Hydrophobic Walls Research Articles

Numerical investigation of heat transfer and entropy generation in serpentine microchannel on the battery cooling plate using hydrophobic wall and nanofluid

Battery cooling is essential in electronic devices since the performance of batteries is negatively influenced by the increase in temperature of batteries. This paper investigates the significance of a serpentine microchannel that is situated on the surface of the battery. The nanofluid flow and thermal behavior are simulated through numerical methods in the serpentine microchannel and battery surface. The results confirmed that the present nanofluid is able to increase heat transfer between serpentine microchannel and battery by up to 20 %. Moreover, the most effective parameter on the heat transfer improvement was the Reynolds number so when the Reynolds number varies from 25 to 150 the heat transfer increased from 6.34 to 12.75. More importantly, the hydrophobic walls of microchannels lead to a 14.4 % enhancement in heat transfer compared with a conventional wall.

Experimental study on the boiling/condensation heat transfer performance of a finned tube with a hydrophilic/hydrophobic surface

Currently, a increasing number of exchange tubes are requied for both boiling heat transfer and condensation heat transfer. Thus, it is necessary to enhance, both the boiling heat transfer performance and condensation heat transfer performance of the tube is necessary. However, few studies have been conducted in this field. A stepped lattice finned tube is suggested to enhance both boiling heat transfer and condensation heat transfer. There is room for the heat transfer enhancment of efficiency considering that wettability can also influence the heat transfer. Hence, in this study, the heat transfer performances of tubes with hybrid Hydrophilic-hydrophobic surfaces and functional fins are experimentally investigated. The condensation heat transfer coeffient and boiling heat transfer coefficient of the tube with an inner hydrophobic cavity wall and outer hydrophilic fin are nearly 3 times and 1.8 times those of the smooth tube, respectively. In boiling heat transfer, the inner hydrophobic surface can lower the bubble nucleation barrier and the outer hydrophilic surface can prevent the heat transfer surface from being covered by a vapour film. In condensation heat transfer, the outer hydrophilic surface can lower the droplet nucleation barrier and the inner hydrophobic surface contributes to dropwise condensation.

Ultra-Fast Preparation of Large-Area Graphdiyne-Based Membranes via Alkynylated Surface-Modification for Nanofiltration.

Graphdiynes (GDYs), two-dimensional graphene-like carbon systems, are considered as potential advanced membrane material due to their unique physicochemical features. Nevertheless, the scale-up of integrated GDY membranes is technologically challenging, and most studies remain at the theoretical stage. Herein, we report a simple and efficient alkynylated surface-mediated strategy to prepare hydrogen-substituted graphdiyne (HsGDY) membranes on commercial alumina tubes. Surface alkynylation initiates an accelerated surface-confined coupling reaction in the presence of a copper catalyst and facilitates the nanoscale epitaxial lateral growth of HsGDY. A continuous and ultra-thin HsGDY membrane (∼100 nm) can be produced within 15 min. The resulting membranes exhibit outstanding molecular sieving together with excellent water permeances (ca. 1100 L m-2 h-1 MPa-1 ), and show a long-term durability in cross-flow nanofiltration, owing to the superhydrophilic surface and hydrophobic pore walls.

Study of low-level pool boiling in vapor chamber of wickless micro-heat pipe based on Lattice Boltzmann pseudopotential method—Effects of superheat and wall wettability

The lattice Boltzmann method, a mesoscopic numerical method with a solid kinetic basis, is used to establish a low-level pool boiling model to exhibit the transport phenomena inside an evaporation chamber of a wickless micro heat pipe using DI water as the working fluid. The effects of wall superheat and wall wettability on bubbles’ nucleation, growth, and detachment in the evaporation chamber were compared and analysed. Moreover, the influence of the wall superheat on the thermal performance of the micro heat pipe was specifically examined. It is found that the low-level pool boiling occurs with a wall superheat that is higher than 0.357T c, indicating a high heat flux for heat removal. Interestingly, when the relatively hydrophobic chamber wall is superheated by 0.46T c, there are more nucleation sites, and the complete bubbles cycle containing nucleation, growth, and detachment is longer. In contrast, on a hydrophilic surface under the same and sufficient superheat condition, the number of bubble nucleation sites is less than that on the hydrophobic surface, and the complete cycle of bubbles is shorter. It is worth mentioning that the model has values for predictions of homogeneous nucleation of bubbles and thermal transport on hydrophobic or hydrophilic surfaces.

