Search

The condensation transport coefficients are higher on the metallic surface because of the high thermal conductivity of metallic surfaces. However, the metallic surfaces have a higher affinity to water in the condensation process which leads to corrosion and results in damage to the condensing metallic surface. Low surface energy and low wettability surfaces promote efficient condensation in drop mode. Therefore, several surface modification techniques have been adopted for modifying the surface wettability of the metallic surfaces. Teflon coating on the metallic surface has been an economically viable and simple method for fabricating low surface energy coating on metallic surfaces. In this work, Cu coil is coated with PTFE film for fabricating hydrophobicity on Cu helical coil. Moist air condensation experiments are carried out on Teflon coated and bare Cu coil to investigate the effect of Teflon coating on the coil. In addition, the effect of moist ambient conditions on the Teflon coated coil is addressed to examine the aging of the Teflon coating on the Cu coil. The results show that the characteristics of hydrophobic Teflon coating deplete with increases in exposure time so the dropwise condensation transits into mixed condensation and ultimately in film mode as the coil is exposed to repeated condensation cycles. The results of the present study are useful to appropriately investigating in which all applications the Teflon coating can be implemented such that all its properties are retained in that time duration.

The unmanned aerial vehicles are getting popular day by day owing to its ability to hover, low cost of maintenance, ease of deployment as well as high mobility. A quadcopter has limited mobility and payload, but they are highly capable to fly in any direction and to stay stationary in the air. Therefore, the battery lifetime is an important aspect to study which help to travel for a long distance and to increase the flight time. In this direction, the present work focuses on the flight time, which is being analyzed experimentally through the integration of solar panels in the quadcopter for utilization of solar energy as a power source along with the conventional DC battery and by efficient weight reduction of the quadcopter. The proposed quadcopter has been designed in SolidWorks© software and analyzed in Ansys© software as well as it has been fabricated successfully to test for flight time.

Moist air condensation is a complex process because it relies on numerous significant parameters such as physio-chemical properties of a surface, thermal-physical properties of the moist air, and environmental conditions. Thus, the manuscript intent to structure the model-framework of sustainable water harvesting based on moist air condensation on mesh-like surfaces to increase the availability of potable water. Hence, the significant key factors related to sustainable water harvesting via condensation are identified from extant literature, consultation from researchers, and practitioners and subsequently confirmed by fabricating the experimental setup. Further than, an attempt by applying Total Interpretive Structural Modelling (TISM) is attained to provide a model framework. Thereafter, the procedure for analysis using MICMAC is implemented which performed to categorize the identified factors into the distinct clusters’ dependent on their driving and dependence powers to justify their interrelationship with one another. The research reveals that surface coating, mesh geometry, and material of condensing surface are the most dominant factor in the required hierarchy which helps in improving the condensation rate. Thus, the prioritization of the factors with improvisation intends to fill the gap for scalable, economic, sustainable, and environment-friendly condensation in various fields. This research work can be benefited to the industry to the area of water harvesting and energy conservation. Also, the researchers can consider the most influential factors identified in this research while fabricating experimental setups.

A number of drag models have been suggested for the interaction of fluid particles in slurry flow over the previous centuries. It is necessary to examine the correctness and applicability of these models in the slurry transportation. Based on this concept, a comparative analysis of the different drag models is performed for the 0.0549 m diameter slurry pipeline. The research is carried out by using three drag models: Syamlal-obrien, Schiller-naumann and Gidaspow due to their accessibility in the Fluent commercial software. The simulation is performed at mean flow velocity range, Vm= 2–5 ms-1 and solid concentration range, Cvf = 10– 20% (by volume) using computational drag models. The simulated outcomes for solid particle size 440 μm having density 2470 kg/m3 are recorded using Eulerian two-phase model with selected drag models in the computational domain. It has been found that the Eulerian two-phase model with Syamlal O’brien drag model gives the accurate and meticulous results with the published data in the literature. Finally, the simulated outcomes of solid concentration contours, solid concentration profiles and pressure drop are predicted at distinct velocity and solid concentration range for chosen drag models.

The recent paper presents the experimental investigation on material removal rate (MRR) and electrode wear ratio (EWR) of hybrid metal matrix composite of Aluminium 7075 reinforced with 10% by wt. Silicon carbide particles and nanoparticles of magnesium (Al 7075/10%SiC/Mg). Magnesium metal matrix composites are of significant importance nowadays because of the increasing demand of light weight structural material in aerospace and automotive applications. Stir casting process has been used for fabrication of hybrid metal matrix composite. The effect of process parameters on responses such as MRR and EWR are evaluated during conventional EDM and rotary EDM. The pulse duration, peak current, duty cycle, and tool speed are selected as machining parameters. A comparative analysis of conventional EDM and rotary EDM of hybrid composite has been done. Experimental results indicated that the rotation of the tool enhances the flow of dielectric and effective evacuation of the debris from the gap between the workpiece and tool. The result shows increased MRR and reduced EWR with rotary EDM as compared to conventional EDM. This work seems to be of novelty and the findings can be useful for aerospace and automotive industry.

