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  • 1
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    Online Resource
    A benchmark study on the thermal conductivity of nanofluids
    AIP Publishing ; 2009
    In:  Journal of Applied Physics Vol. 106, No. 9 ( 2009-11-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 106, No. 9 ( 2009-11-01)
    Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3245330
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2009
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    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 2
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    Correlating contact line capillarity and dynamic contact angle hysteresis in surfactant-nanoparticle based complex fluids
    AIP Publishing ; 2018
    In:  Physics of Fluids Vol. 30, No. 4 ( 2018-04-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 30, No. 4 ( 2018-04-01)
    Abstract: Dynamic wettability and contact angle hysteresis can be correlated to shed insight onto any solid-liquid interaction. Complex fluids are capable of altering the expected hysteresis and dynamic wetting behavior due to interfacial interactions. We report the effect of capillary number on the dynamic advancing and receding contact angles of surfactant-based nanocolloidal solutions on hydrophilic, near hydrophobic, and superhydrophobic surfaces by performing forced wetting and de-wetting experiments by employing the embedded needle method. A segregated study is performed to infer the contributing effects of the constituents and effects of particle morphology. The static contact angle hysteresis is found to be a function of particle and surfactant concentrations and greatly depends on the nature of the morphology of the particles. An order of estimate of line energy and a dynamic flow parameter called spreading factor and the transient variations of these parameters are explored which sheds light on the dynamics of contact line movement and response to perturbation of three-phase contact. The Cox-Voinov-Tanner law was found to hold for hydrophilic and a weak dependency on superhydrophobic surfaces with capillary number, and even for the complex fluids, with a varying degree of dependency for different fluids.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/1.5020334
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 1472743-2
    detail.hit.zdb_id: 241528-8
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  • 3
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    Thermal conductivity enhancement of nanofluids containing graphene nanosheets
    AIP Publishing ; 2011
    In:  Journal of Applied Physics Vol. 110, No. 8 ( 2011-10-15)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 110, No. 8 ( 2011-10-15)
    Abstract: This paper envisages a mechanism of heat conduction behind the thermal conductivity enhancement observed in graphene nanofluids. Graphene nanofluids have been prepared, characterized, and their thermal conductivity was measured using the transient hot wire method. The enhancements in thermal conductivity are substantial even at lower concentrations and are not predicted by the classical Maxwell model. The enhancement also shows strong temperature dependence which is unlike its carbon predecessors, carbon nanotube (CNT) and graphene oxide nanofluids. It is also seen that the magnitude of enhancement is in-between CNT and metallic/metal oxide nanofluids. This could be an indication that the mechanism of heat conduction is a combination of percolation in CNT and Brownian motion and micro convection effects in metallic/metal oxide nanofluids, leading to a strong proposition of a hybrid model.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3650456
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 4
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    Particle and surfactant interactions effected polar and dispersive components of interfacial energy in nanocolloids
    AIP Publishing ; 2017
    In:  Journal of Applied Physics Vol. 122, No. 5 ( 2017-08-07)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 122, No. 5 ( 2017-08-07)
    Abstract: We segregate and report experimentally for the first time the polar and dispersive interfacial energy components of complex nanocolloidal dispersions. In the present study, we introduce a novel inverse protocol for the classical Owens Wendt method to determine the constitutive polar and dispersive elements of surface tension in such multicomponent fluidic systems. The effect of nanoparticles alone and aqueous surfactants alone are studied independently to understand the role of the concentration of the dispersed phase in modulating the constitutive elements of surface energy in fluids. Surfactants are capable of altering the polar component, and the combined particle and surfactant nanodispersions are shown to be effective in modulating the polar and dispersive components of surface tension depending on the relative particle and surfactant concentrations as well as the morphological and electrostatic nature of the dispersed phases. We observe that the combined surfactant and particle colloid exhibits a similar behavior to that of the particle only case; however, the amount of modulation of the polar and dispersive constituents is found to be different from the particle alone case which brings to the forefront the mechanisms through which surfactants modulate interfacial energies in complex fluids. Accordingly, we are able to show that the observations can be merged into a form of quasi-universal trend in the trends of polar and dispersive components in spite of the non-universal character in the wetting behavior of the fluids. We analyze the different factors affecting the polar and dispersive interactions in such complex colloids, and the physics behind such complex interactions has been explained by appealing to the classical dispersion theories by London, Debye, and Keesom as well as by Derjaguin-Landau-Verwey-Overbeek theory. The findings shed light on the nature of wetting behavior of such complex fluids and help in predicting the wettability and the degree of interfacial interaction with a substrate in such multicomponent nanocolloidal systems.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.4997123
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
    detail.hit.zdb_id: 1476463-5