Numerical study of heat transfer and pressure drop of nanofluids in a combined porous media of hydrophobic and hydrophilic surfaces

The present study provides a 3D numerical research on the hydro-thermal performance of water-Al2O3/CuO nanofluids and water/Al2O3-CuO hybrid nanofluid inside a U-bend tube incorporating a porous medium with both hydrophilic and hydrophobic surfaces. Furthermore, a single-phase flow is adopted to simulate the nanofluid flow. Taking into consideration the equation of the Darcy-Brinkman-Forchheimer, to simulate the flow of fluids in the porous media. The influence of Dean number on hydro-thermal performance in the range of (600–1750) was investigated. And according to the results, Dn = 600 had the best performance. Considering the outcomes, a completely hydrophobic wall has a better hydro-thermal performance than a completely hydrophilic one and other hydrophilicity and hydrophobicity combinations. As well, improvement in heat transfer efficiency is considerably influenced by the Darcy number (10−4–10−1) and the augmentation of the porous thickness ratio. Additionally, average Nusselt number and pressure losses for any and all types of nanofluids show an incremental schema with augmenting volume fraction, while PEC exhibits a reducing pattern. Besides this, structures with permeable porous media or ones with Da = 0.1 and rp = 0.6 present the highest PEC. Also, among the reviewed nanoparticles, Al2O3 with a volume percentage of 1% had the maximum PEC.

Structure of fungal cell walls and remodeling by antifungal drugs elucidated using solid-state NMR.

Understanding the cell wall structure, dynamics, and mechanisms of adaptations are important for the development of cell wall-targeted drugs for the treatment of fatal infections caused by fungi. We first combined ssNMR, and functional genomics analysis to identify the functionality of cell wall carbohydrates in Aspergillus fumigatus and four mutants depleted of major structural polysaccharides. We revealed a rigid inner core of the cell wall formed by tightly associated chitin and α-1,3-glucan, which are embedded in a soft matrix of β-glucans and capped by a mobile outer shell rich in galactosaminogalactan and galactomannan. The distribution of α-1,3-glucan in chemically and dynamically distinct domains supports its dual functionality in structure and pathogenicity. Also, ssNMR revealed the modification of polymer dynamics which suggests that fungi produce a denser and hydrophobic cell wall as a response to structural defects. Second, we characterized the structural responses of A. fumigatus cell walls to the treatment of antifungal drugs. The drug-treated cell walls are highly hydrophobic and stiff to resist external stress. The fungi also increased the content of chitin and produced new forms of α-glucans to compensate for the loss of β-glucan due to drug inhibition. Third, we found that the crystalline structure of chitin bears intrinsic heterogeneity, which is resistant to caspofungin treatment. We documented the unique structural fingerprints of chitin across different fungal species. Finally, we used an innovative approach combing the ssNMR with the dynamic nuclear polarization technique to characterize the cell wall organization in different morphotypes varied along with the life cycle, revealing a highly conserved carbohydrate core in both conidia and mycelia. These studies and the biophysical techniques yield essential information that can serve as potential targets for discovering novel antifungal compounds with broad spectrums.

