Nanofluids are engineered colloids made of a base fluid and nanoparticles (1-100 nm) Nanofluids have higher thermal conductivity' and single-phase heat transfer coefficients than their base fluids In particular the heat transfer coefficient increases appear to go beyond the mere thermal-conductivity effect, and cannot be predicted by traditional pure-fluid correlations such as Dittus-Boelter's In the nanofluid literature this behavior is generally attributed to thermal dispersion and intensified turbulence, brought about by nanoparticle motion To test the validity of this assumption, we have considered seven slip mechanisms that can produce a relative velocity between the nanoparticles and the base fluid These are inertia, Brownian diffusion, thermophoresis, diffusioplwresis, Magnus effect, fluid drainage, and gravity We concluded that, of these seven, only Brownian diffusion and thermophoresis are important slip mechanisms in nanofluids Based on this finding, we developed a two-component four-equation nonhomogeneous equilibrium model for mass, momentum, and heat transport in nanofluids A nondimensional analysis of the equations suggests that energy transfer by nanoparticle dispersion is negligible, and thus cannot explain the abnormal heat transfer coefficient increases Furthermore, a comparison of the nanoparticle and turbulent eddy time and length scales clearly indicates that the nanoparticles move homogeneously with the fluid in the presence of turbulent eddies so an effect on turbulence intensity is also doubtful Thus, we propose an alternative explanation for the abnormal heat transfer coefficient increases: the nanofluid properties may vary significantly within the boundary layer because of the effect of the temperature gradient and thermophoresis For a heated fluid, these effects can result in a significant decrease of viscosity within the boundary layer, thus leading to heat transfer enhancement A correlation structure that captures these effects is proposed

Convective Transport in Nanofluids

Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids that are required in many industrial applications. In this paper we propose that an innovative new class of heat transfer fluids can be engineered by suspending metallic nanoparticles in conventional heat transfer fluids. The resulting {open_quotes}nanofluids{close_quotes} are expected to exhibit high thermal conductivities compared to those of currently used heat transfer fluids, and they represent the best hope for enhancement of heat transfer. The results of a theoretical study of the thermal conductivity of nanofluids with copper nanophase materials are presented, the potential benefits of the fluids are estimated, and it is shown that one of the benefits of nanofluids will be dramatic reductions in heat exchanger pumping power.

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Investigation on Convective Heat Transfer and Flow Features of Nanofluids

Turbulent friction and heat transfer behaviors of dispersed fluids (i.e., uttrafine metallic oxide particles suspended in water) in a circular pipe were investigated experimentally. Viscosity measurements were also conducted using a Brookfield rotating viscometer. Two different metallic oxide particles, γ-alumina (Al2O3) and titanium dioxide (TiO2), with mean diameters of 13 and 27 nm, respectively, were used as suspended particles. The Reynolds and Prandtl numbers varied in the ranges l04-I05 and 6.5-12.3, respectively. The viscosities of the dispersed fluids with γ-Al2O3 and TiO2 particles at a 10% volume concentration were approximately 200 and 3 times greater than that of water, respectively. These viscosity results were significantly larger than the predictions from the classical theory of suspension rheology. Darcy friction factors for the dispersed fluids of the volume concentration ranging from 1% to 3% coincided well with Kays' correlation for turbulent flow of a single-phase fluid. The Nusselt n...

Hydrodynamic and heat transfer study of dispersed fluids with submicron metallic oxide particles

Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

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Thermal Conductivity of Nanoparticle -Fluid Mixture

Thermal conductivity of carbon nanotubes and their polymer nanocomposites: A review

Dispositif (20) servant a determiner la contrainte tangentielle instantanee exercee sur une partie de la paroi interne d'un vaisseau sanguin (26) par le sang circulant dans ledit vaisseau. Le dispositif comprend un tube (28) dispose dans le sens de la longueur a l'interieur du vaisseau (22) et possedant une paire de transducteurs de pression (34, 36) espaces dans le sens de la longueur et servant a mesurer une chute de pression a l'interieur du vaisseau. Un circuit electronique (24) recoit un signal emis un element d'echantillonnage (22), un signal indiquant le diametre interieur du vaisseau sanguin et un signal indiquant la distance entre les transducteurs de pression (34, 36) espaces sur la longueur du vaisseau, pour calculer la contrainte tangentielle instantanee.