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  • 5
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    Online Resource
    Mechanism of enhancement/deterioration of boiling heat transfer using stable nanoparticle suspensions over vertical tubes
    AIP Publishing ; 2007
    In:  Journal of Applied Physics Vol. 102, No. 7 ( 2007-10-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 102, No. 7 ( 2007-10-01)
    Abstract: Boiling heat transfer using nanofluids has been a subject of a few investigations in the past few years and incongruous results have been reported in literature regarding the same. Conflicting explanations for deterioration of pool boiling heat transfer coefficient at higher concentrations (4–16wt%) have been presented by various researchers. Recently, a few works have reported a significant enhancement in pool boiling heat transfer coefficient at lower concentrations (0.32–1.25wt%) and the physical reasons for this have not been explained. The present work is aimed at removing these ambiguities. Experiments have been carried out by using stable water based nanofluids containing alumina nanoparticles (average sizes of 47 and 150nm) with vertical tubular heaters of various surface roughnesses (48, 98, and 524nm). It has been observed that with the rough heater (Ra=524nm), heat transfer is significantly enhanced and the enhancement reaches ∼70% at a particle loading of 0.5wt%. With the smooth heater (Ra=48nm), heat transfer is significantly deteriorated and the heat flux reduction reaches ∼45% at a particle loading of 2wt%. Further, it has been observed that a parameter which is the ratio of average size of the particle to the average roughness value of the heater can explain the reported controversy in the pool boiling behavior of these suspensions.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.2794731
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 6
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    Reynolds number dependence of plane jet development in the transitional regime
    AIP Publishing ; 2008
    In:  Physics of Fluids Vol. 20, No. 4 ( 2008-04-01)
    Details
    In: Physics of Fluids, AIP Publishing, Vol. 20, No. 4 ( 2008-04-01)
    Abstract: The transitional characteristics of plane turbulent jets have been investigated in the present study. Hot wire measurements have been performed for a jet issuing from a rectangular nozzle of aspect ratio 20, for Reynolds number varying in the range 250⩽Re⩽6250. In this range, the characteristics of flow development are found to be Reynolds number dependent, in contrast to the fully developed turbulent jets which show features independent of initial conditions such as inlet Re. For low Re jets, the jet spread is significantly influenced by the low frequency oscillations caused by shear layer instability. Large sized vortices are formed in the shear layers at the fundamental frequency of the instability, which lead to subharmonic low frequency oscillations due to vortex pairing and merger, at larger axial distances. Consequently, the far field flow structure of a low Re jet is dominated by large size vortices which give rise to a higher level of flow intermittency, larger entrainment of ambient fluid, and faster jet decay, as compared to high Re jets. Also, in the absence of finer scales and broader spectrum of eddies, the mean flow field achieves self-similar structure much ahead of the fluctuating components and fully developed turbulent flow characteristics are not observed, even in the far field. In high Re jets, on the other hand, the vortex break-up processes also simultaneously occur along with vortex pairing and merger. Therefore, energy transfers to a broad spectrum of scales and finer scales are observed even in the near field of the jet. Although the achievement of self-similarity for the mean field is slightly faster than that for the fluctuating components, turbulence also attains a fully developed state at about a nondimensional axial distance of 20. The associated probability density functions of the fluctuating components evolve into Gaussian profiles, implying isotropic turbulence. Due to the dominance of finer scales, the overall entrainment level is less and decay is slower for a high Re jet.
    Type of Medium: Online Resource
    ISSN: 1070-6631 , 1089-7666
    URL: Article
    DOI: 10.1063/1.2904994
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 1472743-2
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  • 7
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    Rheological and flow characteristics of nanofluids: Influence of electroviscous effects and particle agglomeration
    AIP Publishing ; 2009
    In:  Journal of Applied Physics Vol. 106, No. 3 ( 2009-08-01)
    Details
    In: Journal of Applied Physics, AIP Publishing, Vol. 106, No. 3 ( 2009-08-01)
    Abstract: Nanofluids have shown remarkable attraction in heat transfer community due to its reported enhanced thermal properties. One factor which can restrict nanofluids in heat transfer application is the increased viscosity value (compared to classical predictions). Particle aggregation occurring was the major reason for this observation. Even though majority of the aqueous nanofluids prepared in literature were stabilized electrostatically by adjusting the pH, studies on the effect of the electrical double layer thus created and its influence on viscosity increase has not been investigated for these nanofluids so far. Thus, in the present paper, rheological properties of alumina-water nanofluids, which are electrostatically stabilized, are measured and the increase in suspension viscosity due to presence of this electrical double layer causing additional electroviscous effects is brought out. Based on dynamic light scattering studies, particle agglomeration and its subsequent effect in increasing the viscosity of alumina-ethylene glycol nanofluid, where electroviscous effects are absent, are also considered. It is noted that the understanding of electroviscous effect is equally important as understanding the particle agglomeration effect and understanding both the effects is central to revealing the physics of nanofluid rheology. Further, hydrodynamic experiments are made, which show that nanofluids behaves almost like a homogeneous fluids under flow conditions, and by knowing their properties, such as viscosity and density, pressure drop can be predicted.
