conditions. We use the TNc = 1 approximation to argue that the distribution of homogeneous freezing temperatures observed in the experiments may be partly explained by the spread in the size distribution of droplets used in the particular experiment. It thus appears that the simplicity of this approximation makes it potentially useful for predicting homogeneous freezing temperatures of water droplets in the atmosphere.

Effects of Free Surface Evaporation on Water Nanodroplet Wetting Kinetics: A Molecular Dynamics Study

The wetting kinetics of a water nanodroplet undergoing evaporation on a heated gold substrate were examined using molecular dynamics (MD) simulations. Various substrate and initial droplet temperatures were used to obtain different evaporation rates. The water molecule absorption–desorption behavior was analyzed in the vicinity of the contact line region to show the microscopic details of the spreading–evaporating droplet. Increasing substrate temperatures greatly affected the dynamic wetting process, while the initial water droplet temperature had very little effect. The effects of droplet size and substrate wettability on the droplet spreading–evaporating process were also examined. The radius versus time curves agree well with molecular kinetics theory (MKT) for spreading without evaporation but differ from MKT when the spreading induced evaporation. The enhancement of the wetting kinetics by the evaporation can be attributed to the reduction of the liquid–vapor surface tension and the increased water molecule motion in the contact line region and in the bulk droplet.

Laboratory Study of Effects of Atmospheric Pollutants on Ice Nucleation Activity of Bacteria

Ice nuclei of some bacterial origin as ice catalysts can initiate ice nucleation at temperatures as warm as –2°C in certain laboratory experiments. The ice nucleation activities of airborne bacteria in the real atmosphere may be different from those experiments. To estimate the impact of typical atmospheric pollutants including monocarboxylic acids (MCAs), dicarboxylic acids (DCAs) and ammonia sulfate on ice nucleation activity of P.syringae pv lachrymans and P.syringae pv.panici, we have conducted some experiments by means of the modified Vali’s droplet freezing testing method in the immersion freezing mode with the mixture of the pure water and the polluted water. Our results show that the ice nucleation activity of bacterial origins can be regulated by such pollutant compounds even though the onset freezing temperatures of water droplets mainly depend on the concentrations of ice nucleation-active bacteria. Atmospheric acids can decrease ice nucleation activity of P.syringae pv lachrymans and P.syringae pv.panici. However, the onset freezing temperatures of water droplets immersed with ice nucleation-active P.syringae pv lachrymans will be enhanced by the low concentration of such atmospheric pollutants.

G133 不凍タンパク質を基にしたポリペプチドを固定した面における氷成長の抑制(OS-14:凝固・融解伝熱および結晶成長の新展開(3))

The development of icephobic surfaces is an important issue in recent years. We have created a new functional surface for lowering the freezing temperature of a water droplet by adhering polypeptides on the surface. These polypeptides are based on the part of winter flounder antifreeze protein. To examine the effectiveness of the surface, we conducted simultaneous measurements of water droplet temperature on the cooling surface with a fine thermocouple and solidification of the droplet with a microscope. Although there is no change in the coagulation of water droplet, we obtained the depression of freezing temperature due to the surface.