Pool boiling performance of porous surface tubes under vacuum conditions

Two types of tube bundles are designed,which are,respectively,composed of six tubes arranged in the boiling chamber.The nucleate pool boiling performance of smooth tube bundles and sintered porous surface tube bundles with deionized water as a medium are experimentally studied at atmospheric and sub-atmospheric pressures,respectively.The experimental results indicate that the boiling heat transfer coefficients of the two types of tube bundles increase with the increase in pressure under vacuum conditions as they behave under ordinary pressure.As the pressure varies from 10 to 100 kPa,it also can be seen that the heat transfer coefficient of the sintered porous surface tube is increased by 0.2 to 4 times compared with the smooth one under the same operating parameters.In addition,the experimental data show that a definite bundle effect exists in both sintered porous surface tubes and smooth tubes under vacuum conditions.

Heat transfer and nanofluid flow over a porous plate with radiation and slip boundary conditions

Presence of different terms with various values can alter the thermal behavior of the nanofluids flow over porous surfaces.The aim of this research is to study the influence of nanoparticles volume fraction,nanoparticles type,suction or injection,the heat generation or absorption,the Eckert number,thermal and velocity slip parameters,and radiation on the velocity and temperature fields on the flow and heat transfer over a porous flat plate.Four different types of nanoparticles including metal nanoparticles (Cu),metal oxide nanoparticles (Al2O3) and carbon-based nanomaterials (MWCNTs and SWCNTs) which were dispersed in the water (as based fluid) are studied.The governing equations are converted into the ordinary differential equations using similarity solution and solved numerically by the RKF45 algorithm.The results of the simulations showed a contradiction with the results of other researchers who expressed that using nanoparticles with higher thermal conductivity and volume fraction led to increasing heat transfer rate in nanofluids;this study proves that,in some cases,boosting the volume fraction of nanoparticles has a potential to decrease the heat transfer rate due to significant changes in values of some parameters including radiation,heat generation,and viscous dissipation.

Low-cost, green synthesis of highly porous carbons derived from lotus root shell as superior performance electrode materials in supercapacitor

Facile production of high quality activated carbons from biomass materials has greatly triggered much attention presently. In this paper, a series of interconnected porous carbon materials from lotus root shells biomass are prepared via simple pyrolysis and followed by a KOH activation process. The prepared carbons exhibit high specific surface areas of up to 2961 m^2/g and large pore volume～1.47 cm3/g. In addition, the resultant porous carbons served as electrode materials in supercapacitor exhibit high specific capacitance and outstanding recycling stability and high energy density. In particular, their specific capacitance retention was almost 100% after 10500 cycles at a current density of 2 A/g. Remarkabely, the impact of the tailored specific surface areas of various carbon samples on their capacitive performances is systematically investigated.Generally, it was believed that the highly-developed porosity features（including surface areas and pore volume and pore size-distributions）, together with the good conductivity of activated carbon species, play a key role in effectively improving the storage energy performances of the porous carbon electrode materials in supercapacitor.

Heat Transfer of Boiling R134a and R142b on a Twisted Tube with Machine Processed Porous Surface

The objective of this work was to investigate nucleate pool boiling heat transfer performance and mechanism of R134a and R142b on a twisted tube with machine processed porous surface （T-MPPS tube） as well as to determine its potential application to flooded refrigerant evaporators. In the experimental range, the boiling heat transfer coefficients of R134a on a T-MPPS tube were 1.8-2.0 times larger than those of R134a on a plain tube. In addition, the developed experimental correlations verified that the predictions of the heat transfer coefficients of boiling R134a and R142bon a T-MPPS tube at the experimental conditions were considerably accurate.

Convection of Maxwell fluid over stretching porous surface with heat source/sink in presence of nanoparticles:Lie group analysis

The convection of a Maxwell fluid over a stretching porous surface with a heat source/sink in the presence of nanoparticles is investigated. The Lie symmetry group transformations are used to convert the boundary layer equations into coupled nonlinear ordinary differential equations. The ordinary differential equations are solved numerically by the Bvp4c with MATLAB, which is a collocation method equivalent to the fourth-order mono-implicit Runge-Kutta method. Furthermore, more attention is paid to the effects of the physical parameters, especially the parameters related to nanoparticles, on the temperature and concentration distributions with consideration of permeability and the heat source/sink.