Computational Multiphase Flow Modelling of Oil Spill Through a Hydrophobic Mesh

The current technologies for handling oil spill clean-up vary in expense and effectiveness and are largely ineffective. Oil spills occur due to accidents from well-heads and damaged facilities in the creeks of the Nigerian Delta and along the coastline of waters where hydrocarbons are prospected all over the world. They are unexpected and known to cause irreparable damage to aquatic environments and marine life. The development of a hydrophobic mesh is proposed to prevent oil from spreading into larger areas and from reaching sensitive coastlines. This will help engineers and clean-up crews in their quest to find an appropriate response to a given oil spill scenario as they race against the clock to prevent further damage and improve the oil recovery process. The overall goal of this project is to create a Numerical Simulation of meshes that repel water and attract oil using ANSYS, a Finite Element Analysis software. The mesh was modelled as a porous medium that acts like a filter that retains water on one side while allowing the passage of oil through it. In the course of this work, appropriate materials selection in fluid flow analysis was carried out. Also, the flow domain geometry was developed in such a way as to simulate a system containing an oil-water interface. Next, domain discretization (meshing) was carried out appropriately. After which appropriate boundary conditions and operating conditions were implanted in the model. Fluent was then set to initialize and run calculations. After calculations were run, results were gotten. These results were then interpreted pictorially. It was seen that the velocity streamlines for the oil phase passed through the hydrophobic mesh, while the velocity streamlines for the water phase were repelled from the hydrophobic mesh wall.

Cyclodextrin Inclusion Complexes and Their Application in Food Safety Analysis: Recent Developments and Future Prospects.

Food safety issues are a major threat to public health and have attracted much attention. Therefore, exploring accurate, efficient, sensitive, and economical detection methods is necessary to ensure consumers' health. In this regard, cyclodextrins (CDs) are promising candidates because they are nontoxic and noncaloric. The main body of CDs is a ring structure with hydrophobic cavity and hydrophilic exterior wall. Due to the above characteristics, CDs can encapsulate small guest molecules into their cavities, enhance their stability, avoid agglomeration and oxidation, and, at the same time, interact through hydrogen bonding and electrostatic interactions. Additionally, they can selectively capture the target molecules to be detected and improve the sensitivity of food detection. This review highlights recent advances in CD inclusion technology in food safety analysis, covering various applications from small molecule and heavy metal sensing to amino acid and microbial sensing. Finally, challenges and prospects for CDs and their derivatives are presented. The current review can provide a reference and guidance for current research on CDs in the food industry and may inspire breakthroughs in this field.

Ice friction at the nanoscale

The origin of ice slipperiness has been a matter of great controversy for more than a century, but an atomistic understanding of ice friction is still lacking. Here, we perform computer simulations of an atomically smooth substrate sliding on ice. In a large temperature range between 230 and 266 K, hydrophobic sliders exhibit a premelting layer similar to that found at the ice/air interface. On the contrary, hydrophilic sliders show larger premelting and a strong increase of the first adsorption layer. The nonequilibrium simulations show that premelting films of barely one-nanometer thickness are sufficient to provide a lubricating quasi-liquid layer with rheological properties similar to bulk undercooled water. Upon shearing, the films display a pattern consistent with lubricating Couette flow, but the boundary conditions at the wall vary strongly with the substrate's interactions. Hydrophobic walls exhibit large slip, while hydrophilic walls obey stick boundary conditions with small negative slip. By compressing ice above atmospheric pressure, the lubricating layer grows continuously, and the rheological properties approach bulk-like behavior. Below 260 K, the equilibrium premelting films decrease significantly. However, a very large slip persists on the hydrophobic walls, while the increased friction on hydrophilic walls is sufficient to melt ice and create a lubrication layer in a few nanoseconds. Our results show that the atomic-scale frictional behavior of ice is a combination of spontaneous premelting, pressure melting, and frictional heating.

