We report graphene composite membranes with nominal areas more than 25 mm2 fabricated by transfer of a single layer of CVD graphene onto a porous polycarbonate substrate. A combination of ...pressure-driven and diffusive transport measurements provides evidence of size-selective transport of molecules through the membrane, which is attributed to the low-frequency occurrence of intrinsic 1–15 nm diameter pores in the CVD graphene. Our results present the first step toward the realization of practical membranes that use graphene as the selective material.
•Flow boiling in a copper microchannel for different surface conditions was studied.•Two-phase heat transfer coefficient for the aged (oxidized) surface was poor.•Both surface wettability and surface ...roughness appear to influence the boiling.•Existing correlations for two-phase heat transfer and pressure drop were assessed.
Experiments were carried out to investigate the effect of surface characteristics on flow boiling heat transfer and pressure drop in a microchannel using degasified and deionized water as the working fluid. Test section consists of a 40 mm long, 0.5 mm wide and 0.24 mm deep microchannel machined in copper. Experimental results are reported for three different surface characteristics – fresh machined surface (case-1), the same channel surface when aged after repeated experimentation (case-2) and the surface obtained after cleaning the same aged surface with 0.1 M hydrochloric acid (case-3). Parameters considered include inlet temperature 95 °C, mass flux from 1000 to 2220 kg/m2 s and heat flux from 400 to 1200 kW/m2. Single-phase experiments have been performed to estimate the heat loss from microchannel and also to validate the experimental setup. The results indicate that the boiling heat transfer performance of case-2 is lower than that of case-1 and the performance of case-3 is higher than that of case-1. The main reason behind the reduction of two-phase heat transfer coefficient for case-2 as compared to case-1 is attributed to the increased wettability due to the thermal oxidation of the heating surface caused by the repeated experimentation. The enhanced boiling performance of case-3 is attributed to the increased nucleation site density. However, the change in the two-phase pressure drop is relatively small. The experimental results were compared with the available correlations in the literature to check the predictability of the correlations for the three cases. The degree of agreement (or disagreement) varies depending on the correlation and the surface characteristic. The reasons for the deviations are discussed.
Plasmonic nanomaterials have the opportunity to considerably improve the specificity of cancer ablation by i.v. homing to tumors and acting as antennas for accepting externally applied energy. Here, ...we describe an integrated approach to improved plasmonic therapy composed of multimodal nanomaterial optimization and computational irradiation protocol development. We synthesized polyethylene glycol (PEG)-protected gold nanorods (NR) that exhibit superior spectral bandwidth, photothermal heat generation per gram of gold, and circulation half-life in vivo (t(1/2), approximately 17 hours) compared with the prototypical tunable plasmonic particles, gold nanoshells, as well as approximately 2-fold higher X-ray absorption than a clinical iodine contrast agent. After intratumoral or i.v. administration, we fuse PEG-NR biodistribution data derived via noninvasive X-ray computed tomography or ex vivo spectrometry, respectively, with four-dimensional computational heat transport modeling to predict photothermal heating during irradiation. In computationally driven pilot therapeutic studies, we show that a single i.v. injection of PEG-NRs enabled destruction of all irradiated human xenograft tumors in mice. These studies highlight the potential of integrating computational therapy design with nanotherapeutic development for ultraselective tumor ablation.
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A systematically designed study has been conducted to understand and demarcate the degree of contribution by the constituting elements to the surface tension of nanocolloids. The effects of ...elements such as surfactants, particles and the combined effects of these on the surface tension of these complex fluids are studied employing the pendant drop shape analysis method by fitting the Young-Laplace equation. Only the particle has shown an increase in the surface tension with particle concentration in a polar medium like DI water, whereas only a marginal effect of particles on surface tension in weakly polar mediums like glycerol and ethylene glycol has been demonstrated. Such behaviour has been attributed to the enhanced desorption of particles to the interface and a theory has been presented to quantify this. The combined particle and surfactant effect on the surface tension of a complex nanofluid system showed a decreasing behaviour with respect to the particle and surfactant concentration with a considerably feeble effect of particle concentration. This combined colloidal system recorded a surface tension value below the surface tension of an aqueous surfactant system at the same concentration, which is a counterintuitive observation as only the particle results in an increase in the surface tension and only the surfactant results in a decrease in the surface tension. The possible physical mechanism behind such an anomaly happening at the complex fluid air interface has been explained. Detailed analyses based on thermodynamic, mechanical and chemical equilibrium of the constituents and their adsorption-desorption characteristics as extracted from the Gibbs adsorption analysis have been provided. The present paper conclusively explains several physical phenomena observed, yet hitherto unexplained, in the case of the surface tension of such complex fluids by segregating the individual contributions of each component of the colloidal system.
