Altering surface fluctuations by blending tethered and untethered chains

J. K. Lee; B. Akgun; Z. Jiang; S. Narayanan; M. D. Foster

doi:10.1039/c7sm01616f

Experimental Model of Temperature-Driven Nanofluid

Journal of Heat Transfer ◽

10.1115/1.2717239 ◽

2006 ◽

Vol 129 (6) ◽

pp. 697-704 ◽

Cited By ~ 152

Author(s):

A. G. Agwu Nnanna

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Convective Heat ◽

Small Volume ◽

Volume Fraction ◽

Convective Heat Transfer Coefficient ◽

Isothermal Condition ◽

Carrier Fluid ◽

Small Volume Fraction ◽

The Impact

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

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Loading Rate Effect on Translaminar Fracture Toughness of Hybrid Composite Laminate

10.1115/imece2000-1960 ◽

2000 ◽

Author(s):

Paul Moy ◽

Jerome Tzeng

Keyword(s):

Fracture Toughness ◽

Composite Laminates ◽

Glass Matrix ◽

Small Volume ◽

Loading Rate ◽

Volume Fraction ◽

Rate Effect ◽

The Matrix ◽

Small Volume Fraction ◽

Matrix Property

Abstract Fracture toughness properties of composite laminates were evaluated at a loading rate commonly observed in ordinance applications. The laminates are composed of IM7 graphite and a small volume fraction of S2 glass plies to form a cross-ply laminate. Fracture toughness appears to be very rate sensitive if the crack growth perpendicular to the plane dominated by glass/matrix property. Experimental data shows a 30–40% increase of fracture toughness for various layup as the loading rate was increase by 1000 times. The specimens examined under microscopic indicates the strengthening might due to different failure mechanism in the matrix. In addition, there is no visible rate effect if the crack propagation is perpendicular to the graphite dominant plane.

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Stress–Corrosion Cracking of AISI 316L Stainless Steel in Seawater Environments: Effect of Surface Machining

Metals ◽

10.3390/met10101324 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1324

Author(s):

Zhe Ren ◽

Frank Ernst

Keyword(s):

Stress Corrosion ◽

Small Volume ◽

Volume Fraction ◽

Single Point ◽

Crack Density ◽

Aisi 316L ◽

Surface Machining ◽

Subsurface Zone ◽

Small Volume Fraction ◽

Effect Of Surface

To understand the effect of surface machining on the resistance of AISI 316L to SCC (stress–corrosion cracking) in marine environments, we tested nuts surface-machined by different methods in a seawater-spraying chamber. Two forms of cracks were observed: on the machined surface and underneath it. On the surface, cracks connected with the pitting sites were observed to propagate perpendicular to the hoop-stress direction, identifying them as stress–corrosion cracks. Under the surface, catastrophic transgranular cracks developed, likely driven by hydrogen embrittlement caused by the chloride-concentrating level of humidity in the testing environment. Under constant testing conditions, significantly different SCC resistance was observed depending on how the nuts had been machined. Statistical evaluation of the nut surface-crack density indicates that machining by a “form” tool yields a crack density one order of magnitude lower than machining by a “single-point” tool. Microstructural analysis of form-tool-machined nuts revealed a homogeneous deformed subsurface zone with nanosized grains, leading to enhanced surface hardness. Apparently, the reduced grain size and/or the associated mechanical hardening improve resistance to SCC. The nanograin subsurface zone was not observed on nuts machined by a single-point tool. Surface roughness measurements indicate that single-point-tool-machined nuts have a rougher surface than form-tool machined nuts. Apparently, surface roughness reduces SCC resistance by increasing the susceptibility to etch attack in Cl--rich solutions. The results of X-ray diffractometry and transmission electron microscopy diffractometry indicate that machining with either tool generates a small volume fraction (< 0.01) of strain-induced martensite. However, considering the small volume fraction and absence of martensite in regions of cracking, martensite is not primarily responsible for SCC in marine environments.

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A 2D Multiphase Model of Drop Behavior during Electroslag Remelting

Metals ◽

10.3390/met10040490 ◽

2020 ◽

Vol 10 (4) ◽

pp. 490

Author(s):

Jérémy Chaulet ◽

Abdellah Kharicha ◽

Sylvain Charmond ◽

Bernard Dussoubs ◽

Stéphane Hans ◽

...