Effect of porous surface layer on wave propagation in elastic cylinder immersed in fluid

To study the damage to an elastic cylinder immersed in fluid, a model of an elastic cylinder wrapped with a porous medium immersed in fluid is designed. This structure can both identify the properties of guided waves in a more practical model and address the relationship between the cylinder damage degree and the surface and surrounding medium. The principal motivation is to perform a detailed quantitative analysis of the longitudinal mode and flexural mode in an elastic cylinder wrapped with a porous medium immersed in fluid. The frequency equations for the propagation of waves are derived each for a pervious surface and an impervious surface by employing Biot theory. The influences of the various parameters of the porous medium wrapping layer on the phase velocity and attenuation are discussed. The results show that the influences of porosity on the dispersion curves of guided waves are much more significant than those of thickness,whereas the phase velocity is independent of the static permeability. There is an apparent “mode switching” between the two low-order modes. The characteristics of attenuation are in good agreement with the results from the dispersion curves.This work can support future studies for optimizing the theory on detecting the damage to cylinder or pipeline.

Photo-responsive droplet manipulation slippery lubricant-infused porous surface with ultra-high durability

Photo-responsive slippery lubricant-infused porous surface(SLIPS) for droplet manipulation is flexible, noncontact and non-destructive in droplet manipulation, which has promising applications in flexible robotics, microfluidics,biomedicine, and chemical analysis. However, the repeated manipulations for droplets of SLIPSs are quite limited in the works reported so far, the poor durability of droplet manipulation severely limits the practical application of the surfaces. In this paper, an Fe3O4-doped polydimethylsiloxane(PDMS)-based SLIPS is proposed and implemented to achieve ultra-high repeated droplet manipulation numbers under near-infrared ray(NIR) laser irradiation. Firstly, a micron columnar array structure with micro-pits on the top side, as well as, a wall structure out of the array is designed on SLIPS to reserve the lubricant. Secondly, the prototype of the SLIPS is fabricated by a 3-step ultraviolet(UV) lithography, and subsequently immersed in silicone oil for more than 96 h to obtain the ultra-high durability slippery lubricant-infused porous surface(UD-SLIPS). With a power of 25 m W–85 m W NIR laser, the repeated manipulation of microdroplets(≤ 5 μL) in the scale of 1 cm can exceed more than 3000 times which is far beyond that in previous reports. Finally, the droplet manipulation performance of this photo-responsive UD-SLIPS and the influence of infusion time on durability are investigated. The mechanism of the PDMS swelling effect is found to be the key factor in improving the droplet manipulation durability of SLIPS. The findings of this work would be of great significance for the development of highly durable photo-responsive functional surfaces for droplet manipulation.

Micro-configuration Observation of Porous Bioceramic for Sliding on Intestinal Mucus Film

The microstructure of the prepared porous bioceramic material, including surface porosity and apparent contact area with the artificial mucus film are computed and analyzed. The surface micro-configurations of the porous material before and after sliding on the mucus film are observed in 2 D and 3 D by digital microsco py, We describe how much mucus enters and stays within different pares, and how the porous material with rough/ porous surface contacts with the mucus film （ elastic surfucel gel ） . The presented results illustrate that the material with different porous structure can lead to different mucus suction, surface scraping and changes of contact area and condition during sliding, which will be active for high friction of robotic endoscope with the intestinal wall for intestinal locomotion.

Enhanced Pool Boiling Heat Transfer on Copper Foam Welded Surfaces

Enhanced pool boiling heat transfer of the porous structure is critical to the thermal management technology.In this paper,pool boiling heat transfer experiments are performed on copper foam welded surfaces in de-ionized water to investigate the effects of basic parameters of copper foam on heat transfer enhancement.Boiling phenomenon is observed to facilitate the understanding of enhancement mechanism.The results show that copper foam welded surfaces can significantly enhance the pool boiling heat transfer performance,reduce the boiling incipience temperature by 7-9℃,and reach two times heat transfer coefficient compared with smooth plain surfaces due to numerous nucleation sites,extended surface areas,and enhanced turbulent effect.Pore density and thickness of foam have two side effects on heat transfer.