Effect of Hydrophilicity/Hydrophobicity of the Injector Wall on Atomization Performance

Hydrophilicity/hydrophobicity is a common physical property of the material. Water droplets roll on lotus leaf, and a lot of dust and dirt on the surface of the lotus leaf will be taken away, playing a certain cleaning role. The hydrophobic surface has drag reduction effect that would produce slip on the hydrophobic wall. There are some studies on hydrophilicity/hydrophobicity in channels, most of which focus on the effect of surface drag reduction and heat transfer on microchannels. However, few people pay attention to the effect of the hydrophilicity/hydrophobicity of the injector inner wall on the atomization performance. In this paper, three groups of the open-end swirl injector with different tangential channels were designed to study the effect of hydrophilicity/hydrophobicity on atomization performance. The hydrophobic coating was prepared and used on the inner wall of the injector, and the atomization experimental system was built. In the experiment, the liquid film thickness was measured using the conductance method. Details of the liquid film breakup and spray development were recorded with a high-speed camera. The average droplet diameter was measured by the Malvern particle size analyzer. The atomization performance of injectors with different tangential channels on the hydrophilicity/hydrophobicity was compared, and the effect of the velocity profile on the jet stability is discussed.

The encapsulation of lycopene with α-lactalbumin nanotubes to enhance their anti-oxidant activity, viscosity and colloidal stability in dairy drink

Nano-encapsulation is promising in improving the stability and biological activity of bioactive compounds. Here, the food-sourced protein nanotubes (NTs) from self-assembly of partially hydrolyzed α-lactalbumin (α-lac) were developed. The α-lac NTs had a dimension of 20 nm in diameter and 200–1000 nm in length. Lycopene (LYC) was loaded into the hydrophobic inner wall of NTs via hydrophobic interaction. Interestingly, we discovered that NTs became nanospheres in gastrointestinal conditions and LYC was mainly released under intestinal condition. The stability of LYC loaded in NTs against temperature and UV light was greatly improved. Besides, LYC showed an improved antioxidant property after NTs loading both by DPPH method and Caco-2 cellular antioxidant activity method. Additionally, the colloidal stability of LYC was greatly enhanced by NTs and therefore lycopene-loaded α-lac nanotubes (NTs/LYC) can be successfully added in the dairy drink, showing an increased viscosity and a long-term stability. α-Lac NTs have shown a promising future in protecting and delivering the hydrophobic compounds in food system. • A lycopene nanocarrier was formed by α-lac self-assembled nanotubes (NTs). • Lycopene loaded in NTs was beneficial to improve its stability and solubility. • Lycopene loaded in NTs were majorly released at small intestine. • The α-lac NTs with high aspect ratios improves the viscosity of dairy drink. • a-lac NTs showed a promising potential as food delivery systems.

The Structure of Water in Silica Mesopores – Influence of the Pore Wall Polarity

AbstractIn the spatial confinement of cylindrical mesopores with diameters of a few nanometers, water molecules experience restrictions in hydrogen bonding. This leads to a different behavior regarding the molecular orientational freedom (‘structure of water') compared to the bulk liquid state. In addition to the pore size, the behavior is also strongly affected by the strength of the pore wall‐to‐water interactions, that is, the pore wall polarity. In this work, this is studied both experimentally and theoretically. The surface polarity of mesoporous silica (SiO2) is modified by functionalization with trimethylsilyl moieties, resulting in a change from a hydrophilic (pristine) to a hydrophobic pore wall. The mesopore surface is characterized by N2 and H2O sorption experiments. Those results are combined with IR spectroscopy to investigate pore wall‐to‐water interactions leading to different structures of water in the mesopore. Furthermore, the water's structure is studied theoretically to gain deeper insight into the interfacial interactions. For this purpose, the structure of water is analyzed by pairing densities, coordination, and angular distributions with a novel adaptation of surface‐specific sum‐frequency generation calculation for pore environments.

Ultrafast Solar-Vapor Harvesting Based on a Hierarchical Porous Hydrogel with Wettability Contrast and Tailored Water States.