    Type of Medium: Online Resource
    ISSN: 0021-8979 , 1089-7550
    URL: Article
    DOI: 10.1063/1.3182807
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 220641-9
    detail.hit.zdb_id: 3112-4
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  • 8
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    A microfluidic platform for studying the effects of small temperature gradients in an incubator environment
    AIP Publishing ; 2008
    In:  Biomicrofluidics Vol. 2, No. 3 ( 2008-09-01)
    Details
    In: Biomicrofluidics, AIP Publishing, Vol. 2, No. 3 ( 2008-09-01)
    Abstract: Studies on the effects of variations in temperature and mild temperature gradients on cells, gels, and scaffolds are important from the viewpoint of biological function. Small differences in temperature are known to elicit significant variations in cell behavior and individual protein reactivity. For the study of thermal effects and gradients in vitro, it is important to develop microfluidic platforms which are capable of controlling temperature gradients in an environment which mimics the range of physiological conditions. In the present paper, such a microfluidic thermal gradient system (μTGS) system is proposed which can create and maintain a thermal gradient throughout a cell-seeded gel matrix using the hot and cold water supply integrated in the system in the form of a countercurrent heat exchanger. It is found that a uniform temperature gradient can be created and maintained in the device even inside a high temperature and high humidity environment of an incubator. With the help of a hot and cold circuit controlled from outside the incubator the temperature gradient can be regulated. A numerical simulation of the device demonstrates the thermal feature of the chip. Cell viability and activity under a thermal gradient are examined by placing human breast cancer cells in the device.
    Type of Medium: Online Resource
    ISSN: 1932-1058
    URL: Article
    DOI: 10.1063/1.2988313
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 2265444-6
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  • 9
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    Interplay of chemical and thermal gradient on bacterial migration in a diffusive microfluidic device
    AIP Publishing ; 2017
    In:  Biomicrofluidics Vol. 11, No. 2 ( 2017-03-01)
    Details
    In: Biomicrofluidics, AIP Publishing, Vol. 11, No. 2 ( 2017-03-01)
    Abstract: Living systems are constantly under different combinations of competing gradients of chemical, thermal, pH, and mechanical stresses allied. The present work is about competing chemical and thermal gradients imposed on E. coli in a diffusive stagnant microfluidic environment. The bacterial cells were exposed to opposing and aligned gradients of an attractant (1 mM sorbitol) or a repellant (1 mM NiSO4) and temperature. The effects of the repellant/attractant and temperature on migration behavior, migration rate, and initiation time for migration have been reported. It has been observed that under competing gradients of an attractant and temperature, the nutrient gradient (gradient generated by cells itself) initiates directed migration, which, in turn, is influenced by temperature through the metabolic rate. Exposure to competing gradients of an inhibitor and temperature leads to the imposed chemical gradient governing the directed cell migration. The cells under opposing gradients of the repellant and temperature have experienced the longest decision time (∼60 min). The conclusion is that in a competing chemical and thermal gradient environment in the range of experimental conditions used in the present work, the migration of E. coli is always initiated and governed by chemical gradients (either generated by the cells in situ or imposed upon externally), but the migration rate and percentage of migration of cells are influenced by temperature, shedding insights into the importance of such gradients in deciding collective dynamics of such cells in physiological conditions.
    Type of Medium: Online Resource
    ISSN: 1932-1058
    URL: Article
    DOI: 10.1063/1.4979103
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 2265444-6
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  • 10
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    Low intermittent flow promotes rat mesenchymal stem cell differentiation in logarithmic fluid shear device
    AIP Publishing ; 2020
    In:  Biomicrofluidics Vol. 14, No. 5 ( 2020-09-01)
    Details
    In: Biomicrofluidics, AIP Publishing, Vol. 14, No. 5 ( 2020-09-01)
    Abstract: Bone marrow mesenchymal stem cells are an ideal candidate for bone tissue engineering due to their osteogenic potential. Along with chemical, mechanical signals such as fluid shear stress have been found to influence their differentiation characteristics. But the range of fluid shear experienced in vivo is too wide and difficult to generate in a single device. We have designed a microfluidic device that could generate four orders of shear stresses on adherent cells. This was achieved using a unique hydraulic resistance combination and linear optimization to the lesser total length of the circuit, making the device compact and yet generating four logarithmically increasing shear stresses. Numerical simulation depicts that, at an inlet velocity of 160 μl/min, our device generated shear stresses from 1.03 Pa to 1.09 mPa. In this condition, we successfully cultured primary rat bone marrow mesenchymal stem cells (rBMSCs) in the device for a prolonged period of time in the incubator environment (four days). Higher cell proliferation rate was observed in the intermittent flow at 1.09 mPa. At 10 mPa, both upregulation of osteogenic genes and higher alkaline phosphatase activity were observed. These results suggest that the intermittent shear of the order of 10 mPa can competently enhance osteogenic differentiation of rBMSCs compared to static culture.
    Type of Medium: Online Resource
    ISSN: 1932-1058
    URL: Article
    DOI: 10.1063/5.0024437
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2020
    detail.hit.zdb_id: 2265444-6
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