Analysis of A Porous and Flexible Cylinder in Waves

The hydrodynamic response of a porous flexible circular-cylinder in regular waves was analytically studied. To simplify the problem, the cover and the bottom of the cylinder were ignored. Small amplitude water wave theory and structural responses were assumed. The velocity potentials were solved using the Fourier-Bessel series expansion method and the least squares approximation method. The convergence of the series was numerically tested to determine the number of terms in the series expansion. Two types of installations were considered for deformation, hydrodynamic forces, structural flexibility, drafts, and porosity. The present study represented a preliminary step in the study of the fish cage.

Influence of Brownian Motion, Thermophoresis and Magnetic Effects on a Fluid Containing Nanoparticles Flowing over a Stretchable Cylinder

The influence of Brownian motion and thermophoresis on a fluid containing nanoparticles flowing over a stretchable cylinder is examined.The classical Navier-Stokes equations are considered in a porous frame.In addition,the Lorentz force is taken into account.The controlling coupled nonlinear partial differential equations are transformed into a system of first order ordinary differential equations by means of a similarity transformation.The resulting system of equations is solved by employing a shooting approach properly implemented in MATLAB.The evolution of the boundary layer and the growing velocity is shown graphically together with the related profiles of concentration and temperature.The magnetic field has a different influence(in terms of trends)on velocity and concentration.

Preparation of porous structures on copper microchannel surfaces by laser writing

A laser writing method is developed to fabricate porous structures on copper microchannel wall surfaces for enhanced microchannel heat sinks(MHSs). The formation feasibility together with its mechanism of such porous structures is explored by the comparison of dry and wet laser writing process, i.e., in both air atmosphere and under de-ionized water. Rectangular microchannels with ripples-like porous structures on the wall surfaces, which consisted of numerous micro-holes and micro-cavities,have been successfully formed in the dry laser writing process. Nevertheless, the microchannel wall surfaces were hardly altered in wet conditions. Besides, the effect of laser fluence on the formation of porous structures on the microchannels was also assessed in both dry and wet conditions. In dry laser writing process, the microchannel depth and surface roughness of wall surface increased monotonically, whereas the microchannel bottom width decreased continuously with increasing the laser fluence. On the other hand, the microchannel wall kept almost unchanged with smooth surfaces with increasing laser fluence in wet conditions.

Anti⁃icing/De⁃icing Mechanism and Application Progress of Bio⁃inspired Surface for Aircraft

Icing on the surface of aircraft will not only aggravate its quality and affect flight control,but even cause safety accidents,which is one of the important factors restricting all-weather flight.Bio-inspired anti-icing surfaces have gained great attention recently due to their low-hysteresis,non-stick properties,slow nucleation rate and low ice adhesion strength.These bio-inspired anti-icing surfaces,such as superhydrophobic surfaces,slippery liquid-infused porous surfaces and quasi-liquid film surfaces,have realized excellent anti-icing performance at various stages of icing.However,for harsh environment,there are still many problems and challenges.From the perspective of bioinspiration,the mechanism of icing nucleation,liquid bounce and ice adhesion has been reviewed together with the application progress and bottleneck issues about anti-icing in view of the process of icing.Subsequently,the reliability and development prospect of active,passive and active-passive integrated anti-icing technology are discussed,respectively.

