Superhydrophobic surfaces have myriad industrial applications, yet their practical utilization has been limited by their poor mechanical durability and longevity. We present a low-cost, facile ...process to develop superhydrophobic copper-based coatings via an electrodeposition route, that addresses this limitation. Through electrodeposition, a stable, multiscale, cauliflower shaped fractal morphology was obtained and upon modification by stearic acid, the prepared coatings show extreme water repellency with contact angle of 162 ± 2° and roll-off angle of about 3°. Systematic studies are presented on coatings fabricated under different processing conditions to demonstrate good durability, mechanical and underwater stability, corrosion resistance, and self-cleaning effect. The study also presents an approach for rejuvenation of slippery superhydrophobic nature (roll-off angle <10°) on the surfaces after long-term water immersion. The presented process can be scaled to larger, durable coatings with controllable wettability for diverse applications.
•Presents a facile, low energy, electrodepostion method for fabrication of copper-based superhydrophobic surfaces.•Presents, for the first time, a systematic study on the effect of surface ...functionalization time.•Presents the corrosion inhibition characteristics of superhydrophobic surfaces in a wide range of corrosive environments.•Reports corrosion resistance of superhydrophobic copper surfaces, for the first time, as a function of temperature.•Presents a study of corrosion durability of the surfaces under long-term immersion in the corrosive environments.
This study considers the corrosion characteristics of superhydrophobic copper surfaces with multiscale asperities formed inherently on a copper substrate, using a facile, low energy, electrodepostion method. A systematic study is presented for the first time on the effect of surface functionalization time on long-term immersion in a wide range of corrosive environments from the extremely acidic to the extremely alkaline. The corrosion resistance is also reported for the first time as a function of temperature in the range 23–85 °C. The superhydrophobic surfaces are shown to enhance corrosion resistance by up to four orders of magnitude compared to bare copper.
This paper presents a fractal model to describe wettability on multiscale randomly rough surfaces. Hydrophobic or superhydrophobic surfaces, produced by processes such as electrodeposition and ...etching, lead to the creation of random roughness at multiple length scales on the surface. This paper considers the description of such surfaces with a fractal asperity model based on the Weierstrass–Mandelbrot (W-M) function, where the fractal parameters are uniquely determined from a power spectrum of the surface. By use of this description, a model is presented to evaluate the apparent contact angle in the different wetting regimes. The model is predictive in that it does not use any empirical or correlatory fitting of parameters to experimental data. Experimental validation of the model predictions is presented on various hydrophobic and superhydrophobic surfaces generated on several materials under different processing conditions. The contact angle is found be strongly dependent on the range of asperity length scale and weakly dependent on the fractal dimension for a surface with stable Cassie state. Based on the fractal description, desired surface roughness characteristics for generating superhydrophobicity on a particular substrate are also derived.
Integrating TES (thermal energy storage) in a CSP (concentrating solar power) plant allows for continuous operation even during times when solar irradiation is not available, thus providing a ...reliable output to the grid. In the present study, the cost and performance models of an EPCM-TES (encapsulated phase change material thermal energy storage) system and HP-TES (latent thermal storage system with embedded heat pipes) are integrated with a CSP power tower system model utilizing Rankine and s-CO sub(2) (supercritical carbon-dioxide) power conversion cycles, to investigate the dynamic TES-integrated plant performance. The influence of design parameters of the storage system on the performance of a 200 MW sub(e) capacity power tower CSP plant is studied to establish design envelopes that satisfy the U.S. Department of Energy SunShot Initiative requirements, which include a round-trip annualized exergetic efficiency greater than 95%, storage cost less than $15/kWh sub(t) and LCE (levelized cost of electricity) less than 6 cents/kWh. From the design windows, optimum designs of the storage system based on minimum LCE, maximum exergetic efficiency, and maximum capacity factor are reported and compared with the results of two-tank molten salt storage system. Overall, the study presents the first effort to construct and analyze LTES (latent thermal energy storage) integrated CSP plant performance that can help assess the impact, cost and performance of LTES systems on power generation from molten salt power tower CSP plant.
•Presents a three-dimensional simulation model of thermochemical heat storage bed.•Presents novel constructal design of fins embedded in thermochemical energy storage for enhanced thermal ...transport.•Analyzes the thermal energy storage (TES) density and levelized cost of thermochemical heat storage.•Optimizes the parameters of constructal fins to maximize energy storage density and minimize levelized cost of storage.•Presents design window that meets the targets of the U.S. Department of Energy Buildings Technologies Office.
Because of their potential for long-term and loss-free thermal energy storage, thermochemical materials are attractive candidates for storing solar thermal energy in buildings applications. A drawback, however, is that of poor heat transport in the thermochemical material bed during charging and discharging. This study presents a novel thermochemical energy storage system with embedded constructal fin tree structure to enhance the discharge process. The influence of the constructal fin design parameters on the energy storage density and levelized cost of storage is studied to establish design envelopes that satisfy the U.S. Department of Energy Buildings Thermal Energy Storage program requirements, which include a round-trip thermal energy storage density of more than 80 kWh/m3 and storage cost less than $15/kWh. The study reports optimum designs of the constructal fin tree enhanced thermochemical reactor bed based on minimum levelized cost of storage and maximum energy storage density for building-integrated thermal energy storage applications.