Graphical abstract
The present article discusses the numerical simulation results of laminar mixed convection flow in vertical tubes. A comparative analysis of the thermal and hydrodynamic features of both ...buoyancy-assisted and opposed flows was performed for Reynolds number (
), Grashof number (
) and Richardson number (
) with uniform heat flux boundary condition. 2-D axisymmetric steady state simulations were carried out for a length-to-diameter (
) ratio of
with water as the working fluid. Numerical simulations were performed by employing SIMPLE scheme for pressure-velocity coupling in momentum equations and second order UPWIND scheme for solving energy equations. In case of assisting flow (
), at fully developed state the centerline velocity decreases, and velocity is increased near the tube wall due to heat flux induced free convection. With increasing heat flux, the decrement in centerline velocity compared to the no-heat flux condition increases. Further, with increasing heat flux, the increase in friction factor and Nusselt number was observed. Therefore, at the same
the variation of heat flux led to unique velocity profiles and temperature gradients. The variation of centerline velocity and temperature in developing region was also studied. While centerline temperature was monotonically increasing with length, the centerline velocity increased up to a maximum in the developing region and then attained the steady state at a lower value in the fully developed state. Subsequently we studied the dependence of
on the hydrodynamic and thermal features. For constant
friction factor and Nusselt number was observed to increase with increase in
from 0.1 to 1.5 range. At fixed
variation of heat flux leads to variation of
or
Hence, the buoyancy effect has a significant role in the entrance length development. The hydrodynamic entry length after an initial increase, attained an almost constant value with increasing
On the other hand, the thermal entry length exhibited a decreasing trend with increasing
Similarly, at constant
Nusselt number increased with increasing
for a range of 100-1000. It was evident that for a given
and
the heat transfer in the developing flow is always higher as that of the fully developed flow. Contrasting observations were observed for buoyancy-opposed flow. Velocity is accelerated at the center as compared to the tube wall in case of opposing flow for same
and
For a fixed
the friction factor and Nusselt number decreased with increasing the
Both the hydrodynamic and thermal entry length increases for opposing flows. Finally, we have developed correlations for fully developed friction factor (
) with
as well as
and Nusselt number (
) with
for buoyancy-assisting and buoyancy-opposing flows. Two independent correlations are also produced for
with Graetz number (
) for developing and fully developed regimes in both assisting as well as opposing flows.
An experimental investigation on the convective heat transfer characteristics in the developing region of tube flow with constant heat flux is carried out with alumina–water nanofluids. The primary ...objective is to evaluate the effect of particle size on convective heat transfer in laminar developing region. Two particle sizes were used, one with average particle size off 45
nm and the other with 150
nm. It was observed that both nanofluids showed higher heat transfer characteristics than the base fluid and the nanofluid with 45
nm particles showed higher heat transfer coefficient than that with 150
nm particles. It was also observed that in the developing region, the heat transfer coefficients show higher enhancement than in the developed region. Based on the experimental results a correlation for heat transfer in the developing region has been proposed for the present range of nanofluids.
One of the reasons for the controversy on the thermal conductivity enhancement of nanofluids is the lack of extensive data over a wide range of parameters. In the present study, a comprehensive ...experimental dataset is obtained for thermal conductivity of nanofluids with variation in nanoparticle material, base liquid, particle size, particle volume fraction and suspension temperature. Transient hot wire (THW) equipment as well as Temperature Oscillation equipment are developed for the measurement of thermal conductivity of liquids. The measurements show that, in general, thermal conductivity values of all the nanofluids are higher than that of the equivalent macro-particle suspensions. Metallic nanofluids are found to give higher enhancements than that of oxide nanofluids. Particle size is found to have a tremendous impact on the thermal conductivity of nanofluids with enhancement in the thermal conductivity increasing almost inversely with reduction in the particle size. Increase in temperature significantly increases the thermal conductivity of a nanofluid. It is also observed that the thermal conductivity of nanoparticle suspensions is relatively higher at lower volume fractions, thereby giving a non-linear dependence on the particle volume fraction.
This study is aimed to prepare a novel class of nanofluid phase change material (NFPCM) by dispersing a small amount of multi-walled carbon nanotubes (MWCNT) in liquid paraffin, to enhance the heat ...transfer properties and examine the characteristics of the NFPCM during the solidification process. The stable NFPCMs are prepared by dispersing the MWCNT in liquid paraffin at 30°C with volume fractions of 0.15, 0.3, 0.45 and 0.6% without any dispersing agents. The rheology measurement illustrates the Newtonian fluid behavior in the shear stress range of 1–10 Pa. The differential scanning calorimetric results showed that there is no observable variation in the freezing/melting temperature of the NFPCM, and only a small observable change in the latent heat values. The thermal conductivity of various NFPCM is measured. The enhancement in thermal conductivity increases with the increased volume fraction of the MWCNT, and shows a weak dependence on the temperature. Further, for the NFPCM with a volume fraction of 0.6%, there is an appreciable increase in heat transfer with a reduction in the solidification time of 33.64%. The enhancement in the heat transfer performance would alleviate the major problems that have been encountered in the conventional phase change materials since several years.
A mathematical model for multistage flash (MSF) desalination system with brine recirculation (BR) configuration is developed in this study. The heat source for BR-MSF is chosen to be a ...nanofluid-based direct absorption solar collector (DASC) for which a numerical model is developed. Both these systems, BR-MSF and DASC are coupled via a counter-flow heat exchanger. The overall performance of the combined system is quantified in terms of gained output ratio (GOR). Moreover, the variation in GOR caused by various influencing parameters such as height (H) and length (L) of solar collector, nanoparticle volume fraction (fv) and incident flux on the collector (q) is studied in detail. The effect of these parameters on the top brine temperature (To) is also discussed. The study shows that DASC can be used as a heat source for BR-MSF system and gives high GOR ranging between 11 and 14 depending on the various operating conditions. This system is also compared with a parabolic trough collector (PTC) based BR-MSF system and it is found that DASC-based BR-MSF system gives higher GOR under identical conditions (relatively 11% higher). The exergy analysis is also presented for this system which shows the irreversibilities associated with various physical processes and components of the overall system and in addition to that exergy efficiency is also calculated for the overall system.
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•Direct absorption solar collector has been coupled with BR-MSF desalination system.•Overall thermal performance of the system is measured in terms of GOR.•The parameters related to DASC influence the overall system performance.•DASC-based MSF system has better thermal performance than PTC-based system.•Specific entropy generation is calculated for the various components of the system.
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