Fouling-resistant Behavior of Liquid-infused Porous Slippery Surfaces

Marine economy is seriously affected by marine biofouling, which has plagued people for thousands of years. Although various strategies have been developed to protect artificial surfaces against marine biofouling, cost-effective biofouling-resistant coating is still a goal in pursue. Herein, a cost-effective liquid-infused porous slippery surface （LIPSS） was facilely prepared by using poly（styrene-b-（ethylene-co-butylene）-b-styrene） （SEBS） elastomer to form microsphere surfaces, followed by infusing fluorocarbon lubricants into the porous structure. The as-prepared slippery surfaces were characterized by static water contact angle, sliding velocity and sliding angle analysis. We also investigated the adhesion behavior of Escherichia coli （E. coli） and limnetic algae on different surfaces. It is confirmed that the slippery surfaces have better anti-biofouling properties than the porous SEBS reference. This cost-effective approach is feasible and easily produced, and may potentially be used as fouling-resistant surfaces.

Detecting Latent Prints on Stone and Other Difficult Porous Surfaces via Indanedione/Zinc Chloride and Laser

Lasers and alternate light sources have been recognized as effective tools for latent print detection for over three decades.Luminescence often increases friction ridge contrast to reveal impressions otherwise undetectable.Indanedione/zinc chloride excited by a forensic light source is widely recognized as an effective process for developing latent prints on porous surfaces.This study was designed to evaluate the use of a combination of luminescence excitation and indanedione with zinc chloride to detect latent prints on stones,bricks,and similar difficult porous surfaces.The wavelengths evaluated included 400 nm(violet),447 nm(blue),532 nm(green),and 645 nm(red).Latent prints were deposited on a variety of porous surfaces including bricks,cement stones,wood,and cotton fabric,all commonly encountered at crime scenes in China.The surfaces were examined using white light(light‑emitting diode flashlight)and laser light sources separately,both before and after treatment with indanedione/zinc chloride.The goal of this study was to evaluate various light sources for their effectiveness in detecting impressions developed by indanedione/zinc chloride on difficult porous surfaces.Results indicated that latent prints on some brick and cement stone surfaces may be effectively detected using 532 nm laser excitation after indanedione/zinc chloride processing.

Vacuum wetting of Ag/TA2 to develop a novel micron porous Ti with significant biocompatibility and antibacterial activity

Porous Ti with low modulus,excellent bio-corrosion resistance,biocompatibility,and antibacterial activity is highly pursued as advanced implant materials.In this work,a new approach to prepare micron porous structures on the surface layer of a grade 2 commercially-pure Ti(TA2)was proposed,which utilized a simple vacuum wetting process of pure Ag on the surface of TA2.The microstructure,corrosion resistance,biocompatibility,mechanical properties,antibacterial ability,and formation mechanism of the asfabricated porous Ti were studied.The results show that the pores(with average pore sizes of 0.5-5μm)are distributed on the surface layer of the TA2 with a depth of~10μm.In particular,a large number of silver nanoparticles(Ag NPs)form which are dispersed on the porous structures.The formation mechanisms of the porous structures and Ag NPs were elucidated,suggesting that the volatilization/sublimation of Ag in TA2 is crucial.The porous Ti possesses excellent bio-corrosion resistance,surface wettability,biocompatibility,antibacterial activity,and a relatively low elastic modulus of 40-55 GPa,which may have a promising future in the field of orthopedic implants.This work also provides a novel idea for the development of advanced porous Ti materials for orthopedic-related basic research and biomedical applications.

Reconstruction of Surface Porous PEEK Decorated with Strontium-doped Calcium Phosphate Coatings for Enhancing Osteogenic Activity

The aim of this study was to reconstruct surface porous structure with hundreds of micrometers and then bio-mineralize Sr-doped Calcium Phosphate(Sr-doped CaP)on Polyetheretherketone(PEEK)profile to enhance its bioactivity.A surface porous structure was prepared on PEEK profile by embedding and acid-etching of SiO2 particles as porogen(SP-PEEK).Then the Sr-doped CaP was further decorated on the porous surface after sulfonation,introduction of Sr-doped CaP crystal seeds and bio-mineralization in 1.5 times simulated body fluid(BSSP-PEEK-CaP/Sr).It was feasible to reconstruct the surface porous structure with hundreds of micrometers on PEEK profile by the present method without damaging its mechanical properties.The Sr-doped CaP crystal seeds effectively promoted the bio-mineralization of bio-inertness PEEK.All as-prepared PEEK did not inhibit the proliferation of cells.ALP of bio-mineralized groups was significantly increased than that of the other groups.The BSSP-PEEK-CaP/Sr obviously affected the morphology and promoted the adhesion and spreading of cells.As a result,the cyto-biocompatibity and bioactivity of PEEK were improved after bio-mineralization.Sr-doped CaP on PEEK most likely was beneficial for cells,which was associated with the increasing of the hydrophilicity on PEEK.This study provided a candidate method to improve the osteogenesis of PEEK implants.