Rough surfaces in contact with a flow of fluid exhibit alternating no-slip and free shear boundary conditions at the solid–liquid and air–liquid interfaces, respectively, thereby potentially offering ...drag reduction benefits. The balance between the dynamic pressure in the flow and the restoring capillary pressure in the interasperity spaces determines the stability of the Cassie state of wettability and is a function of the relative extent of no-slip and free shear regions per unit surface area. In the present study, using a fractal representation of rough surface topography, an analytical model is developed to quantify the stability of the Cassie state of wettability as well as drag reduction and the friction factor for laminar flow in a rectangular channel between nonwetting multiscale rough surfaces. A systematic study is conducted to quantify the effects of fractal parameters of the surfaces and the flow Reynolds number on drag reduction and the friction factor. The studies are used to develop friction factor curves extending the classical Moody diagram to hydrophobic and superhydrophobic surfaces. On the basis of the studies, regime maps are derived for estimating the extent of drag reduction offered by hydrophobic and superhydrophobic surfaces, revealing that superhydrophobic surfaces do not always offer the best drag reduction performance. The application of the fractal model to practical topographies of nonwetting surfaces of copper, aluminum, and zinc oxide fabricated via electrodeposition and etching is also discussed.
Zinc coatings are widely used in the surface finishing industry to improve the corrosion resistance of steel structures. Generally, an additional decorative hexavalent chromium layer is deposited for ...corrosion protection, which leads to carcinogenic chrome emissions. In this work, we present an electrodeposition based approach to fabricate superhydrophobic zinc coatings, that eliminates the need for the additional chromium layer while enhancing the corrosion resistance of the zinc coating by about one order of magnitude. Through electrodeposition in a highly conductive electrolyte, multiscale needle and branch-shaped fractal morphology was obtained in the coatings, which were treated with stearic acid to obtain extreme water repellency, with a contact angle of more than 160° and roll-off angle of about 4–7°. Detailed microstructural and mechanical characterization studies are presented on the fabricated coatings under different processing conditions to demonstrate their durability, stability, longevity, and corrosion resistance. The presented process can be scaled to larger durable non-wetting coatings for diverse applications.
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•Presents a method for fabricating fractal-textured zinc coatings integral to the substrate•Coatings eliminate the need for a chrome layer while enhancing corrosion resistance by about an order of magnitude.•Presents extensive characterization of the coatings for their superhydrophobic performance•Elucidates durability, stability and corrosion resistance of the coatings under a wide range of conditions
Mitigation of corrosion of structural materials in contact with molten salts is imperative in high temperature applications such as nuclear and solar thermal power plants. This paper introduces, for ...the first time, a novel approach to corrosion mitigation through fractal surface texturing and details a systematic corrosion study of a variety of structural materials. Multiscale fractal textured surfaces on SS316, In800H, In718, In625, and Ha230 were fabricated via chemical etching, whose parameters were optimized to obtain surface fractal dimensions above 1.90. The influence of grown oxides was examined by annealing the optimized etched surfaces with high fractal dimensions at a high temperature. The corrosion mitigation characteristics of plain, etched and etched-annealed surfaces were systematically studied in molten 60% NaNO3 + 40% KNO3 at 600 °C. The fractal textured surfaces are shown to reduce corrosion rate by 30% for ferrous alloys and by over 80% and up to 87% for high nickel content alloys. Elemental composition analysis reveals that the corrosion oxides are correspondingly diminished on fractal textured surfaces compared to plain surfaces. The study is significant in that any existing material may be made more corrosion resistant through this simple surface modification and treatment.
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Fouling is a ubiquitous issue in several environmental and energy applications. Here we introduce novel nonwetting solid-infused surfaces (SIS) with superior anti-fouling ...characteristics that are durable than conventional nonwetting surfaces in a dynamic flow environment. A systematic study is presented to elucidate the fouling mitigation performance of SIS in comparison to lubricant-infused surface (LIS) and conventional smooth surface. Copper tubes with SIS, LIS or smooth inner walls are fabricated and subjected to accelerated calcium sulfate fouling in a flow fouling experimental setup. Fouling on the various surface types is quantified in terms of asymptotic fouling resistance, and the fundamental morphological differences in the interactions of the foulant and the various surface types are analyzed. Based on a systematic sweep of the parameter combinations using design of experiments and Taguchi analysis, an analytical dependence of asymptotic fouling resistance on the governing parameters namely, Reynolds number, foulant concentration and temperature is derived. The analytical model is shown to predict the asymptotic fouling resistance to within 20% accuracy with a 95% confidence. In addition, for the first time, the effects of shear durability on the fouling mitigation performance of LIS vis-à-vis SIS are studied. It is shown that the novel nonwetting SIS offers a robust option for superior fouling mitigation over LIS in the long run.
This paper introduces a novel approach to corrosion mitigation using electrodeposited, fractal Ni and NiYSZ coatings. Highly adherent, durable multiscale coatings with fractal dimensions above 1.80 ...were fabricated. Corrosion characteristics of coated plain and etched surfaces of In800H, SS310, SS316 and SS347, in comparison to Ha230, were studied in molten 60% NaNO3 + 40% KNO3 at 600 °C. The corrosion rate of coated Fe-based alloys reduced by up to 68% compared to uncoated alloys and was on par with or lower than the corrosion rate of Ha230. The corrosion-resistant coatings provide for use of low-cost alloys in high temperature corrosive environments.
•Novel fractal coatings of Ni and NiYSZ were developed on Fe-based alloys using electrodeposition method.•The coatings were systematically optimized based on adhesion strength using Taguchi method.•The coatings have multiscale topography with high fractal dimensions that were durable under harsh shear/erosion conditions.•Ni and NiYSZ coatings with fractal surfaces provide dramatically reduced corrosion rate of ~20 µm/y in solar salt at 600 °C.