Keyword(s):

Small Volume ◽

Slag Phase ◽

Volume Fraction ◽

Liquid Pool ◽

Electroslag Remelting ◽

Multiphase Model ◽

Momentum Exchange ◽

Small Volume Fraction ◽

Drag Law ◽

Two Fluid

Electroslag remelting is a process extensively used to produce metallic ingots with high quality standards. During the remelting operation, liquid metal droplets fall from the electrode through the liquid slag before entering the liquid pool of the secondary ingot. To better understand the process and help to optimize the operating condition choice, a 2D axisymmetric multiphase model of the slag domain has been developed using a two fluid Eulerian approach. During their fall, droplets hydrodynamic interactions are calculated thanks to an appropriate drag law. Influence of droplets on the electromagnetic field and on the slag hydrodynamics is discussed, as well as their heat exchange with the slag. Even with a small volume fraction, the droplets influence is noticeable. The present investigation shows that small droplets have a large influence on the slag hydrodynamics, due to a great momentum exchange. However heat transfer is more influenced by large drops, which are found to be relatively far from the thermal equilibrium with the slag phase.

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Flow past periodic arrays of spheres at low Reynolds number

Journal of Fluid Mechanics ◽

10.1017/s002211209600448x ◽

1997 ◽

Vol 335 ◽

pp. 189-212 ◽

Cited By ~ 7

Author(s):

HONGWEI CHENG ◽

GEORGE PAPANICOLAOU

Keyword(s):

Reynolds Number ◽

Viscous Flow ◽

Small Volume ◽

Volume Fraction ◽

Periodic Array ◽

Periodic Arrays ◽

Flow Past ◽

Random Array ◽

Single Sphere ◽

Small Volume Fraction

We calculate the force on a periodic array of spheres in a viscous flow at small Reynolds number and for small volume fraction. This generalizes the known results for the force on a periodic array due to Stokes flow (zero Reynolds number) and the Oseen correction to the Stokes formula for the force on a single sphere (zero volume fraction). We use a generalization of Hasimoto's approach that is based on an analysis of periodic Green's functions. We compare our results to the phenomenological ones of Kaneda for viscous flow past a random array of spheres.

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New developments in understanding interfacial processes in turbulent flows

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2010.0332 ◽

2011 ◽

Vol 369 (1937) ◽

pp. 702-705 ◽

Cited By ~ 8

Author(s):

I. Eames ◽

J. B. Flor

Keyword(s):

Turbulent Flows ◽

Small Volume ◽

Volume Fraction ◽

Flow Properties ◽

Theme Issue ◽

New Developments ◽

Interfacial Processes ◽

Recent Developments ◽

Small Volume Fraction ◽

Entire Flow

Interfaces, across which fluid and flow properties change significantly, are a ubiquitous feature of most turbulent flows and are present within jets, plumes, homogeneous turbulence, oceans and planetary atmospheres. Even when the interfaces occupy a small volume fraction of the entire flow, they largely control processes such as entrainment and dissipation and can act as barriers to transport. This Theme Issue brings together some of the leading recent developments on interfaces in turbulence, drawing in many methodologies, such as experiments, direct number simulations, inverse methods and analytical modelling.

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Low volume-fraction microstructures in martensites and crystal plasticity

Mathematical Models and Methods in Applied Sciences ◽

10.1142/s0218202516500317 ◽

2016 ◽

Vol 26 (07) ◽

pp. 1319-1355 ◽

Cited By ~ 6

Author(s):

Sergio Conti ◽

Barbara Zwicknagl

Keyword(s):

Small Volume ◽

Materials Science ◽

Volume Fraction ◽

Variational Problems ◽

The Other ◽

Microstructure Formation ◽

Branching Patterns ◽

Small Volume Fraction ◽

New Phase

We study microstructure formation in two nonconvex singularly-perturbed variational problems from materials science, one modeling austenite–martensite interfaces in shape-memory alloys, the other one slip structures in the plastic deformation of crystals. For both functionals we determine the scaling of the optimal energy in terms of the parameters of the problem, leading to a characterization of the mesoscopic phase diagram. Our results identify the presence of a new phase, which is intermediate between the classical laminar microstructures and branching patterns. The new phase, characterized by partial branching, appears for both problems in the limit of small volume fraction, that is, if one of the variants (or of the slip systems) dominates the picture and the volume fraction of the other one is small.

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