Simultaneous Evaporation and Foaming for Batch Coaxial Extrusion of Liquid Metal/Polydimethylsiloxane Porous Fibrous TENG

The utilization of textile-based triboelectric nanogenerators(t-TENGs)offers great potential for providing sustainable and wearable power.Nevertheless,the current designs of t-TENGs present limitations in terms of low electrical outputs and less developed,straightforward batch processing techniques.Herein,a facile bottom-up foaming-combined coaxial extrusion method is developed for the massive fabrication of liquid metal/polydimethylsiloxane(PDMS)core–shell porous fibrous TENG,which can be directly woven to form t-TENGs.Ink designs are studied for high-fidelity fibrous TENG manufacturing and porosity-controlled micropore formation.Furthermore,porous fibrous TENGs are applied to integrate different woven structures,and the electrical and mechanical performances of the t-TENGs are optimized.Compared with plain surface fibrous TENG,the porous fibrous TENG achieves a~fivefold improvement in the open-circuit voltage(V_(OC))and a~sevenfold improvement in the short-circuit current(I_(SC)).These outcomes indicate that we can prepare a range of polymers for t-TENGs with enhanced output performance even though they do not demonstrate great triboelectrification.This work also demonstrates successful integration for sustainably powering miniature electronics.These results can contribute to human motion energy harvesting for wearable self-powered sensors.

Development of Slippery Liquid-Infused Porous Surface on AZ31 Mg Alloys for Corrosion Protection

The relatively poor corrosion resistance remarkably limits the wide applications of Mg alloys in practice,although they possess many attractive properties,like low density,high specific strength,and good biocompatibility.The formation of a protective coating can effectively suppress the corrosion.In this work,a slippery liquid-infused porous surface(SLIPS),with good surface hydrophobicity,stability,and self-healing property,was formed on AZ31 Mg alloys.The development of SLIPS requires suitable porous micro/nanostructures.Layered double hydroxide(LDH),with effective corrosion resistance for Mg alloys,was a good candidate to accommodate the liquid lubricant.Especially,different temperatures were applied to in situ form MgAl-LDH on AZ31 Mg alloys.The results showed that the temperature of 120℃was the best condition for the SLIPS to provide good corrosion protection for Mg alloys,with the lowest corrosion current density of 3.19×10^(-9)A cm^(−2).In addition,the SLIPS performed well in the long-term immersion test and abrasion test.The AZ31 Mg alloys with superior corrosion resistance and good mechanical and chemical stability can be extensively applied in areas of automotive,electronics,and aerospace.

Synthesis and electrocatalytic activity of Au@Pd coreshell nanothorns for the oxygen reduction reaction

Bimetallic core-shell nanostructures with porous surfaces have drawn considerable attention due to their promising applications in various fields, including catalysis and electronics. In this work, Au@Pd core-shell nanothorns （CSNTs） with rough and porous surfaces were synthesized for the first time through a facile co-chemical reduction method in the presence of polyallylamine hydrochloride （PAH） and ethylene glycol （EG） at room temperature. The size, morphology, and composition of Au@Pd CSNTs were investigated by transmission electron microscopy （TEM）, X-ray diffraction （XRD）, energy dispersive spec- troscopy （EDX）, EDX mapping, and X-ray photoelectron spectroscopy （XPS）. The electrochemical properties of as-synthesized Au@Pd CSNTs were also studied by various electrochemical techniques. Au@Pd CSNTs exhibited remarkably high electrocatalytic activity and durability for the oxygen reduction reaction （ORR） in the alkaline media, owing to the unique porous structure and the synergistic effect between the Au core and Pd shell.