The surface morphology alike lotus leaf has high contact angle and low contact angle hysteresis with respect to water droplet because of nanoscale roughness superimposed on micro order roughness in well-organized manner. The major application of superhydrophobic metallic substrate is in the condensing unit of energy and water harvesting devices. In this work, nanoscale roughness is superimposed on micro-order roughness of Aluminum substrate. The chemical texturing method is used to create micro-scale roughness onto Al surface. However, 0.6 keV Ar ions are irradiated for various time span to fabricate nano order roughness on chemically etched substrate. The roughness of samples is measured by Atomic Force Microscopy and static contact angles and their hysteresis are measured by lab customize Goniometer. It is found that the static contact angle and contact angle hysteresis increases after irradiation on chemical etched surfaces. Multi-scale roughness is observed on irradiated substrate. Results also shows that contact angle increases with increasing time of irradiation. However, maximum change in static contact angle is observed for samples irradiated for 45 s. Eventually, the static contact angle is correlated with its surface roughness. This correlation is vital for optimizing parameter affecting condensation rate in dropwise condensation. Finally, the moist air condensation experiments are conducted to know the condensation efficacy of the irradiated substrate. Also, it is found that the drop sliding frequency on vertical irradiated Al substrate is higher than the chemical etched Al substrate.

The super-hydrophobic surfaces enhance the transport coefficients of the condensation process and therefore it is very useful in water harvesting devices. In the present study, super-hydrophobic substrates are fabricated by growing self-assembled silica nanostructures on copper (Cu) and aluminum (Al) surfaces by a sol-gel based solution immersion method at room temperature. The contact angles measured were 155 ± 2° and 156 ± 2° on coated Cu and Al surfaces respectively. The water condensation rate on the coated Cu surface significantly increased from 188 ml/m2-hr to 630 ml/m2-hr, while that of the coated Al surface increased from 190 ml/m2-hr to 650 ml/m2-hr. The present work shows that the metallic substrates with super-hydrophobic coatings have excellent potential for water harvesting from moist air, and they were effectively used for more than 120 days.

Moist air condensation is of significant scientific and societal interest especially for harvesting potable water from atmospheric air. Dropwise condensation of water vapor present in moist air is preferred when compared to filmwise condensation because of high transport coefficients that augment condensation rate of the distillate. The efficacy and sustainability of dropwise condensation depends on various operating parameters, for instance, temperature of moist air, relative humidity, subcooling of the substrate, thermophysical properties of moist air and physico-chemical properties of the condensing substrate. In this context, a mathematical model of dropwise condensation of moist air over a textured surface has been developed in the present work. Jointly, an experimental study of moist air condensation over a specially prepared superhydrophobic surface has been carried out for model validation. By suitably deriving the correction factor for the interfacial resistance to account for the presence of noncondensable gases, good agreement has been obtained between the model and experiments. Thereafter, simulations have been performed over a range of conditions from the viewpoint of maximizing the condensate output. Results of the study show that a vertical substrate with a high equilibrium contact angle and low contact angle hysteresis increases drainage of water drops. Hence, there is an increase in the water productivity of the surface. In addition, the condensation rate increases with increase in relative humidity, degree of subcooling and saturation temperature of moist air. The results of the study can be utilized towards designing devices for water harvesting from the atmosphere.

Clusters of liquid drops growing and moving on physically or chemically textured surfaces are encountered in dropwise mode of vapor condensation. This process can be sustained only if the surface integrity is maintained over a long period of time. Surface features are altered when sliding drops leach away the promoter layer. In the absence of chemical reactions between the promoter and the condensing liquid, the wall shear stress is the primary parameter controlling the physical leaching. In turn, wall shear stress depends on the relative speed between the drop and the substrate surface and the shape of the drop. Given a wall shear stress distribution for individual drops, the net effect of an ensemble of them during continuous quasi-steady state dropwise condensation can be determined using the population density of drops. Wall shear stress and local heat fluxes have been determined in the present work by solving the Navier–Stokes and energy equations in three-dimensions on an unstructured tetrahedral grid that represents an individual droplet. The drop size and relative velocity are parameterized by the Reynolds number (Re = 10–1000), apparent contact angle (90–120°) and its shape. The simulations presented here are for a wide range of Prandtl numbers, i.e., 0.005–30. The wall shear stress and wall heat flux are expressed in terms of the skin friction coefficient and the Nusselt number, respectively. While these two quantities show an increase with Reynolds number, they decrease at higher values of the drop contact angle on/underneath hydrophobic surface. At low Prandtl numbers, heat transfer is mainly diffusional and the wall Nusselt number is practically independent of Reynolds number at any given Pr. The maximum wall shear stress as well as heat flux occurs at the corners of the drop close of the three-phase contact line. The surface averaged shear stress and heat flux are expressed in terms of appropriate correlations that include Reynolds number, Prandtl number, and the apparent contact angle. The wall shear stress in the relatively inactive central region at the drop base is smaller than the overall base average by a factor of 6, while that for heat transfer, the corresponding factor is in the range of 1.3–1.8. The figure of merit function, represented by the ratio of average Nusselt number to the friction coefficient, increases with contact angle, indicating an advantage to be gained from hydrophobic surfaces. The information presented in this paper is vital for further improvement of the available models of dropwise condensation on textured surfaces.