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

It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter <10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity.

Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles

Heat transfer characteristics of nanofluids: a review

In this paper we present a novel and versatile t e c h n i q u e f o r t h e p r o d u c t i o n o f u l t r a f i n e m e t a l p a r t i c l e s by evaporation from a temperature‐regulated oven containing a reduced atmosphere of an inert gas. An extensive investigation of particles of oxidized Al, with diameters of 3 to 6 nm, has been performed. We have also studied ultrafine particles of Mg,Zn, and Sn produced in the same manner. A supplementing investigation has been carried out for particles of Cr, Fe, Co, Ni, Cu, and Ga, as well as larger Al particles, produced by ’’conventional’’ inert‐gas evaporation from a resistive filament. Diameter as a function of evaporation rate, inert‐gas pressure, and the kind of inert gas are reported. Crystalline particles smaller than 20 nm look almost spherical in the electron microscope, while larger ones often display pronounced crystal habit. S i z e d i s t r i b u t i o n s have been investigated in detail, and consistently the logarithm of the particle diameter has a Gaussian distribution to a high precision for the smallest sizes, whereas larger particles deviate from such a simple behavior. A statistical growth model, based on the Central Limit Theorem, has been formulated for liquidlike coalescence of particles; this theory accounts satisfactorily for all our data, as well as for most size distributions published in the literature. Applications of the model to colloids, discontinuous films, and supported catalysts are discussed. By comparing size distributions for particles produced by a variety of techniques we found a number of empirical rules for the width of the distributions, as defined by a (geometric) standard deviation σ. For crystalline inert‐gas‐ evaporated particles we obtained consistently 1.36?σ?1.60; for coalescing islands in discontinuous films we found 1.22?σ?1.34; and similar rules are applicable to colloids, supported catalysts, and to ultrafine droplets.

Ultrafine metal particles

Domain aspects of multi-ferroics are reviewed, i.e. of materials, in which two or all three of the properties ‘ferroelectricity.’ ‘ferromagnetism’ and ‘ferroelasticity’ occur simultaneously in the same phase, and in which the magnetic point group has been reliably established by magnetoelectric, optical, dielectric, magnetic and related studies on single crystals and single domains. Nearly only members of the boracite crystal family are concerned, whereas for the perovskite family and other classes of material there is great paucity of data on single crystals. Polarized light microscopy is shown to be an indispensable tool for the study of multi-ferroics, in particular when ferroelasticity is involved. Potential multi-ferroic magnetoelectrics, so far only known in ceramic form, are excluded from the survey.

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Multi-ferroic magnetoelectrics

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Magnetic susceptibility measurements on hemoproteins down to 4.2°K

Hyperfine particles (100 to 1000 A) of vanadium were prepared by the evaporation method and the magnetic susceptibility of these fine particles was measured in the temperature range between 1.6 to 300 K. The magnetic susceptibility of these fine particles was found to consist of two parts, one was the Pauli type which was also observed in the bulk state of the metal and the other was the Curie-Weiss type overlapping the temperature independent one. The C-W component of the susceptibility increases with the decrease of particle size as the inverse of average diameter, suggesting that the magnetic moment which revealed the Curie-Weiss type susceptibility originates from the surface region of the particle. Localization of 3d-electron at the surface of particle is a probable origin of the magnetic moment.

Appearance of Magnetic Moments in Hyperfine Particles of Vanadium Metal

Fine structure of iron ion in deoxymyoglobin and deoxyhemoglobin

Magnetoelectric effect of the low temperature phase of magnetite was measured at 77 K. It was confirmed that the magnetic crystal symmetry at 77 K is triclinic but the breaking of the mirror symmetry parallel to the (1\bar10) plane is very small. Dispersion of the magnetoelectric effect was observed with the relaxation time of approximately 2 µs. Magnitude of magnetoelectric susceptibility depends on the direction of the applied electric field. Both phenomena were attributed to the dispersion and the anisotropy of the electric susceptibility. The structure of the low temperature phase was discussed briefly in connection with the model proposed by Mizoguchi (J. Phys. Soc. Jpn. 44 (1978) 1512).

Akira Tasaki

Papers

Magnetic properties of ferromagnetic ultrafine particles prepared by vacuum evaporation on running oil substrate

Magnetic susceptibility measurements on hemoproteins down to 4.2°K

Appearance of Magnetic Moments in Hyperfine Particles of Vanadium Metal

Fine structure of iron ion in deoxymyoglobin and deoxyhemoglobin

Magnetoelectric Effect of Fe 3 O 4 at 77 K. I. Crystal Symmetry