Optimizing the water bonding network in an evaporator is significant for efficient solar-driven vapor generation (SVG). Herein, we report a facile one-pot method to regulate the hydrated structure and wettability in a hierarchical porous hydrogel. An ovalbumin (OVA)-polyacrylamide hydrogel foam was fabricated in a cake-making fashion. Because of the enrichment of amphiphilic OVA at the interface, the hydrophobic walls of the air pores in the foam provide vaporization sites and help reduce parasitic heat loss, while the hydrophilic skeleton with the secondary pores effectively pumps capillary water. Notably, the proportion of intermediate water in the foam reaches 87.6% with the melting point as low as -10 °C. All these features contribute to an exceptional evaporation rate of 3.4-4.5 kg m-2 h-1 under 1 sun and robust SVG performances at high-humidity, weak sunlight, or cold weathers. The strategy of using amphiphilic molecules to optimize the hydrated structures both at the interface and in bulk promises the reasonable design of SVG materials with superior efficiency and weather adaptability.

Solubility and solvation features of native cyclodextrins in 1-ethyl-3-methylimidazolium acetate

The comprehension of the mechanism entailing efficient solvation of cyclodextrins (CD) by green solvents is of great relevance to boost environmentally sustainable usages of smart supramolecular systems. Here, 1-ethyl-3-methylimidazolium acetate, an ecofriendly ionic liquid (IL), is considered as an excellent solvent for native CDs. This IL efficiently dissolves up to 40 wt.% β- and γ-CD already at ambient temperature and X-ray scattering indicates that CDs do not tend to detrimental flocculation under these drastic concentration conditions. Simulation techniques reveal the intimate mechanism of CD solvation by the ionic species: while the strong hydrogen bonding acceptor acetate anion interacts with CD's hydroxyl groups, the imidazolium cation efficiently solvates the hydrophobic CD walls via dispersive interactions, thus hampering CD's hydrophobic driven flocking. Overall the amphiphilic nature of the proposed IL provides an excellent solvation environment for CDs, through the synergic action of its components.

Influence of effective polarization on ion and water interactions within a biomimetic nanopore

Interactions between ions and water at hydrophobic interfaces within ion channels and nanopores are suggested to play a key role in the movement of ions across biological membranes. Previous molecular-dynamics simulations have shown that anion affinity for aqueous/hydrophobic interfaces can be markedly influenced by including polarization effects through an electronic continuum correction. Here, we designed a model biomimetic nanopore to imitate the polar pore openings and hydrophobic gating regions found in pentameric ligand-gated ion channels. Molecular-dynamics simulations were then performed using both a non-polarizable force field and the electronic-continuum-correction method to investigate the behavior of water, Na+, and Cl- ions confined within the hydrophobic region of the nanopore. Number-density distributions revealed preferential Cl- adsorption to the hydrophobic pore walls, with this interfacial layer largely devoid of Na+. Free-energy profiles for Na+ and Cl- permeating the pore also display an energy-barrier reduction associated with the localization of Cl- to this hydrophobic interface, and the hydration-number profiles reflect a corresponding reduction in the first hydration shell of Cl-. Crucially, these ion effects were only observed through inclusion of effective polarization, which therefore suggests that polarizability may be essential for an accurate description for the behavior of ions and water within hydrophobic nanoscale pores, especially those that conduct Cl-.

Numerical study of a water droplet impacting on a moving hydrophobic wall using a 3D lattice Boltzmann method

Numerical study of a water droplet impacting on a moving hydrophobic wall using a 3D lattice Boltzmann method

A study on the electroosmotic flow of micropolar fluid in a channel with hydrophobic walls

A study on the electroosmotic flow of micropolar fluid in a channel with hydrophobic walls

Physicochemical properties of yogurt fortified with microencapsulated Sacha Inchi oil