Systeme pour determiner la contrainte tangentielle instantanee exercee sur la paroi d'un vaisseau sanguin

La presente invention concerne un rheometre a balayage destine a la mesure de proprietes rheologiques de fluides electrorheologiques (ER) et magnetorheologiques (MR) a l'aide d'un modele viscoplastique non lineaire, fonde sur la variation de hauteur du fluide par rapport au temps. Ce rheometre comprend de facon fondamentale une source de fluide statique (par exemple un reservoir suspendu) ou dynamique, un canal ou une fente dont les cotes forment des electrodes qui sont en contact avec le fluide ER d'ecoulement, ou un tube capillaire expose a un champ magnetique statique/alternatif destine aux fluides MR d'ecoulement, un tube de transfert, soit une soit deux colonnes de montee, et un detecteur de niveau de colonne destine a surveiller la colonne de fluide lorsque celui-ci se deplace dans une des colonnes de montee. Ce detecteur de niveau de colonne est couple a un processeur qui analyse, entre autres choses, la hauteur de colonne en fonction de donnees de temps de facon a determiner la viscosite et l'effort de deformation permanente. Ce rheometre surmonte un des principaux inconvenients du rheometre traditionnel: l'incapacite de produire l'effort de deformation permanente du fluide ER ou MR dans la plage de vitesse de cisaillement du zero absolu. Les resultats obtenus avec ce rheometre sont compares avec ceux obtenus a partir d'un rheometre disponible sur le marche qui remporte un excellent accueil.

Rheometre a balayage de fluide electrorheologique et magnetorheologique

An inline blood viscometer that continuously monitors the circulating blood of a living being undergoing a surgical procedure where knowledge of the being's current blood viscosity is crucial. The viscometer diverts a portion of a living being's circulating blood into a pair of riser tubes (R1, R2), connected together at upper and lower ends. The lower ends are connected through respective valves and a flow restrictor (52) of known dimensions. Through valve manipulation, the viscometer creates a respective blood column in each riser tube of a different height to establish a pressure differential between the columns. The blood columns are then placed into fluid communication through the flow restrictor and the changing heights of the columns are monitored over time. Using this data along with flow restrictor/riser tube dimensions, blood viscosity is calculated. The flow restrictor/riser tubes are then rinsed/dried in preparation for the next viscosity determination run.

Inline blood viscometer for continually monitoring the circulating blood of a living being

Nonequilibrium Plamsa Liquid Water - Dynamics of Generation and Quenching

This study introduces a new approach to a falling ball viscometer by using a high speed motion camera to measure the viscosity of both Newtonian and non-Newtonian fluids from the velocity-time data. This method involves capturing continuous photographs of the entire falling motion of the ball as the ball accelerates from the rest to the terminal velocity state. Ball’s velocity was determined from the distance traversed by the ball by examining video tape frame by frame using the marked graduations on the surface of the falling ball cylinder. Each frame was pre-set at 0.01. Glycerin 74% was used for Newtonian solution, while aqueous solutions of Polyacrylamide and Carboxymethyl Cellulose were for non-Newtonian solutions. The experimental viscosity data were in good agreements with the results obtained from a rotating Brookfield viscometer.

Young I. Cho

Papers

Systeme pour determiner la contrainte tangentielle instantanee exercee sur la paroi d'un vaisseau sanguin

Rheometre a balayage de fluide electrorheologique et magnetorheologique

Inline blood viscometer for continually monitoring the circulating blood of a living being

Nonequilibrium Plamsa Liquid Water - Dynamics of Generation and Quenching

A novel viscosity measurement using a falling ball viscometer with a high-speed camera