Yogurt can be fortified with polyunsaturated fatty acids such as Sacha Inchi oil (SO) whose stability can be improved by microencapsulation. The comparison on yogurt properties after addition of microcapsules with hydrophobic and hydrophilic wall materials is scare. The aim of this work was to compare physicochemical properties of yogurt during 30-day storage at 4 °C after fortifying with 1 g SO/100-g-yogurt in the unencapsulated or microencapsulated form. Freeze-dried SO microcapsules (FDSOMs) were prepared with hydrophobic zein, and spray-dried SO microcapsules (SDSOMs) were prepared with hydrophilic maltodextrin and modified starch. Yogurt samples had a desirable pH from 3.88 to 4.23 during storage and had a light-yellow appearance. Microcapsules were homogeneously distributed in the yogurt, while big oil droplets were observed for the unencapsulated SO. The addition of SO and microcapsule powders weakened the yogurt network, most significant for FDSOMs due to the most incompatible hydrophobic zein. Syneresis of yogurt samples was 3.09–4.07 g/10-g-yogurt, lowest for the SDSOM treatment. The release of free fatty acids after simulated gastrointestinal digestions was significantly improved for FDSOMs (94.27%) and SDSOMs (103.29%) when compared to the unencapsulated SO (89.20%). Findings from this study may be significant to manufacturing functional yogurts with polyunsaturated fatty acids.

Methods to stabilize aqueous supercooling identified by use of an isochoric nucleation detection (INDe) device

Stable aqueous supercooling has shown significant potential as a technique for human tissue preservation, food cold storage, conservation biology, and beyond, but its stochastic nature has made its translation outside the laboratory difficult. In this work, we present an isochoric nucleation detection (INDe) platform for automated, high-throughput characterization of aqueous supercooling at >1 mL volumes, which enables statistically-powerful determination of the temperatures and time periods for which supercooling in a given aqueous system will remain stable. We employ the INDe to investigate the effects of thermodynamic, surface, and chemical parameters on aqueous supercooling, and demonstrate that various simple system modifications can significantly enhance supercooling stability, including isochoric (constant-volume) confinement, hydrophobic container walls, and the addition of even mild concentrations of solute. Finally, in order to enable informed design of stable supercooled biopreservation protocols, we apply a statistical model to estimate stable supercooling durations as a function of temperature and solution chemistry, producing proof-of-concept supercooling stability maps for four common cryoprotective solutes.

Numerical investigation of power-law hybrid nanofluid in a wavy micro-tube with the hydrophobic wall and porous disks under a magnetic field

In the current study, the second law of thermodynamics and heat transfer of a power-law hybrid nanofluid in a micro-tube with a variable heat flux on the hot wall, the attendance of two porous disks and the hydrophobic wall under a magnetic field with Finite Volume Method (FVM) has been studied. The non-Newtonian nanofluid has contained water/Al2O3-TiO2 in the volume concentrations of 1.5% and 2% nano-particles. The present study has been investigated in four parts in the range of the Reynolds number (10−100) and the nanoparticles volume concentrations (1.5–2%). The first part has examined the influence of using porous disks in the Darcy number (5 × 10−4–5 × 10−6) on nano-fluid flow, cooling and entropy generation. The results showed that the porous medium improves the mean Nusselt number and decreases and increases thermal entropy generation and frictional entropy generation, respectively. In the second part, the impacts of the thermal conductivity ratio (1–16) of the porous disks were studied. Increasing this parameter caused a slight improvement in the mean Nusselt number in almost all cases and enhancing the thermal entropy generation. In the third part, the influences of the Hartmann number (0−30), which shows the strength of the magnetic field, were investigated. Increasing the magnetic force led to improvements in the mean Nusselt number. It also decremented the thermal entropy generation but increased the generation of frictional entropy and added the term's magnetic entropy. In the fourth part, the effects of the hydrophobic wall in first-order and second-order models, and the slip coefficient (0–0.1) were examined. The results determined that the hydrophobicity of the surfaces and the development of the slip factor in both models improves the mean Nusselt number and decreases in all the parameters of the thermodynamics second law, which were seen more changes in the first-order model.